Reverse current flow through an IGBT

[Mook Johnson]

For applications like high voltage three phase PWM inverters when the high
and low FETS are complementary to each other, the effect is similar to a
synchronous rectifier circuit. When the top FET turns off and the bottom
FET turns on, the freewheeling current flows backwards through the bottom
fet. With Mosfets, the channel will allow current to flow in either
direction and the Mosfet shorts out its antiparallel diode Vf for increased
efficiency.

With an IGBT, is that also the case that the biased ON IGBT will short out
the diode Vf and reduce the voltage across the C-E pins in this condition?

 

[Tim Williams]

With an IGBT, is that also the case that the biased ON IGBT will short out
the diode Vf and reduce the voltage across the C-E pins in this

condition?

I don't think so.

They make IGBTs with integral reverse diodes for this purpose.

Tim

 

[Mook Johnson]

I don't think so.

They make IGBTs with integral reverse diodes for this purpose.

Tim

Yup, appears so. From what I've read there is the equivilent of a forward
biased diode in series with the collector pin. The antiparallel diode goes
around this so the reverse current voltage drop is entirely dependant on the
voltage drop of the antiparallel diode.

I'm looking at ways to reduce this voltage. Looks putting a better
antiparellel doide in parallel is the only way.

thanks Tim

 

[Tim Williams]

I'm looking at ways to reduce this voltage. Looks putting a better
antiparellel doide in parallel is the only way.

The entire advantage to IGBTs is their low Vce(sat), which is only a few
diode drops typical. This is of no advantage to lower voltages (under
100-200V, say), where MOSFETs of comparable ratings have Rds(on) giving
lower voltage drop for the same load currents.

So, what I'm saying is, why are you interested in an IGBT when you seem to
be looking for a MOSFET?

What specs are you looking for in saturation voltage, current, peak voltage
capacity, rise/fall time, etc.?

Tim

 

[[email protected]]

For applications like high voltage three phase PWM inverters when the high
and low FETS are complementary to each other,

Nobody does it this way in practice, N channel devices are almost
allways used.

the effect is similar to a

synchronous rectifier circuit. �When the top FET turns off and thebottom
FET turns on, the freewheeling current flows backwards through the bottom
fet. �With Mosfets, the channel will allow current to flow in either
direction and the Mosfet shorts out its antiparallel diode Vf for increased
efficiency.

With an IGBT, is that also the case that the biased ON IGBT will short out
the diode Vf and reduce the voltage across the C-E pins in this condition?

There are NO P channel igbt's.

 

[Fred Abse]

There are NO P channel igbt's.

Toshiba GT20D201, for one.

-250V, 20A

 

[Tim Williams]

There are NO P channel igbt's.

Sure there are. At least, I recall seeing some listed in an older issue of
Mouser's catalog. Hmm, don't see any at the usual suspects.

Certainly, not many people _use_ them.

Tim