| Electronics > Beginners |
| AC to DC converter problem in negative side (toroidal transformer) |
| (1/1) |
| basantab:
UPDATE: so i now have 24 volt plus minus on both side finally after swapping different parts but i still do not know the reasons for it as all swapped parts are working correctly and i kept back all old parts which did not gave required voltage but now they do give. i had wrong formula before but this is what i am supposed to get.. anyway i have equal voltage now. Hi The problem is shown in the picture but just in case , here is the problem. The output of toroidal transformer almost 15 volt 1 amp rms dual output. I want plus minus (5 and 12v)dc. After bridge rectifier the rms is around 17... (before bridge it is around 17 rms, no load condition). ripple is around 23volt.(both side plus minus) When i put 3300uf cap in positive side the ripple flatens and gives around 15 vdc. BUT! When i put electrolytic cap in negative side to smoothen out negative ripple i get -23 volt dc. :-DMM (which burned my neg volt reg. 7912) |O Polarity of electrolytic cap was negative side to negative output and positive side to ground. Can anyone give me some hint about it ? I tried disconnecting everything and only putting cap plus bridge rectify but still it gives -23volt dc on negative side. Thankyou |
| RoGeorge:
I had a similar fail myself some time ago: https://hackaday.io/project/7590-retardo-davinci/log/24810-assumption-is-the-mother-of-all-fuckups Are you sure your AC waveform in the secondary of the transformer is symmetric? |
| Gyro:
My question would be, why are you ONLY getting +15V on the positive side? :-\ With the 3300uF capacitor on the positive side, the unregulated voltage should rise to the peak waveform value. With a 15V (RMS) transformer this should be around 22-23V (1.414 x 15). The negative side is correct, I think you have a connection problem on the positive. Also, if you don't have a load on the regulator outputs yet and the 7912 is burning, then check its pinnout - (hint) It is not the same as the 7812. |
| basantab:
yes quite sure. checked it with oscillaocope. :) thanks |
| basantab:
--- Quote from: Gyro on May 17, 2018, 02:23:36 pm ---My question would be, why are you ONLY getting +15V on the positive side? :-\ With the 3300uF capacitor on the positive side, the unregulated voltage should rise to the peak waveform value. With a 15V (RMS) transformer this should be around 22-23V (1.414 x 15). The negative side is correct, I think you have a connection problem on the positive. Also, if you don't have a load on the regulator outputs yet and the 7912 is burning, then check its pinnout - (hint) It is not the same as the 7812. --- End quote --- yes i now have 24 volt rectifies smooth dc voltage output after swapping bridge rectifier diode but i dnot know if thsi was the problem .. sometime i got 32 volt on negative and 24 volt dc out on positive and i still donot know the reson but for now i think 24 volt like you said is achieved . a bit of formula incorrect on my side. thanks for help |
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