1. Home
  2. Electronics Down Under
  3. EA 40V/3A power supply kit problem

EA 40V/3A power supply kit problem

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?!

Reply to
chinsta00
Loading thread data ...

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?

Reply to
The Real Andy

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 limiting!

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:

Reply to
chinsta00

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.

Reply to
The Real Andy

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.

Reply to
chinsta00

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.