1
\$\begingroup\$

I made a bridge rectifier using 4 1N4007 diodes, a capacitor filter with capacitance of 470 micro farad (25V), and a resistance of 1k ohm as a bleeder resistor and a step down transformer with converts 220V to 12V.

On checking with multimeter, I saw step down voltage to be 13.5V, but my capacitor was showing me a DC of 16.8V. The same voltage was across the resistor (resistor and capacitor are in parallel)

Is it possible that a capacitor can amplify voltage? If so pls explain how? Or what have I done wrong.

This is my reference image

\$\endgroup\$

2 Answers 2

1
\$\begingroup\$

Is it possible that a capacitor can amplify voltage?

A bridge rectifier and smoothing capacitor is basically a peak detector. So, even though your AC voltage is 12 volts RMS, it will peak \$\sqrt2\$ higher at nearly 17 volts minus a couple of diode volt drops (bridge rectifier) leaving maybe around 15.5 to 16 volts as a DC level: -

enter image description here

Image from here.

If your AC voltage is a tad higher than 12 volts then the DC level across the capacitor will be a bit higher too.

\$\endgroup\$
3
  • \$\begingroup\$ Thanks a lot for answering my query. Can you please explain why is this happening? \$\endgroup\$ Nov 18, 2022 at 18:24
  • \$\begingroup\$ Can you be more specific and targeted? I mean, I'm used to this concept for over 40 years so it's second nature to me <-- that makes it tricky for me to guess which bit you are having problems with @FrozenGod \$\endgroup\$
    – Andy aka
    Nov 18, 2022 at 18:56
  • \$\begingroup\$ I understood what you are trying to say after reading your answer couple of times. I misread a line which made me confused. I got it what you meant. Thank you for your help \$\endgroup\$ Nov 19, 2022 at 7:28
0
\$\begingroup\$

12 V is the RMS voltage of the output voltage transformer.

When we rectify this voltage with the 4 diodes (full bridge) with only the capacitor, we can get the maximum voltage of 12 x sqrt(2) V = ~ 16.9 V minus 2 x diodes voltage drop. It is likely that you have a little more then 12 V RMS.

Then, wiring the 1 k resistor, voltage fall to a "mean" which can be known with the "Schade" chart or a simulator.

\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.