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17 V linear voltage regulator
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Mochuelo
electronics forum Guru Wannabe


Joined: 10 May 2005
Posts: 128

PostPosted: Fri Jul 14, 2006 11:57 am    Post subject: 17 V linear voltage regulator Reply with quote

Hi,

I need to go from Vin={18 V to 24 V} down to Vout=17 V with a linear
regulator. Iout is 60 mA. The LM317 and similar ones seem to need
around 3 V input-to-output to provide good regulation, which is too
much for me. I only have 1 V available. Does anyone know of a good smd
part for this? Of course, I already count on having to use resistors
to set the output voltage.

Thanks in advance,
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PeterSmith1954@googlemail
electronics forum addict


Joined: 04 Jul 2006
Posts: 79

PostPosted: Fri Jul 14, 2006 1:58 pm    Post subject: Re: 17 V linear voltage regulator Reply with quote

Mochuelo wrote:
Quote:
Hi,

I need to go from Vin={18 V to 24 V} down to Vout=17 V with a linear
regulator. Iout is 60 mA. The LM317 and similar ones seem to need
around 3 V input-to-output to provide good regulation, which is too
much for me. I only have 1 V available. Does anyone know of a good smd
part for this? Of course, I already count on having to use resistors
to set the output voltage.

Thanks in advance,

You'll need a low dropout regulator (LDO). check the usual suspects web
sites (National, TI, Linear, Maxim, Zetec, On Semi, Fairchild, ST to
name but a few).

Most give parametric search

You'll need Vin (max) > 26V (have some headroom), Vo-Vi <= 0.8V @ load

Cheers

PeteS
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Mochuelo
electronics forum Guru Wannabe


Joined: 10 May 2005
Posts: 128

PostPosted: Fri Jul 14, 2006 6:25 pm    Post subject: Re: 17 V linear voltage regulator Reply with quote

On 14 Jul 2006 06:58:53 -0700, "PeterSmith1954@googlemail.com"
<PeterSmith1954@googlemail.com> wrote:

Quote:
Mochuelo wrote:
Hi,

I need to go from Vin={18 V to 24 V} down to Vout=17 V with a linear
regulator. Iout is 60 mA. The LM317 and similar ones seem to need
around 3 V input-to-output to provide good regulation, which is too
much for me. I only have 1 V available. Does anyone know of a good smd
part for this? Of course, I already count on having to use resistors
to set the output voltage.

Thanks in advance,

You'll need a low dropout regulator (LDO). check the usual suspects web
sites (National, TI, Linear, Maxim, Zetec, On Semi, Fairchild, ST to
name but a few).

Most give parametric search

You'll need Vin (max) > 26V (have some headroom), Vo-Vi <= 0.8V @ load

Cheers

PeteS

Thank you. I know what I'm looking for, and how it is called. I just
wanted to know if someone is already using a suitable part that can
recommend to me, especially one that can be easily obtained through
distributors like Farnell, DigiKey, Amidata...

Ideally, it should be one with a PMOS pass transistor and a very low
quiescent current (100 uA max). So far, not much luck with Farnell.

Best,
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mmm
electronics forum beginner


Joined: 25 Jun 2005
Posts: 26

PostPosted: Fri Jul 14, 2006 8:48 pm    Post subject: Re: 17 V linear voltage regulator Reply with quote

Mochuelo wrote:
Quote:
On 14 Jul 2006 06:58:53 -0700, "PeterSmith1954@googlemail.com"
PeterSmith1954@googlemail.com> wrote:



Thank you. I know what I'm looking for, and how it is called. I just
wanted to know if someone is already using a suitable part that can
recommend to me, especially one that can be easily obtained through
distributors like Farnell, DigiKey, Amidata...

Ideally, it should be one with a PMOS pass transistor and a very low
quiescent current (100 uA max). So far, not much luck with Farnell.


lp2951 or lp2950 from national should fit the bill, dil and soic
versions available from farnell
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PeterSmith1954@googlemail
electronics forum addict


Joined: 04 Jul 2006
Posts: 79

PostPosted: Sat Jul 15, 2006 11:13 am    Post subject: Re: 17 V linear voltage regulator Reply with quote

mmm wrote:
Quote:
Mochuelo wrote:
On 14 Jul 2006 06:58:53 -0700, "PeterSmith1954@googlemail.com"
PeterSmith1954@googlemail.com> wrote:



Thank you. I know what I'm looking for, and how it is called. I just
wanted to know if someone is already using a suitable part that can
recommend to me, especially one that can be easily obtained through
distributors like Farnell, DigiKey, Amidata...

Ideally, it should be one with a PMOS pass transistor and a very low
quiescent current (100 uA max). So far, not much luck with Farnell.


lp2951 or lp2950 from national should fit the bill, dil and soic
versions available from farnell


National's page for this device at:

http://www.national.com/pf/LP/LP2951.html

Cheers

PeteS
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Mochuelo
electronics forum Guru Wannabe


Joined: 10 May 2005
Posts: 128

PostPosted: Sat Jul 15, 2006 2:19 pm    Post subject: Re: 17 V linear voltage regulator Reply with quote

On 15 Jul 2006 04:13:36 -0700, "PeterSmith1954@googlemail.com"
<PeterSmith1954@googlemail.com> wrote:

Quote:
mmm wrote:
Mochuelo wrote:
On 14 Jul 2006 06:58:53 -0700, "PeterSmith1954@googlemail.com"
PeterSmith1954@googlemail.com> wrote:



Thank you. I know what I'm looking for, and how it is called. I just
wanted to know if someone is already using a suitable part that can
recommend to me, especially one that can be easily obtained through
distributors like Farnell, DigiKey, Amidata...

Ideally, it should be one with a PMOS pass transistor and a very low
quiescent current (100 uA max). So far, not much luck with Farnell.


lp2951 or lp2950 from national should fit the bill, dil and soic
versions available from farnell


National's page for this device at:

http://www.national.com/pf/LP/LP2951.html

Cheers

PeteS

Thanks again to both of you. The ground pin current (approx 3 mA @ 60
mA) kills me. That's due to the PNP. I have to connect around 200
units in parallel, hanging on a 24 V bus, and I'm trying to minimize
the losses. I must say, I'm quite amazed that I cannot find one with a
PMOS pass transistor that works at these voltage levels.

Best,
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mmm
electronics forum beginner


Joined: 25 Jun 2005
Posts: 26

PostPosted: Sat Jul 15, 2006 2:53 pm    Post subject: Re: 17 V linear voltage regulator Reply with quote

Mochuelo wrote:
Quote:
On 15 Jul 2006 04:13:36 -0700, "PeterSmith1954@googlemail.com"
PeterSmith1954@googlemail.com> wrote:


National's page for this device at:

http://www.national.com/pf/LP/LP2951.html

Cheers

PeteS


Thanks again to both of you. The ground pin current (approx 3 mA @ 60
mA) kills me. That's due to the PNP. I have to connect around 200
units in parallel, hanging on a 24 V bus, and I'm trying to minimize
the losses. I must say, I'm quite amazed that I cannot find one with a
PMOS pass transistor that works at these voltage levels.


Now I can be saying the biggest bull***t of my life:

what about the use of the schematic on the national page with the added
pass mosfet ?
you should be able to lowering the ground current at desidered level
augmenting the 2K resistor on OUT pin

a bit of overkill, the IC and an external MOS, but if you don't have
other solutions ....
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