I am making a inverter (DC to 3 phase 2 level inverter) using IRF640 mosfets. I get my triggering pulses form a dspace kit (with matlab). I want to make drive circuit for my mosfets. I have seen a model circuit given by my teacher and it has both buffer (hcf4010be) and opto-coupler (TLP250) for pulses before giving to gate. From what I know opto-coupler can both isolate and boost the pulses whereas buffer only helps in providing load current without loading DSP pins (which I think opto-coupler does automatically).

My question is do we need both? I think opto-coupler alone is enough.

And one more, do we need to have separate DC supplies for each opto-coupler? I mean can't we use same dc supply circuit for all opto-couplers? (I will be using 6 opto-couplers)

  • \$\begingroup\$ Please use proper posting guidelines related to proper use of case. \$\endgroup\$ Oct 7, 2013 at 4:15

1 Answer 1


The TLP250 you mentioned requires 5 mA input current to guarantee turning on. If you need to operate 6 of them together, you might need to source 30 mA from the controlling device. A higher current might be desirable to give faster switching (although the datasheet makes no promises about this).

For some microcontrollers or DSP's 30 mA would be no problem. For others, it might violate the output load specs.


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