H-Bridge design - Page 1
Forum section: electronics / projects

author: anshulsanam
author_rank: Newbie
timestamp: November 26, 2013, 10:04:56 pm
content: Hello everyone I realized after burning through 6 L293D's that they were getting old. I hated them mostly due to the fact that they were fragile. I also burned 3 of them because of static electricity. So I decided to try and make a cheap H-Bridge from transistors. This is just a test circuit what I need to know is: is the circuit correct, can this type of H-Bridge handle more than 2 Amps depending on the transistors used, and do you guys have any suggested modifications if it is wrong.

author: Psi
author_rank: Super Contributor
timestamp: November 26, 2013, 10:32:28 pm
content: You need resistors on the base, they cant be connected together like that.

author: w2aew
author_rank: Super Contributor
timestamp: November 27, 2013, 12:15:44 am
content: In addition to the required base current limiting resistors, the two transistors on the right side aren't correct (collectors should be tied together, not the emitters).

author: c4757p
author_rank: Super Contributor
timestamp: November 27, 2013, 12:28:11 am
content: Quote from: anshulsanam on November 26, 2013, 10:04:56 pmYour schematic suggests you burned them for a different reason.

author: anshulsanam
author_rank: Newbie
timestamp: November 27, 2013, 04:19:23 am
content: I am sorry I have made another version here.

author: Zero999
author_rank: Super Contributor
timestamp: November 27, 2013, 11:10:19 pm
content: Quote from: anshulsanam on November 27, 2013, 04:19:23 amAs soon as T3 is turned on, all the transistors will burn.Perhaps you destroyed your L293Ds by using them incorrectly?

author: Psi
author_rank: Super Contributor
timestamp: November 28, 2013, 12:00:19 am
content: You forgot the base resistors again.

author: calexanian
author_rank: Super Contributor
timestamp: November 28, 2013, 03:36:20 am
content: A couple things. Your input 1 should be common (With current limiting resistors as mentioned) to Q1 and what i believe is listed as T3 and conversely input 2 to Q3 and T1. Additionally this will only work if the driving voltage of the inputs are up with the total load voltage source. Otherwise you would need a driving transistor on the inputs to handle that. Additionally the transistors you have picked there are kinda whimpy. I would look at like TIP122 and TIP127 darlingtons for ease of driving, current cap, etc etc.. Just my thoughts. I use that kind of affair for driving single coil latching solenoids and relays.

author: codeboy2k
author_rank: Super Contributor
timestamp: November 28, 2013, 08:27:00 am
content: what are you doing?"is the circuit correct, can this type of H-Bridge handle more than 2 Amps depending on the transistors used, and do you guys have any suggested modifications if it is wrong"because you seem like you don't know what you are doing, even the basics of Ohms law, circuit analysis, and power dissipation, which you should try to know before you design a circuit.It's like me putting gunpowder into a toilet paper tube, rolling up the end into a cone shape and asking a NASA rocket engineer if it will fly, and what should I do to make it fly (just in case I was wrong in my rocket design and it won't actually fly.)