Hello All!

I have not previously used an IGBT, and I have uncertainties regarding their application. For example, I have an Infineon IKP40N65H5 device which I'd like to use to control current (36A, @24V) through a nominal 0.5-ohm resistor (a bolometer). The idea is shown in the attached circuit. I would supply the trigger to the IGBT gate with a microcontroller (MCU), or with the MCU feeding an IGBT gate driver and the gate driver feeding the IGBT gate.

Data sheet:
https://www.digikey.com/htmldatashe...iTNOvYlb8diRKM7PkDHwVGbBe-mEToURoCch4QAvD_BwE

My question: Assuming I'm willing to accept that there will be a 1.65V drop (from the data sheet) across the IGBT above the resistor, can this work?
All comments/suggestions much appreciated.

Thanks!!

 

where is the attached circuit?

 

I would supply the trigger to the IGBT gate with a microcontroller (MCU), or with the MCU feeding an IGBT gate driver and the gate driver feeding the IGBT gate.

that can work as long as you drive the gate with suitable stage. MCU outputs are normally 3.3V or 5V and both are insufficient to drive IGBT directly. to get 36A with 1.7V across transistor you need gate voltage of 15-18V.

and since this is a low voltage application (24VDC) why use IGBT? use MOSFET. IGBTs are meant for high voltage (500-1500V).
36A * 1.75V = 63W and that needs massive heatsink

using mosfet with low Rdson you get way less heat.
even if your MOSFET has 5mOhm dissipation is 36A*36A*0.005 Ohm = 6.48W
but you can get one with lower on resistance.

 

Hello All!

I have not previously used an IGBT, >< snip

Thanks!!

where is the attached circuit?

I wasn't sure how best to include the circuit. Clicking on the attachment icon will download the schematic to your computer. Then click on your downloads and click again on the IGBT-ckt.docx file which should show the schematic. I apologize for adding the attachment the way I did.

 

you should attach picture, not word document. nobody likes to open files that could be malicious.

that will NOT work....
you need gate voltage to be 15-18V higher than emitter voltage.
so if your Vce = 2V (just an example - easier math)
then Ve=24V-2V=22V and Vg need to be at 15-18V higher than that (37V - 40V).
so 5V pulse will do nothing.

if the load is in collector circuit, then you need Vg that is 15-18V.

do you need to switch high side? if so use P-channel mosfet.

 

to get 36A with 1.7V across transistor you need gate voltage of 15-18V.

The data sheet states a gate-emitter threshold voltage of 3.2-4.0-4.8 (min-typ-max) But maybe I'm not understanding the "threshold" term. I thought it was the minimum required gate voltage to put the IGBT into saturation. My mistake.

why use IGBT?

The data sheet C-E saturation voltage was stated as 1.65V typical. Since the IGBT would be used as a low-side switch I thought I could avoid having to raise the gate signal much higher if using an N-MOSFET on the low side. Again my misunderstanding.

 

datasheet shows this:


the point is that to get low Vce saturation, you need to drive the transistor hard. sure you can use low Vge like 6 or 7V to pass current of 36A if you have sufficiently low resistance load and sufficiently high supply voltage but ... can you see what the Vce would be?

 

The data sheet states a gate-emitter threshold voltage of 3.2-4.0-4.8 (min-typ-max) But maybe I'm not understanding the "threshold" term. I thought it was the minimum required gate voltage to put the IGBT into saturation. My mistake.


The data sheet C-E saturation voltage was stated as 1.65V typical. Since the IGBT would be used as a low-side switch I thought I could avoid having to raise the gate signal much higher if using an N-MOSFET on the low side. Again my misunderstanding.

Thanks for taking the time to reply. I'll go back to the drawing board and try to improve my understanding ).
Best regards,
-Steve

 

The circuit on the right is simple to drive. Zero volts and Q1 is off. 18V and Q1 is on.