finding and using an integrated H bridge - Page 1
Forum section: electronics / beginners

author: Simon
author_rank: Unknown
timestamp: August 08, 2011, 10:18:46 am
content: This is a sort of follow on from a previous topic about controlling a motorised water valve. Basically the valve is operated by a 24V motor that opens or closes the valve and to go the other way the polarity is reversed. So a H bridge drive is required. Given the fact that I'm going to need 4 mosfets (well BJT's also ok) plus the shoot through protection circuitry I may be better seved with an integrated H bridge.Does such a device exist ? This is only for 26 mA so i'm hoping to fing an all in one "power control" chip rather than a mosfet driver IC. What should i be looking for ? searches on Farnell have not turned up what I'm looking for withput spending some serious money. I could perhaps use two opamps to do the job ? (a dual opamp 8 pin IC)

author: Psi
author_rank: Super Contributor
timestamp: August 08, 2011, 10:33:35 am
content: Not really my area, but you could also have a look at high current/voltage opamps, you can get some pretty powerful ones.If you got a 'dual opamp' package you'd only need one IC. I've seen them in T0-220 style packages (lots more pins) and able to handle up to 60V and 10A.But i'm sure they do sell proper H bridge chips.

author: Simon
author_rank: Unknown
timestamp: August 08, 2011, 10:46:00 am
content: hm I'm trawling around, I may stick with discrete bridges, my main concern is shoot through although as it is only 26mA I could put a decent resistor on each side to help take that up plus come up with some sort of physical protection, and review the control software.My other concern was the heat in the mosfets but some of that may be back EMF that I was not worrying about on the breadboard, perhaps snubber diodes are a good idea even on a 26 mA motor, my aim is to use TO220 mosfets and no heatsinks (IRF9540 and IRL540 so plenty of overhead)

author: hacklordsniper
author_rank: Frequent Contributor
timestamp: August 08, 2011, 12:51:38 pm
content: When i was digging in some medical equipment i found halfbridge intgrated modules on some swtiching boards. Im sure a H-bridge is also available

author: Zero999
author_rank: Super Contributor
timestamp: August 08, 2011, 05:26:51 pm
content: There are lots of ICs which can do this.Are you sure it's only 26mA? That sounds too low, what about the start-up current?SN754410http://www.ti.com/lit/ds/symlink/sn754410.pdfL295http://www.st.com/internet/com/TECHNICAL_RESOURCES/TECHNICAL_LITERATURE/DATASHEET/CD00000061.pdfL293http://www.datasheetcatalog.org/datasheet/texasinstruments/l293.pdf

author: Simon
author_rank: Unknown
timestamp: August 08, 2011, 09:03:00 pm
content: well spec sheet says 26mA but obviously a higher startup current. Personally I'd use a min 1A driver

author: ivan747
author_rank: Super Contributor
timestamp: August 08, 2011, 10:54:48 pm
content: Quote from: Simon on August 08, 2011, 09:03:00 pmI have used the L298. It's 2A I think, a bit of an overkill for you. It contains H bridges and it is bipolar. You can control it with 2 pins. There is an enable input to leave the H bridge floating, good for feeding in a PWM signal and doing some speed control. Also, there is no way of leaving it into a state on which the H-bridge can short. The TI part recommended before works pretty much the same way, so you can give that one a try.The bad thing about the L298 is that it needs external Schottky diodes that increase the cost, complexity and drill holes to do at home.Ivan

author: Zero999
author_rank: Super Contributor
timestamp: August 09, 2011, 04:30:59 pm
content: The L298 also has two channels which can be paralleled to give close to 4A as the transistors should current share pretty well, being on the same piece of silicon.