H Bridge Inverter Circuit Design Full Bridge Driver

The continuous running current is 1A for the L293SN754410 or 0.6A for the L293D. It is packaged as a normal DIP IC so if you need to heat sink it youre recommended to have a big ground plane connected rather than a heat sink block.

To apply a voltage across the motor a pair of diagonally opposite switches need to be turned on.

Depending on which pair of switches are turned on the motor will turn one way or another.

If both the top or both the bottom switches are turned on the motor will have no voltage difference across it so it wont move at all.

If the top and bottom switches on one side are turned on together by accident we will short out the supply, so you need to be careful if youre building your own H-bridge.

Most pre-packaged ones will have internal logic to prevent this.

Essentially if you take the average of the signal over time then it has a varying analog level, however in the short term it is digital.

This makes it easy to generate and efficient as transistors are most efficient when on or off rather than partially conducting.

Most modern microcontrollers have the ability to generate PWM built in, including the Arduino and derivatives.

You could theoretically use just the two PWM outputs, however you need to be careful about the polarity of the signal compared to the transistor youre driving.

H Bridge Inverter Circuit Design Full Bridge Driver

Some microcontrollers include a full bridge driver (Microchip call this Enhanced CaptureComparePWM or ECCP on their 8bit PIC chips) which drives 4 outputs and you can hook up to the H-bridge.

If you can drive both your PNP and NPN transistors from the same logic line (i.e.

In this configuration however you have to invert the duty-cycle when you are running in reverse because its the low part of the duty cycle that turns the motor on, shown as Inverted PWM above.

Essentially what we want is to add an over-all enable line to the H-bridge so we can use one enable line controlled by PWM rather than using a complex H-bridge driver.

One way is to add another transistor to the circuit that only connects the bottom rail of the H-bridge to the negative supply.

Pulsing this will make the motor run only while the control is high so PWM on this would make an overall speed control without having to worry about which direction the motor is running.

The cost of the extra transistor could be quite high if youre using high power transistors or MOSFETS and depending on your voltage rails this might be eating into your motor voltage as therell be a 0.7-0.4V drop across each transistor or MOSFET.

The other option then is to use logic to filter the control lines so that the PWM signal is combined with the direction signals.

In fact using a chip can save you a lot of trouble with offset voltages; if you have a different motor supply voltage from your logic voltage youll need drivers between the logic and the power transistors.

There are a couple of chips Id recommend and it depends really on how powerful your motors are which one to use, both are dual H-bridge chips (so you can control 2 motors) and both have 2 enable lines so you can connect a PWM line for each motor.

Its in a big heat-sinkable package and if youre running it close to the limit Id recommend using this heat sink.

The 298 also has current sense lines on each of the two channels which you can add a low value resistor to ground and monitor the current being drawn by each motor.

If you need to save some pins you can bridge the direction lines with a not gate and only use one line for direction control.

Yu can also parallel up the inputs and outputs on this chip to make a 4A continuous drive bridge but you need to be careful to wire up the inputs in the right order.

You need to provide your own protection diodes to suppress the inductive response of the motor and protect your circuit from negative voltages, these are wired backwards across your motor supply.

The continuous running current is 1A for the L293SN754410 or 0.6A for the L293D.

It is packaged as a normal DIP IC so if you need to heat sink it youre recommended to have a big ground plane connected rather than a heat sink block.