[SOLVED] Problems with 7912 regulator

[alexan_e]

dear just reverse the polarity of C2 and C6.
I think yur problem will be solved.

You can't be serious!
You have a supply line with a lower voltage when referenced to the ground and you think that the positive side of the capacitor should be connected to that?

 

[shahbaz.ele]

dear just invert the C1 and C6 capacitors

 

[alexan_e]

dear just invert the C1 and C6 capacitors

Is this your idea of a joke?

 

[shahbaz.ele]

The last thing remainig is that you should use new 7912 and first test it separatly. then embed in circuit.

 

[dselec]

Hello shahbaz whats wrong with u u trying to kill him or what ?
alllllllll goood rdiaz u r in the right way increase the resistor to 510 ohm or more up to 1 kohm and u will get more voltage...well done.

forget for now about pin 1 or 2 talk about your resistor on c2 and the resistor got hot cause u potentially have 0.4watts now and it will go up higher once u change the resistor.. well done do what i said and give me the good news.
check out polarity of c2 c6 make sure they r like in my diagram now3 here

 

[rdiaz]

Now I put a 1K resistor instead dselec, and following your diagram without ic2. I checked the input voltage between d1 cathode and gnd and is 15.7Vdc, so I guess that's good. Then I measured the voltage in c2 and this is -5.7Vdc. are these values expected?

 

[dselec]

Now I put a 1K resistor instead dselec, and following your diagram without ic2. I checked the input voltage between d1 cathode and gnd and is 15.7Vdc, so I guess that's good. Then I measured the voltage in c2 and this is -5.7Vdc. are these values expected?

No u should get about 12 v on c1/c2 . remove d2 and check out ac voltage at between centertap to x 1-1 x1-2 and post
make sure (measure with ohmmeter) that cent..tap its actually connected to c1 c2 junction.
check out d2 and its polarity cathode going to transformer . all tests from now on u do fron c1 c2 junction.


" 1/2W resistor between pin 1 and pin 2 of ic2(already taken off of course), but it gives me -10Vdc aprox"
and what happened to the -10 v how did u get -10 with 330 ohm and lower with 1k ohm ?
make sure your resistor is on c2 was 300ohm now 1000 ohm make sure it is 1000 ohm

 

[rdiaz]

D2 was already inverted dselec, I forgot to make that clear. I checked the voltages in the transformer and in the diodes and it seems to be working properly, 13.5Vac each side and 27Vac between extreme wires. In the anode of d1 and tap centre there's 15.7Vdc, and in the cathode of d2 and tap centre there's 15.7Vdc too. But measuring voltage between c2 pins...-5.7Vdc....it's a nightmare!

 

[dselec]

NO its not a night mare ... first goback to the oiint where u got 10v on c2
re member no ic2 7915 diode d2 cathod going to transformer what about the grd to centertap connection .
remember all measure u do and did with fluke blk lead only on c1 c2 junc.

all tests with grd= c1/2 junc
1. remove 79.. and check volts at x1-1 ...cent tap...x1-2 and post
2. check volts at c1+ c2- and post... check d2 with ohm meter and recheck and post.
3. if all ok checkout if c2 heating if so replace c2 and attach 510 ohm across c2 and recheck all and post.

 

[rdiaz]

I put a 4.7K resistor in each output and it came out good, now it's +12V and -12V and no heating, I'll do a PCB and post the results later, thanks guys!

 

[dselec]

I put a 4.7K resistor in each output and it came out good, now it's +12V and -12V and no heating, I'll do a PCB and post the results later, thanks guys!

before u do that i advice u to do full wave rectifier... later-on u will not have enough current... if u using 0.5 amp regs your regs should work with resistor 24 ohms
12v/24 ohms=0.5 amps and the capacitors should be 2200 u f and then they will not fit in pcb.
Hmmm... i cant find out what output current u want from each supply ????
How did we all GET SO FAR without ask a simple stupid question about your output current ?????????????????????????????????????????????????????