Re: learning about transistor equivalent to R_ds_on

mrdarrett@xxxxxxxxx wrote:
In this data *** for the TIP31A:

http://www.fairchildsemi.com/ds/TI/TIP31A.pdf

The spec is given:
VCE(sat) * Collector-Emitter Saturation Voltage IC = 3A, IB = 375mA:
1.2 V

Does this mean then that the resistance between the collector and
emitter is (1.2V) / (3A) = 0.4 ohms, when the transistor is carrying
3A through the collector to the emitter?

If so, that's a bit higher than the Rds_on for the IRF530, at 0.1 ohm.


Pretty much. But the BJT needs a whole lot of base current to keep it there and it needs a long time to come back out of saturation. IOW if you want to switch something at a reasonable efficiency you are usually better off with a FET.

--
Regards, Joerg

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