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I am trying to build a PWM circuit to control a 6 VDC motor. I have used a 555 timer and have tried using two NAND gates. Both work on very small amp motors, but don't work with motors with 1 to 2 amps cont. It appears to be not getting a flywheel effect started to overcome the motors inductance. What do I do? H bridge driver circuit maybe? Use higher freq PWM? etc etc Any suggestions are welcome.

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>I am trying to build a PWM circuit to control a 6 VDC motor. >I have used a 555 timer and have tried using two NAND gates. That won't push an amp.. unless they're damned big NAND gates. >Both work on very small amp motors, but don't work with motors with >1 to 2 amps cont. Not surprising,.. NAND gates are logic parts, not power parts. >It appears to be not getting a flywheel effect started to overcome >the motors inductance. Nope, it's simply one of output drive capacity,... Most gates would be hard pressed to supply more than 10mA or so, even into a short circuit. >What do I do? H bridge driver circuit maybe? Use higher freq PWM? >etc etc Investigate chips like a ULN2003 or other high current drivers.... Logic level inputs, high current outputs... Note that they "invert" in a way,.. when the logic input is "H", the driver is "ON", which means it drags its output down to ground. You can build a H bridge out of BC547/557 transistors,... I have a circuit somewhere that I cobbled up that drove a 12V motor up to about 500mA.. If you put bigger transistors in, it could do an amp or so. Otherwise yeah, go buy an H-Bridge chip, it'll save you a bundle of wiring and other hassles... ;-) David. _________________________________________________________________ Get your FREE download of MSN Explorer at http://explorer.msn.com/intl.asp

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