Purpose Of Desaturation Detector In IGBT Driver

[Alexsgarage]

I recently found a schematic for an IGBT driver, it has something called a desaturation detector connected to the collector of the transistor. This desaturation detector uses a voltage comparator. Can someone tell me what this circuit is used for and what benefit it has to the driver and IGBT.

 

[dknguyen]

It probably tries to keep the IGBT in quasi saturation so it can trade more efficient conduction for much higher switching frequency.

 

[Alexsgarage]

Maybe, It was connected to a voltage comparator whose reference voltage was set with a potentiometer. The output of the comparator went back to the oscillator to clamp the duty cycle in the event of a signal lasting longer than one half cycle of the oscillator. So I think it is to prevent damage to the IGBT in case of high collector voltages over a longer time than needed.

 

[tcmtech]

got a schematic or specs sheet so we all can look and ponder upon its function?

 

[dknguyen]

I found these.

An overcurrent condition is one of the fatal drive faults
that could destroy IGBT devices in a motor-drive system.
IGBT overcurrent conditions basically fall into three
categories—line-to-line short, ground fault and shootthrough.
Table 1 lists overcurrent conditions and their
potential causes.
When considering an IGBT overcurrent protection
scheme, two important factors must be evaluated.

An IGBT desaturation circuit is the alternative way to
protect the IGBTs. The discrete circuit can be constructed
in the secondary side of the opto gate driver or the optoisolated
device that has a desaturation circuit. The circuit
detects voltage buildup across the collector and emitter
while the device is fully on. If the voltage exceeds a certain
limit, the desaturation circuit shuts off the associated gate
signal. When implemented as a discrete circuit, the required
components are a comparator with voltage reference, a
high-voltage diode, and resistors and capacitors.

4.5 Desaturation protection
Desaturation protection ensures the protection of the IGBT in the event of overcurrent.

 

[Alexsgarage]

Here is the page that I found the device on: **broken link removed**