EA 40V/3A power supply kit problem

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Bought this kit a while ago when it was on special @ $100.

Finally completed assembly and it works except for one annoying problem
that I discovered during stress testing.

When the output is short circuit, the current limiter works as it
should but only to about 2A.  Above that and the blinkety-blink of the
ceiling fluro plays havoc with the positive rail regulator section.  I
wouldn't have discovered this problem had the fluro tube not started
dying (blinkety-blinkety-blinkety-blink)

When the current limit is set above about 2.2A and the fluro starts
blinking, the positive regulator stops current limiting and fully
saturates, dumping over 5A into the short before I flick the load
switch off.  When the fluro is turned off the limiter behaves normal.

The negative regulator behaves normally all the way to 3A and is
unaffected by the blinking.

Anyone have any idea what is going on?!

Re: EA 40V/3A power supply kit problem

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I built one of these when i was an apprentice. They have some nasty
problems with oscillation, and if IIRC, the fix requires a cap across
one of the pots and and across a couple of tracks. You might get lucky
and find that google will turn up the fix.

What is the kit number?

Re: EA 40V/3A power supply kit problem

I have googled and only found a reference to a 0.47uF cap fitted to the
voltage pot's wiper & gnd.  I didn't have one handy so I tried a 0.1uF
and it did not solve the +ve regulator saturation problem during fluro
blinking.  If anything I think it made the circuit worse because I can
hear a (much louder) screeching noise from the supply during current

I found no reference to the cap across tracks, so would be interested
to know which nodes the cap is placed across.

The DSE catalogue number for this kit is K3206.

The Real Andy wrote:
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Re: EA 40V/3A power supply kit problem

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I think you may have done something wrong whilst constructing it. The
design is a bit unstable, but your problems sounds nothing like what i
remember. Time to recheck you construction me thinks.

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Re: EA 40V/3A power supply kit problem

That's what I initially thought so checked for solder bridges, blobs,
dry joints, incorrect component placement, etc.  Even replaced a number
of components including the IC and the output transistors in the
positive regulator stage.  I don't think the PCB pads can't take much
more rework before lifting!

I tested the supply within the vincinity of other lights (incandescent
& fluro), and the fridge.  The circuit seems very susceptible to mains
switching events.

Like I said in my original post though, the circuit works perfectly
with current limits of less than 2A, which is what I'll mainly use
anyway.  If I want to use higher currents I might have to keep it away
from "highish-switch-on-current" appliances.

What might help me would be voltage measurements around the circuit
with the current limit set at 3A.  The voltages given in the assembly
manual have the output set to 1A and voltage checks at this current
level were correct.

One question though, what is it about the fluro and fridge switching
that could be influencing the circuit?  Is it the surge current in the
mains line, or the RF/EMF pulse, or what?

The Real Andy wrote:
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