Society of Robots - Robot Forum
Electronics => Electronics => Topic started by: RITESH29 on January 08, 2012, 10:49:40 AM
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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...
(http://www.societyofrobots.com/images/schematics_h-bridge.jpg)
Please put some light on this..!!
Thanks
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Help needed.......
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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.
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This circuit was used to explain on how H-Bridges work by Admin.
http://www.societyofrobots.com/schematics_h-bridgedes.shtml (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/images/schematics_h-bridge.jpg)
http://www.societyofrobots.com/robotforum/index.php?topic=1589.msg10740#msg10740 (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 (http://www.societyofrobots.com/robotforum/index.php?topic=9442.msg72844#msg72844)
So what is your questions?
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Hi,
Is that MOS that are indicated on fig??
IRF540N->http://www.irf.com/product-info/datasheets/data/irf540n.pdf (http://www.irf.com/product-info/datasheets/data/irf540n.pdf)
IRF9540->http://www.vishay.com/docs/91078/91078.pdf (http://www.vishay.com/docs/91078/91078.pdf)
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Hi,
Is that MOS that are indicated on fig??
IRF540N->http://www.irf.com/product-info/datasheets/data/irf540n.pdf (http://www.irf.com/product-info/datasheets/data/irf540n.pdf)
IRF9540->http://www.vishay.com/docs/91078/91078.pdf (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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Here is my H bridges Under construction...............
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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.
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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):
(http://www.societyofrobots.com/robotforum/index.php?action=dlattach;topic=14760.0;attach=5999;image) (http://www.societyofrobots.com/robotforum/index.php?topic=14760.msg107533#msg107533)
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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...
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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.
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Will this schematic will work fine.......?
and what should best PWM freq ...??
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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
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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!!
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...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.
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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
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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?
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Hi,
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.
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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.