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UC3843 power supply help needed!!!
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PostPosted: Mon May 16, 2005 5:13 am    Post subject: UC3843 power supply help needed!!! Reply with quote

Hi to all.
I have built a power supply using a uc3843 chip and need some help.
The supply takes 220Vac and steps it down to 14Vdc(approx).
I have managed to get the supply working OK , but I still need a bit of
help.The schematic is attached , in LTSpice format.I modeled the
schematic and it seems to be ok , but I'm not sure how much you can
trust a simulation it this sort of level.
I've attached the model file for anyone who would like to simulate the
schematic. Hope it does not make the file to big , but I don't have any
access to any other binary groups to send it to.

When I first powered up the circuit the output was very noisy , and got
worse as the load increaced.I found by lots of trial and error that if
I put a small(100pF) cap across R11(3k3) the output stabilizes and
everything seems good.There is a bit of high frequency noise on the
output at the switching frequency , but I am sure this is to be
expected.
Now the problem...

I found by checking the drive to the FET that the loop seems unstable
at certain loads.As I increace the load from 0A to 2.5A
you can see the gate drive pulse width increacing as expected , but at
certain loads it seems to jump all over the place and the scope can't
trigger.From about 300mA to say 1,5A the gate drive is a mess , and
after that it seems to settle down nicely.

How do I go about fixing this.It does not seem to be causing a problem
on the output , but I would like to fix it up anyway.
I am sure it is a loop/compensation problem , but I am not sure how to
go about fixing it.I have tried changing the gain resistor(R5) to 100k
and 147K to no avail.Same with the compensation cap C2(100p / 200p). I
have also fiddled with the resistor/cap combination around the TL431 ,
also without much luck.
I am not very experienced with this type of power supply , so I am in
the dark a bit!!
It may also be a board layout problem.I did the board in a hurry
and did not pay HUGE amount of attention to layout , but I did try and
keep high current areas away from control lines etc.It is single sided.
This is a sort of hobby project , so time is not really of the
esscence. I only have a scope and meter to work with , so any solutions
that involve using other expensive equipment will be out of my
capability.My maths is also not very hot , so any solution that involve
lots of complex maths may be beyound me , but post them anyway as the
may be of interest to someone else.(they will be of interest to me ,
even if over my head!!)


Any help would be appreciated.
Cheers Rob.

Here is the cct , and the model/symbol also follow.(hope that is
everything)

Version 4
SHEET 1 1916 688
WIRE -720 384 -720 256
WIRE -592 176 -720 176
WIRE -592 208 -592 176
WIRE -528 144 -528 -144
WIRE -528 624 -528 272
WIRE -464 384 -720 384
WIRE -464 384 -464 208
WIRE -288 192 -320 192
WIRE -288 288 -288 272
WIRE -288 320 -368 320
WIRE -288 624 -528 624
WIRE -288 624 -288 384
WIRE -256 192 -288 192
WIRE -176 288 -176 272
WIRE -160 320 -288 320
WIRE -160 448 -160 400
WIRE -160 464 -160 448
WIRE -160 624 -288 624
WIRE -160 624 -160 528
WIRE -96 192 -176 192
WIRE -96 288 -176 288
WIRE -96 288 -96 256
WIRE -80 448 -160 448
WIRE -80 448 -80 384
WIRE -32 192 -96 192
WIRE -32 256 -96 256
WIRE -32 320 -160 320
WIRE -32 384 -80 384
WIRE -16 320 -32 320
WIRE 0 -144 -528 -144
WIRE 0 -128 0 -144
WIRE 0 -48 0 -64
WIRE 112 624 -160 624
WIRE 112 640 112 624
WIRE 128 128 128 32
WIRE 128 448 128 432
WIRE 128 624 112 624
WIRE 128 624 128 448
WIRE 144 -144 0 -144
WIRE 144 -32 144 -64
WIRE 144 32 128 32
WIRE 144 32 144 -32
WIRE 352 -32 144 -32
WIRE 352 48 352 32
WIRE 352 352 288 352
WIRE 352 400 352 352
WIRE 352 496 352 400
WIRE 352 624 128 624

Here is the uc384x models:

*=========================================================* UC3842B
* ON Semiconductor
* PWM Controller
*
* This model was developed for ON Semiconductor by:
* AEI Systems, LLC
* 5777 W. Century Blvd. Suite 876
* Los Angeles, California 90045
* Copyright 2002, all rights reserved.
*
* This model is subject to change without notice.
* Users may not directly or indirectly re-sell or
* re-distribute this model. This model may not
* be used, modified, or altered
* without the consent of ON Semiconductor.
*
* For more information regarding modeling services,
* model libraries and simulation products, please
* call AEi Systems at (310) 863-8034, or contact
* AEi by email: info@aeng.com. http://www.AENG.com
*
* Revision: 1.0
*=========================================================*
* PSpice translation by Christophe Basso, christophe.basso@onsemi.com
*
..SUBCKT UC3842B 3 14 15 1 18 4 20 2
* E/A FDBK IS RT/CT GND OUT VC VREF
****OSCILLATOR*****
XTOF1 8 18 1 18 SWhyste params: RON=.01 ROFF=1MEG VT=2.05 VH=.8
GBDISCH 1 18 Value = { IF ( V(8,1Cool < 2.5 & V(13,1Cool > 2.5, 8.3M, 0 ) }
RPULL 8 2 100K
****UVLO***********
XTOF2 20 19 20 18 SWhyste params: RON=.01 ROFF=1MEG VT=13 VH=3
RUVLO 19 18 1MEG
RSTDBY 20 18 32K
ROP 10 18 500
****REFERENCE*******
EBREF 13 18 Value = { IF ( V(19,1Cool > 6, 5, 0 ) }
RREG 10 2 .33
CREF 2 18 1n
V3 13 10
GB6 19 18 Value = { I(V3) }
****CURRENT COMPARATOR*******
EB3 21 18 Value = { IF ( V(15,1Cool > V(16,1Cool, 5, 0 ) }
R7 15 18 1MEG
RDELAY 21 22 1K
CDELAY 22 18 150P
****ERROR AMPLIFIER**********
XAMP 2 14 3 18 1845AMP
****OFFSET LIMITER***********
R4 12 11 2MEG
R6 11 18 1MEG
EB2 16 18 Value = { IF ( V(11,1Cool > 1, 1, V(11,1Cool ) }
V4 3 9 1
D1 9 12 D2
..MODEL D2 D
****OUTPUT DRIVER************
XDRIVE 19 18 5 4 1845OUT
****S-R LATCH****************
XLATCH 8 2 22 18 6 7 FFLOP
****OUTPUT AND GATE**********
EB8 5 18 Value = { IF ( V(2,1Cool > 2.5 & V(7,1Cool > 2.5 & V(8,1Cool > 2.5,
10, 0 ) }
..ENDS
********
*=========================================================* UC3843B
* ON Semiconductor
* PWM Controller
*
* This model was developed for ON Semiconductor by:
* AEI Systems, LLC
* 5777 W. Century Blvd. Suite 876
* Los Angeles, California 90045
* Copyright 2002, all rights reserved.
*
* This model is subject to change without notice.
* Users may not directly or indirectly re-sell or
* re-distribute this model. This model may not
* be used, modified, or altered
* without the consent of ON Semiconductor.
*
* For more information regarding modeling services,
* model libraries and simulation products, please
* call AEi Systems at (310) 863-8034, or contact
* AEi by email: info@aeng.com. http://www.AENG.com
*
* Revision: 1.0
*=========================================================*
* PSpice translation by Christophe Basso, christophe.basso@onsemi.com
*
..SUBCKT UC3843B 3 14 15 1 18 4 20 2
* E/A FDBK IS RT/CT GND OUT VC VREF
****OSCILLATOR*****
XTOF1 8 18 1 18 SWhyste params: RON=.01 ROFF=1MEG VT=2.05 VH=.8
GBDISCH 1 18 Value = { IF ( V(8,1Cool < 2.5 & V(13,1Cool > 2.5, 8.3M, 0 ) }
RPULL 8 2 100K
****UVLO***********
XTOF2 20 19 20 18 SWhyste params: RON=.01 ROFF=1MEG VT=8 VH=.4
RUVLO 19 18 1MEG
RSTDBY 20 18 16.8K
ROP 10 18 500
****REFERENCE*******
EBREF 13 18 Value = { IF ( V(19,1Cool > 6, 5, 0 ) }
RREG 10 2 .33
CREF 2 18 1n
V3 13 10
GB6 19 18 Value = { I(V3) }
****CURRENT COMPARATOR*******
EB3 21 18 Value = { IF ( V(15,1Cool > V(16,1Cool, 5, 0 ) }
R7 15 18 1MEG
RDELAY 21 22 1K
CDELAY 22 18 150P
****ERROR AMPLIFIER**********
XAMP 2 14 3 18 1845AMP
****OFFSET LIMITER***********
R4 12 11 2MEG
R6 11 18 1MEG
EB2 16 18 Value = { IF ( V(11,1Cool > 1, 1, V(11,1Cool ) }
V4 3 9 1
D1 9 12 D2
..MODEL D2 D
****OUTPUT DRIVER************
XDRIVE 19 18 5 4 1845OUT
****S-R LATCH****************
XLATCH 8 2 22 18 6 7 FFLOP
****OUTPUT AND GATE**********
EB8 5 18 Value = { IF ( V(2,1Cool > 2.5 & V(7,1Cool > 2.5 & V(8,1Cool > 2.5,
10, 0 ) }
..ENDS
********
*=========================================================* UC3844B
* ON Semiconductor
* PWM Controller
*
* This model was developed for ON Semiconductor by:
* AEI Systems, LLC
* 5777 W. Century Blvd. Suite 876
* Los Angeles, California 90045
* Copyright 2002, all rights reserved.
*
* This model is subject to change without notice.
* Users may not directly or indirectly re-sell or
* re-distribute this model. This model may not
* be used, modified, or altered
* without the consent of ON Semiconductor.
*
* For more information regarding modeling services,
* model libraries and simulation products, please
* call AEi Systems at (310) 863-8034, or contact
* AEi by email: info@aeng.com. http://www.AENG.com
*
* Revision: 1.0
*=========================================================*
* PSpice translation by Christophe Basso, christophe.basso@onsemi.com
*
..SUBCKT UC3844B 3 14 15 1 18 4 20 2
* E/A FDBK IS RT/CT GND OUT VC VREF
****OSCILLATOR*****
XTOF1 8 18 1 18 SWhyste params: RON=.01 ROFF=1MEG VT=2.05 VH=.8
GBDISCH 1 18 Value = { IF ( V(8,1Cool < 2.5 & V(13,1Cool > 2.5, 8.3M, 0 ) }
RPULL 8 2 100K
****UVLO***********
XTOF2 20 19 20 18 SWhyste params: RON=.01 ROFF=1MEG VT=13 VH=3
RUVLO 19 18 1MEG
RSTDBY 20 18 32K
ROP 10 18 500
****REFERENCE*******
EBREF 13 18 Value = { IF ( V(19,1Cool > 6, 5, 0 ) }
RREG 10 2 .33
CREF 2 18 1N
V3 13 10
GB6 19 18 Value = { I(V3) }
****CURRENT COMPARATOR*******
EB3 21 18 Value = { IF ( V(15,1Cool > V(16,1Cool, 5, 0 ) }
R7 15 18 1MEG
RDELAY 21 22 1K
CDELAY 22 18 150P
****ERROR AMPLIFIER**********
XAMP 2 14 3 18 1845AMP
****OFFSET LIMITER***********
R4 12 11 2MEG
R6 11 18 1MEG
EB2 16 18 Value = { IF ( V(11,1Cool > 1, 1, V(11,1Cool ) }
V4 3 9 1
D1 9 12 D2
..MODEL D2 D
****OUTPUT DRIVER************
XDRIVE 19 18 5 4 1845OUT
****S-R LATCH****************
XLATCH 8 2 22 18 6 7 FFLOP
****50% LIMIT TOGGLE*********
X9 8 150 18 18 50 51 FFLOP
EBTRY 150 18 Value = { IF ( v(2,1Cool > 2.5 & v(50,1Cool > 2.5, 5, 0 ) }
****OUTPUT AND GATE**********
EB8 5 18 Value = { IF ( V(2,1Cool > 2.5 & V(7,1Cool > 2.5 & V(8,1Cool > 2.5 &
+ V(50,1Cool > 2.5, 10, 0 ) }
..ENDS
********
*=========================================================* UC3845B
* ON Semiconductor
* PWM Controller
*
* This model was developed for ON Semiconductor by:
* AEI Systems, LLC
* 5777 W. Century Blvd. Suite 876
* Los Angeles, California 90045
* Copyright 2002, all rights reserved.
*
* This model is subject to change without notice.
* Users may not directly or indirectly re-sell or
* re-distribute this model. This model may not
* be used, modified, or altered
* without the consent of ON Semiconductor.
*
* For more information regarding modeling services,
* model libraries and simulation products, please
* call AEi Systems at (310) 863-8034, or contact
* AEi by email: info@aeng.com. http://www.AENG.com
*
* Revision: 1.0
*=========================================================*
* PSpice translation by Christophe Basso, christophe.basso@onsemi.com
*
..SUBCKT UC3845B 3 14 15 1 18 4 20 2
* E/A FDBK IS RT/CT GND OUT VC VREF
****OSCILLATOR*****
XTOF1 8 18 1 18 SWhyste params: RON=.01 ROFF=1MEG VT=2.05 VH=.8
GBDISCH 1 18 Value = { IF ( V(8,1Cool < 2.5 & V(13,1Cool > 2.5, 8.3M, 0 ) }
RPULL 8 2 100K
****UVLO***********
XTOF2 20 19 20 18 SWhyste params: RON=.01 ROFF=1MEG VT=8 VH=.4
RUVLO 19 18 1MEG
RSTDBY 20 18 16.8K
ROP 10 18 500
****REFERENCE*******
EBREF 13 18 Value = { IF ( V(19,1Cool > 6, 5, 0 ) }
RREG 10 2 .33
CREF 2 18 1N
V3 13 10
GB6 19 18 Value = { I(V3) }
****CURRENT COMPARATOR*******
EB3 21 18 Value = { IF ( V(15,1Cool > V(16,1Cool, 5, 0 ) }
R7 15 18 1MEG
RDELAY 21 22 1K
CDELAY 22 18 150P
****ERROR AMPLIFIER**********
XAMP 2 14 3 18 1845AMP
****OFFSET LIMITER***********
R4 12 11 2MEG
R6 11 18 1MEG
EB2 16 18 Value = { IF ( V(11,1Cool > 1, 1, V(11,1Cool ) }
V4 3 9 1
D1 9 12 D2
..MODEL D2 D
****OUTPUT DRIVER************
XDRIVE 19 18 5 4 1845OUT
****S-R LATCH****************
XLATCH 8 2 22 18 6 7 FFLOP
****50% LIMIT TOGGLE*********
X9 8 150 18 18 50 51 FFLOP
EBTRY 150 18 Value = { IF ( v(2,1Cool > 2.5 & v(50,1Cool > 2.5, 5, 0 ) }
****OUTPUT AND GATE**********
EB8 5 18 Value = { IF ( V(2,1Cool > 2.5 & V(7,1Cool > 2.5 & V(8,1Cool > 2.5 &
+ V(50,1Cool > 2.5, 10, 0 ) }
..ENDS
*********
..SUBCKT 1845AMP 4 1 9 20
* VREF INV OUT V-
..MODEL QPMOD PNP
..MODEL DCLAMP D (RS=10 BV=5 IBV=.01)
..MODEL DMOD D
R1 10 4 100K
R2 10 20 100K
R3 6 20 316MEG
C1 6 20 15.9P
E1 5 20 6 20 1
R4 1 20 8MEG
I2 4 9 .8M
D12 9 4 DMOD
R6 20 3 300
D11 9 12 DMOD
Q1 20 13 12 QPMOD
I3 13 20 68U
D14 3 13 DMOD
D15 20 6 DCLAMP
L1 2 3 10U
C2 3 20 200P
R9 5 2 5
C5 2 20 .02U
G1 20 6 10 1 100U
..ENDS
*********
..SUBCKT 1845OUT 4 7 3 12
* +V -V IN OUT
..MODEL QMOD NPN RC=1.5 RE=.5 RB=100 IKF=0.5 CJC=0.4P
..MODEL QMOD2 NPN TF=400P TR=400P
..MODEL QIN NPN BF=100 BR=2 IS=1E-16 VAF=50
+ CJE=1.5P CJC=.15P TR=1N TF=4N
..MODEL DMOD D RS=1 IS=0.4U
I3 4 8 100U
D3 8 4 DMOD
D4 12 8 DMOD
Q3 8 1 9 QIN
Q4 12 9 7 QMOD
Q5 4 8 6 QMOD
I4 7 1 .9M
R1 3 2 10K
Q8 1 2 7 QIN
Q2 4 6 12 QMOD2
..ENDS
******************
..SUBCKT FFLOP 1 2 11 12 5 6
* CLK D R S QB Q
X1 7 4 2 8 NAND3_0
X2 8 3 10 9 NAND3_0
X3 1 8 10 7 NAND3_1
X4 4 9 1 10 NAND3_0
X5 4 7 6 5 NAND3_1
X6 5 10 3 6 NAND3_0
X7 11 4 INV
X8 12 3 INV
..ENDS FFLOP
*
..SUBCKT NAND3_0 1 2 3 4
E1 5 0 VALUE = { IF ( (V(1)>800mV) & (V(2)>800mV) & (V(3)>800mV), 0, 5
) }
R1 5 4 400
C1 4 0 20P IC=0
..ENDS NAND3_0
*
..SUBCKT NAND3_1 1 2 3 4
E1 5 0 VALUE = { IF ( (V(1)>800mV) & (V(2)>800mV) & (V(3)>800mV), 0, 5
) }
R1 5 4 400
C1 4 0 20P IC=5
..ENDS NAND3_1
*
..SUBCKT INV 1 2
E1 3 0 VALUE = { IF ( V(1)>800mV, 0, 5 ) }
R1 3 2 100
C1 2 0 10P IC=5
..ENDS INV
*
..SUBCKT SWhyste NodeMinus NodePlus Plus Minus PARAMS: RON=1 ROFF=1MEG
VT=5 VH=2
S5 NodePlus NodeMinus 8 0 smoothSW
EBcrtl 8 0 Value = { IF ( V(plus)-V(minus) > V(ref), 1, 0 ) }
EBref ref1 0 Value = { IF ( V(Cool > 0.5, {VT-VH}, {VT+VH} ) }
Rdel ref1 ref 100
Cdel ref 0 100p IC={VT+VH}
Rconv1 8 0 10Meg
Rconv2 plus 0 10Meg
Rconv3 minus 0 10Meg
..model smoothSW VSWITCH (RON={RON} ROFF={ROFF} VON=1 VOFF=0)
..ends SWhyste
*
****** Application models *****
..SUBCKT MOC8101 1 2 3 5
* ISOLATOR A C COL EMITTER
RB 4 0 100Meg
VM 1 6
D1 6 2 LED
H1 7 0 VM .0055
R1 7 8 1K
C1 8 0 3.35nF
G1 3 4 8 0 1
Q1 3 4 5 MPSA06
..MODEL LED D(N=1.7 RS=.7 CJO=23.9P IS=85.3p BV=6 IBV=10U
+ VJ=0.75 M=0.333 TT=4.32U)
..MODEL MPSA06 NPN (IS=15.2F NF=1 BF=589 VAF=98.6 IKF=90M ISE=3.34P NE=2

+ BR=4 NR=1 VAR=16 IKR=0.135 RE=0.343 RB=1.37 RC=0.137 XTB=1.5
+ CJE=9.67P VJE=1.1 MJE=0.5 CJC=7.34P VJC=0.3 MJC=0.3 TF=10.29n
TR=276N)
..ENDS MOC8101
*$
**** MULTI-WINDING TRANSFORMER ****
..SUBCKT XFMR2 1 2 3 4 10 11 PARAMS: RATIO1=1 RATIO2=1
RP 1 2 1MEG
E1 5 4 VALUE = { V(1,2)*RATIO1 }
G1 1 2 VALUE = { I(VM1)*RATIO1 }
RS1 6 3 1U
VM1 5 6
E2 20 11 VALUE = { V(2,1)*RATIO2 }
G2 2 1 VALUE = { I(VM2)*RATIO2 }
RS2 21 10 1U
VM2 20 21
..ENDS XFMR2
*$
**** SINGLE WINDING TRANSFORMER ****
..SUBCKT XFMR1 1 2 3 4 PARAMS: RATIO=1
RP 1 2 1MEG
E 5 4 VALUE = { V(1,2)*RATIO }
G 1 2 VALUE = { I(VM)*RATIO }
RS 6 3 1U
VM 5 6
..ENDS XFMR1
*$
*********
..model mbr140p d
+ is= 4.41547e-06
+ rs= 0.103922
+ n= 1.03751
+ tt= 1e-12
+ cjo= 1.598e-10
+ vj= 0.4934
+ m= 0.4258
+ eg= 0.6
+ xti= 3.29768
+ fc= 0.5
+ bv= 48
+ ibv= 0.01
+ kf= 0
+ af= 1
*******
*$
..MODEL 1n962A d
+RS=5.2600 BV=10.940
+CJO=710.46P TT=20N N=2
+IS=1E-9 IBV=11.364M
******
*$
..MODEL dn752a d
+RS=6.1685 BV=5.4766
+M=.33 VJ=.75 IS=1E-11
+CJO=376.59P TT=50N
+N=1.27 IBV=10MA
******
*$
..SUBCKT TL431 7 6 11
V1 1 6 2.495
R1 6 2 15.6
C1 2 6 .5U
R2 2 3 100
C2 3 4 .08U
R3 4 6 10
G2 6 8 3 6 1.73
D1 5 8 DC
D2 7 8 DC
V4 5 6 2
G1 6 2 1 11 0.11
..MODEL DC D
+IS=13.5N RS=25M N=1.59
+ CJO=45P VJ=.75 M=.302
+ TT=50.4N BV=34V IBV=1MA
..ENDS
*$
********
..subckt mtd1n60e 10 20 30
*
* 10 = Drain 20 = Gate 30 = Source
*
******************************************************************************
*
*------------------------ EXTERNAL PARASITICS
--------------------------------
* PACKAGE INDUCTANCE
*
LDRAIN 10 11 4.5e-09
LGATE 20 21 7.5e-09
LSOURCE 30 31 7.5e-09
*
* RESISTANCES
*
RDRAIN1 4 11 RDRAIN 6.853
RDRAIN2 4 5 RDRAIN 0.088
RSOURCE 31 6 RSOURCE 0.1
RDBODY 8 30 RDBODY 0.061
*
RGATE 21 2 5
*
*--------------------------------------------------------------------------
*
*--------------- CAPACITANCES AND BODY DIODE
------------------------------
*
DBODY 8 11 DBODY
DGD 3 11 DGD
CGDMAX 2 3 3e-10
RGDMAX 2 3 1e+08
CGS 2 6 2.2e-10
*
*--------------------------------------------------------------------------
*
*----------------------- CORE MOSFET
--------------------------------------
*
M1 5 2 6 6 MAIN
*
*--------------------------------------------------------------------------
*
..MODEL RDRAIN RES (
+TC1 = 0.008186
+TC2 = 1.74896e-05)
*
..MODEL RSOURCE RES (
+TC1 = -0.001057
+TC2 = 6.14713e-05)
*
..MODEL RDBODY RES (
+TC1 = 0.002026
+TC2 = 1.49534e-05)
*
*
..MODEL MAIN NMOS (
+LEVEL = 3
+VTO = 3.89
+KP = 1.75
+GAMMA = 3
+PHI = 0.6
+LAMBDA = 0.0001
+RD = 0
+RS = 0
+CBD = 0
+CBS = 0
+IS = 1e-14
+PB = 0.8
+CGSO = 0
+CGDO = 0
+CGBO = 0
+RSH = 0
+CJ = 0
+MJ = 0.5
+CJSW = 0
+MJSW = 0.33
+JS = 1e-14
+TOX = 1e-07
+NSUB = 1e+15
+NSS = 0
+NFS = 1.1e+12
+TPG = 1
+XJ = 0
+LD = 0
+UO = 600
+UCRIT = 1000
+UEXP = 0
+UTRA = 0
+VMAX = 0
+NEFF = 1
+KF = 0
+AF = 1
+FC = 0.5
+DELTA = 0
+THETA = 0
+ETA = 0
+KAPPA = 0.2)
*
*--------------------------------------------------------------------------
*
..MODEL DGD D (
+IS = 1e-15
+RS = 0
+N = 1000
+TT = 0
+CJO = 1.403e-10
+VJ = 0.1366
+M = 0.6185
+EG = 1.11
+XTI = 3
+KF = 0
+AF = 1
+FC = 0.5
+BV = 10000
+IBV = 0.001)
*
*--------------------------------------------------------------------------
*
..MODEL DBODY D (
+IS = 1.891e-11
+RS = 0
+N = 1.196
+TT = 5e-07
+CJO = 1.364e-10
+VJ = 0.9158
+M = 0.6082
+EG = 1.11
+XTI = 4.5
+KF = 0
+AF = 1
+FC = 0.5
+BV = 658.9
+IBV = 0.00025)
..ENDS
*$
******

WIRE 352 624 352 560
WIRE 416 -32 352 -32
WIRE 416 400 352 400
WIRE 448 224 288 224
WIRE 496 48 352 48
WIRE 496 80 496 48
WIRE 512 48 496 48
WIRE 512 48 512 32
WIRE 640 -32 480 -32
WIRE 640 48 512 48
WIRE 688 224 528 224
WIRE 736 -144 144 -144
WIRE 736 -112 736 -144
WIRE 736 144 736 -32
WIRE 736 400 496 400
WIRE 736 400 736 240
WIRE 736 464 736 400
WIRE 736 624 352 624
WIRE 736 624 736 544
WIRE 864 448 864 432
WIRE 864 528 864 512
WIRE 864 544 864 528
WIRE 896 432 864 432
WIRE 912 544 864 544
WIRE 912 544 912 448
WIRE 944 -32 864 -32
WIRE 960 48 864 48
WIRE 960 80 960 48
WIRE 960 432 960 400
WIRE 960 480 960 432
WIRE 960 528 960 480
WIRE 960 624 960 608
WIRE 992 480 960 480
WIRE 1024 448 912 448
WIRE 1024 448 1024 400
WIRE 1024 528 1024 512
WIRE 1024 624 960 624
WIRE 1024 656 1024 624
WIRE 1056 -32 1008 -32
WIRE 1056 -16 1056 -32
WIRE 1056 48 960 48
WIRE 1072 528 1024 528
WIRE 1072 624 1024 624
WIRE 1088 -32 1056 -32
WIRE 1088 528 1072 528
WIRE 1184 -32 1168 -32
WIRE 1184 -16 1184 -32
WIRE 1184 48 1056 48
WIRE 1248 -32 1184 -32
WIRE 1248 -32 1248 -112
WIRE 1248 48 1184 48
WIRE 1312 -112 1248 -112
WIRE 1312 528 1264 528
WIRE 1312 528 1312 384
WIRE 1344 -112 1312 -112
WIRE 1344 -64 1344 -112
WIRE 1344 16 1344 0
WIRE 1344 48 1248 48
WIRE 1344 48 1344 16
WIRE 1344 592 1264 592
FLAG 112 640 0
FLAG 0 -48 0
FLAG 496 80 0
FLAG 960 80 0
FLAG 1344 592 Vfb
FLAG -320 192 Vfb
FLAG 1024 656 0
FLAG 1312 -112 Vout
FLAG -368 320 Vref
FLAG 1312 384 Vref
FLAG -288 288 0
FLAG 1056 -32 Vsense
FLAG 1024 320 Vsense
FLAG 960 320 Vout
SYMBOL UC3845B 128 288 R0
SYMATTR InstName U1
SYMATTR Value UC3842B
SYMBOL res -176 304 R0
SYMATTR InstName R1
SYMATTR Value 15k
SYMBOL res 512 384 R90
WINDOW 0 0 56 VBottom 0
WINDOW 3 32 56 VTop 0
SYMATTR InstName R4
SYMATTR Value 1k
SYMBOL cap -176 464 R0
SYMATTR InstName C1
SYMATTR Value 1n
SYMBOL cap -112 192 R0
SYMATTR InstName C2
SYMATTR Value 220p
SYMBOL res -192 176 R0
SYMATTR InstName R5
SYMATTR Value 47k
SYMBOL res 720 448 R0
SYMATTR InstName R6
SYMATTR Value 0.22
SYMBOL cap 336 496 R0
SYMATTR InstName C3
SYMATTR Value 470p
SYMBOL res 544 208 R90
WINDOW 0 0 56 VBottom 0
WINDOW 3 32 56 VTop 0
SYMATTR InstName R7
SYMATTR Value 22
SYMBOL res 128 -160 R0
SYMATTR InstName R8
SYMATTR Value 100k
SYMBOL cap -16 -128 R0
SYMATTR InstName C4
SYMATTR Value 100µ
SYMATTR SpiceLine Rser=0.1
SYMBOL ind2 720 -128 R0
SYMATTR InstName L1
SYMATTR Value 500µ
SYMATTR Type ind
SYMBOL ind2 624 64 M180
WINDOW 0 36 80 Left 0
WINDOW 3 36 40 Left 0
SYMATTR InstName L2
SYMATTR Value 15µ
SYMATTR Type ind
SYMBOL schottky 480 -48 R90
WINDOW 0 0 32 VBottom 0
WINDOW 3 32 32 VTop 0
SYMATTR InstName D3
SYMATTR Value 1N5819
SYMATTR Description Diode
SYMATTR Type diode
SYMBOL cap 336 -32 R0
SYMATTR InstName C5
SYMATTR Value 68µ
SYMATTR SpiceLine Rser=0.1
SYMBOL ind2 880 64 R180
WINDOW 0 36 80 Left 0
WINDOW 3 49 40 Left 0
SYMATTR InstName L3
SYMATTR Value 15µ
SYMATTR Type ind
SYMBOL schottky 944 -16 R270
WINDOW 0 32 32 VTop 0
WINDOW 3 0 32 VBottom 0
SYMATTR InstName D4
SYMATTR Value MBR735
SYMATTR Description Diode
SYMATTR Type diode
SYMBOL cap 1040 -16 R0
SYMATTR InstName C7
SYMATTR Value 220µ
SYMATTR SpiceLine V=25 Rser=0.05 MTBF=1000 Lser=0 ppPkg=1
SYMBOL voltage -720 160 R0
WINDOW 123 0 0 Left 0
WINDOW 39 24 132 Left 0
SYMATTR SpiceLine Rser=1
SYMATTR InstName V1
SYMATTR Value SINE(0 311 50)
SYMBOL ind 1184 -48 R90
WINDOW 0 5 56 VBottom 0
WINDOW 3 32 56 VTop 0
SYMATTR InstName L4
SYMATTR Value 10µ
SYMATTR SpiceLine Rser=0.01
SYMBOL cap 1168 -16 R0
SYMATTR InstName C6
SYMATTR Value 470µ
SYMATTR SpiceLine V=25 Rser=0.05 MTBF=1000 Lser=0 ppPkg=1
SYMBOL res 1232 -48 R0
SYMATTR InstName R10
SYMATTR Value 14
SYMBOL Optos\\4N25 1168 592 R0
SYMATTR InstName U4
SYMBOL mystuff\\my\ nmos 688 144 R0
SYMATTR InstName U5
SYMATTR SpiceModel irfbe30
SYMBOL mystuff\\tl431 1008 448 R0
SYMATTR InstName U7
SYMBOL res 944 512 R0
SYMATTR InstName R11
SYMATTR Value 3.3k
SYMBOL res 1008 304 R0
SYMATTR InstName R13
SYMATTR Value 2.2k
SYMBOL res 944 304 R0
SYMATTR InstName R14
SYMATTR Value 10k
SYMBOL cap 960 416 R90
WINDOW 0 0 32 VBottom 0
WINDOW 3 32 32 VTop 0
SYMATTR InstName C9
SYMATTR Value 220n
SYMBOL res 848 432 R0
SYMATTR InstName R17
SYMATTR Value 1k
SYMBOL res -304 176 R0
SYMATTR InstName R2
SYMATTR Value 1k
SYMBOL res -160 176 R90
WINDOW 0 0 56 VBottom 0
WINDOW 3 32 56 VTop 0
SYMATTR InstName R3
SYMATTR Value 10k
SYMBOL cap -304 320 R0
SYMATTR InstName C8
SYMATTR Value 100n
SYMBOL current 1344 -64 R0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName I1
SYMATTR Value PULSE(0 5 412m 100n)
SYMBOL bridgerec -528 208 R0
SYMATTR InstName X1
TEXT -98 560 Left 0 !.tran 0 500m 0 40u startup
TEXT -48 480 Left 0 !.include uc384x.lib
TEXT 816 -96 Left 0 !k l1 l2 l3 1
TEXT 1416 504 Left 0 ;.ic V( VFb) = 0
TEXT -648 344 Left 0 ;.ic v(n001) = 200
RECTANGLE Normal 880 96 624 -128


Here is the uc3842 Symbol:


Version 4
SymbolType CELL
RECTANGLE Normal -160 -160 160 160
WINDOW 0 8 -176 Left 0
WINDOW 3 8 176 Left 0
SYMATTR Value UC3845B
SYMATTR Prefix X
SYMATTR Description High Speed Current Mode Pulse Width Modulator
PIN -160 -32 LEFT 8
PINATTR PinName COMP
PINATTR SpiceOrder 1
PIN -160 -96 LEFT 8
PINATTR PinName FB
PINATTR SpiceOrder 2
PIN 160 64 RIGHT 8
PINATTR PinName Isense
PINATTR SpiceOrder 3
PIN -160 96 LEFT 8
PINATTR PinName Rt/Ct
PINATTR SpiceOrder 4
PIN 0 160 BOTTOM 8
PINATTR PinName GND
PINATTR SpiceOrder 5
PIN 160 -64 RIGHT 8
PINATTR PinName Output
PINATTR SpiceOrder 6
PIN 0 -160 TOP 8
PINATTR PinName Vcc
PINATTR SpiceOrder 7
PIN -160 32 LEFT 8
PINATTR PinName Vref
PINATTR SpiceOrder 8
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Pooh Bear
electronics forum Guru


Joined: 24 Mar 2005
Posts: 3507

PostPosted: Mon May 16, 2005 6:07 am    Post subject: Re: UC3843 power supply help needed!!! Reply with quote

seegoon99@yahoo.com wrote:

Quote:
Hi to all.
I have built a power supply using a uc3843 chip and need some help.
The supply takes 220Vac and steps it down to 14Vdc(approx).
I have managed to get the supply working OK , but I still need a bit of
help.

Take a closer look at pcb layout and the loop response.

Did you follow an app note ?


Graham
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Genome
electronics forum Guru


Joined: 30 Apr 2005
Posts: 789

PostPosted: Mon May 16, 2005 8:56 am    Post subject: Re: UC3843 power supply help needed!!! Reply with quote

<seegoon99@yahoo.com> wrote in message
news:1116227614.747750.258110@z14g2000cwz.googlegroups.com...
Quote:
Hi to all.
I have built a power supply using a uc3843 chip and need some help.
The supply takes 220Vac and steps it down to 14Vdc(approx).
I have managed to get the supply working OK , but I still need a bit of
help.The schematic is attached , in LTSpice format.I modeled the
schematic and it seems to be ok , but I'm not sure how much you can
trust a simulation it this sort of level.
I've attached the model file for anyone who would like to simulate the
schematic. Hope it does not make the file to big , but I don't have any
access to any other binary groups to send it to.

Unfortunately your schematic, with the additional bits, won't fully load for
me and I'm a bit lazy so I haven't tried to fix things. I have got enough of
it to get some idea about what you are doing.

If I am interpreting it correctly, the TL431 isn't there but its associated
components are, then your connection in that part of the circuit is wrong.

You are driving the LED in the opto-isolator from the TL431 Anode. If you
download a TL431 data sheet then you will see that the anode is its ground
reference. The Ref terminal is regulated at +2V5 with respect to the Anode.

The LED and series resistor should be placed in series from the Cathode to
Vout. The Anode should be connected to ground. You should take the feedback
from Vsense. It looks like you have Vsense and Vout swapped as well as
having the LED in the wrong position.

If the forward drop of the LED is about 1V2 and you add the 2V5 reference
voltage that places the reference terminal at 3V7 and the circuit, as drawn,
will try to regulate Vout/Vsense at about 15V. In that respect it's
right...... but otherwise it's wrong.

Hope that makes sense.....

I'll poke about a bit more.

DNA
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Guest






PostPosted: Mon May 16, 2005 9:56 am    Post subject: Re: UC3843 power supply help needed!!! Reply with quote

Genome wrote:
Quote:
seegoon99@yahoo.com> wrote in message
news:1116227614.747750.258110@z14g2000cwz.googlegroups.com...
Hi to all.
I have built a power supply using a uc3843 chip and need some help.
The supply takes 220Vac and steps it down to 14Vdc(approx).
I have managed to get the supply working OK , but I still need a bit
of
help.The schematic is attached , in LTSpice format.I modeled the
schematic and it seems to be ok , but I'm not sure how much you can
trust a simulation it this sort of level.
I've attached the model file for anyone who would like to simulate
the
schematic. Hope it does not make the file to big , but I don't have
any
access to any other binary groups to send it to.

Unfortunately your schematic, with the additional bits, won't fully
load for
me and I'm a bit lazy so I haven't tried to fix things. I have got
enough of
it to get some idea about what you are doing.

If I am interpreting it correctly, the TL431 isn't there but its
associated
components are, then your connection in that part of the circuit is
wrong.

You are driving the LED in the opto-isolator from the TL431 Anode. If
you
download a TL431 data sheet then you will see that the anode is its
ground
reference. The Ref terminal is regulated at +2V5 with respect to the
Anode.

The LED and series resistor should be placed in series from the
Cathode to
Vout. The Anode should be connected to ground. You should take the
feedback
from Vsense. It looks like you have Vsense and Vout swapped as well
as
having the LED in the wrong position.

If the forward drop of the LED is about 1V2 and you add the 2V5
reference
voltage that places the reference terminal at 3V7 and the circuit, as
drawn,
will try to regulate Vout/Vsense at about 15V. In that respect it's
right...... but otherwise it's wrong.

Hope that makes sense.....

I'll poke about a bit more.

DNA


Thanks for the reply.
I have indeed got the opto connected on the wrong side of the tl431.
Going to correct that in the next revision.(currently in progress).
That would explain why my output was higher than I thaught it should
be!!
The connections to the tl431 I think are correct. I got them from Dean
Venable's paper "New techniques for measuring feedback loop transfer
functions in current mode controllers".FIG 1. I think my misleading
naming of those nets may be confusing the issue.Naughty me....:0(

Thanks for the tips.
Rob
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colin
electronics forum Guru Wannabe


Joined: 30 Apr 2005
Posts: 247

PostPosted: Mon May 16, 2005 1:27 pm    Post subject: Re: UC3843 power supply help needed!!! Reply with quote

<seegoon99@yahoo.com> wrote in message
news:1116227614.747750.258110@z14g2000cwz.googlegroups.com...
Hi to all.
I have built a power supply using a uc3843 chip and need some help.
The supply takes 220Vac and steps it down to 14Vdc(approx).
I have managed to get the supply working OK , but I still need a bit of
help.The schematic is attached , in LTSpice format.I modeled the
schematic and it seems to be ok , but I'm not sure how much you can
trust a simulation it this sort of level.
I've attached the model file for anyone who would like to simulate the
schematic. Hope it does not make the file to big , but I don't have any
access to any other binary groups to send it to.

When I first powered up the circuit the output was very noisy , and got
worse as the load increaced.I found by lots of trial and error that if
I put a small(100pF) cap across R11(3k3) the output stabilizes and
everything seems good.There is a bit of high frequency noise on the
output at the switching frequency , but I am sure this is to be
expected.
Now the problem...

I found by checking the drive to the FET that the loop seems unstable
at certain loads.As I increace the load from 0A to 2.5A
you can see the gate drive pulse width increacing as expected , but at
certain loads it seems to jump all over the place and the scope can't
trigger.From about 300mA to say 1,5A the gate drive is a mess , and
after that it seems to settle down nicely.

How do I go about fixing this.It does not seem to be causing a problem
on the output , but I would like to fix it up anyway.
I am sure it is a loop/compensation problem , but I am not sure how to
go about fixing it.I have tried changing the gain resistor(R5) to 100k
and 147K to no avail.Same with the compensation cap C2(100p / 200p). I
have also fiddled with the resistor/cap combination around the TL431 ,
also without much luck.
I am not very experienced with this type of power supply , so I am in
the dark a bit!!
It may also be a board layout problem.I did the board in a hurry
and did not pay HUGE amount of attention to layout , but I did try and
keep high current areas away from control lines etc.It is single sided.
This is a sort of hobby project , so time is not really of the
esscence. I only have a scope and meter to work with , so any solutions
that involve using other expensive equipment will be out of my
capability.My maths is also not very hot , so any solution that involve
lots of complex maths may be beyound me , but post them anyway as the
may be of interest to someone else.(they will be of interest to me ,
even if over my head!!)


ive used this chip in probaly a dozen designs, its a realy neat little
package, i cldnt load your circuit, but if u cld post a jpg il have a look
at it, the spec sheet for this device is realy good, if u have loop
stability problems you realy need to analyse your loop charecteristics
carefully.

with opto feed back you need to acount for the wide variation in loop gain
they can have.

some designs rely on a smal amount of esr in the output caps to ensure
stability, although persoanly i would try to avoid this.

with current mode control its realy easy to charecterise the output, its
just like a big integrator, so
any roll of in the rest of feedback loop needs to occur when the overall
gain is less than 1. finding the loop gain at wich it becomes unstable and
reducing it by a factor of 2 or so is one posibility.

Colin =^.^=
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Guest






PostPosted: Tue May 17, 2005 4:17 am    Post subject: Re: UC3843 power supply help needed!!! Reply with quote

colin wrote:
Quote:
seegoon99@yahoo.com> wrote in message
news:1116227614.747750.258110@z14g2000cwz.googlegroups.com...
Hi to all.
I have built a power supply using a uc3843 chip and need some help.
The supply takes 220Vac and steps it down to 14Vdc(approx).
I have managed to get the supply working OK , but I still need a bit
of
help.The schematic is attached , in LTSpice format.I modeled the
schematic and it seems to be ok , but I'm not sure how much you can
trust a simulation it this sort of level.
I've attached the model file for anyone who would like to simulate
the
schematic. Hope it does not make the file to big , but I don't have
any
access to any other binary groups to send it to.

When I first powered up the circuit the output was very noisy , and
got
worse as the load increaced.I found by lots of trial and error that
if
I put a small(100pF) cap across R11(3k3) the output stabilizes and
everything seems good.There is a bit of high frequency noise on the
output at the switching frequency , but I am sure this is to be
expected.
Now the problem...

I found by checking the drive to the FET that the loop seems unstable
at certain loads.As I increace the load from 0A to 2.5A
you can see the gate drive pulse width increacing as expected , but
at
certain loads it seems to jump all over the place and the scope can't
trigger.From about 300mA to say 1,5A the gate drive is a mess , and
after that it seems to settle down nicely.

How do I go about fixing this.It does not seem to be causing a
problem
on the output , but I would like to fix it up anyway.
I am sure it is a loop/compensation problem , but I am not sure how
to
go about fixing it.I have tried changing the gain resistor(R5) to
100k
and 147K to no avail.Same with the compensation cap C2(100p / 200p).
I
have also fiddled with the resistor/cap combination around the TL431
,
also without much luck.
I am not very experienced with this type of power supply , so I am
in
the dark a bit!!
It may also be a board layout problem.I did the board in a hurry
and did not pay HUGE amount of attention to layout , but I did try
and
keep high current areas away from control lines etc.It is single
sided.
This is a sort of hobby project , so time is not really of the
esscence. I only have a scope and meter to work with , so any
solutions
that involve using other expensive equipment will be out of my
capability.My maths is also not very hot , so any solution that
involve
lots of complex maths may be beyound me , but post them anyway as the
may be of interest to someone else.(they will be of interest to me ,
even if over my head!!)


ive used this chip in probaly a dozen designs, its a realy neat
little
package, i cldnt load your circuit, but if u cld post a jpg il have a
look
at it, the spec sheet for this device is realy good, if u have loop
stability problems you realy need to analyse your loop
charecteristics
carefully.

with opto feed back you need to acount for the wide variation in loop
gain
they can have.

some designs rely on a smal amount of esr in the output caps to
ensure
stability, although persoanly i would try to avoid this.

with current mode control its realy easy to charecterise the output,
its
just like a big integrator, so
any roll of in the rest of feedback loop needs to occur when the
overall
gain is less than 1. finding the loop gain at wich it becomes
unstable and
reducing it by a factor of 2 or so is one posibility.

Colin =^.^=


Hi there. I don't have any access to any other groups , how can I post
a jpg to this group?
Do you have an email I can send it to.
Cheers
Rob
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Pooh Bear
electronics forum Guru


Joined: 24 Mar 2005
Posts: 3507

PostPosted: Tue May 17, 2005 5:23 am    Post subject: Re: UC3843 power supply help needed!!! Reply with quote

seegoon99@yahoo.com wrote:

Quote:

Hi there. I don't have any access to any other groups

How so ?

Quote:
how can I post a jpg to this group?

You can't - it's not a binaries group although it's possible it might get
through.

a.b.s.e is the preferred group for posting binaries.

Graham
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Guest






PostPosted: Tue May 17, 2005 6:15 am    Post subject: Re: UC3843 power supply help needed!!! Reply with quote

Pooh Bear wrote:
Quote:
seegoon99@yahoo.com wrote:


Hi there. I don't have any access to any other groups

How so ?

how can I post a jpg to this group?

You can't - it's not a binaries group although it's possible it might
get
through.

a.b.s.e is the preferred group for posting binaries.

Graham

Hi there.
I am behind a firewall , and cant access the news groups by news
reader. I have to go through Google , and they don't seem to carry
a.b.s.e .

Cheers
Rob
Back to top
Don Pearce
electronics forum Guru Wannabe


Joined: 03 May 2005
Posts: 112

PostPosted: Tue May 17, 2005 6:27 am    Post subject: Re: UC3843 power supply help needed!!! Reply with quote

On 17 May 2005 01:15:15 -0700, seegoon99@yahoo.com wrote:

Quote:

Pooh Bear wrote:
seegoon99@yahoo.com wrote:


Hi there. I don't have any access to any other groups

How so ?

how can I post a jpg to this group?

You can't - it's not a binaries group although it's possible it might
get
through.

a.b.s.e is the preferred group for posting binaries.

Graham

Hi there.
I am behind a firewall , and cant access the news groups by news
reader. I have to go through Google , and they don't seem to carry
a.b.s.e .

Cheers
Rob

Being behind a firewall shouldn't stop you accessing a news server,
unless it is also blocking ports. If you open up port 119, you should
be able to use any news service.

d

Pearce Consulting
http://www.pearce.uk.com
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Pooh Bear
electronics forum Guru


Joined: 24 Mar 2005
Posts: 3507

PostPosted: Tue May 17, 2005 6:44 am    Post subject: Re: UC3843 power supply help needed!!! Reply with quote

seegoon99@yahoo.com wrote:

Quote:
Pooh Bear wrote:
seegoon99@yahoo.com wrote:


Hi there. I don't have any access to any other groups

How so ?

how can I post a jpg to this group?

You can't - it's not a binaries group although it's possible it might
get
through.

a.b.s.e is the preferred group for posting binaries.

Graham

Hi there.
I am behind a firewall , and cant access the news groups by news
reader. I have to go through Google , and they don't seem to carry
a.b.s.e .

Google doesn't carry any binaries groups AFAIK.

Whose firewall are you behind ? Can you get your IT ppl to let you acces
a.b.s.e ?

Graham
Back to top
petrus bitbyter
electronics forum Guru


Joined: 24 Mar 2005
Posts: 363

PostPosted: Tue May 17, 2005 6:52 am    Post subject: Re: UC3843 power supply help needed!!! Reply with quote

<seegoon99@yahoo.com> schreef in bericht
news:1116310676.797823.110320@g44g2000cwa.googlegroups.com...
Quote:

colin wrote:
seegoon99@yahoo.com> wrote in message
news:1116227614.747750.258110@z14g2000cwz.googlegroups.com...
Hi to all.
I have built a power supply using a uc3843 chip and need some help.
The supply takes 220Vac and steps it down to 14Vdc(approx).
I have managed to get the supply working OK , but I still need a bit
of
help.The schematic is attached , in LTSpice format.I modeled the
schematic and it seems to be ok , but I'm not sure how much you can
trust a simulation it this sort of level.
I've attached the model file for anyone who would like to simulate
the
schematic. Hope it does not make the file to big , but I don't have
any
access to any other binary groups to send it to.

When I first powered up the circuit the output was very noisy , and
got
worse as the load increaced.I found by lots of trial and error that
if
I put a small(100pF) cap across R11(3k3) the output stabilizes and
everything seems good.There is a bit of high frequency noise on the
output at the switching frequency , but I am sure this is to be
expected.
Now the problem...

I found by checking the drive to the FET that the loop seems unstable
at certain loads.As I increace the load from 0A to 2.5A
you can see the gate drive pulse width increacing as expected , but
at
certain loads it seems to jump all over the place and the scope can't
trigger.From about 300mA to say 1,5A the gate drive is a mess , and
after that it seems to settle down nicely.

How do I go about fixing this.It does not seem to be causing a
problem
on the output , but I would like to fix it up anyway.
I am sure it is a loop/compensation problem , but I am not sure how
to
go about fixing it.I have tried changing the gain resistor(R5) to
100k
and 147K to no avail.Same with the compensation cap C2(100p / 200p).
I
have also fiddled with the resistor/cap combination around the TL431
,
also without much luck.
I am not very experienced with this type of power supply , so I am
in
the dark a bit!!
It may also be a board layout problem.I did the board in a hurry
and did not pay HUGE amount of attention to layout , but I did try
and
keep high current areas away from control lines etc.It is single
sided.
This is a sort of hobby project , so time is not really of the
esscence. I only have a scope and meter to work with , so any
solutions
that involve using other expensive equipment will be out of my
capability.My maths is also not very hot , so any solution that
involve
lots of complex maths may be beyound me , but post them anyway as the
may be of interest to someone else.(they will be of interest to me ,
even if over my head!!)


ive used this chip in probaly a dozen designs, its a realy neat
little
package, i cldnt load your circuit, but if u cld post a jpg il have a
look
at it, the spec sheet for this device is realy good, if u have loop
stability problems you realy need to analyse your loop
charecteristics
carefully.

with opto feed back you need to acount for the wide variation in loop
gain
they can have.

some designs rely on a smal amount of esr in the output caps to
ensure
stability, although persoanly i would try to avoid this.

with current mode control its realy easy to charecterise the output,
its
just like a big integrator, so
any roll of in the rest of feedback loop needs to occur when the
overall
gain is less than 1. finding the loop gain at wich it becomes
unstable and
reducing it by a factor of 2 or so is one posibility.

Colin =^.^=


Hi there. I don't have any access to any other groups , how can I post
a jpg to this group?
Do you have an email I can send it to.
Cheers
Rob


Rob,

Consider to use Andy´s ASCII-Circuit
www.tech-chat.de

petrus bitbyter
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Genome
electronics forum Guru


Joined: 30 Apr 2005
Posts: 789

PostPosted: Tue May 17, 2005 9:50 am    Post subject: Re: UC3843 power supply help needed!!! Reply with quote

<seegoon99@yahoo.com> wrote in message
news:1116244560.585586.272390@z14g2000cwz.googlegroups.com...
Quote:

Thanks for the reply.

Thanks for the tips.
Rob


I think you might have large signal problems... in addition to concerns
about loop stability. This is DNA speak for 'I haven't figured it out yet'.

Spice is nice but... you have to nurse it in the same way you would with a
real circuit. Fortunately it doesn't go bang when things go wrong. However
you have to take care with what you use and how you use it. Keep it simple
and test the things you are using to see how they behave or if they behave
the way you expect them to. Oh, draw pretty circuit diagrams and try to
stick to the standard bits and pieces.

Now, this isn't going to solve your problem.

Here's your first part. The opto-coupler.

***
Version 4
SHEET 1 880 904
WIRE -144 512 -144 176
WIRE -144 624 -144 592
WIRE -144 656 -144 624
WIRE 16 176 -144 176
WIRE 16 272 16 176
WIRE 16 400 16 368
WIRE 16 512 16 480
WIRE 16 624 -144 624
WIRE 16 624 16 592
WIRE 48 272 16 272
WIRE 48 368 16 368
WIRE 272 176 16 176
WIRE 272 272 240 272
WIRE 272 272 272 176
WIRE 272 336 240 336
WIRE 272 512 272 336
WIRE 272 624 16 624
WIRE 272 624 272 592
WIRE 320 336 272 336
FLAG 320 336 EMITT
IOPIN 320 336 Out
FLAG -144 656 0
SYMBOL res 0 384 R0
WINDOW 3 36 66 Left 0
SYMATTR InstName RLED
SYMATTR Value 220R
SYMBOL Optos\\4N25 144 336 R0
WINDOW 0 -81 -123 Center 0
WINDOW 3 -67 -99 Center 0
SYMATTR InstName U1
SYMBOL res 256 496 R0
WINDOW 3 36 64 Left 0
SYMATTR InstName R1
SYMATTR Value 1K
SYMBOL voltage 16 496 R0
WINDOW 0 41 42 Left 0
WINDOW 3 41 85 Left 0
WINDOW 123 39 62 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName VAC
SYMATTR Value 3.1
SYMATTR Value2 AC 1 0
SYMBOL voltage -144 496 R0
WINDOW 0 36 42 Left 0
WINDOW 3 39 64 Left 0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName VSUPP
SYMATTR Value 5V
TEXT -152 696 Left 0 !.ac dec 20 1 1E6
***

It's not what you are using in your circuit but it's what I've got in mine.
The voltage source VAC is set at a DC level that the circuit works at and
has its AC part set to 1V.

Run the AC analysis and plot V(EMITT). That gives you the opto-isolator
transfer function.

If you are lucky then you will see something with about 10dB (3 in real
money) gain up to about 10KHz. Stick a cursor on it and you'll find that
it's 3dB down at about 30KHz with the phase at 135 degrees.

Between 100KHz and 1MHz the gain drops by 20dB. All that makes it a first
order roll off at about 30KHz with no other nasties. It may, or may not, be
important to your overall loop response.

More importantly.... Does the behaviour of that model agree with the actual
part you are going to use?

Colin has mentioned that opto-isolators tend to be 'dirt' when you look at
tolerances. They are also piss poor over most other parameters. Read the
data sheets.

So, you've characterized that part.

Time for some Maths.....

If you look at Figure 1Cool of On-Semi's data sheet then after them there 2
diodes at the output of the Error Amplifier you will see an 2R/R divider.
Call the input to that Vpea. Call your current sense resistor Rsns. The peak
current in your primary inductance, Lpri, is

Ipk = Vpea/3Rsns

The 3 comes from the 2R/R divider.

I have sort of noticed that you have cunningly designed your circuit to
operate discontinuously..... hmmmmmmmmmm.

The energy stored is

Epri = Lpri.Ipk^2/2

Which gets 'completely' delivered to the output.

Esec = Lpri.Ipk^2/2

And that happens at the switching frequency, Fs, which gives the output
power as

Pout = Fs.Lpri.Ipk^2/2
= Fs.Lpri/2 * (Vpea/3.Rsns)^2

Since.....

Pout = Vout.Iout

Iout = Pout/Vout
= Fs.Lpri/2.Vout * (Vpea/3Rsns)^2
= Vpea^2 * Fs.Lpri/18.Vout.Rsns^2

You are meant to be checking this as I go along. Sheesh...

Differentiate with respect to Vpea

dIout/dVpea = 2Vpea.Fs.Lpri/18.Vout.Rsns^2
= Vpea.Fs.Lpri/9.Vout.Rsns^2

Which is the small signal thingummyjig gain.

Unfortunately it depends on Vpea in the first place, or the second place,
or...

Anyway

Back to

Pout = Fs.Lpri/2 * (Vpea/3.Rsns)^2

and try and rearrange that to make Vpea the subject.

Pout = Vpea^2 * Fs.Lpri/2 * 1/(9.Rsns^2)

So

Vpea^2 = 2.9.Rsns^2/Fs.Lpri

and

Vpea = SQRT(2.9.Rsns^2/Fs.Lpri)

I assume you have not been confused by the use of . and * as multiplication
symbols..... That's 2 times 9.

Right
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Pooh Bear
electronics forum Guru


Joined: 24 Mar 2005
Posts: 3507

PostPosted: Tue May 17, 2005 10:21 am    Post subject: Re: UC3843 power supply help needed!!! Reply with quote

Genome wrote:

Quote:
seegoon99@yahoo.com> wrote in message
news:1116244560.585586.272390@z14g2000cwz.googlegroups.com...

Thanks for the reply.

Thanks for the tips.
Rob


I think you might have large signal problems... in addition to concerns
about loop stability. This is DNA speak for 'I haven't figured it out yet'.

Spice is nice but...

If you don't really have a mental understanding of how the circuit will work -
it'll simply do the garbage in - garbage out trick.

Graham
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Genome
electronics forum Guru


Joined: 30 Apr 2005
Posts: 789

PostPosted: Tue May 17, 2005 11:35 am    Post subject: Re: UC3843 power supply help needed!!! Reply with quote

"Genome" <ilike_spam@yahoo.co.uk> wrote in message
news:hUkie.13632$he1.7102@newsfe6-gui.ntli.net...
Quote:


Oh crap, coitus interupptus. (Request for a Woodgate)

Clicked Send instead of save....

Nerr.

Later

DNA
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Genome
electronics forum Guru


Joined: 30 Apr 2005
Posts: 789

PostPosted: Tue May 17, 2005 11:45 am    Post subject: Re: UC3843 power supply help needed!!! Reply with quote

"Pooh Bear" <rabbitsfriendsandrelations@hotmail.com> wrote in message
news:4289E1AE.F5498C2E@hotmail.com...
Quote:
Genome wrote:

seegoon99@yahoo.com> wrote in message
news:1116244560.585586.272390@z14g2000cwz.googlegroups.com...

Thanks for the reply.

Thanks for the tips.
Rob


I think you might have large signal problems... in addition to concerns
about loop stability. This is DNA speak for 'I haven't figured it out
yet'.

Spice is nice but...

If you don't really have a mental understanding of how the circuit will
work -
it'll simply do the garbage in - garbage out trick.

Graham


Hey, chill out.

I'm listening to Rush, Signals.

Nice!

Would you like to give a hint about the company you work for so I don't have
to work for them when they f*** you off.

DNA
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Google

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