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EDIT: I was mistaken about the motors, I actually have a pair of DC motors

I want to construct an h bridge that would allow me to control the servos in a boebot. However, I want to maximize the speed and torque attainable. Two wheeled servo bots are common, so I was wondering if there are any existing robust and efficient designs available for something like this?

to clarify, I need this to not be a packaged hbridge. I have to construct it on a breadboard, and that requires transistors and diodes.

Should I do darlingtons?

Chetan Bhargava
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mugetsu
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  • These servos have integrated h-bridges as part of their control electronics package. What makes you believe you need an external h-bridge? – HikeOnPast Oct 30 '12 at 03:57
  • @DeanB actually I was mistaken, I actually have a pair of DC motors – mugetsu Oct 30 '12 at 04:01
  • You would have to tell us what sort of voltage and current levels your motor needs for your application, and what sort of power source you're using. Also, what kind of control do you need? Just on off'? Speed? Direction? – Chintalagiri Shashank Jan 28 '13 at 15:00
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    For the record, you can quite well use a packaged H Bridge on a breadboard. – Chintalagiri Shashank Jan 28 '13 at 15:02
  • MOSFETs, correctly used, will give you lower losses than bipolar transistors. However, you have to ensure sufficient gate drive, be substantially more careful with ESD than with bipoloar transistors, and make sure you have sufficient back EMF absorbtion and spike suppression - as you risk not only confusing any connected computer, but actually destroying the MOSFETs at relatively low overvoltages. – Chris Stratton Feb 27 '13 at 15:04

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To maximize torque you will want to source 6V @as close to the max current as you are comfortable with. I like the TLE 5205 chip its 7pin hbridge that can handle up to 5 amps digikey http://www.digikey.com/product-detail/en/TLE5205-2G/TLE5205-2GINTR-ND/1283075 has a couple different pin layouts but this chip can handle sources from 5.3-40V and is a hog. This will be capable of maxing the output for the motor. You can control it any number of ways with PWM or just forward or reverse bias currents.

KP44
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  • sorry I was not clear, but I'm looking to design the h bridge from scratch – mugetsu Oct 30 '12 at 03:58
  • Use two pnp and two npn your big concern here will be gain and the voltage across the motor. You will need to pick your resistors and know the base currents of your logic signals to design the bridge to ensure 6V @ 200 mA – KP44 Oct 30 '12 at 04:03
  • do I need a separate h-bridge for each motor? Or is there someway to work in having them both in the same one? – mugetsu Oct 30 '12 at 04:06
  • You will need a seperate bridge wouldnt work with one bridge well – KP44 Oct 30 '12 at 04:09
  • And darlingtons would be too much gain for your purpose – KP44 Oct 30 '12 at 04:11
  • A beta of 300 should be plenty – KP44 Oct 30 '12 at 04:12
  • any reason for two pnp and two npn? I currently have an hbridge made from 4 npn, each of them are in parallel with a diode. – mugetsu Oct 30 '12 at 04:13
  • The two npn and pnp are nice because when you want current travel you give one side logic 0 and the other side logic 1 and it will spin the motor 1 direction or the dual. The npn and pnp configuration allows you to use only two logic pins and then your gain eqn is simplified. – KP44 Oct 30 '12 at 04:15
  • It also causes the motor to not spin for a 0 on both or a 1 on both to protect your circuit from bad inputs – KP44 Oct 30 '12 at 04:17
  • The diodes are also fine they just protect the transistors from fly back current since a motors basically a big inductor – KP44 Oct 30 '12 at 04:18
  • Heres a visual aid http://www.google.com/search?q=h+bridge&hl=en&client=ms-android-sprint-us&tbo=u&tbm=isch&source=univ&sa=X&ei=x1WPUI3IBsnWygGA0oCYAw&ved=0CDUQsAQ&biw=360&bih=592#i=6 – KP44 Oct 30 '12 at 04:23