Weird problem in Full wave (FW) bridge rectifier

[dkmishra@gmail.com]

I am working on a implementation of FW bridge rectifier (without any
filter). I am applying a sinusoidal input (1 Phase, +- 20, 60 Hz) to
the bridge and measuring the voltage across the load resistance. When
I am trying to dispaly the output waveform in a CRO, I am seeing
only one half of the rectified waveform. I cross checked the
individual diodes and I found that all are in perfect condition and
working nice when using in HW rectifier mode. I want to know why I am
seeing such a wierd results.

 

[Spehro Pefhany]

I am working on a implementation of FW bridge rectifier (without any
filter). I am applying a sinusoidal input (1 Phase, +- 20, 60 Hz) to
the bridge and measuring the voltage across the load resistance. When
I am trying to dispaly the output waveform in a CRO, I am seeing
only one half of the rectified waveform. I cross checked the
individual diodes and I found that all are in perfect condition and
working nice when using in HW rectifier mode. I want to know why I am
seeing such a wierd results.

Are you sure you are actually measuring the voltage across the load
and not the voltage from one side of the load to one side of the
input? Eg. single-ended input (one scope probe) with the other side
at earth.

Best regards,
Spehro Pefhany

 

[John Devereux]

I am working on a implementation of FW bridge rectifier (without any
filter). I am applying a sinusoidal input (1 Phase, +- 20, 60 Hz) to
the bridge and measuring the voltage across the load resistance. When
I am trying to dispaly the output waveform in a CRO, I am seeing
only one half of the rectified waveform. I cross checked the
individual diodes and I found that all are in perfect condition and
working nice when using in HW rectifier mode. I want to know why I am
seeing such a wierd results.

Is the centre tap earthed?

 

[Ecnerwal]

I am working on a implementation of FW bridge rectifier (without any
filter). I am applying a sinusoidal input (1 Phase, +- 20, 60 Hz) to
the bridge and measuring the voltage across the load resistance. When
I am trying to dispaly the output waveform in a CRO, I am seeing
only one half of the rectified waveform. I cross checked the
individual diodes and I found that all are in perfect condition and
working nice when using in HW rectifier mode. I want to know why I am
seeing such a wierd results.

If the parts are working correctly, then the circuit, simple though it
is, must be wrong. Go back to the very basics and check everything -
less time spent saying "it can't be" is less time wasted on the way to
making it work.

Either it's wired up incorrectly, or something that looks connected is
not actually connected.

 

[dkmishra@gmail.com]

If the parts are working correctly, then the circuit, simple though it
is, must be wrong. Go back to the very basics and check everything -
less time spent saying "it can't be" is less time wasted on the way to
making it work.

Either it's wired up incorrectly, or something that looks connected is
not actually connected.

This is the configuration I am using. (+) (-) represents the source.
Now I am taking the +-10 Volt source from function generator embedded
in CRO. One CRO for measurement and one for generating sine wave.

---------------------------
| | | |
D D | |
| | | C (+ probe RED )
(+) | | R
| | R O
| (-) | | (GND probe BLACK)
D D | |
| | | |
| | | |
------------------------------

 

[Ecnerwal]

---------------------------
| | | |
D D | |
| | | C (+ probe RED )
(+) | | R
| | R O
| (-) | | (GND probe BLACK)
D D | |
| | | |
| | | |
------------------------------

Cleaning up that gibberish:

---(+)---------------------
| | | |
_ _ | |
^ ^ | | (+ probe RED )
| | | C
(~) (~) \ R (Oscilloscope, in elderly TLA)
| | / R O
_ _ \ | (GND probe BLACK)
^ ^ | |
| | | |
| | | |
----(-)----------------------

If you are feeding it a signal (~) that goes from oscilloscope ground to
a positive voltage, there will be no negative part of the waveform -
this is perhaps what is happening if you are using a scope probe test
signal as your AC source. Try a plain old transformer. Diodes have
polarity, so drawing them as "D" is not useful.

 

[dkmishra@gmail.com]

Cleaning up that gibberish:

---(+)---------------------
| | | |
_ _ | |
^ ^ | | (+ probe RED )
| | | C
(~) (~) \ R (Oscilloscope, in elderly TLA)
| | / R O
_ _ \ | (GND probe BLACK)
^ ^ | |
| | | |
| | | |
----(-)----------------------

If you are feeding it a signal (~) that goes from oscilloscope ground to
a positive voltage, there will be no negative part of the waveform -
this is perhaps what is happening if you are using a scope probe test
signal as your AC source. Try a plain old transformer. Diodes have
polarity, so drawing them as "D" is not useful.

Thanks Lawrence you are correct. Circuit is behaving as it should
behave with plain old transformer.
Regards
Deepak