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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

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2 Answers 2

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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.

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  • \$\begingroup\$ Thanks a lot for answering my query. Can you please explain why is this happening? \$\endgroup\$
    – Frozen God
    Commented 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
    Commented 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\$
    – Frozen God
    Commented Nov 19, 2022 at 7:28
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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.

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