Saturday, January 8, 2011

L293D Interfacing

L293D is a motor driver used for bidirectional control of the DC motors. It is capable of delivering upto 600mA per channel. These also have output clamp diodes for inductive transient suppression. It consists of four individual drivers. The block diagram and pinout are given below.

As shown above it has to two Vcc's. Vcc1 & Vcc2. Vcc1 is the power for the working of the logic controls and Vcc2 is the power for the motor drive. This separate power supply system is implemented for reducing the power dissipation. Vcc2 can range from 4V to 34V and Vcc1 is typically 5V. 1A,2A,3A,4A are the control inputs and are TTL compatible. 1,2EN and 3,4EN are enable inputs for each pair of drivers. Only if you enable a driver, you can use it. So the required driver enable inputs should be driven logic high to enable them as shown in the figure.1Y,2Y,3Y,and 4Y are the outputs.


The output of each of the driver follows its input. For example if the 1A is pulled high, the 1Y will be high. Here the output high voltage value corresponds to Vcc2. If the input 1A is pulled down to ground, then the output 1Y will be grounded. This is how the driver works. Thus by applying proper input combinations to the driver inputs we can achieve the bidirectional control of the motor. Consider the figure given below.

Here the drivers 1&2 are combined to control the motor bidirectionally. Observe the input combination of drivers 1&2. Here the driver 1 input is high, so the output 1Y will be high and equal to Vcc2. Driver 2 input is low, so the output 2Y will be low. Thus the current flows from the driver one through the motor and finally to the driver 2. Now the motor will rotate in one direction. Next reverse the input combination of the drivers 1&2 i.e. 1A=LOW(0), 2A=HIGH(1). As a result 2Y will be high and 1Y will be low. Thus the current flows from the driver 2 through the motor to driver 1. Here the direction of the current flow is reversed and the motor rotates in the opposite direction. Thus we can control the motor bidirectionally. 

In the above diagram single directional control of the motors is also illustrated using the drivers 3&4.


Anonymous said...

Nice explanation. I am an electronics newbie and was trying to measure the output of the 1Y and 2Y using an oscilloscope in an existing controller using this chip. If I have the probe tip connected to one output and the ground clip on the other output, the motor does not turn. If I leave the ground clip floating it does. Can you tell me what I am doing wrong.

Anil said...

It may be the problem of probes. First you better test the probes. Then check whether any chance of 1Y and 2Y getting shorted while you test.

Anonymous said...

Funny, I'm having exactly the same problem as anonymous. Using a multimeter rather than an oscilloscope. Probes are okay and neither Y is getting shorted. Really stumped on this one.

Anil C S said...

Could you send me the circuit to which L293D is connected?

Anonymous said...

I cannot reproduce the problem that Anonymous had. Connecting DMM to outputs does not affect the motor for me.

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