[SOLVED] Brushed DC Motor Control Power stage design

[KlausST]

Hi,

* You need a stable, low impedance GND wiring
--> I recommend a solid GND plane

All supplies need at least one big bulk capacitor
--> update schematic and circuit

* use high speed (ceramics) capacitors at each supply pin of each load
--> update schematic and circuit

* you drive the low side Mosfet gate with 5V only
--> either use a suitable "logic level Mosfet" or change the drive voltage (circuit)

* Why 2k2 (4×. They just make voltage rise unnecessary slow and increase Mosfet power dissipation)
--> replace them with 100R (to avoid ringing. Set dead time with software. You may omit the diodes)

* Why R1, R10 (they decrease bootstrap performance)
--> short them (after you added the supply Cs)

* Why R4, R5 (they decrease bootstrap performance)
--> short them

* Why D7, D8 (They are useless)
--> You may omit them

****Filter:
It should attenuate PWM frequency (8000Hz), but should give fast response (maybe 10Hz) of average current
I recommend to use fc = about sqrt(8000Hz x 10Hz) = about 300Hz
To suppress 8kHz amplitude to less than 1% you need at least 2nd order LPF

* C3 is useless
--> you may omit it

* replace R6 with about 26k (to act as LPF)
* add about 40nF across R7 (to act as LPF)
* replace R8 with about 1k5 to set gain of about 7.7. This gives about 3V output for 4A bridge GND pin current)
* replace D9 with 100R ( to generate stable ADC source)

******
I used "why" when your circuit is not according datasheet..--> Use the datasheet and application notes.
(Maybe you have an explanation for the modifications, maybe you used circuit from the internet - and maybe the modifications make sense for other applications...but I don't see a benefit for your application)


Klaus

 

[abc_de]

Helpful information
I do not have enough experience of analog design. I just follow some application notes and observe reading. I will changes as u suggest.
R4,R5 and D7,D8 are used to prevent negative transients from motor suggested by application notes from international rectifier, also I watch masters 2017 by microchip they also suggest it.

One more thing I did not get ur explanation for filter design can u elaborate more For better understanding

 

[KlausST]

Hi,

D7, D8...
On first sight it makes sense...but
* if on one motor side is negative voltage, then I expect positive voltage on the other side. Thus it makes sense to put diode across the high side FETs, too, then you need 4 diodes.
Another BUT...the Mosfets already have built in diodes.If you want to prevent them from getting conductuve (because usually they are slow) you should consider to use schottky diodes.

R4, R5 are not able to prevent negative transients.

Filter: What do you want to know?

Klaus

 

[abc_de]

****Filter:
It should attenuate PWM frequency (8000Hz), but should give fast response (maybe 10Hz) of average current
I recommend to use fc = about sqrt(8000Hz x 10Hz) = about 300Hz
To suppress 8kHz amplitude to less than 1% you need at least 2nd order LPF

I did not get about fast reponse etc.

 

[KlausST]

Hi,

You want to build a regulation loop..where the current is the feedback..
The faster the filter response ... the faster the feedback ... the more stable and precise is the regulation.

Klaus