DMM to measure leakage current between source and drain terminals of MOSFET (at 600V)

[providev]

Hi

I'm currently conducting a project that conducts a burn-in test on a power MOSFET. We are applying 600V betwen the Drain and Source terminals and attempting to monitor the leakage current flowing through the MOSFET in a continuos manner.

The project involves a very high DUT count and therefore we are unable to cater for each DUT to have it's own current measurement channel. We are also unable to switch the cicuit to a shared multi-meter since the requirement is to have the voltage be present throughout the testing.

The existing solution I'm thinking of is to use a sense resistor in series to the circuit. However this will cause the DMM to have a loading effect during the voltage measurement and give erroneous results.

I would really appreciate any feedback on the possible measurement methods I could use in this scenario. My leakage currents range from 100nA to 5mA based on the DUT.

Thank you.

Cheers!

Sanka

[Henrik_Volkers]

How about using an  OP as a current to voltage converter and provide a low impedance voltage to a mux?

OP + to ground

OP - to source

R1 of 1k from OP output to OP -

D1 for protection between OP + and OP - .

+/- 10 to 15 volt supply to power the OP with 100nF Buffer.(maybe 10µF and 2x 10R for additional decoupling)

Without failure the voltage between + and - will be zero -> no current  in D. All leakage current will flow through R1 ( plus I_bias) and the OP will provide the voltage (and current) such that your source pin is virtually allways at ground level.  

Output voltage will be U_out= - I_measure*R1 (+ U_offset +I_bias*R1).

With R1 = 1k you have a 0.1V to 5V output signal.

NS LMP7721 has a bias in the fA range (but lower supply voltage)