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Author Topic: Help regarding H-briges......  (Read 1568 times)

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Offline RITESH29Topic starter

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Help regarding H-briges......
« on: January 08, 2012, 10:49:40 AM »
Hello everyone,

I was just wondering who this circuit really work as in this there is no information provided for MOSFET whether its N or p-channel MOSFET ...?
If both are same then here might will problem in common drain where gate voltage require will be higher as compared to common source...


Please put some light on this..!!

Thanks

Offline RITESH29Topic starter

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Re: Help regarding H-briges......
« Reply #1 on: January 09, 2012, 04:02:58 AM »
Help needed.......

Offline Soeren

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Re: Help regarding H-briges......
« Reply #2 on: January 09, 2012, 05:29:34 AM »
Hi,

I was just wondering who this circuit really work as in this there is no information provided for MOSFET whether its N or p-channel MOSFET ...?
Just read right under the schematic!

Always include a link to what you ask about if possible. It gets you a faster reply when we don't have to search for it.
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
Engineering is based on numbers - not adjectives

Offline billhowl

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Re: Help regarding H-briges......
« Reply #3 on: January 09, 2012, 05:40:39 AM »
This circuit was used to explain on how H-Bridges work by Admin.
http://www.societyofrobots.com/schematics_h-bridgedes.shtml
The two top were p-channel MOSFET and bottom two were n-channel MOSFET

I personally discourage making your own drivers, and recommend just buying them. They have gotten really cheap in the last year.

This is my schematic for back when I used to make them:


http://www.societyofrobots.com/robotforum/index.php?topic=1589.msg10740#msg10740
Topic: What mosfet to buy for H-Bridge? Also voltage amplifier 5v-->??
http://www.societyofrobots.com/robotforum/index.php?topic=9442.msg72844#msg72844

So what is your questions?


Offline RITESH29Topic starter

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Re: Help regarding H-briges......
« Reply #4 on: January 10, 2012, 08:04:22 AM »

Offline newInRobotics

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Re: Help regarding H-briges......
« Reply #5 on: January 10, 2012, 12:09:44 PM »
Hi,

Is that MOS that are indicated on fig??
IRF540N->http://www.irf.com/product-info/datasheets/data/irf540n.pdf
IRF9540->http://www.vishay.com/docs/91078/91078.pdf
These two MOSFETs would go well together, correct me if I'm wrong  :)

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Offline RITESH29Topic starter

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Re: Help regarding H-briges......
« Reply #6 on: January 11, 2012, 09:14:34 PM »
Here is my H bridges Under construction...............

Offline RITESH29Topic starter

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Re: Help regarding H-briges......
« Reply #7 on: January 13, 2012, 02:33:37 AM »
Hi,

I am using this circuit with MOSFET IRF9540 AND IRF540 ....
The circuit is also working fine with 12V supply ( i am using only switch to control motor now no PWM). So i want to use 24V power supply please tell how to drive gate.....
The motor are brushed DC gear motor of 6-24V at stall current 8Amp.

Offline newInRobotics

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Re: Help regarding H-briges......
« Reply #8 on: January 13, 2012, 02:54:04 AM »
Hi RITESH29,

Your design is missing pull-up/down resistors and another set of N-ch MOSFETs.

It should be something like this (ignore 1k resistor - it's a placeholder for motor):

"Computer games don't affect kids; I mean if Pac-Man affected us as kids, we'd all be running around in darkened rooms, munching magic pills and listening to repetitive electronic music." - Kristian W

Offline RITESH29Topic starter

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Re: Help regarding H-briges......
« Reply #9 on: January 13, 2012, 03:29:37 AM »
Hi,

I think using resistance at gate will decrease speed to to large capacitance across MOSFET gate itself(inbuilt)
and i want to use 24V with uC...

Offline newInRobotics

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Re: Help regarding H-briges......
« Reply #10 on: January 13, 2012, 03:46:24 AM »
I think using resistance at gate will decrease speed to to large capacitance across MOSFET gate itself(inbuilt)
Think of it this way, if You don't use resistors, H-bridge will not work as expected: N-ch MOSFET gate will float, switching it ON an OFF constantly and possibly burning it as it will not be in saturation; P-ch MOSFET will be always ON as gate voltage will never raise above 0V without pull-up resistor.

and i want to use 24V with uC...
Unless You use Buck Converter (or DC-DC switching regulator), that is not a good idea as using LDO regulator or resistors will generate a lot of heat (eg.: If Your uC draws 200mA at 5V, that means LDO reg. will have to drop 19V; 19V with 200mA draw dissipates 3.8W of heat).

NOTE: Just realised that H-bridge in the drawing below lacks two pull-down resistors at upper N-ch MOSFETs' gates.
"Computer games don't affect kids; I mean if Pac-Man affected us as kids, we'd all be running around in darkened rooms, munching magic pills and listening to repetitive electronic music." - Kristian W

Offline RITESH29Topic starter

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Re: Help regarding H-briges......
« Reply #11 on: January 13, 2012, 07:11:26 AM »
Will this schematic will work fine.......?
and what should best PWM freq ...??

Offline newInRobotics

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Re: Help regarding H-briges......
« Reply #12 on: January 13, 2012, 07:52:55 AM »
Will this schematic will work fine.......?
1. When uC pin is HIGH, then Comparators output HIGH (near 24V I assume), hence P-ch MOS will be OFF and N-ch MOS will be ON.
2. When uC pin is LOW, then Comparators output LOW (sinks current), VGS will be at around -12V hence P-ch MOS will burn as Max. VGS allowed is -4V and N-ch MOS will be OFF.

To answer in short - no it will not work, correct me if I'm wrong.

and what should best PWM freq ...??
Well, frequency in Your application is not that much important as inductance of the motor will smooth PWM signal out. OK, have You ever seen DIY robot arms with analog servos? Did You notice how robot arm jitters under? Partly that is because analog servos work at 50Hz frequency, in other words, they reposition 50 times per second. Jittering is lower in digital servos which reposition at higher frequencies. As mentioned before, in Your application probably You would see much difference between 50Hz PWM and 1kHz PWM. I would most likely go for PWM based on 8-bit timer with no pre-scaler, so if I had uC running at 1MHz then my PWM would run at = 1000000Hz / 256 = 3906.25Hz
« Last Edit: January 13, 2012, 10:04:01 AM by newInRobotics »
"Computer games don't affect kids; I mean if Pac-Man affected us as kids, we'd all be running around in darkened rooms, munching magic pills and listening to repetitive electronic music." - Kristian W

Offline RITESH29Topic starter

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Re: Help regarding H-briges......
« Reply #13 on: January 13, 2012, 11:05:15 AM »
The circuit is working fine....
One problem is there i.e. when i stop the motor it does start quickly as it was working with direct power source and some noise is also cumming from motor ...and i am not using Capacitor as shown in upper side of P- MOS!!

Offline Billy

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Re: Help regarding H-briges......
« Reply #14 on: January 13, 2012, 02:42:42 PM »
...and i am not using Capacitor as shown in upper side of P- MOS!!

Use the capacitors, and don't be cheap about it. Use big fat electrolytic ones and a couple small ceramic ones.

If motor runs slow, you're likely not getting fets fully turned on...which could be caused by lack of the proper capacitors...or your gate drive isn't supplying enough current...you can get around that by lowering PWM frequency.

The noise is a byproduct of a PWM frequency less than 20kHz.

Offline RITESH29Topic starter

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Re: Help regarding H-briges......
« Reply #15 on: January 13, 2012, 09:05:29 PM »
Quote
he noise is a byproduct of a PWM frequency less than 20kHz.

I am n ot using any PWM i.e. direct connection of wires to gnd and 5V

Offline Billy

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Re: Help regarding H-briges......
« Reply #16 on: January 13, 2012, 09:16:57 PM »
Quote
direct connection of wires to gnd and 5V

Is 5V enough to fully turn on the FET? Is your circuit shown in the chain above?

Offline RITESH29Topic starter

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Re: Help regarding H-briges......
« Reply #17 on: January 13, 2012, 11:39:58 PM »
Hi,
Quote
Is 5V enough to fully turn on the FET? Is your circuit shown in the chain above?

I think you are not getting me...as the comparator is used when the output is low the two 4.7K will make voltage divider and we will get 12V to P-MOS....like that.

Offline RITESH29Topic starter

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Re: Help regarding H-briges......
« Reply #18 on: January 14, 2012, 07:35:52 AM »
HI again,

Today i have tested the H-BRIDGES with 12V and 12V series connection i.e. 24V with PMDC motor.
The maximum current that i have seen seen on multimeter is 6-7Amp that was the limited current from battery.

OK, when i have used Brushed DC gear motor at 24V and switching the freq (of 555 using pot meter) to the input of LM339 as shown in circuit before.
there was lot of spark at the brushes at low freq. so i think it require snubber circuit at motor terminal.
So, please suggest how to build snubber circuit.

 


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