On brake driver (HW) implementation

[markoseverin]

Hi Guys,
I’m looking at the schematics/implementation of the brake resistor driver on the odrive (V3.5). It uses a fully featured half-bridge driver. I’m no motor control guru for sure, but I cannot help but wonder, why is a half bridge driver used? Shouldn’t just a resistor tied to VDD and a low side switch be enough? It would also support a 100% duty cycle, which the half bridge does not. In case of odrive, the bottom two mosfets serve no purpose, apart from bringing the switch node down to 0V, so that the bootstrap capacitor of the half bridge driver can recharge. Or is there something I’m not getting right?

Thanks for any input; I like the simplicity of odrive-s hardware, but this brake circuitry really bothers me.

Regards,
Marko

[towen]

What does an AUX Terminal on the Odrive is used for?

It’s a generic half-bridge power output, i.e. it can be driven to VBUS or 0V or neither. I think the developers didn’t know what they wanted to do with it when they first designed it. You could use it as a high power audio amplifier for a loudspeaker. However, in the current firmware, its function is to dump power via the brake resistor when necessary, to prevent the VBUS voltage rising above 56V or whatever limit has been configured.

You’re right, the bottom two mosfets are not used. I’m not sure why it was done like that, but it is.