[moved] H Bridge Gets Hot (using Transistor)

[gauravkothari23]

I am trying to make a H Bridge to drive a Small Motor (Circuit Attached)
But my issue is without load even all transistor gets extreme hot.
can anybody please let me know where the issue is.

 

[barry]

Re: H Bridge Gets Hot (using Transistor)

This implies that you're turning on both top and bottom transistors at the same time. With no other information its impossible to tell anything else.

 

[gauravkothari23]

Re: H Bridge Gets Hot (using Transistor)

This implies that you're turning on both top and bottom transistors at the same time. With no other information its impossible to tell anything else.

The code is:

        lcdclear();
	lcdrow1();
	LCD_puts("MOTOR CLOCK-WISE");			
	motor1=0;
	motor2=1;
	msdelay(5000);
	lcdclear();
	lcdrow1();
	LCD_puts("MOTOR ANTI-CLOCK");			
	motor1=1;
	motor2=0;
	msdelay(5000);
	lcdclear();
	lcdrow1();
	LCD_puts("MOTOR STOP");			
	motor1=1;
	motor2=1;
	msdelay(2000);

- - - Updated - - -

i am using 8051 Microcontroller AT89S52.
MUC pin 1 goes to Port 0.3 and MCU pin 2 goes to Port 0.2.
have also added 10K pull up resistor to both the port pins.

 

[asdf44]

Re: H Bridge Gets Hot (using Transistor)

The circuit posted will enable top and bottom transistors when any votlage between ~0.7 and ~4.4V is present.

This is bad but also what's your MCU voltage? If its less than 5 then your upper transistors will never turn off.

See this link where someone is having the exact same problem and a solution is posted.
https://electronics.stackexchange.c...dge-transistor-smoking-bipolar-bjt-transistor

 

[KlausST]

Re: H Bridge Gets Hot (using Transistor)

Hi,

It seems you use a simulation tool.

Then think about this:
The microcontroller output is
* LOW = 0V (ideally)
* HIGH = 5.0V (ideally)

Now it should be obvious that the voltage has to travel from 0V to 5V in a finite time.
It surely passes 2.5V..

Now do your simulation for the case when the microcontroller output is just 2.5V.
--> check the current through the transistors and through the motor.

Klaus

 

[FvM]

Re: H Bridge Gets Hot (using Transistor)

The short answer is: It's impossible to operate the circuit from X51 open drain IO port without an additional CMOS buffer, e.g. HC04. Pull-up resistor can't do.

asdf44 has explained about the "forbidden" voltage range. You can your own calculations about the required drive strength to guarantee clear low and high level at the driver input.

 

[BradtheRad]

Since this is a low power application, I wonder if it isn't easier to create a bipolar supply and half-bridge? Then you need turn on only one device to drive the motor.

An oscillating converter can derive a negative supply from your existing +5v. It breaks down your problem into two tasks: (1) creating a stable supply of a desired polarity, and (2) switching it rapidly off and on through your motor.

On the other hand notice that the H-bridge method requires doing both at the same time. That task is more problematic.

 

[KlausST]

Hi,

I assume there are many - even cheap - ready to buy solutions (ICs or modules).
Do an internet search.

The benefit:
* Low pin count
* Low part count
* Reliable function
* Often they have protection built in (overcurrent, overvoltage, thermal shutdown....)
* Maybe additional features

Klaus