EA 40V/3A lab power supply K-3206
Sam Highley
tough time getting it working properly. The first time I powered it up
I realised I hadn't correctly hooked up the collectors on Q1 and Q4 as
they were connected to the heatsink, rather than their respective
transistor cases (collector).
Needless to say things were not running properly at this point. I
powered it down, made a thorough inspection of things and worked out
the Q1/Q4 collector problem. I fixed this up and powered up the supply
again, but things are still not working properly. This is what the
supply is doing:
* "limit" light is on pretty much continuously, other than when both
voltage and current dials are wound almost right down
* with voltage and current set to maximum, total voltage output is
only around 4.5 to 5 volts
Anyway, i've pulled out all the capacitors and checked them, as well
as the transistors, but I have no idea how to go about checking the
IC's, which I suspect might be the problem.
How do I go about checking the IC's, which are 3x TL072's and a TL071
Sam
Ken Taylor
news:d18d670f.03071...@posting.google.com...
Can you post a link to the circuit?
Ken
Sammy
> > How do I go about checking the IC's, which are 3x TL072's and a TL071
> >
> > Sam
>
> Can you post a link to the circuit?
I'll scan it and upload shortly.
Sammy
Rob Judd
I just rooted around and found the circuit for this, which I had
sensibly filed away with other test equipment circuits in a manila
folder.
As I understand it, the collectors of Q3 and Q4 were both shorted to the
heatsink, right? If you have a look at what this does, it effectively
short-circuits from +20v to -20v. So, the most likely problem is a
failure in the raw power supply, at bottom left of the circuit.
Check with a voltmeter that you have raw +20v and -20v first, and if not
you should test/replace the bridge and/or regulators. Let us know how it
goes.
Rob
The real Andy
oscillation. If you can get access to CRO I highly recomend doing so. I did
build one of these many years ago and I remember adding a couple of caps
accros the pot(s) to help alleviate the oscillations. Might pay to check the
SC site for errata that might not be included in the kit.
Another design fault is the earthing. If they still sell these kits with the
metal front and back panels, do your self a favour and earth them..
"Rob Judd" <ju...@ob-wan.com> wrote in message
news:3F122DB9...@ob-wan.com...
GM
limiting to work properly. ie if i put a short on the output, you would
expect it to limit the output current irrespective of whatever volts have
been dialed up. Instead it just goes into full output and bends the needle.
The 3 amp range is fine. (Interesting though about the oscillation. I'll
have a look with the CRO )
"The real Andy" <ihatehi...@yahoo.com.au> wrote in message
news:3f1260ad$0$26536$afc3...@news.optusnet.com.au...
Sammy
> Another design fault is the earthing. If they still sell these kits with the
> metal front and back panels, do your self a favour and earth them..
The rear panel is earthed, not sure about the front panel though, i'll
check on that.
Sam
Sammy
> As I understand it, the collectors of Q3 and Q4 were both shorted to the
> heatsink, right? If you have a look at what this does, it effectively
> short-circuits from +20v to -20v. So, the most likely problem is a
> failure in the raw power supply, at bottom left of the circuit.
I suspect you are thinking of Q1 and Q4, and the way I read the
instructions, the collectors have to be isolated from the heatsinks, and
hooked up to their appropriate points on the PCB.
> Check with a voltmeter that you have raw +20v and -20v first, and if not
> you should test/replace the bridge and/or regulators. Let us know how it
> goes.
Where would be the best point to check this?
Sam
Sammy
> I inherited one of these and it is impossible to get the 300mA range current
> limiting to work properly. ie if i put a short on the output, you would
> expect it to limit the output current irrespective of whatever volts have
> been dialed up. Instead it just goes into full output and bends the needle.
> The 3 amp range is fine. (Interesting though about the oscillation. I'll
> have a look with the CRO )
With this in mind, what do people think about the value of the following
kit, which is currently on sale:
http://www.dse.com.au/cgi-bin/dse.storefront/3f13763808bc09e02740c0a87f9c
06c9/Product/View/K3202
Sam
The real Andy
news:usenet-281EF5....@news-server.bigpond.net.au...
Never seen it or tried it, but it is probably based on the same concept as
the one the OP is talking about, and is no doubt dogged with the same
problems.
As for the dual powersupply, once you find all the problems (and there is a
few) it is quite a good unit - especially when consider the price compared
professional units.
Tom L
Don't know about this one, but if you are after a 40V 3A pws I can
recommend the Altronics K3330 switchmode kit with current limiting and
digital readout.
It set up and worked as expected first time and I've not had any
trouble with it during the past 7 or so years of heavy use.
Unfortunately after a quick scan of the Altronics web site, it seems
this kit is no longer sold. However it was featured in Silicone Chip
(some time in 1995) and the PCBs should still be available from RCS.
It has bugger all ripple (<1mV up to about 25V then <5mV up to 40V @
3A) and only dissipates about 10W worst case.
Tom L.