How to stop L6235 and BLDC motor from generating voltage when power is turned off.

[KFowl.1]

I have been using the L6235 for more than 10 yease with no problems. Great part!!!

Powered from an AC to DC suppply with 24, +5 and -5 output. The motor of course runs off of the 24V. We have recently changed to a single 24V output AC to DC and the +/-5V is generated from the 24V. When the AC power is removed the motor freewheels and generates voltage back into the system and continues to supply +/-5V until the motor comes to a stop.

What can be done to keep the motor from powering the system once AC is removed?

[Cristiana SCARAMEL]

Hello @KFowl.1​ and welcome to the ST Community.

My suggestion is brake the motor before removing of AC power supply.

The L6235 BRAKE pin can be used to quickly stop the motor while it is running: providing a low logic level to this pin all the high-side DMOS switch on, making a short-circuit across the motor windings.

In this way, while the motor is braking, both Thermal and Over Current protections still work, avoiding BEMF to cause a current exceeding the device's maximum ratings.

Let me know if these info are useful to you, if yes please "Select as Best" button to close the topic.

[KFowl.1]

The only problem with braking before the motor stops is that the customer often remotely kills power to the device to perform a power on reset.
It is not known when the power is going to be turned off.
I thought about putting a diode in series to the motor power but I am concerned that voltage will build up and destroy something.
Any other ideas?
Keith

[Cristiana SCARAMEL]

Hello @KFowl.1​,

a suggestion is connect the BRAKE pin to a circuitry able to detected the presence - in your case the removal - of the power supply.

[KFowl.1 · Accepted solution]

That is what I worked out Friday afternoon. There is a fan control output on the AC to DC and I am going to drive a relay for the ±5V switcher input.
When the power supply turns off the relay will open to the ±5V. ☺
Simple fix.
Thanks for your input
Keith