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dc mototr driver with direction control from single pin

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what waveforms do you want to see?
 

Hi,

I just recognized one problem: The high side must be PWM´d because of the bootstrap circuit.
* therefore I corrected my logic of post#14
* (I think Tony´s solution has the same problem)

****
In post#8 i told to read about decay modes. This also has an effect on dead time.
With fast decay mode there usually is no problem of cross conducting.

Additionally the RC combination at the gate, like R2D2 (funny!), can be used to avoid cross conducting of a half bridge.

Klaus
 

Hi,

sorry I meant "R-D" combination.

The R makes slow turn ON, but the D makes fast turn OFF. (relatively)

Klaus
 

in post #14 you mean AND gate instead of XOR?
 

Yes,

AND = AND
"!" = inverted

Klaus
 

with AND gate , the motor motion becomes very slow and I also am not able to decrease Vcc to 24 volt as it stopped.
another problem, When Q1 and Q4 is on Q3 has voltage on its gate. when Q3 and Q2 is on Q1 has voltage on its gate.
 

Hi,

again: read about decay modes.

For some regulation loops slow decay is useful, especially when you want "speed control".
For some regulation loops fast decay is useful, especially when you want "torque control".
But with both modes you can control torque as well as speed 0% to 99.9%.

Klaus
 

I read about decay in this article https://ebldc.com/?p=86 and I got that I need freewheeling diode, so I added fast switching diode for every mosfet but nothing changed it is still slow.
why does the motion slow down when i increase the frequency ?
 
Last edited:

Hi,

decay mode with a full bridge has nothing to do with diodes.
btw. diodes are already included in the Mosfets.

From your link:
In Slow Decay mode we use the FETs on the same H Bridge segment. Per example you can use either both high side FETs or both low side FETs. The typical convention is to use the low side FETs.
Click to expand...

Klaus
 

So what is the solution now?
 

Hi,

For me IT JUST SEEMS you need slow decay mode. But you have to decide.

***
If so, then...

Q1 = DIR AND PWM
Q3 = !DIR AND PWM
Q2 = !DIR OR !PWM
Q4 = DIR OR !PWM

PWM can be 0...99% (not 100%, bootstrap circuit)
And - because both MOSFETS of a halfbridge are PWM´d - you need to take care of dead time.

*********
Maybe you can imagine this "forward" example:
When DIR = 1:
Q1 = PWM
Q2 = !PWM
Q3 = 0
Q4 = 1

Klaus
 

why did you use OR gate , Is that related to the decay mode?
 

Hi,

Is there an alternative to achieve the slow_decay function?
Then for sure you are free to use it. ;-)

Klaus
 

I don't understand why do you use the slow decay method and your configuration didn't solve my problem yet.
 

Hi,

I´m confused about your posts, because I think it is explained enough.

**
You didn´t clearely say, but (because you complained about motor speed. post#28, post#30) I think you want to achieve motor speed control.
The solution in post#14 is fast_decay. Maybe I should have mentioned this more clearely.
In post#29 I said that slow_decay is suitable for speed control.

Therefore now I changed the circuit (post#14) from fast_decay to slow_decay (post#33)
..and tried to explain this:
For me IT JUST SEEMS you need slow decay mode. But you have to decide.

***
If so, then...
Click to expand...

***
I try to give recommendations. But you have to decide if it makes sense for your circuit or not. I´m not into that deep in your application.

***

Did you test the slow_decay?
I hope this solves your problem.

If not, then please be very descriptive: What exactely did you do? What did you expect? And what is not like expected?
You know we are thousands of kilometers apart....and maybe I´m a bit slow in understanding your problems.


Klaus
 

I applied both of your circuits , I can control direction but the problem till now the motor speed is very slow at high frequencies . this is the main problem in this thread. when i reduce frequency to 1 hz it gives logic speed in simulation
the problem is still existed
 
Last edited:

Hi,

but the problem till now the motor speed is very slow at high frequencies . this is the main problem in this thread.
Click to expand...

Again the request for precise informations.
* I don´t see how slow "very slow" motor speed is
* I don´t see how high "very high frequency is"

***
Then you talk about simulation:
When you talk of motor speed is this "real circuit" or is it simulation?

Independent whether simulation or real circuit:
Please show one scope picture with the two halfbridge outputs. If possible: 1kHz, 90% duty cycle.
We need to see timing and voltages.

Klaus
 

it is simulation on proteus. the output on the motor terminal is just constant dc volt as shown in post #38.
channel C and B are 14.6 v ,11.6 v
channel A is connected to PWM
at 100 hz and 10k hz with duty cycle 90%



 

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