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how to measure the resistance value of power transistor??

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now ,i wann to measure the resistance of power transistor in buck dc-dc.
 

Re: how to measure the resistance value of power transistor

rameshchand said:

i mean that i want to measure the resistance of switching transistor(for example ,PMOSFET OR NMOSFET when the dc-dc in buck type is working
how to measure by oscillograph ??
 

Re: how to measure the resistance value of power transistor

You can only calculate the device resistance in circuit while operating. You CAN measure the voltage drop across the drain/source and measure the current and then calculate device resistance.
 

Re: how to measure the resistance value of power transistor

You can use a current probe to measure the output current and use a voltage probe connect both to the same oscilliscope. That you can do the calculation to get the Resistance. Only if you are measure the dynamics resistance of the power mos.

But normally, we measure it when fully turn on the MOSFET. That means you can just turn on the MOSFET with the operating Vcc and pump in a current source (depending on your rating such as 500mA), and measure the Voltage at the output. The resistance can be calculated. Take care on the max allowable power dissipation of the device when you pump in the currrent on the MOSFET.
 

Re: how to measure the resistance value of power transistor

WindRay said:
You can use a current probe to measure the output current and use a voltage probe connect both to the same oscilliscope. That you can do the calculation to get the Resistance. Only if you are measure the dynamics resistance of the power mos.

But normally, we measure it when fully turn on the MOSFET. That means you can just turn on the MOSFET with the operating Vcc and pump in a current source (depending on your rating such as 500mA), and measure the Voltage at the output. The resistance can be calculated. Take care on the max allowable power dissipation of the device when you pump in the currrent on the MOSFET.

i know your meaning ,but,if i get out of the inductorwhich is connected to pin of power NMOS or PMOS when you are measuring the resistance in test proceding

because i wann to measure the resistance in my project which is buck synchronous dc-dc that has two power MOS--NMOS and PMOS .I want to measure the resistance when the voltage and current output of power MOS is steady , dynamics resistance of the power mos is easy to measure ,but the result ,changing all the time , is not availbale ,,canyou give me a good instruction ,thanks !!
 

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