STM l293E H-bridge/driver?

rwgast_logicdesign

So right now im trying to wire up this H-bridge its pretty much the same thing as an l293D except it can handel 1-2amps and its a 20pin dip. Last nigh I bread boarded the thing just like an l293D would be wired up but I left the extra sense pins alone. The h-bridge functionality seemed fine, I set the chip for 5 volt logic and tested it buy connecting input 1 to 5v then input 2 to 5v the motor flipped polarity etc. My supply was 9.6v and for some reason I was only getting three volts to the motor with no PWM signal or anything just a straight 5v to hi.

Well today I wanted to wire two in parallel because im acually going a little over 2 amps when the motor stalls when running in higher voltages. Anyways I figured maybe the sense pin was causing the voltage drop or something I looked through the data sheet and couldnt figure out what it does, there was a schematic with it hooked up to opamps and a bunch of stuff but thats way more than Im trying to do. I also realized they had diodes around the motor, All the 293d schematic dont have the diodes im guessing becuase they have built in clamping diodes, im not sure if this chip need them or not. I have some other drivers that I wanted to use but they need 1n418s all i have is 1n4001s and a buch of glass diodes that have less voltage drop but dont know if there fast switching.

My circuit also stopped working after a bit, im not sure if I killed the chip somehow it never got too hot and when I replaced the vhip with a new one it still wasnt working so im not sure what was going on maybe a problem with one of the wires. I have two new chips wired in parrallel ready to hook up but id really appreciate it if someone could maybe tell me what the sense pin does and give me some advice about what may have been giving me a crazy 6v drop

rwgast_logicdesign

sorry somehow i forgot to link the data sheet

http://www.st.com/internet/com/TECHNICAL_RESOURCES/TECHNICAL_LITERATURE/DATASHEET/CD00000058.pdf

Beau Schwabe

Don't the sense pins need to be grounded? ... the idea, normally is to place a small valued resistor to ground, so you can measure the voltage across the resistor... since your not using that feature, those pins should be taken to ground.

RobotWorkshop

Why are you using the L293E instead of the L293B? According to the datasheet both have the similar ratings. I've yet to see someone using the 20-pin version of the chip. The 16-pin version is a standard format that a lot of devices use. You're using a chip that looks only different because of 4 pins that you aren't using anyway?? Unless you need the version with the extra sense resistors you're better off avoiding it and using a more common part. There have been other suggestions about H-bridges in other threads of yours that list parts that may be more appropriate. If you are starting small then the TI SN754410 is a good option (doesn't need the extra diodes) and can easily be doubled up. Beyond that some of the other chips like the LMD18200 work well.

In regards to the voltage drop you may be using a 9.6V pack but when you measured the lower voltage was that just at the motor or did you also take a reading again back at the battery? If you are using an old battery it may show almost 9.6V but under a real load it can drop quite a bit. You may be surprised to find out that under load the battery itself only puts out a low voltage.

You may have an open or un-connected ground, etc. We'd need a schematic of exactly how you wired it and maybe even a picture to try and troubleshoot it.

rwgast_logicdesign

Im using the E becuas I didnt know there was a difference and acually now that I know what the sense pins are for I kind of like it. I got the 6205 also but have no fast switching diodes I know of on hand. One E is probably enough to run my motors fine as long as I keep them from stalling. I decided id hook these up just to get going with so I can test my bot, next time I acually order some parts Im going to get the right passives for the 6205 along with the stuff for my switching power supply. I thought the sn7544 needed diodes while the l293d didnt, and am still confused on if I acually need diodes on the E it hasnt seemed to cause a problem but the vague data sheet shows them without telling you if they need to be fast switching or what.. I know my vdrop isnt a low battery becuase when I hook the battery up straight to the motor it gets way more power. Im sitting down right now to two of them wired in parallel(im only doing this until I have a way to detect stalls and deal with them) im going to reconnect it all and play with the sense pin.

rwgast_logicdesign

Ok so grounding or using the sense pins correctly fixed all my problems. But im still unclear on wether I need diodes or nit, I havent had a problem withough them but ive just been sending pwm to one input or ther other and grounding the secon, im assuming those diodes are so when the motor free wheels it doesnt send current back at the chip?

Secondly I set these up in parallel and then stalled the motor I read 2.5amp on my meter. in a parallel set up I should be able to get 2-4 amps, the chips both heat up pretty evenly too, not like one is taking all the load while the other does nothing, im going to guess these arent BJT. So if you were running a 2 to 4 amp hbridge at 2.5 amps for maybe 20 seconds would it be normal for it to get hot enough to start burning you? I have plenty of sinks and fans that should work but I want to make sure that what im experincing is normal before calling it a day

agfa

I've been very pleased with 754410s. It's data sheet application information shows external diodes, but I haven't had any problems with out them. None of the online samples of their use, that I've seen, suggested they be used. Data sheets indicate both the l293 and 754410 have thermal protection to protect from over current conditions.

Beau Schwabe

rwgast_logicdesign,

Might want to check your propeller to make sure it's still alive in the sense that it can still drive the pins to the 293 ... I just had two 293D's powered with a 12V supply on Vcc2 fail because of a dumb mistake on my part.... consequently their failure caused an over voltage on the Propeller I/O pins driving the enable and controls. The Propeller Identifies, but the pins no longer work as an output. ... another dumb mistake on my part. .... time for some current limiting resistors.

rwgast_logicdesign

EEEwwwww thank you Beau!!! I have not used the board with a prop yet only tested it using my bus pirate to generate pwm signal. When I take the chip of the breadboard and wire it to a piece of permanent perf board ill make sure to but a 200ohm resistor and diode on each of the inputs. Im glad you said that becuase ive made a couple mistakes with the connections already.