Current Sensing Resistors in an H Bridge Circuit

[EEstudentNAU]

I am using the UC3638 PWM chip to drive a motor. I was wondering if the current sensing resistors are required, and if someone could translate how they work? How are they used for peak current limit control and in their absence what happens?

If more information is needed, its powered from a 12V 5A power source, using 2 complimentary half bridge mosfet chips, the Si4500DY.

 

[MATLABdude]

The current sensing just works via Ohm's Law, V = I*R

In applications like this, you want to use a small resistor (usually less than an ohm, but I haven't read through the particular datasheet in great detail) because the higher your sensing voltage, the less voltage you have across your motor.

You can often get away with not using the sense resistor (by replacing it with a wire / cable) but you don't get any current information (useful, for instance, in ensuring motors don't overheat or that a certain torque is applied).

 

[oswaler]

I can provide you with information about the use of current sensing resistors in an H bridge circuit and their role in controlling peak current limit.

Current sensing resistors are commonly used in H bridge circuits to measure the current flowing through the motor. This is important for several reasons. Firstly, it allows for monitoring and control of the motor's performance, ensuring it is operating within safe limits. Secondly, it enables the implementation of peak current limit control, which is crucial for protecting the motor and other components from damage due to excessive current.

In an H bridge circuit, the UC3638 PWM chip controls the switching of the Si4500DY mosfet chips to control the direction and speed of the motor. The current sensing resistors are placed in series with the motor, and their resistance changes in proportion to the current flowing through them. This change in resistance is then measured by the UC3638 chip, which uses this information to adjust the switching of the mosfets, thereby controlling the motor's current.

In the absence of current sensing resistors, the UC3638 chip would not have a way to measure the current flowing through the motor. This could lead to an uncontrolled increase in current, which could damage the motor and other components in the circuit. The inclusion of current sensing resistors allows the UC3638 chip to detect and limit the peak current, ensuring the motor operates within safe limits.

In conclusion, current sensing resistors play a crucial role in an H bridge circuit, especially when driving a motor. They enable the implementation of peak current limit control, which is essential for protecting the motor and other components from damage. Therefore, it is recommended to use current sensing resistors in your circuit to ensure safe and efficient operation of your motor.