I think I need a switched mode regulator....

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I need 5v at 380mA when powered from a car battery, nominally 13.2V, but varying between 10v and 14.5V

At 14.5v supply, a 7805 is dissipating 3.6 watts and a serious heatsink (incompatible with the overall product design) is required :(

So I've discovered the single component SM regulator, but the product choice seems huge.

Cost is fairly important, plus availability in the UK and US.

So which one would you choose?..or would you do it a different way?

(...and as I'm not into SMPS's, are we saying that if I find one with 85% efficiency, the power dissipation will be 5*0.38*0.15 = 285mW - which would be nice!)

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You need a DC-DC convertor... but you are not mentioning whether you need any isolation between the input and the output . Assunimng you do not , National Semi . has a large range of easy to use Simple Switchers . http://www.national.com/pf//LM/LM5008.html

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Linear Technology is my favorite for this sort of stuff. Check out the LT1076.

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This thread triggered this question I've been wondering about.

I've noticed that there seems to be a new generation of wall-wart. New mobile phones have AC adaptors that are about the size of 3 AA batteries. Radio Shack has a couple small general purpose ones too. And they handle almost 1800mW, ie dang near 2A.

Anybody know anything about these cool little beasties? I'm assuming they're switching mode power supplies.

-- Hank

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Ive taken apart one of the slim Motorola adapters and its a small SMPS. Pretty cool little power supply.

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ahank wrote:
This thread triggered this question I've been wondering about.

I've noticed that there seems to be a new generation of wall-wart. New mobile phones have AC adaptors that are about the size of 3 AA batteries. Radio Shack has a couple small general purpose ones too. And they handle almost 1800mW, ie dang near 2A.

Anybody know anything about these cool little beasties? I'm assuming they're switching mode power supplies.

-- Hank

Yes, they are switching power supplies. The heavy input transformer is missing, and it is replaced by a simple switcher. There is one much smaller transformer since it is working in the range of few hundreds kHz.

Pop

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I purchased a couple of Recom R-785.0-0.5 5V, 500mA switching regulators that have the same pinout as a normal 7805, haven't used them yet but may be of interest.

John Samperi

Ampertronics Pty. Ltd.

www.ampertronics.com.au

* Electronic Design * Custom Products * Contract Assembly

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Apart from the SMPS issue, you must also look at the input protection. Auto electrics aren't quite as friendly as you would like - you've got to cope with the legendary alternator 'load dump' that will give you around 40V. So look at incorporating a varistor and a polyswitch on the input side to protect your psu. As for choice - something like the NS simple switcher as mentioned previously has served me well. Something like a LM2574N would serve nicely. It would be worth looking at their newer, higher frequency parts as this may allow you not to use electrolytics (bad news in cars due to temperature). Be sure to read the datasheets CAREFULLY! The components specs are critical in SMPS. As for dissipation - you'll probably not need a heatsink.

Whilst we're talking about automotive apps - don't forget about temperature and vibration - any large components must be properly supported otherwise they'll fall of the board in time. Expect the inside temp of the car to reach around 70C.

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Quote:
Something like a LM2574N would serve nicely

I've been working with the LM2671,LM2672, and LM2673
parts. They run at 260 khz and so far have not
exibited any unpleasant qualities. I'm using them
for 3.3 volt "main bus" power, and also to do the
grunt work in a Nimh battery charging application
(using a Tiny13 for supervisory control).

Transorb diodes deal nicely with transients.

Tom Pappano
Tulsa, Oklahoma

Tom Pappano
Tulsa, Oklahoma

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MartinM57 wrote:

...plus availability in the UK and US.

LM2575 satisfies that - would that do?

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I am rather fond of the LM2595T-ADJ, as it runs at 150KHz, and with a low cost 100uH bobin inductor and a schottkey diode, usual bypass caps and electros, make quite an efficient power supply, noting that NSC has newer IC's for the same task.

OT:

Quote:
I've noticed that there seems to be a new generation of wall-wart. New mobile phones have AC adaptors that are about the size of 3 AA batteries. Radio Shack has a couple small general purpose ones too. And they handle almost 1800mW, ie dang near 2A.

Anybody know anything about these cool little beasties? I'm assuming they're switching mode power supplies.

Watch out how you use these new switching supplies.

Every one I have tested has one inherent problem which could lead to the distruction of your project!

They have one or more small high voltage capacitors between the DC side of their bridge rectifier to usually the negative output terminal. This I think is to return the floating output to a low impeadence point for EMC issues. So What! you say....

Well, I say that one end of this cap is at rectified mains potential, as there is no earth connection, and the other is connected to your load. If the load is not floating and is connected to earth directly, or via test equipment (CRO, PC-Comms ETC) dammage may occur.

The possibility of dammage is worst when an isolated load is probed with ground referenced equipment.

As a test, just measure one of the output terminals of the supply with a CRO. "Several Hundred Volts p-p" and on a 240V mains, about 85V AC WRT earth on a Volt Meter.

Not just stray pick-up such as when you touch the cro probe with your finger.

Be warned, We lost a programming board by connecting the PC-Serial port to it while it was being powered by one of these. New Programmer now has old fashioned transformer plugpack, switching plug pack destroyed to prevent further dammage.

Take Care,
Ron.

 

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ahank wrote:
This thread triggered this question I've been wondering about.

I've noticed that there seems to be a new generation of wall-wart. New mobile phones have AC adaptors that are about the size of 3 AA batteries. Radio Shack has a couple small general purpose ones too. And they handle almost 1800mW, ie dang near 2A.

Anybody know anything about these cool little beasties? I'm assuming they're switching mode power supplies.
-- Hank

Does anybody know what chip can be used (bought) when I want to transform 230VAC to something between 5VDC-50VDC? I cannot find any in my country...
I have disassembled one cheap switcher - there were two transistors only and small transformer plus few caps, resistors and diodes... - no sw. regulator - is IC regulator really needed (true - it burnt out after few hours of using:) )?