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Topic: H-Bridge with High Current Transistors (Read 17469 times) previous topic - next topic

Grumpy_Mike

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That is, if you only need 4 switches why you should use 5?

Because those extra 4 switches are very much simpler and cheaper to implement as a realy than as a transistor. so while there is an extra switch the design is not complicated and there is no danger of shoot through.

westfw

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if you only need 4 switches why you should use 5?

Note that four of those switches are typically contained in a SINGLE (DPDT) relay.  So it's one relay and one transistor...

michinyon

The problem the OP will run into,  is that it is easy to drive the bottom two transistors in the H bridge,  but hard to drive the top two transistors in the H bridge,  which he will need to be able to control the gate voltage around 17-19 volts.    cannot do with arduino output.

MarkT


I would go along with this with a caveat.   READ THE DATA SHEET
many FET's are advertised as 50 amp, and then you find out that is good for pulsed operation with a 10% duty cycle. and the FET is rated for 8 amps at 100% duty cycle.   Many are being advertised as the 100% duty cycle, but this only takes a few seconds to verify before purchase.


You would never choose a MOSFET by its current rating ever.  That's just noise in
the datasheet, since the key parameter is the on-resistance.

If the on-resistance is low enough for the power dissipation of the package, the
current is automatically within spec (the current limit is thermal in a power MOSFET).

The only caveat is check the package current limit - this is the current where the
pins and bonding wires of the packaging will start to fail.  For instance IR sell
a whole raft of TO220 MOSFETs with a ~240A rating, but admit in a footnote that
the package is limited to 75A (which is also a dodgy assertion, 30A is more reasonable).

So they claim the specs for the bare silicon die, despite not packaging it in a manner
that can carry anything like the current....

The other check you maybe should make (other than I-squared-R power dissipation) is
the Vsat (I-times-R), which needs to be well below the gate drive voltage.  So for instance
a 0.03 ohm MOSFET with 35A would have Vsat of 1.05V, which is OK if the gate
drive is 10V, but not with a 3.3V logic-level MOSFET since the you're in danger
of entering the linear region.  Normally a glance at the curves on the datasheet is
enough to confirm you are OK with Vsat

A 0.03ohm MOSFET with 35A would need to be in a package / heatsink able to
deal with 40W or so of course...
[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]

tetris911

I have 6 of these they seem to work really well.
http://www.ebay.com/itm/Semiconductor-BTS7960B-Stepper-Motor-Driver-43A-H-Bridge-Drive-PWM-For-Arduino-/131077219871?ssPageName=ADME:L:OC:CA:3160

Domino60

#35
Jun 24, 2014, 10:05 am Last Edit: Jun 24, 2014, 12:07 pm by Domino60 Reason: 1
Hi all and  thanks for reply,

Sorry If I interrupt your conversation but nowadays I had really bad day when I found out that I burned my arduino so even If I wanna build a H-Bridge with transistors I will not be able to control it with arduino because I don't have any arduino devices now.

What I decided to do as I replied that few days ago is to take a transistor, DC Motor and DPDT Switch.
If you think about the transistor state, because as I replaied that, I'm  gonna use about 5A and 15v to 30v I found out
this transistor :
Pdf. 2n3055. Datasheet :
http://html.alldatasheet.com/html-pdf/21680/STMICROELECTRONICS/2N3055/1620/1/2N3055.html

Fig 1. 2n3055 Transistor


I tested it Personally, I tested it and it's working really well and it's not burning at all, even if it will I have a huge heatsink for it, but as i tested it for about 5~10 min the transistor was really cold.


About the DPDT Swich not use if you all know about it.
It's a swich that can change the polarity of a motor or led or anything you wanna change.
Fig 2. DPDT Swich


I realy feel bad that my arduino burned so that's the only way to control a motor in my case.


I see many people suggesting to buy H-Bridge from ebay or different sites, thanks alot for help but I'm not the type of guy that buy everything, I wanna have the experience to build something on my own. To upgrade my skill lvl and to be able in future to build the same stuff easy and fast because i will know that it's working, and if someone ask me for help I will be able to answer many questions because I will know that I didn't bought that ready circuit from Ebay or other websites but I builded on my own.

Thanks a lot all, I got many ideas searching for different ways to control a motor and reverse the polarities.
But I have one more question about the transistor that I posted :
a) What's the needed voltage and amperage I need to apply at the base of the transistor to activate and run the motor
         at full power of the powersupply ?

(It's maybe a silly question because I already learned about transistors but I'm not sure how you calculate that in different types of a transistor.)
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knut_ny

The datasheet says you may need up to 4A  to base to get a safe saturation when collectorcurrent is 10A.
This 'problem' is why mosfets often replaces it as a switching transistor
Ny

Domino60

#37
Jun 25, 2014, 02:04 pm Last Edit: Jun 25, 2014, 02:06 pm by Domino60 Reason: 1
I done few experiments with the transistor and I find out that a PC_USB 5v_400mA (I think it is) it's the best
Base Voltage/Current from the transistor to release all the power supply voltage and current to pass thru the
transistor.

Best way to find something is to test it on your own :)  Btw I runned the Transistor with a power supply of
5A and 30V for 10min without stop and the transistor was realy cold, no heat at all :) that's nice results for me.

I will try to record a video about the transistor, power supply, DPDT Swich and how they work with a motor :)
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Grumpy_Mike

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Best way to find something is to test it on your own

Yes but only if you test it correctly.

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Btw I runned the Transistor with a power supply of 5A and 30V for 10min without stop

Yes the power supply was that but what was the actual load. The value of the resistance between the supply and collector.

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and the transistor was realy cold,

Which suggests that you had only an insignificant load and your test was a bit useless. If you did run it at 5A and it was cold then it was not actually working.

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I done few experiments with the transistor and I find out that a PC_USB 5v_400mA (I think it is) it's the best
Base Voltage/Current from the transistor to release all the power supply voltage and current to pass thru the
transistor.

OK the real words for this are "to drive the transistor into saturation" and you did not do that with 400mA and a 5A load. You are going to have to drive that transistor with an arduino, you can only get 40mA out of an arduino so you need another transistor in front of this one to get the base current to what you want.

No one suggested using a DPDT switch. It was a relay with DPDT contacts that was suggested so you could control the diesction with the arduino.

Domino60

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Which suggests that you had only an insignificant load and your test was a bit useless. If you did run it at 5A and it was cold then it was not actually working.


Ok, I didn't ment that was cold cold, was about from 15 to 30 celcius and i don't think that was a fail test because I
tested in diferent ways and the tongue of the motor was same with or without the transistor.

Quote
OK the real words for this are "to drive the transistor into saturation" and you did not do that with 400mA and a 5A load. You are going to have to drive that transistor with an arduino, you can only get 40mA out of an arduino so you need another transistor in front of this one to get the base current to what you want.

No one suggested using a DPDT switch. It was a relay with DPDT contacts that was suggested so you could control the diesction with the arduino.


As I said few days ago my arduino burned, so I'm not gonna use arduino at all.
About the DPDT Switch i found about it on the internet I suggested it

That's the Switch that I bought and soldered few jumper wires to be easier to test.
Fig 1. DPDT Switch.


About all that system I'm trying to make, you said that I done useless test.
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your test was a bit useless

I don't think so I tested it I saw it with my own eyes that it's working without problems and the tongue of the motor is the same as I expected.
I'm gonna do a video in the following days.
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Grumpy_Mike

What is :-
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the tongue of the motor

?

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was about from 15 to 30 celcius and i don't think that was a fail test because Itested in diferent ways

If a 2n3055 transistor did not get mad jumping hot with 5A flowing through it something is very wrong. You might think you have done a test but those results simply do not make sense. You should have nearly 5W of energy to burn off as heat, because you did not then I suspect you did not test it at 5A and so your tests do not show what you think they show.

Still if you will not give details of the test you did it is hard to say where you are going wrong, but wrong you are going somewhere. I suspect you did not test it at anything like 5A.

MarkT

About 2.3W with 2N3055 in saturation at 5A with 300mA base drive, Vsat = 0.4V, I make it...
Given the large metal TO3 package that would take a little while to heat up.
[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]

Grumpy_Mike


About 2.3W with 2N3055 in saturation at 5A with 300mA base drive, Vsat = 0.4V, I make it...
Given the large metal TO3 package that would take a little while to heat up.

The data sheet I read did not give such a tiny value for Vsat it was between 1 and 2V.
Have you used those transistors? There is no appreciable "time to warm up" with them.

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