JSR04, +12V, +5V (from the negative side)

[builder brad]

oh s***t

I have another problem with the -5 volt section. R8 has always run very hot, certainly too hot to touch, and it was dropping 1.4 AC across this 1 ohm resistor. I tried to connect the ps up today and was suddenly measuring almost 12volts out of the 5 volt side, the odd thing here is that R8 is now not getting hot.

any ideas here?

This is getting really silly now. I have built loads of diy project, withou any problems - I for example the 2 x jsr06 power supplies that I built earlier this year were completed in 2 days and worked 1st time around.

I am at the point where I think I may just build 2 x linear PS with basic regulators and smoothing caps. This is really frustrating as I know how good your designs are I just want to get this working.

[builder brad]

ok

I have now taken some more measurements of the 5v section

regulated output 10.6v (was 5v dead, I have got not idea what has gone wrong except that R8 is no longer heating up)

un regulated 13.1v

AC in 10.1v

op amp pins

1 7.1v
2 4.1v
3 3.4v
4 gnd 0v
5 .6v
6 1.2v
7 11.2v
8 11.2v

the LM431 has 2.5v on both its Anode and reference

HELP!

[peranders]

When you had it working, what exactly did you do in order to break the regulator?

R8 and the other series resistors must be tuned for the load and the unregulated voltage.

Can you check the voltages around the transistors. Only 1.2 volts out from the opamp and still 10 volts out indicates that T10 might not be working.

[builder brad]

Thank you,

I really appreciate your patience with this.

I tested an additional IN5407 diode connected in series with a 1 ohm resistor from ground to the 5v supply, effectively using R7 and D7, to create what I thought would be the other 1/2 of the rectifier circuit.

This involved a little reworking of the board, but I was confident that there this was done correctly.

It certainly does seem that this has caused the failure of one half of the PS, its just strange as I also did the same thing on the +12v section and this is still working!

[peranders]

Is the PS working properly now?

[builder brad]

Hi P-A

no the 5 volt section is still not working. The problem is the overvoltage output which seems to have been caused by my attempt to create full wave rectification by adding an extra diode and resistor as described in my last post.

I have a number of spare transistors and regulators, so its no problem to test by simply swaping out any suspect components. You mentioned that IC10 may be faulty - are there any other parts that I should check if replacing IC10 does not fix the problem.

thank you

[peranders]

Brad, I recommed you to make the rectification according to my directions. You can't make a fullwave rectification with a center tapped transformer and dual voltages out.

Did the 5 volts work? What did you do when it stopped working?

If the opamp is in a socket pull it out and take a resistor (1-10 k) from the base of T10 and short to ground. If the transistors are working the output voltage should go from "high" to almost zero (1-2 volts max). When the voltage is high you should also get 2.5 volts from your LM431.

[builder brad]

Hi P-A

congratulations on the new forum - looks good!

I removed the op amp and connected a 5k resistor between the base of t10 and gnd, as sugested, and did not see a change to the output voltage.

I am running the rectification exectly as you sugested, it was when I tried to add the extra diode and resistor that I developed the high voltage fault on the 5v section.

[peranders]

Now when the opamp is removed you can easily check weather the transistors are alive or dead. If T10, base is grounded you must have 0.7 volts across base-emitter, if not dead. Check also the other transistors for these 0.7 volts. Does the LED's shine? You should disconnect the preregulator also becasue it won't work without the opamp.

[builder brad]

I traced the fault to T10 and I now have 5v output - but it keeps jumping up to 11v and then after a few seconds it goes back to 5v

I am concerned about the high temperature of R8 - this really looks like something is drawing a current somewhere. T10 is also getting very hot and I wonder if this shuts down because of the temperature, causing the voltage change from 5v to 11v.

The op amp gets slightly warm, but no other components seem to be affected.

[peranders]

R8 should not get particular hot without a load.

The thing that the output is 11 volts for a while may have to do with the opamp. Did you have this problem before?

The current consumption with no load should be 30-50 mA, not enough to make R8 hot.

[builder brad]

wow, that was a quick reply.

I am not sure if I had the voltage changing problem before as I did not really get round to testing the PS before it stopped working.

The hot resistor problem has occured from day 1

I have plenty of components now, so I am happy to really push this PS to get it working perfectly. I have just placed an extra 1 ohm resistor across R8 to see what changes that made and within a few seconds T10 destroyed itself

[builder brad]

The op amp is the same as on the 12v side and I have not observed any voltage fluctuation

[peranders]

If you have the opamp in a socket, remove it for a while and test the transistors only.

First not part should be warm or hot with thwe base of T10 grounded via a couple of kohms.

Active transistors should have 0.7 volts across base-emitter.

If you connect a pot as a voltage divider to T10 (variable voltage) you should also get a rather stable output voltage  even with a moderate load. Both LED's should shine.

How much AC voltage (ripple) do you have at the raw DC voltage? Should be rather little.

Have you disconnectred the LM317 (if you use it)? Will only work IF you have a workong feedback via the oapmp.

I haven't tested that NE5534 works proberly at 11 volts as supply voltage and only 5 volts out so I can't garantee that.

[builder brad]

I have just tested the transistors with T10 transistors base connected to ground with a 2.2k resistor and measured .69v on all transistors between base and ground, so they all appear to be working.

I have also taken the pre regulator out of the circuit, just to be sure.

I am still having heat issues with R8, I do wonder if this is the op amp?

here is a link to a local supplier and their web page for op amps, if you sugest an alternative from this list I will visit their local shop and buy one tommorow to try and see if that solves the problem:

http://www.maplin.co.uk/search.aspx?MenuNo=464&MenuName=OP%20Amps&FromMenu=y&criteria=OP%20Amps&doy=13m9&worldid=3