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'voltage regulator question'
1999\05\14@143102 by Andy Kunz

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Anybody know of a SMT regulator which can handle 45V input, 5V/50mA output?
40V * 50mA = 2W - an awful lot for a tiny PCB to handle.

I'm finding very few options in the datasheets.

PCB size is a premium. Reliability is SUPER important, component
cost/complexity is secondary.

Ideas?

Thanks!

Andy

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1999\05\14@144515 by William Chops Westfield

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   Anybody know of a SMT regulator which can handle 45V input, 5V/50mA output?
   40V * 50mA = 2W - an awful lot for a tiny PCB to handle.

That's well within the range of telco-oriented dc/dc converters (which have
input voltage of typically 36-72V), although those tend to start with a
particular package size and cram as many watts as possible into them, rather
than picking a number of watts and making the package as small as possible.
For example, in about the size of a 24pin DIP, Datel has a 3W converter.

I suspect you had something much smaller in mind...

BillW

1999\05\14@150731 by MEDICINTEKNIK KB

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The TL317CD is the SO8 version of a LM317 regulator. Max 40 V and 100 mA, but - I guess it ould run too hot...

You don't have room to help this little fellow out do you ?;  with a zener in series to the input or soething ?

Anyway - just look at the size of a SO8 product. Whatever it contains, it needs thermal assistance with black aluminium somehow in my opinion. Can you fit a cooler on top ?

Sven
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Datum: den 14 maj 1999 20:31
€mne: voltage regulator question


{Quote hidden}

1999\05\14@160418 by Andy Kunz

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>The TL317CD is the SO8 version of a LM317 regulator. Max 40 V and 100 mA,
>but - I guess it ould run too hot...

Thnks.  I'll check.

>You don't have room to help this little fellow out do you ?;  with a zener
>in series to the input or soething ?

Room?  It's about 1cm square.  A Zener would be possible, but it'll still
be warm.

>Anyway - just look at the size of a SO8 product. Whatever it contains, it
>needs thermal assistance with black aluminium somehow in my opinion. Can you
>fit a cooler on top ?

Cooler?  HA!

Andy

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1999\05\14@162816 by MEDICINTEKNIK KB
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Hi again Andy ,

A whole sq cm ? That is not so bad. An SO8 and a zener would find room.

Not knowing your product, and how this PCB is to be used, I am not joking, as I suggest that you should look for a 1x1 cm cooler. Maybe 6 - 8 mm high. Just guessing - but a block like that (with small "fins" of course) would just get luke warm at 2 Watts. That's how I would look at it. Such coolers are available. And again - 2 Watts is always 2 Watts. Whatever the compmonent. Color, material  and size counts.

But again - I don't know if that is to tall, impossible to affix, or whatever. Depending on quantity, a custom designed cooler might be a solution.

Best Regards


Sven
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Datum: den 14 maj 1999 22:04
€mne: Re: SV: voltage regulator question


{Quote hidden}

1999\05\14@164837 by Geier, David

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Hello

Check out Infineon(formally Siemens) TLE 4274 G V50.  Siemens has a good
selection of LDO regulators that they spec to 45V.  That is still a lot of
power to dissipate.  Good luck.

David

> {Original Message removed}

1999\05\14@171154 by Jay.R.Vijay-Indra

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You will find  power supply chips for Telecom circuits does this. First try
siliconix, then maixm, linear tech, SGS, to name few. U/Interface on ISDN
is powered from 48V to 5V converters.

Regards,

Jay

PS If I find part numbers I will post it next week.

At 14:28 14/05/99 -0400, you wrote:
{Quote hidden}

1999\05\14@185527 by Jamil J. Weatherbee

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I am doing something similar to this with an lm3480, but the entire PCB is
encased in a heat conductive potting compound (an epoxy)


On Fri, 14 May 1999, MILTON MEDICINTEKNIK KB wrote:

{Quote hidden}

1999\05\14@211206 by ns

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What about National's HV versions of simple switcher.  LM2594HV is 5V,
SOIC 8pin, max Vin 60V.

On Fri, 14 May 1999, Andy Kunz wrote:

{Quote hidden}

1999\05\14@231811 by William K. Borsum

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At 02:28 PM 5/14/99 -0400, you wrote:
>Anybody know of a SMT regulator which can handle 45V input, 5V/50mA output?
> 40V * 50mA = 2W - an awful lot for a tiny PCB to handle.
>
>I'm finding very few options in the datasheets.
>
>PCB size is a premium. Reliability is SUPER important, component
>cost/complexity is secondary.
>

Check with National Semi.  They have variants of the 78xx series in a
"DPAK" configuration.  Gets over 30 volts on the inputs, but I don't recall
how far over.

Unless you need a really WIDE input range, put a power zener in series to
drop the voltage to an acceptable level.  A 30 volt .05 A zener would need
to be 2 watts and would drop your 40 volts to 15 which most SMT devices
will handle (16 volt MAX).

A note to everyone: Check out the TELCOM TC55 series!  200 mA output, 3
microamps quiescent current, VERY low dropout voltage, and CHEAP.  SOT-23
package.  We plan on buying a reel of 5 and 3.3 volt parts and would
consider selling in smaller quantities.  This is a really good part!


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1999\05\15@084229 by wwl

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On Fri, 14 May 1999 20:15:18 -0700, you wrote:

>At 02:28 PM 5/14/99 -0400, you wrote:
>>Anybody know of a SMT regulator which can handle 45V input, 5V/50mA output?
>> 40V * 50mA = 2W - an awful lot for a tiny PCB to handle.
>>
>>I'm finding very few options in the datasheets.
>>
>>PCB size is a premium. Reliability is SUPER important, component
>>cost/complexity is secondary.
If reliability is important, you don't want to be dissipating 2 watts,
especially in a small space. Use a switcher, e.g. nat. semi. LM2574HV
which takes up to 60V input and comes in a 14 pin SO or 8 pin DIP.
Although it will take more board space for components, you'll save the
space you'd otherwise use on the heatsinking you'd need for a linear
reg, as well as drastically reducing the power draw from the 40V
supply.
At 50mA o/p you should be able to use a pretty small inductor, diode
and caps.

1999\05\15@090728 by Russell McMahon

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Andy

A series resistor will get the majority of the dissipation away from
the IC.

You can let the regulator drop only a few volts when you are at full
design current. At low or no current the regulator will take most of
the dissipation and voltage but it will be less critical. You
nominated SMT but the resistors may not have to be. 4 x Philips SFR16
series resistors will handle max required dissipation (and will mount
in about 6mm x 3mm space each if necessary) and there are of course
lots of metal film resistors which will handle this power in a single
unit.


regards

               Russell McMahon.


{Original Message removed}

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