Hi!

I'm currently studying EE (second semester) and just started analysing analog circuits and filters. In the circuits we're designing, there's a diode rectifier, but it is a bit different than a typical full-bridge and I can't seem to grasp the way it works!
Help is welcome and circuit will follow as an image. (EDIT: I made a little mistake on the circuit, the LM324 is powered by a +12V and a -12V, in the circuit it seems there's two -12V sources!)

 

hi 98.
Welcome to AAC.
The LM324 output pin is not connected.??
E

Corrected.

 

hi 98.
Welcome to AAC.
The LM324 output pin is not connected.??
E

Woops! My bad, I'll make another image!

 

There you go!

 

hi 98.
Welcome to AAC.
The LM324 output pin is not connected.??
E

Corrected.

There it is.

 

That's a full-wave bridge rectifier, you're just confused by how it's drawn.

 

That's a full-wave bridge rectifier, you're just confused by how it's drawn.

A bridge rectifier doesn't have a place that connects to all four diodes.

It is a kind of precision rectifier. Compare with this: https://en.wikipedia.org/wiki/Precision_rectifier

 

The TS's circuit has positive feedback.

Even if you changed the op amp to negative feedback, it's still a rather odd circuit.
The output would be the negative half cycle with a gain of two.
And it's not a true precision rectifier since D3 is not inside the feedback loop.
Also R4 likely needs to be connected to ground and the output taken from the junction of D3 and R4.
Not sure what R3, R5, and D4 are supposed to do.

 

Something like this ?

Regards, Dana.

 

The TS's circuit has positive feedback.

Even if you changed the op amp to negative feedback, it's still a rather odd circuit.
The output would be the negative half cycle with a gain of two.
And it's not a true precision rectifier since D3 is not inside the feedback loop.
Also R4 likely needs to be connected to ground and the output taken from the junction of D3 and R4.
Not sure what R3, R5, and D4 are supposed to do.

R4 is connected to another op-amp that has a gain equal to the voltage loss from the two diodes.

 

R4 is connected to another op-amp that has a gain equal to the voltage loss from the two diodes.

How are we supposed to answer your questions if you don't show the complete circuit?

Sounds like rather a kludge of a circuit.
Where did it come from?

 

How are we supposed to answer your questions if you don't show the complete circuit?

Sounds like rather a kludge of a circuit.
Where did it come from?

I just wanted to understand the principle of the diode bridge. And it's from my Analog Electronics/Continuous time maths class !

 

The TS's circuit has positive feedback.

Oh yes, I just assumed it was negative. It doesn't make much sense with positive feedback.

 

I just wanted to understand the principle of the diode bridge. And it's from my Analog Electronics/Continuous time maths class !

Well, that's not a bridge, since two diodes are shorted together.

And whoever designed that circuit, does not now much about circuit design.
Or he's trying to throw you a curve-ball with a very odd circuit.

 

Well, that's not a bridge, since two diodes are shorted together.

And whoever designed that circuit, does not now much about circuit design.
Or he's trying to throw you a curve-ball with a very odd circuit.

Well it clearly works as a rectifier though. As seen from my oscilloscope and from Altium.

 

Well it clearly works as a rectifier though. As seen from my oscilloscope and from Altium.

I don't disagree that it works.
It just is more complex and convoluted than is needed to perform that task.

 

I don't disagree that it works.
It just is more complex and convoluted than is needed to perform that task.

Yeah I give that to you, maybe they made it harder so we would easily understand the simpler ones, I dunno ahaha

 

A bridge rectifier doesn't have a place that connects to all four diodes.

It is a kind of precision rectifier. Compare with this: https://en.wikipedia.org/wiki/Precision_rectifier

I wasn't referring to the whole design, just the portion with the diodes.

 

No. A rectifier doesn't usually change voltage (except for a quirk of maths related to the way AC voltage is calculated, but that's beyond ELI5, and I'm sure it's not what you're talking about.)

A transformer changes voltage.

A power supply often contains a transformer (to change the voltage) and a rectifier (to convert the power to DC). They are two separate functions.

If that still doesn't make sense, then some more context might help. What type of devices are these rectifiers intended to be used with?