Mr.Cool
Joined: 20 Jun 2001
Posts: 526
Helped: 16
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 11 Oct 2004 20:10 Re: How to test Rdson for DC/DC |
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Rdson is the drain-source resistance of a MOSFET during its conduction period. it really doesn't have anything to do with DC/DC converter - though mosfets are usually a part of the circuit which makes up a DC/DC converter.
i shall assume u mean to measure the Rdson of a MOSFET (and not, say the output terminals of a transformer). u should know that Rdson changes drastically (maybe 300%) based on the amount of current flowing through the device. also changes due to gate-source voltage and temperature, but most due to current though the drain-source of a MOSFET. therefore you should think, not to measure a specific value, but a range. take for example a 10A continuous rated MOSFET. how to test?
use a 10A power supply with digital over-current protection. measure the drain-source terminals with a digital volt meter set for very low Ohms. connect the MOSFET drain to the positive terminal of power supply, and source to the negative terminal. put the over-current on lowest level and voltage to some low voltage, say 20Vdc. have a seperate power supply (with common ground system) turn the MOSFET on, and keep it on.
Then turn on the main power supply and it should go immediately into current control mode. at every 1A interval measure the voltage across drain-source. this voltage should be very low, so use a good volt meter. plot the results in excell, Rdson vs. current.
Rdson = Vmeasure / ShortCircuitCurrent
interesting, to repeat experiment but change the gate-source voltage to half of its value.
Mr.Cool
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