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Topic: H-bridge not working (Read 1 time) previous topic - next topic

ali_imranTW

I am using irf630 and irf9630 mosfetsfor my H-bridge circuit. The problem is, when both the battery and the arduino are connected, the circuit doesnt work. However, if i put my finger on any one of the transistor (mosfet), it starts working. please help.

keeper63

Well - that would indicate either some kind of capacitive coupling issue (?) - or loose breadboard connections.

It might be nice if we had a picture of your circuit (that is, a photo of the thing), plus a properly drawn schematic (no fritzing diagrams, please).

Throw in your code, too just for completeness (though I doubt its the issue - but you never know).
I will not respond to Arduino help PM's from random forum users; if you have such a question, start a new topic thread.

MarkT

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TomGeorge

Hi,

Can you please post a copy of your circuit, in CAD or a picture of a hand drawn circuit in jpg, png?

Can you please post a copy of your sketch, using code tags?
They are made with the  </> icon in the reply Menu.
See section 7 http://forum.arduino.cc/index.php/topic,148850.0.html

Can you also post a picture of your project so we can see your layout.

Thanks.. Tom... :)
Everything runs on smoke, let the smoke out, it stops running....

ali_imranTW

here's the schematic,
http://www.bristolwatch.com/ele/h_bridge.htm

I have remade the circuit and a new problem has come up. As soon as i connect the battery (11.1V), with no inputs yet, the wire connected to the negative terminal of the battery and the mosfets start getting hot. I have looked for any terminals shorted, but didnt find any. any possible reasons?

jremington

#5
Mar 26, 2016, 03:39 pm Last Edit: Mar 26, 2016, 03:39 pm by jremington
That is a very bad design with "shoot through" and should be avoided.

ali_imranTW

That is a very bad design with "shoot through" and should be avoided.
what should i do to improve it?


MarkT

Replace the lower MOSFETs with logic level n-channel ones.  Do _not_ connect the low-side and
high-side gates together, but drive all four switches separately and in such a way that there is
several microseconds between switching off a high-side switch and switching on a low-side switch
on the same side.  (or vice versa).

That circuit shorts the supply rail to ground HARD every time it switches over, potentially pulling
20 to 100A from your LiPo - no wonder the wires get hot!

The absolute fundamental rule with high power MOSFET H-bridges is no shoot-through.  There must
be no point in time with both high and low side switches on (on the same side), however brief.  This
means there must be dead time (time with both definitely off) during switch over, which means
you cannot switch high and low side switches (of the same side) simultaneously.  The simplest
way to ensure this is build an H-bridge using MOSFET high-low driver chips that enforce dead-time.

Checkout data sheets for such chips (HIP4081, FAN7388, IRS2004, many more are available)
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Southpark

#8
Mar 27, 2016, 11:16 am Last Edit: Mar 27, 2016, 11:37 am by Southpark
That circuit shorts the supply rail to ground HARD every time it switches over, potentially pulling
20 to 100A from your LiPo - no wonder the wires get hot!
Yep. Better put a fuse. Just in case. Although several microseconds should still be relatively low energy. But if both transistors on one side both get stuck in the conduction state, then that wouldn't be good.


I am using irf630 and irf9630 mosfetsfor my H-bridge circuit. The problem is, when both the battery and the arduino are connected, the circuit doesnt work. However, if i put my finger on any one of the transistor (mosfet), it starts working. please help.
Maybe you can put some kind of protective current limiting resistor in series (temporarily) with the drain/source, and then test one side of the H-bridge. Ensure that the inputs to the transistors (gates) are set to either your LOW state or HIGH state. And use your multimeter to measure currents and voltages in all the relevant parts of your circuit - to make sure that your circuit is behaving properly for whatever input states you set for your transistors.

MarkT

Fuse is not much use against shoot-through as MOSFETs can become vapour far faster than the fuse.
But fuse will protect the wiring.
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