I want to control the current on an inductive load (electromagnet) by the means of PWM switching. I have done some research and saw a lot of different circuit configurations.

  1. The electromagnet will act on a metal rod so changing polarity is not of interest.
  2. A capacitor should handle the reactive currents when switching (there will be a lot of wasted power if not)
  3. I want to control the PWM with an arduino micro-controller so logic level mosfet or gate drivers. I think I will need gate drivers anyway for high side switching
  4. Power is relatively low maybe 12V power supply and 3A max. and PWM switching will be just above audible frequencies ~20 kHz.

My initial idea was to use only one N-channel MOSFET on the low side, plus a diode but I found more interesting circuits that are maybe more efficient.

This is the circuit I am going with:


simulate this circuit – Schematic created using CircuitLab

When MOSFETs are switched on the current flows from the capacitor to inductive load and when they are switched off the capacitor recharges. The power supply will give only active power.

I am aware that I have a high side N-channel MOSFET that needs a driver. I have seen some high-channel and low-channel drivers on the net but It is not clear for me how the bootstrap capacitor is getting charged

  1. How does a bootstrap solution gets charged in this configuration? when both mosfets are off there is no link from V1 to charge the capacitor, it will leak charge with time. Maybe I am wrong?
  2. Also, what is really the advantage of this Half H-bridge over a single MOSFET in the low side?
  3. What is the best way to do a current sensing feedback to the Arduino? A shunt?
  • \$\begingroup\$ Welcome to EE.SE! One half of an H-bridge is normally called a half bridge. \$\endgroup\$
    – winny
    Jul 7, 2020 at 17:51
  • \$\begingroup\$ I don't see what the second switch gives you at all. Just wire L1 to V1 and omit M2,D2. \$\endgroup\$
    – user16324
    Jul 7, 2020 at 18:25
  • \$\begingroup\$ That was my plan at the beginning but this half bridge seems quite a popular design \$\endgroup\$ Jul 7, 2020 at 18:55
  • \$\begingroup\$ @BrianDrummond I think it gives you more precise control of the current, since the current decays at the same rate it builds up, instead of only decaying through a diode. But the one-transistor one-diode solution certainly uses less parts. \$\endgroup\$ Jul 7, 2020 at 18:58
  • \$\begingroup\$ It also allow to charge the capacitor the half bridge right? In The one diode one mosfet solution the coil is just shorted when the mosfet is off \$\endgroup\$ Jul 7, 2020 at 19:03


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