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dc mototr driver with direction control from single pin

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mshh

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I am trying to do Dc motor driver with single direction pin (forward / reverse). I simulated it on proteus but the motor is very slow with high frequency PWM(clock). when i decrease its frequency the motor speed is increased. what is the problem in this circuit is it the components?
 

The mosfets need to be driven so they turn on fully. To do this you must apply a sufficiently high voltage to the gates (since your mosfets are N type). This is easier to do for N devices at the low side. However the upper Nmos may be difficult to drive so they turn on fully. Can you verify what voltage their gates are getting?

It may be easier if you use Pmos at the high side.
 

Hi,

Nice circuit design, I haven't seen that control of the bridge FETs using AND and NOT before, I like the method, thanks.

Is it possible that the higher frequency lowers the clock signal voltage, and that causes the signal to the AND gates to fall into the grey area, or possibly not be enough to generate a strong high signal, if you understand what I'm attempting to describe.

Maybe not the problem, but perhaps measuring input and output voltages on logic devices and on NMOS device gates is one place to start troubleshooting.
 

I used optocoupler with N mosfet to give VGs on and I used p mosfet with the high side. it runs for seconds and the simulation stopped


 

* Try changing the timestep to a larger amount.

* To turn off the P devices, the gate needs a voltage at the same level as its more positive terminal. It will help if you add pullup resistors (similar to the pulldown resistors you added to the N devices).

You need to make sure that each mosfet turns fully off and fully on. Construct basic test simulations, so you can discover the operating characteristics of the mosfet.
 

Hi,

Isn't it easier, smaller and cheaper to use a ready to buy motor driver?

Like DRV8838.
https://www.ti.com/lit/pdf/slvsba4

It includes all the gate driver circuitry, and includes overcurrent and overtemperature protection...

Klaus
 

I need higher specs like . the motor power supply 24 Vdc with drive current up to 3 Amp. I also need the direction pin to be controlled with logic 1 or 0 on the same pin.
 

Hi,

From the beginning you gave no single specification, therefore could give just an example.

But if you go to IC manufacturers or distributors web sites you will find hundreds of motor drivers.

With your solution you need a lot of external devices, with an integrated solution they maybe have built in motor direction control.
In many caes just an XOR gate will do.

Read about decay modes of the drivers, you may find it useful even for a duscrete solution.

Klaus
 

How to do the direction control to be logic 0 or 1?
 

How to do the direction control to be logic 0 or 1?

It may be as simple as changing the 0 to 1, at the top left corner of your post #4 schematic. (That is only tentative since there may be more involved for all I know.)

Logic 1 provides a path to supply+.
Logic 0 provides a path to 0V ground.

You can send one or the other signal in several ways. Example, manual switch, pushbutton, programming an output pin. If it is a momentary switch then you need to feed it to a memory circuit which maintains its state after you let up the button.
 

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Re: gate driver h bridge

You have the Ho and Lo of U2 transposed.

To get forward/reverse you need to switch between one pair of transistors. That can be either upper pair Q1 and Q3, or right hand side Q3 and Q4, it really does not matter which.
But one of the pair needs to be on, the other off all the time to select the direction.

Then you PWM lower pair Q2 and Q4 alternately, or left hand side Q1 and Q2 alternately to get speed.
 

yes , I transposed it to work because it wasn't working on simulation.
now How to apply your proposal on the gate driver to control all the h bridge.?
 

Hi,

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

(Edit: I changed the logic. Now the high side is PWM´d. Before the high side was only controlled with "almost static" DIR signal, but this created problems with bootstrap circuit)

Klaus
 
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Hi,

Yes there are many ways....

Tony´s picture seems to be correct. But at first I was confused by the XORs. The output is inverted so indeed they are XNORs.
I think XOR is more conveniant. If you want to use XOR, then just connect the "fix" input to VCC insted of GND. Both U5 and U6.

Klaus
 

Klaus is right, there are several different ways to configure this, that are all equally valid.

U4 needs to be an XOR gate to invert (or non invert) the PWM for forward/reverse.
It "could" be done in software, but doing it with an XOR gate in the hardware makes the software simpler and more intuitive.

U5 and U6 could just be simple inverters, that is all they do. But I suggest using the unused XOR gates as simple inverters rather than having to use an extra chip.

- - - Updated - - -

Anyhow, fire up your simulator and give it a go.

As Klaus says, either XOR or XNOR gates can be made to work, just tie the second input to Vdd or Vee for U5 and U6.
 

Its a good idea to have only two control signals - PWM and DIR.
But the dead time between the High side gate signal and the low side gate signal has to be considered, to avoid shoot-through.
In the circuit using AND gate and NOT gates, AND gate output will turn on low side MOSFET,
where the NOT gate (which has a propagation delay), may not turn off High side MOSFET immediately.
 

Dead time could be included a couple of ways in hardware.
R2, R5, R4, and R8 could be made much larger, say 220 ohms.

Or a similar fast "off" slow "on" circuit could be added at the inputs of U2 and U3 with an RC time constant and a diode across the resistor.
 
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