Looking at an commercial electronic speed controler for a brushless motor, there is two big transistors on one side. For controling a motor, you have to switch the current on three wire, so you need six big transistor.

So, how is it possible to use only two big transistors ?

  • \$\begingroup\$ Where did you get the assumption of needing to switch 3 wires with 6 transistors? What other components are present? Can you share a PN or schematic? \$\endgroup\$
    – I. Wolfe
    Mar 20, 2015 at 16:20
  • \$\begingroup\$ or even a picture ? \$\endgroup\$
    – brhans
    Mar 20, 2015 at 16:35
  • \$\begingroup\$ The OP is correct, the TYPICAL configuration is a 3 phase bridge driving a 3 phase BLDC motor. That doesn't rule out other topologies, but just 2 transistors would be strange. A schematic would be key to understanding what's going on. \$\endgroup\$
    – John D
    Mar 20, 2015 at 18:07
  • \$\begingroup\$ Is it possible that the big transistors cuts the circuits before changing the path in the Hbridge. That way, the transistors in the Hbridge don't have to make the transition between on and off, don't dissipate power and can be small. \$\endgroup\$ Mar 23, 2015 at 15:48

1 Answer 1


In all my ESCs, those two "big transistors" are actually voltage regulators (I think they're part of the BEC circuitry).

If you look at the wikipedia image about "ESC" for example, you'll see that they're two 7805 regulators.

enter image description here


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