H bridge controlling DC motor with polarity for direction

Thread Starter

slegha

Joined Nov 23, 2016
4
Hello,

I am designing a circuit that will have a DC motor powered by DC voltage (at line 1) and then a control voltage (line 2) that for example:
1- Line 2 = +V, Motor will rotate clockwise
2- Line 2 = -V, Motor will rotate counter clockwise
3- Line2 = 0V, Motor is not rotating.

Line 1 ~ 170V
Line 2 ~ +/- 25V

Motor: 150V, 300mA max

I came with the following schematic. What do you think and what can you advice.

Thanks.Circuit.png
 

crutschow

Joined Mar 14, 2008
25,377
That circuit requires a gate voltage for the N-MOSFETs Q1 and Q3 equal to 10V above the line 1 voltage to turn them fully ON, so it will not work as shown.

You either need a H-bridge such as this or a bridge driver such as one of these.

If you wanted to roll your own, you would need to change Q1 and Q3 to P-MOSFETs with circuitry to drive their gates between the Line 1 voltage (P-MOSFET OFF) and to the Line 1 voltage minus 10V (P-MOSFET ON) such as shown below:

What is the maximum speed that you need to switch the circuit?

upload_2016-12-8_13-2-1.png
 

Thread Starter

slegha

Joined Nov 23, 2016
4
That circuit requires a gate voltage for the N-MOSFETs Q1 and Q3 equal to 10V above the line 1 voltage to turn them fully ON, so it will not work as shown.

You either need a H-bridge such as this or a bridge driver such as one of these.

If you wanted to roll your own, you would need to change Q1 and Q3 to P-MOSFETs with circuitry to drive their gates between the Line 1 voltage (P-MOSFET OFF) and to the Line 1 voltage minus 10V (P-MOSFET ON) such as shown below:

What is the maximum speed that you need to switch the circuit?

View attachment 116579
Hello Crutschow,

Thanks for reply. After posting this thread, I was looking at it and I noticed something wrong with it so I think I have it correct now. Check the schematic attached.
Turning it on doesn't have to be fast. Just command to turn CW and CCW with long pause between each.
Circuit.png
 

crutschow

Joined Mar 14, 2008
25,377
You didn't fully read what I said. :rolleyes:
As I previously stated you need a gate voltage of 10V above the Line1 voltage to fully turn on Q1 and Q3 as a switch (the gate voltage needs to be 10V greater than the source voltage).
Your circuit can't do that.
 

Thread Starter

slegha

Joined Nov 23, 2016
4
Assuming that I can send a voltage 10V greater than line 1. How to handle the Line 2 -V to rotate in the opposite direction?
 
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