Combining PWM with DC motor braking?

[Hatchet Jack]

Howdy to all, neat site you have here.

Been awhile since I dabbled in electronics. I have a gear-reduction 12VDC motor which needs speed control (direction control too if possible) and braking. This would all be done with some sort of foot switch, maybe start with a DPDT H-wired (ON)OFF(ON)switch?

I've seen a PWM circuit and a DC motor braking circuit but looking at both, I'm lost as to how to combine them. Am looking to build something with discrete components, can't go the route of a PIC chip.

(Doesn't have to be PWM, motor responds well, has adequate torque with my variable power supply)

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[dknguyen]

An H-bridge (if you have independent control of each transistor) is capable of both braking and bidirectional PWM control. So if you need bidirectional you need an H-bridge anyways. If you want to add braking, then you need to add in independent control of each transistor. In practice this means more control logic/gates if you don't use a PIC.

https://www.modularcircuits.com/h-bridge_secrets1.htm
https://www.modularcircuits.com/h-bridge_secrets2.htm
https://www.modularcircuits.com/h-bridge_secrets3.htm

As for combining PWM with braking for a unidirectonal system, it involves just havign both PWM and braking switches in the same circuit- one in series with the motor and battery for PWM, and one across the motor terminals to short it in order to brake (this one must be capable of two-way blocking so a MOSFET won't work).

 

[Hatchet Jack]

H-Bridge! Seems the best most direct way to go, thanks.

Yes, bidirectional, but how does it work to achieve braking?
Can't remember....which mosFETs have to be ON? Off?

Ooooops---------I posted this after your amended post with the links,
I'll read up on them.

 

[dknguyen]

High-side Transistor + Low-side Transistor of opposite leg ON = Fwd or Rev

Both High-Side Transistors OR Both Low-side transistors on = Brake (short circuits the motor, turns the motor into a generator driving a very large load, dissipatign energy and slowing it down).

Obviously you never want the high-side and low-side transistors in the same leg to both be on...short-circuit between the battery! Remember to into account finite MOSFET turn on and turn off times when changing direction or braking otherwise some shoot-through (short-circuit) will occur. This is what deadtime is for.

Because of the finite switchign time we tend not to PWM both transistors. We tend to leave one on continuously (usually the low-side) and PWM the high-side.

 

[Hatchet Jack]

Yeah it's coming back to me, along with the logic of why programable devices are so beautiful, LOL!!!!!!!! To accomplish all this mechanically....well it's gonna take a few beers