Electronic – Active load with mosfet and op-amp

batteriesmosfetoperational-amplifier

Below is the circuit I used to implement an active load which use an op-amp to adjust the mosfets' resistance based on DAC voltage at the op-amp input.

VIN_NANO is about 10VDC.

Mosfet is IXYS IXFH28N60P3, Vds: 600V, On-resistance: 260mOhm @ 14A,10V Vgs, power dissipation: 695 Watt.

The scheme works well with Battery String voltage of 12VDC. When I increase it to 125 VDC, the mosfets die almost instantaneously. What would be the reason behind this?

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Test load current looks like this:

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Best Answer

The devices you have do not have a suitable DC SOA. The device is rated only for pulse operation at high powers. Going beyond 1 ms on time puts you in a very dark place.

You need to use something like an IXTH30N60L2 ...these devices are rated for large linear load dissipation.

Read this on the L2 range from IXYS.

For the devices you chose, SOA is this: enter image description here

You actually need something like this: enter image description here

....for your application you could use just two devices with plenty of margin or select a larger one and use just a single device.

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