Full Wave Vs. Half Wave Rectifier at Small Voltages

Discussion in 'General Electronics Chat' started by rperea, Jul 24, 2009.

Apr 7, 2009
15
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Hello, I am creating a rectifier but apparently the full wave rectifier looks less adequate than the half wave one.
I am trying to convert an AC voltage to DC of 1Hz amplitude of ~0.2V.
I am using a half wave and a full wave rectifier with some capacitors.. I just got the negative amplitude turned into positive once with the FW rectifier but then I tried again and it just bulges a little bit. The HW rectifier just gets rid of all the negative signal which is similar with the FW since it bulges very very little (around 0.010V).
What could have happened? I have two questions:

1. Why is the half wave rectifier better, does the diode have a minimun voltage to operate? Could I've broke the diodes somehow?

2. Any equations I can look to check the adequate Capacitor value that depends on my resistance?

Thank you!

2. mik3 Senior Member

Feb 4, 2008
4,846
70
Neither the half way nor the full way rectifier are suitable for this application. The half way works better in this case because there is only one diode drop subtracted from the rectified signal. With a full wave there are two diode drops. However, you have to use a precision rectifier for this job because your voltage is small. Google precision rectifier.

3. SgtWookie Expert

Jul 17, 2007
22,201
1,809

Apr 7, 2009
15
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Thank for your reply. But why a precision rectifier? Can you give me an explanation why this will be better? Because the small voltage? What happen if I use a half wave instead?

Apr 5, 2008
19,908
4,138
Hello,

A precision rectifier is better as it has a much lower threshold.
A silicium diode has a threshold of 0.6 - 0.8 volts.
A scottky diode has a threshold of 0.3 - 0.5 volts.
A germanium diode has a threshold of 0.2 - 0.4 volts.
A precision rectifier will have a threshold of several milivolts.

Greetings,
Bertus