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High power H Bridge

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niak32

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Hi all, This is my first post on this forum, horray!!

What i have been trying to do for a while is make a high powered H-Bridge, well actually 2 of them for a skid steer system, first a little tank and second a remote control wheel chair with out using the existing wheel chairs control box.

this is the circuit i started with and then changed the BC327 and BC337 for MJE2955T and MJE30. this got a fair bit more power but a lot more heat as well. I dont think the transistors are eithre on or off, more likely mostly on or off so i have been told

Sorry no circuit diagram for pic connection but that is pretty straight forward, instead of the inverter I connected it straight to my pic (pic16F84) and ran the whole thing off 5 volts

The pic program basicly changed the RC signal for 2 channels to 4 outputs high and low (because there are 2 h-bridges) so there is off forward and backwards for each channel, no speed settings. I can write the code for the speed settings but what i am after is which parts to replace the transistors with to get the output up high enough to drive a wheel chair motor with out using the controls on the wheel chair?



Will try to get full circuit diagram when i can, I believe one set of resistors is 380Ohm instead of 1k, with that i got more speed but didn't get too far past that.

Hope this isn't too much of a noobie request.

EDIT: Wow, there are alot of questions already for H-Bridges, perhaps something that might benefit the mass's is a a nice big transistor \ fet chart like in the back of the dick smith catalog so we can see what does what at what A's etc. Oh, and i am in Australia so basicly everything that i have to get will most likely come from china ><
 
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MikeMl

Well-Known Member
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The base current required to saturate (to get the lowest power dissipation possible when ON) the transistors is much higher than either a 74HC or your PIC pin can source in the high state. This only partially turns on the transistors in the HBridge, causing them to run hot.

Use logic-gate NFETs, or darlingtons, or boost the base current with a hex driver chip capable of sourcing 20mA.
 
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niak32

New Member
The base current required to saturate (to get the lowest power dissipation possible when ON) the transistors is much higher than either a 74HC or your PIC pin can source in the high state. This only partially turns on the transistors in the HBridge, causing them to run hot.

Use logic-gate NFETs, or darlingtons, or boost the base current with a hex driver chip capable of sourcing 20mA.
That makes sense, from what i can tell from that in my terms, a bigger inverter or use one H-Bridge to drive a second more power full one as the PIC itself can't supply enough grunt?

perhaps the H-Bridge in the picture to drive the bigger FETS?

Thanks for the quick reply too
 
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smanches

New Member
Most of the time it's easiest to use dedicated driver chips. Pic->Driver->Transistor. Most of the time NFETs are used as the main power transistor, although in very high voltage or high power, IGBTs are often used. These types of transistors have the lowest "on" resistance, hence why they are used.

You could use your old transistors as the drivers for the new ones. Since it seems the PIC could drive those without problem, they would be a good candidate.
 

tcmtech

Banned
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If you dont mind having an extra chip for each half of the H - bridge just use a high/low side driver IC. They are cheap and will solve all of your switching device drive issues and give you an independent control line capability for each switching device.
IR2110 or IR2113 IC's (or any of their cousins) are cheap, simple to use, and very durable too!
They take 3.3 v and up logic level input and translate that to a fully isolated line voltage (up to 500 - 600 volts DC) at 2 amps peak output for the drive signal going to the big switching devices.
 

niak32

New Member
If you dont mind having an extra chip for each half of the H - bridge just use a high/low side driver IC. They are cheap and will solve all of your switching device drive issues and give you an independent control line capability for each switching device.
IR2110 or IR2113 IC's (or any of their cousins) are cheap, simple to use, and very durable too!
They take 3.3 v and up logic level input and translate that to a fully isolated line voltage (up to 500 - 600 volts DC) at 2 amps peak output for the drive signal going to the big switching devices.
Thanks for that, When I had a look at the data sheet for the IR2110 \ 2113 It looked like there are 2 different pins for high and low output. If that is correct, I'm not really sure how to connect them, both outputs together for each side of the H-Bridge? That kind of makes sense but kind of doesn't to me, mind posting a link or drawing a quick sketch on how it would fit in please? I'm still pretty new at the electronics side of things. Cheers
 

tcmtech

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The data sheet I have has the full connection diagram on the first page. Maybe you are not reading it right or possibly you have a low end data sheet.
Heres a copy of mine. The first diagram labeled 'typical connection' is the full set up for one side of an H bridge.

I personally have run pairs of 1200 volt 600 amp IGBT's with the IR2110 IC without problems! They are that good!
 

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Hero999

Banned
How much current does the motor require?

If it's anything more than a tiny remote control car then the traisistors will be toast.
 

niak32

New Member
The data sheet I have has the full connection diagram on the first page. Maybe you are not reading it right or possibly you have a low end data sheet.
Heres a copy of mine. The first diagram labeled 'typical connection' is the full set up for one side of an H bridge.

I personally have run pairs of 1200 volt 600 amp IGBT's with the IR2110 IC without problems! They are that good!
Same datasheet, just looks to be lack of understanding on how it works from my end, only H-Bridge is the one that I'm using at the top, with different FETS though. Still learning alot about electronics. This may sound dumb, but I use one pin from a PIC for each side of the H-Bridge, Looking at that setup I think i would need extra pins to use that chip plus a whole lot of other connections. Think I will try to keep what I have until I understand how exactly to use that chip.


How much current does the motor require?

If it's anything more than a tiny remote control car then the traisistors will be toast.
The motors that I'm working with at the moment are pretty small but the original circuit just didn't cut it, don't think they would pull much before the motors burnt out. I will be moving up to wheel chair motors and I would imagine that they require quite a bit more, not sure how much of course at this stage, just figure LOTS. I might be naive in thinking so, but i think i can bank up the FETS that I use in a nice neat line to get more power out of them (you can start laughing if you know that just wont work)
 
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tcmtech

Banned
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I'm not sure how you can work with a pic chip and find a simple high/low driver with only two inputs and two outputs to complicated?

You just use the high side input on one IC and the low side input on the other IC tied together for one direction and then do the opposite connection with a second input going to the other two inputs of the driver IC's.
The IC's themselves can drive any voltage or current controlled switching device that takes less than the maximum continuous ratings.
 
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