PWM motor control HELP, URGENT

[NickUSA79]

Hello, I need to know how to stop a motor faster... I am using the H-bridge to driving the motor foward and backwards, but when I shut off the PWM the motor keeps spinning... free run, I need it to stop as fast as possible, what do I do ? I've read somewhere that if it is running foward, to stop faster simply shut off PWM, and send 1 to the two botton mosfets would that work ??? Please help out ... thanks

 

[hameeds01]

to stop the motor quickly u have to short the two wires of the motor which is known as Electrical Brake

 

[miredox]

It depends on how your H-bridge is built. If the bottom mosfets are both directly connected to the ground, switching on both mosfets will short the two wires of the motor to the ground, which will indeed act as an electrical brake.

A mosfet is not an ideal switch, so the amount of electrical braking current depends on the on-resistance of the mosfets. Also, some H-bridges may have a series-resistor between the bottom-mosfets and the ground in order to measure the current through the motor.

 

[nandhu015]

Another option is to give supply in the opposite direction (for a short period)

Nandhu

 

[NickUSA79]

I am thinking about using an optocoupler such as the TIL111, but at a PWM frequency of 10Khz, would it switch fast enough ??? Does anyone know its maximum switching speed ?? Thanks

 

[hameeds01]

check out in a Datasheet

 

[atferrari]

Turning both bottom (or both upper) transistors ON will surely brake your motor.

Seen circuits with resistors to be put in series, to cope with the high currents involved. Not in my designs, all of low power motors.

Is your question URGENT because your motor is still running?

 

[khansaab21]

Motor is a high inertial load. Hence it could not be stopped or turned off like a electrical bulb. There is time involved for its complete shutdown after the switches have been turned off.

A suggestion to turn it off immediately is to apply external brakes to it simultaneously with turning off the PWM. (I used the stated technique in my stair climbing robot as braking had to be very precise in that project)

Secondly, quiet a few popular methods have been posted on this thread only.

Thirdly, if you have interest in power electronics, then you can always use self commutating circuit of the SCR.

 

[NickUSA79]

Hey guys, thanks for all your help. The braking of the motor has finally worked thanks to your help. Now I am having trouble simulating this in PROTEUS, the Till111, represented by the opto you see in the picture, but the problem is that I am no getting the full speed out of the motor after the mosfet turns on, could it be that my circuit is wrong ? Can anybody help out ? Thanks again...

 

[hakeen]

Hi,

Did you check MOS Gate Signals? Are they as expected?

By the way 111 has Vceo of 30V. In your circuitry collector of 111 is going to see ~22-23V when upper MOS are ON. It is quite close to abs max of 30V. Due to inductance in the load you might easily reach to 30V levels. I would recommend using something higher, 70-80V.

Maybe like CNY17
e.g.

Regards