Replace Darlington with IGBT

Thread Starter

JeanBaptiste

Joined Jan 17, 2018
1
Hi Folks,

i'm gonna replace a defect old Darlington Power Transistor with a modern IGBT.
The Darlington was a 600V 50A type.
The IGBT is an Infineon 1200V 80A type.

The device is an old Sharp Microwave Oven Inverter Unit.

The drawing...
The Darlington is the Q1.
The R1 is an 3.3 Ohm.

To prevent the IGBT Gate from over saturation, i'm gonna put a 100 Ohm in parallel to ZD2.

Has anybody done something similar and has any advice for me?
 

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DickCappels

Joined Aug 21, 2008
10,152
Back in the mid-1980's when logic level MOSFETs first became available I replaced six Darlingtons with MOSFETS in a 6 phase motor drive circuit and efficiency went up while failures from secondary breakdown were eliminated.

Without evaluating the details of your modification it seems that you are pointed in the right direction.
 

ian field

Joined Oct 27, 2012
6,536
Hi Folks,

i'm gonna replace a defect old Darlington Power Transistor with a modern IGBT.
The Darlington was a 600V 50A type.
The IGBT is an Infineon 1200V 80A type.

The device is an old Sharp Microwave Oven Inverter Unit.

The drawing...
The Darlington is the Q1.
The R1 is an 3.3 Ohm.

To prevent the IGBT Gate from over saturation, i'm gonna put a 100 Ohm in parallel to ZD2.

Has anybody done something similar and has any advice for me?

You need to make sure the VGSthr spec is covered with a safety margin - typically about 8V. Dickcappels mentions logic level devices, which could end up being the only way you get it working. If VGSthr is not met; the switched on device will have high RDSon and get hot.

IGBTs are fine for static switching, they were developed to have VCEsat which was better than the RDSon of MOSFETs back then. They're essentially an N-channel MOSFET with a PNP emitter follower hanging from the drain. Failures in SMPSU applications weren't exactly rare because they can be too slow.
 
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