DIYbanter - View Single Post - power supply "sticks" in current limiting mode

mike[_22_]

On 4/17/2014 10:02 AM, wrote:
"Doesn't change the fact that at least two of us still seek
a solution. "

True, but realize that some newsreaders have this thread waaaaaaay down at the bottom of a very long list. I see you use gmail, so do I. When you post a reply gmail brings it up to the top. This is not always so with people who use other methods of access. To get to the maximum number of people it is better to start a new thread, after seeing if any of the links are good in the old one of course.

It is a bit surprising that there is still a print available via that link. If you see an old post like this and a link is to a tinypic or an imageshack, it is not likely to still be there. Russian (.ru) links seem to stay put, possibly because they are not a throwaway society and keep things running, instead of dumping everything in a landfill every two years.

Anyway, according to the print, current sensing is done by R15. Anythng wrong with N2 or its associated circuitry could be at fault.

Question, what does the current meter read ? Is it zero or does it read a bunch of current ? It could be as simple as something shorted across the output terminals.

I assume the constant current LED is lit, if you turn the voltage all the way down does it switch to the constant voltage LED ?

First problem is that there seems to be a bunch of similar designs with
the same model number.
Mine doesn't match this schematic.

Second problem is that it's an upside-down backward design.
Negative supply floating with the most positive end the internal
ground reference.
Theoretically, not a problem. Practically, it makes it harder to
instrument/diagnose...especially without a correct schematic.
The digital readout is mixed up in all that floating stuff
and the schematic for that part doesn't seem to exist anywhere.

This appears to have been "designed" by someone who had never used
a bench power supply, much less ever designed one.
You can do a working power supply with far fewer parts.
It's a crap design with unbounded op-amp
inputs that can go "out of bounds" and latch up...patched with
a bunch of zeners to try to limit that. But there can be and apparently
are transient issues that can latch it up. Another consequence of this
is that you can't set the current limit near zero. I had to adjust the
minimum
to 340ma to keep it from latching up.

While I'm on a rant, I don't like the way the thing works.
The fine voltage control is a percentage of the coarse setting.
So, with the coarse at zero, the range on the fine setting is from zero
to zero.
The whole purpose of digital readout is to know the outputs.
0.1V resolution is insufficient.
The power switch doesn't turn off the output. Output stays up for
a long time after you cut the input power. Who knows where the
transient voltage/current go during that time.

Mine seems to work kinda normally as long as you don't need a current
limit lower than 340ma and you don't have transient load conditions
near the limit setting and you don't try to hook it to something
with voltage, like to charge a battery. The only things that don't
work are the things I most expect from a bench power supply.

My conclusion was that it isn't really broke; it's a crap design
doing the best it can...and wasn't worth redesigning. But if someone
comes up with a quick patch, I'd do it.

My response to the posting was, "me too", "let us know if you find a
solution." Ranking optimization was not a priority.