How it Works
The IC L293 basically includes a two pairs of outputs which can be be independently used for operating two separate loads in a push pull mode or in a bidirectional manner, also referred to as totem pole mode.Alternatively these couple of pair of outputs can be individually used for operating 4 individual loads in a unidirectional manner.
The above operations of the loads is controlled through corresponding input pinouts, triggered from a external oscillator circuit or a PWM source.
For example if the load is required to be operated in a totem pole manner, the corresponding inputs of the two driver stages of the IC could be triggered from an external oscillator such as through a couple of NAND gates, wherein one gate could be wired as an oscillator while the other as an inverter.
The two anti-phase signals from these NAND gates then could be connected with the inputs of the L293 for operating the relevant outputs in a totem pole (push-pull) manner, which in turn would run the connected load in the same fashion.
Pinouts assignment of the IC L293
Now let's learn the pinout functions of the IC L293 by referring to the following diagram and from the following explanation:
Pin#2 is the control input, which controls the output pin#3.
Similarly, pin#7 is the control input for the output pin#6.
Pin#1 is used for either enabling or disabling the above sets of pinouts. A positive at pin#1 keeps the above sets of pinouts enabled and active, while a negative or 0V supply instantly disables them.
Quite identically, Pin#15 and pin#10 become the control inputs for the corresponding pin#14 and pin#11 outputs, and these remain operational only as long as pin#9 is held at positive logic and is disabled when a 0V logic is applied on this pinout.
As explained previously, pin#3 and pin#6 can be used as totem pole pairs by feeding an anti-phase logic signal on their input pin#7 and pin#2. Meaning, when pin#2 is being fed with a positive logic, pin#7 must be at a negative logic and vice versa.
This will allow the outputs pin#6 and pin#3 to be operate the connected load in a corresponding direction, and conversely when the input logic signals are reversed, the load polarity is also reversed and it will start rotating in the opposite direction.
If this sequence is rapidly switched then the load operates correspondingly in a to-and-fro manner or in a push pull manner.
The above operation can be replicated across the other side pair of drivers also.
The Vcc or the supply positive inputs for the IC are configured independently for two different supply inputs.
Pin#16, (Vcc1) is used for operating the enable pinouts and for operating other internal logic stages of the IC, and this could be supplied with an input of 5V, although maximum limitation is 36V
Pin#8, (Vcc2) is specifically used for powering the motors, and this can be fed with anything from 4.5V to 36V
Electrical Specification of the IC L293
The IC L293 is designed to operate with a any supply between 4.5V and 36V, with a maximum current handling specification of not more than 1 amp (2 Amp in pulse mode, 5ms max)
Therefore any load within the above mentioned specifications can be operated across the discussed outputs of the IC L293.
The Input control logic should not be exceeded above 7V, whether as a continuous supply oir PWM supply.
In my forthcoming articles we will discuss how to make a PWM controlled motor driver circuit using this versatile IC L293 and also many other interesting application circuits.
If you have further doubts regarding the technical specifications, or the datasheet or the pinout details of the IC, you can always feel free to comment below for instant replies.