GGG bipolar power supply problems;

[Bernardduur]

OK, so I tried to build a 12V bipolar PSU from GGG (here) and I have some problems with it.

I suspected that the V+ should be 12V, the V- should be -12V; instead I get 16V on the V+ and -16V on the V-. I get 33V when measured V+ to V-. Is this normal?

I've read the datasheet of the 78** and 79** parts and I noticed that my transformer (I found one in the intercom I use to house my cabsim)is just a few volts under the desired Vmin of the units (needed is 14.8 volt, I only can get 14.3V out of my transformer.... I hoped my measurer was off).

[Bernardduur]

bump

[Nasse]

Maybe you should post voltages on C1 & ground and same for C2. If it is too low transformer voltage yo can use 8 or 9 volt regulators. But don´t understand why it does not work. I did similar circuit few years ago, but vero layout, I needed two of these and they worked okay

[Bernardduur]

Yes I know; the layout is sooo simple, and still I can't get it to work.

As I said I think it is because of the low voltage on the transformer (too low for the regulators)..... but why than a higher voltage?

[niftydog]

Just be sure you're measuring correctly. Put the black lead on the 0V terminal and leave it there for all following measurements. Measure the inputs and outputs of the regulators. If the input is 14.3VDC then there's no way the regulators are increasing the voltage, so something must be wrong.

What is the exact part no. of the regulators? Sure you don't have 7818 and 7918 instead of 7812 and 7912?

[Bernardduur]

Nope. I use the 7812 and the 7912, right pinout, 2x 1000 µf (16V), 4x 0,1 µf and 2x 1N4004's......

I've checked it a couple of times and I get the same readings; transformer is 14,3V and final voltages are 16,4V and -16,4V.

Will try a new transformer today

[Bernardduur]

Build it again and again the same readings..... I am getting nuts here!

[Nasse]

 ???Should we take it from the beginning...

You have some transformers, the first one and the second, they are non center tapped single secondary, check that those give AC voltage, , disconnect any load, measure it and tell what your multimeter shows... they should be about in the range what is suggested at ggg for transformer AC output

If the other one gives out DC, you must open it and remove the rectifier diodes and caps etc. inside, does not work otherwise

When rectified and smoothed you should see +/-  DC voltage, it will be higher value numbers than AC reading, might be something like 1,4x AC figure

And when reading your first post you say you have 16 volt electrolytics... I think they are not safe, I would use 25 volts minimum, hope they are not damaged, or does not explode, check the dc voltage but be careful

I think those regulator chips need at least about 3 volts more dc in input than what goes out

Merry Christmas

[Bernardduur]

OK, OK, OK, OK.....



Thanks for all the help



My DMM battery was a bit low..... dunno why it gives me those weird readings...... With a new battery it gives the right readings.