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All You Need to Know About L293D

August 13, 2018 by ElectroPeak Inc

In this article, we want to take a deeper look at L293D IC. It's theory, features and specifications.


In this article, we want to take a deeper look at L293D IC. It's theory, features and specifications.

L293D & Motors; What’s the story?

Motors used in academic robots normally operate at 5, 6, 9, 12 or 24 volts. Depending on the model, the manufacturing method, price, etc., their current is about 100 mA to 5A. You can use motors in several ways. One method is to connect it directly to a battery, then it spins at its maximum speed in a particular direction, but in practice, we need to control the motors (on and off, speed control, direction control, and position control).

Therefore, we must control motors using controllers (logic circuits or microcontrollers or PCs or computers). But as you know, the output of microcontrollers are 5V and 200mA and can not spin the motor. So we need intermediate circuits to connect the controller to the motor, called drivers.

L293D is one of the most popular drivers in the market. There are several reasons which make L293D the preferred driver to the users, such as, cheap price (compared to other drivers), proper shape and size, easy control, no need for protective circuit and diodes, no need for heat sinks and good resistance to temperature and high-speed variations. This IC can set up motors with a voltage between 5V to 36V and a current of up to 600 mA. However, it can withstand a current up to 1200 mA in 100 microsecond and non-repetitive. The frequency of this IC is 5 kHz. If your motor matches these specifications, do not hesitate to use L293D.

Features and Specifications

The L293 and L293D devices are quadruple high current half-H drivers. The L293 is designed to provide bidirectional drive currents of up to 1 A at voltages from 4.5 V to 36 V. The L293D is designed to provide bidirectional drive currents of up to 600-mA at voltages from 4.5 V to 36 V. Both devices are designed to drive inductive loads such as relays, solenoids, DC and bipolar stepping motors, as well as other high current / high voltage loads in positive supply applications.

Each output is a complete totem-pole drive circuit, with a Darlington transistor sink and a pseudo- Darlington source. Drivers are enabled in pairs, with drivers 1 and 2 enabled by 1,2EN and drivers 3 and 4 enabled by 3,4EN. L293 and L293D are characterized for operation from 0°C to 70°C.

Other important L293D features are:

  • Wide Supply-Voltage Range: 4.5 V to 36 V
  • Separate Input-Logic Supply
  • Internal ESD Protection
  • High-Noise-Immunity Inputs
  • Output Current 1 A Per Channel (600 mA for L293D)
  • Peak Output Current 2 A Per Channel (1.2 A for L293D)
  • Output Clamp Diodes for Inductive Transient Suppression (L293D)

Overall L293D Diagram

Simulation – L293

H-bridge & Half-H

An H bridge is an electronic circuit that enables a voltage to be applied across a load in opposite direction. These circuits are often used in robotics and other applications to allow DC motors to run forwards or backward.

The term H bridge is derived from the typical graphical representation of such a circuit. An H bridge is built with four switches (solid-state or mechanical). When the switches S1 and S4 (according to the first figure) are closed (and S2 and S3 are open) a positive voltage will be applied across the motor. By opening S1 and S4 switches and closing S2 and S3 switches, this voltage is reversed, allowing reverse operation of the motor.

Using the nomenclature above, the switches S1 and S2 should never be closed at the same time, as this would cause a short circuit on the input voltage source. The same applies to the switches S3 and S4. This condition is known as shoot-through.

Simulation – H-Bridge

Simulation – H-Bridge- Guide

But L293 is a quadruple half h-bridge. Half an H-bridge will connect an output pin to either Vcc or Ground or disconnect it. Using the one you can turn a DC motor on or off or apply to brake but can’t reverse the motor. To reverse a DC motor you need both halves of an H-bridge.

Darlington Transistor

In electronics, the Darlington transistor (commonly called a Darlington pair) is a compound structure of a particular design made by two bipolar transistors connected in such a way that the current amplified by the first transistor is amplified further by the second one. This configuration gives a much higher current gain than each transistor taken separately.

Invented in 1953 by Sidney Darlington

If we see the Darlington Transistor’s symbol we can clearly see how two transistors are connected. In the below images, two type of Darlington transistor is shown. On the left side it is NPN Darlington and on the other side, it is PNP Darlington. We can see NPN Darlington consist of two NPN transistors, and PNP Darlington consists of two PNP transistors. The first transistor’s emitter is directly connected across the base of another transistor, also the collector of the two transistors are connected together. This configuration is used for both NPN and PNP Darlington transistors. In this configuration, the pair or the Darlington transistor produces much higher gain and large amplification capabilities.

Simulation – Darlington Transistor

L293D Pinout

L293 or L293D ?!

What is the difference between L293 and L293D? letter D in the name indicates an internally fitted diode and it means that we don’t need to add any external components. This is the main difference. If you look at the data sheet, you could see some other difference like Outputs current. Also, The Continuous current in L293 Outputs is 1A and in L293D Outputs is 600 mA. The Peak current in L293 Outputs is 2ampere and in L293D Outputs is 1.2 A

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