I am building a circuit takes 18V from a regulated bus and uses a switching controller to regulate it to 12V @ 6A, where the switching frequency is around 350kHz. The output then branches off to two places:

  1. To a motor, which at max power draws 3.1A.
  2. To a linear regulator, which regulates to 3.3V @ 1A for control logic

This is a high-level overview of the regulation in my circuit.

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If possible, I'd like some advice since I am new to this:

  1. I figured that I would need to filter the output from the switching regulator (Bus Regulator). Does that seem necessary here since the switching frequency is low? What would be an appropriate filter to use in this scenario since it is a high-current circuit?

  2. I placed a decoupling capacitor between the actuator supply and the logic regulator to protect it if the motor draws too much instantaneous current. That makes sense right?

This is my first time using multiple regulators on a board so any feedback would be greatly appreciated.


1 Answer 1


Your circuit will work as you have drawn it, with the following things to watch out for:

Your linear regulator should give you a clean 3.3-volt signal as long as the VIN_12V voltage stays above the minimum (called "dropout") voltage specified.

To keep your low voltage circuitry noise-free, make sure that your motor current has a ground path back to your bus which does not flow through your low voltage circuit ground paths. Make a separate branch to the motor and the logic ground.

Because you are running your low voltage circuit at 1 ampere, your logic regulator will have (12-3.3) or 8.7 volts across it. At 1 ampere, this means the device is dissipating 8.7 watts, so make sure the regulator can handle this power. Heat sinking will likely be required.

No reasonable amount of capacitance will provide 1 ampere to your logic circuit if your motor pulls the 12 volts down below your logic regulator's dropout voltage, so be sure your logic circuitry is tolerant of brownouts.

Good luck!

  • \$\begingroup\$ Thank you this is helpful! The logic is actually using ~200mA but the regulator can provide at most 1A. I'll double check to make sure the regulator can handle the power. I'll also confirm my circuit is tolerant of brownouts \$\endgroup\$ Nov 17, 2022 at 5:57

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