# Does this IGBT bridge meaningless ?

1. ## Does this IGBT bridge meaningless ?

Hello My Dear Friends!

Hope this post finds you well.

I am trying to develop a AC to DC rectifier 110V/50 A range.
Feeling that I am doing wrong on making the full bridge or half bridge portion.
The IGBT module I am using is FF75R12RT4,https://www.infineon.com/dgdl/Infine...2805fd8fd76151

One module contains 2 IGBT that makes me confusing!
I need to understand my switching topologies first

Take a look my diagram, how the current flows back from primary winding of TR for a full cycle?

1. When point A is positive then Q2 conducts, Q1 is OFF?
2. When point A is negative then Q1 conducts Q2 is OFF?
3. When point B is positive then Q4 conducts, Q3 is OFF?
4. When point B is negative then Q3 conducts Q4 is OFF?

Freewheeling built on doides are available, whats 2uF high voltage is doing here?

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2. ## Re: Does this IGBT bridge meaningless ?

It's a regular full bridge, sketched in a rather nondescriptive way. 2uF are DC bus bypass capacitors, strongly suggested to avoid IGBT overvoltage caused by large di/dt.

1. When point A is positive then Q2 conducts, Q1 is OFF?
2. When point A is negative then Q1 conducts Q2 is OFF?
3. When point B is positive then Q4 conducts, Q3 is OFF?
4. When point B is negative then Q3 conducts Q4 is OFF?
A is DC+, B is DC- bus node. They don't change polarity. Confusion is apparently caused by the inappropriate schematic style.

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3. ## Re: Does this IGBT bridge meaningless ?

Originally Posted by FvM
It's a regular full bridge, sketched in a rather nondescriptive way. 2uF are DC bus bypass capacitors, strongly suggested to avoid IGBT overvoltage caused by large di/dt.

A is DC+, B is DC- bus node. They don't change polarity. Confusion is apparently caused by the inappropriate schematic style.
Question arises if both node remains constant on polarity then why 4 igbts are used? One leg of primary TR connected with a pair of IGBT doesn't tell us that its polarity could interchange? Don't you mean the circuit is not wrong?

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4. ## Re: Does this IGBT bridge meaningless ?

Hi,

the circuit seems to be correct.
Node A is always positive, node B is always negative.

A "full bridge" needs 4 IGBTs. It has two ouputs. The difference voltage of both these outputs may be positive or negative.

Klaus

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