My question is relatively simple. If I arraged four silicon controled swithces, like the one here, to form an h bridge, could I drive it directly from the logic level? Since only gate to gate voltage will turn the switch on or off, it seems like there would be no need for a complex driver to handle high voltages between gates and sources or drains. Is this right?

See this question for some relevant information on silicon controlled switches.

  • \$\begingroup\$ All my ansers to that question still apply. An SCS is an old tech device, fw are available and you can do a better job using modern parts. Even using SCS's you would need high side drivers to translate the drive voltages up to the voltage of the high side switches, Gate drivers are no complex - they are devices that are as complex as they need to be to work properly. ||The fact that SCSs have almost vanished from the marketwhile MOSFETS abd IGBTs proliferate should give you a very good guide to their relative merits. \$\endgroup\$
    – Russell McMahon
    Apr 25 '12 at 19:02
  • \$\begingroup\$ I did not think you would make the distinction "high side" switch or "low side" switch. I thought the gate to gate voltage was completely independent of the bus voltage. So then you could have the logic level running on 12 volts and switch that 12 volts across the two gates. That 12 volts is independent of the bus voltage across the scs. I am probably misunderstanding the nature of driving an scs. \$\endgroup\$ Apr 25 '12 at 19:28
  • \$\begingroup\$ You are misunderstanding ... . The SCS "sees" control voltage across it's control terminals. If one of these is at a high voltage the other must be at a similar voltage for control to be possible. \$\endgroup\$
    – Russell McMahon
    Apr 26 '12 at 2:59

No, you couldn't just drive everything from logic level. That would work for the low side switches, but not the high side, as Russell mentioned.

Another problem is that you would have to be very careful to ensure break before make. Depending on the switch, it can stay on until the next current zero crossing or at least some finite time if you actively try to turn it off. These devices tend to be slow compared to regular transistors. As a result, you have to be conservative in setting the dead time when switching between top and bottom.

FETs, BJTs, and IGBTs are more appropriate nowadays.


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