Half bridge working using gate driver help needed

AlbertHall

Joined Jun 4, 2014
8,540
Lower MOSFET ON, Upper MOSFET OFF, the output will be at -DC-BUS and the other side of the motor is connected to +DC-BUS. The motor will run.
Lower MOSFET ON, Upper MOSFET OFF, the output will be at +DC-BUS so both sides of the the motor are at the same voltage and so the motor will not run.

By feeding the driver with a PWM signal, say 50:50 mark-space ratio, the motor will get power some of the time and so will run at reduced speed.
 

Thread Starter

mishra87

Joined Jan 17, 2016
554
I did not get the exact answer I wanted ?

I wanted to know how dc motor works if it is connected as shown above image .

Actually this circuit is already proven so I wanted to understand how it is working.

Load is permanent dc magnet motor.
Vdc rail is 24v.

So I wanted to understand the signal flow.

Thanks
 

shortbus

Joined Sep 30, 2009
7,080
I wanted to know how dc motor works if it is connected as shown above image .
Magic? Enough with being funny. If it is wired as shown, the high side mosfet does nothing except sort out the DC+ rail if both high and low get turned on at the same time. Since one side of the motor is connected to the DC+ the high side is not functional and not needed to make the motor work. The only thing controlling the motor is the low side mosfet.


So I wanted to understand the signal flow.
The signal flow is - DC+ to motor, from motor to low side mosfet, to DC- when low side is conducting.

This means that my answer in post #5 is still the correct one. Since the high side mosfet is null.
 

BobTPH

Joined Jun 5, 2013
2,055
The DC+ and DC- indicate a bipolar supply. If the motor is connected to the output and the common of the supply, it will function as a half bridge, allowing reversing of the motor. I think that was what was intended.

Bob
 

AlbertHall

Joined Jun 4, 2014
8,540
So does the intrinsic diode in the high side mosfet, even when it isn't conducting.The intrinsic diode is a shunt all of the time.
The motor will be driving the output negative of the positive supply (as wired in the TS diagram) so the diode will be reverse biased. The motor is then running as a generator, not a simple inductor.
 

shortbus

Joined Sep 30, 2009
7,080
The motor will be driving the output negative of the positive supply (as wired in the TS diagram) so the diode will be reverse biased. The motor is then running as a generator, not a simple inductor.
Then wouldn't a simple diode in place of the high side mosfet be just as effective for a brake?

When in the original post did the idea of braking even get mentioned?
 

AlbertHall

Joined Jun 4, 2014
8,540
Then wouldn't a simple diode in place of the high side mosfet be just as effective for a brake?

When in the original post did the idea of braking even get mentioned?
If the diode was the right way round to do braking then it would short the power when the other MOSFET was turned on.
Not much did get mentioned in the original post.
 

shortbus

Joined Sep 30, 2009
7,080
The TS seems to not be here any longer.

The high side mosfet alone wouldn't do braking any way, isn't a resistor(that is missing) be necessary for that? The way the circuit is drawn it is using the source of the mosfet as the drain if being used for braking, so that is why I said a diode with the anode to the negative side of the motor would work just as well.
 
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