# Will a flyback diode damage my battery due to back EMF?

I am following this example of a sensored BLDC motor.

• This post assumes conventional current flow.

I am trying to understand how the diodes in this circuit protects the rest of my circuit from back EMF. If my understanding is right, when the motor produces back EMF, the back EMF will flow from the motor to the positive terminal of my battery because the top diode makes a direct path for the back EMF to flow to the positive battery terminal. Please let me know if my understanding of how current will flow is incorrect.

If my battery is 36 volts and if the back EMF flows directly to the positive terminal of my battery will that damage my battery because of the voltage spikes? If so how do I protect my circuit from back EMF?

• What kind of battery??? Lead acid would eat those spikes up happily. Some others won't be so tolerant Aug 18, 2022 at 4:31
• The battery impedance should look like a brick wall to the flyback energy. You’ll see a similar circuit arrangement on most ESCs. Note that the circuit in the link is not a good reference - the mosfet drive is poor. Aug 18, 2022 at 4:41

• @MissMulan Since $V = L \frac{dI}{dt}$, the voltage and current rate are equivalent. A clamped circuit can be described by either measure. An unclamped circuit permits a high voltage = high dI/dt, by presenting a high impedance to the current (~ V = Z * I). Aug 18, 2022 at 21:35