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sPuDd

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Joined: 10/07/2007
Location: Australia
Posts: 251

Posted: 07:57am 03 Apr 2010

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G'day all,
we use this particular species of 13.8Vdc 5Amp power supply a lot in the security industry. The brand has a very good reputation and is usually only killed by abuse. Normally we just replace a faulty unit with a new one and charge accordingly, but I thought I'd open one up and see what makes it tick.

This one has a faulty regulator as it outputs full rectified voltage. I have tested everything else and compared it to another unit.

However, the regulator is a TO-220 7-pin package and the markings have been deliberately scrubbed off. I searched for a few hours on Google for anything that would fit the bill, but alas only switching regulators come close. This PSU is not designed as a switching regulator as it lacks the necessary inductor, rectifier and output caps etc... it�s just an ultra low drop out series reg.

Anyone got a clue as to what it is?
A new one of these is ~$400

sPuDd..

It should work ...in theory

Gizmo

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Joined: 05/06/2004
Location: Australia
Posts: 5078

Posted: 08:05am 03 Apr 2010

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I think its a crime the way manufacturers deface components so they cant be identified.

I'll have a look though my component draw for any 7 pin regulators and let you know.

Glenn

The best time to plant a tree was twenty years ago, the second best time is right now.
JAQ

sPuDd

Senior Member

Joined: 10/07/2007
Location: Australia
Posts: 251

Posted: 10:17am 03 Apr 2010

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Thanks Gizmo,
I'm thinking I might mod the unit and fit an LM338T which is rated for 5amps continuous and 7amps peak in a TO-220 package.

sPuDd..

It should work ...in theory

Bryan1

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Joined: 22/02/2006
Location: Australia
Posts: 1344

Posted: 10:53am 03 Apr 2010

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G'day Spud,
Off memory I got some samples and the guys at the uni made me a constant current supply for my cnc power supply, I do reckon these had 7 pins and the chip might be the one. Unfortunately being late and a few ales under the belt it will be best to look in the morning.

Cheers Bryan

Edit: by the way is there an inductor on the board as this will give me the clue that I'm on the right trackEdited by Bryan1 2010-04-04

Downwind

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Joined: 09/09/2009
Location: Australia
Posts: 2333

Posted: 11:43am 03 Apr 2010

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What is the 2 components either side of the vreg.
I am guessing they might be bypass transistors.

Pete.

Sometimes it just works

WindChopper
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Joined: 08/02/2007
Location: United States
Posts: 15

Posted: 04:12pm 03 Apr 2010

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Take a look at

http://www.national.com/pf/LM/LM2678.html#Overview

Might be the same family

Russ

sPuDd

Senior Member

Joined: 10/07/2007
Location: Australia
Posts: 251

Posted: 02:11am 04 Apr 2010

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Bryan,
no inductor - its a series regulator.

Pete,
the side devices are twin schottky packs that form two half wave rectifiers.

Russ,
that was one of the devices I found during my search, but its a switch mode device which will not do.

I'll trace out the circuit then mod it for an LM338T. I've got several of them laying about. Just thought someone may have seen a 7-pin TO-220 series reg used somewhere else.

sPuDd..

It should work ...in theory

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