Reduce Peak Voltage of a PWM Signal

[opensourcefan]

I have a DC PWM motor speed controller with an operating voltage of 12v - 60v.

However I need it to run a motor that functions best at 9.6v. The motor will pull about 1.8amps max at 9.6 volts.

The motor controller doesn't play nicely with an input voltage below 12v
.
My initial thought was a simple 7809 circuit on the output of the controller (PWM), however I think I'd have to skip the smoothing caps and I'm not sure the 7809 could handle the PWM frequencies?

Then I thought about a simple voltage divider with a couple resistors. If I'm not mistaken the max wattage dissipated would be 24w (12v x 2A) ??

It's the PWM that has me bothered, not quite sure what would be best practice here.

[Ian.M]

Brushed DC motors don't really care about the peak voltage (subject to insulation limitations).  Their speed is determined by the average voltage.  Therefore, its likely that you all need to do is run on 12V and limit the max. PWM duty cycle to 80%, e.g. if its got a control pot wired as a potential divider, add a fixed resistor of a quarter of its value in series with the top end of its track.

[pqass]

You can connect the controller output to 100R resistor and then to the gate of a N-MOSFET like an IRF640 or better (or any other that can take the current with a max gate voltage above your controller Vcc which is usually 20V).  Don't forget the flyback diode across the motor. Motor Vcc can then be different from controller Vcc.

See attached. Substitute lamp for your motor.

[opensourcefan]

You can connect the controller output to 100R resistor and then to the gate of a N-MOSFET like an IRF640 or better (or any other that can take the current with a max gate voltage above your controller Vcc which is usually 20V).  Don't forget the flyback diode across the motor. Motor Vcc can then be different from controller Vcc.

See attached. Substitute lamp for your motor.

Excellent, thank you.

Will the diode create any issues when a reverse signal is sent from the controller. It has a fwd / rev switch that I need.

[pqass]

Will the diode create any issues when a reverse signal is sent from the controller. It has a fwd / rev switch that I need.

Yeah, that's going to be a problem.  This isn't a solution if your controller has an H-bridge (and you relying on that for reverse drive).  Sorry.

[pqass]

Maybe you can just use 3, 5R resistors in parallel (a combined 1.6R) in series with the motor across controller output pins (controller Vcc=12V).
R = Vdrop / I = 12V - 9.6V = 2.4V / 1.8A = 1.33R  (use 3 * 5R parallel, for close enough).
P = I^2R = 1.8A ^2 * 1.6R = 5.4W / 3 = 1.8W each resistor, say 5W on the safe side.