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To be specific, I am using 6 MosFETs (for ex. PSMN030-60YS) to drive an inductive load. I want to measure drain current of High-Side MosFETs. The way I am doing right now is by lifting the MosFET mounting base (drain pad) and attaching a small loop as possible (I know it does add some extra inductance and have small voltage drop) across the mounting base of MosFET itself and drain landing of PCB (a crude image is attached below).

Lifted MosFET position

I don't know any best way to measure drain current of high side MosFET apart from this.

Is there any proper way to do so without adding extra L or R component by adding a wire like I displayed?

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  • \$\begingroup\$ Do you need to measure DC content of the current? \$\endgroup\$ – JonRB Aug 27 '19 at 19:52
  • \$\begingroup\$ Is measuring the source current not close enough? That you can measure without affecting the thermal performance of the device under load as much, but even then you inevitable affect the circuit by measurement. I use a Hall current probe with a small loop of wire. \$\endgroup\$ – Phil G Aug 27 '19 at 19:55
  • \$\begingroup\$ @JonRb : Current while my PCB is driving inductive load. I expect Sine wave and that is what I measure there, so there is no issue. The query is regarding technique whether it is good idea to use hall current probe with small loop or not. \$\endgroup\$ – Rajan Aug 27 '19 at 19:59
  • \$\begingroup\$ @Phil G: No it is not possible for me. As you mentioned at last, the same way I am also using a hall current probe with small loop of wire. \$\endgroup\$ – Rajan Aug 27 '19 at 20:04
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The problem with the above setup is heat dissipation will be reduced and could overheat the part.

The source current is also the drain current for a mosfet. The way this is typically done is by cutting traces and inserting a series current resistor. If you need to know the swtiching current this is likely the best solution.

It really depends on how accurate you need the measurement to be. One way without cutting traces is to estimate the power of all the circuitry by using a benchtop supply with a current meter and then switching loads on and off to determine how much power they are using. The power of the local circuits can be estimated from the total. The current can be determined if you know the voltage of the local circuit.

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  • \$\begingroup\$ Thanks for your answer. My motivation to do this is to calculate switching loss occurs in High-Side MosFETs. \$\endgroup\$ – Rajan Aug 27 '19 at 20:07

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