# What dc can u measure?

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#### Justin18

##### Newbie level 4
Which DC can you measure according to picture a, b, c?

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i think 19,8V because a diode needs 0,7V so 20,5V-0,7V=19,8V. I dont know if its right.

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#### FvM

##### Super Moderator
Staff member
No, sine peak voltage is sqrt(2)*Vrms (designated Veff in the picture).

Without further information we should assume sinusoidal waveform.

#### wwfeldman

assuming sinusoidal waves, and since there is no apparent load, all three circuits act as peak detectors.

If Veff is Vrms, then Vpeak = sqrt(2) * Veff or Vpeak = sqrt(2) * 20,5 V = 28.99 V

remove the 0.7 V diode drop yields 28.3 V

Since the drawing asks for Uab, point b is the reference
the top drawing would measure +28.3 V
the middle and bottom drawings would measure -28.3V because the diode is in the opposite direction,
making b the more positive location

#### Audioguru

This same German (?) circuit is on two or more other websites today.

#### barry

This same German (?) circuit is on two or more other websites today.

Obviously OP is going to take all the answers and average them.