How does the L239D IC H-bridge work?

Question

I would like to understand the design of the L239D IC. I have read the schematics and datasheet and know how to use it but I wish to know a little more about its design.

The left part of this image shows half of the circuit for one motor (I think,) for the input high of pin 2 and low of pin 7 it should be connecting the motor to rotate in one of two directions. The problem is I can't determine from this schematic which direction the motor will rotate for either input.

I have seen a simplified image for the same circuit except for using 4 transistors in it to control the direction and it makes a lot of sense in contrast of the first image of the IC:

I just need a simple detailed explanation of the IC working in the first image.

Did you not see the transistor diagram (figure 5) of the output stage in the data sheet? — Andy aka, Jul 15 '20 at 11:03
@Andyaka I saw it but I didn't understand the schematic and there is no explanation associated with it — Mahmoud Salah, Jul 15 '20 at 11:10
How does it work? **Badly**. Avoid this and other Darlington designs. Get something with FETs especially if you plan to use batteries. — Chris Stratton, Jul 15 '20 at 14:24
it is not possible to determine the direction of rotation, because that is dependent on the motor — jsotola, Jul 15 '20 at 14:52

score 1 · Accepted Answer · answered Jul 15 '20 at 11:21

The schematic in figure 5 can be redrawn to look like this: -

I've made a mirror image of figure 5 to show the transistors that make up the H-bridge. I've called them Q1 to Q4 to coincide with the transistor names in your final picture.

So if the left-side output was pin 3, Q1 would be activated when pin 2 goes high. The right-side output is therefore pin 6 and Q4 is activated when pin 6 is low.

BTW, these devices are pretty poor these days. See this assassination of the device in terms of poor efficiency and poor ability to drive loads.

How does the L239D IC H-bridge work?

1 Answers1