Designing 3V DC Motor H-Bridge with Power FETs

In summary, the author designed a toy car that could move in both directions using relays and switches. He thanks everyone who helped him, and wants to move on to designing a H-bridge for a 3 volt DC motor. He found several circuits and one-chip devices on Google that he liked, but one problem he still has is trying to find a power FET transistor that will work with a 3 volt power supply. He recommends looking for a PNP bipolar transistor with an emitter tied to Vcc and the collector tied to an N-channel FET gate, which he found on eBay. The part is listed on EBAY now.
  • #1
kthouz
193
0
Hello!
Lastly i was designing a toy car moving in both direction foward and backward using relays and switches. I thank everybody who helped me.
Now i want to move to h-bridge. i have read many books about the h-bridge but one problem that i still have is how to chose power FET transistors. Actually, i want to design a H-bridge for a 3V DC Motor. What type of Power FET am i going to use?
Thanks in advance.
 
Engineering news on Phys.org
  • #2
The main problem is availability.

I did a quick search on Google and found lots of circuits for H Bridges and also one-chip devices that could drive small motors directly.
So, you could have a look through those circuits and pick one that seems OK for 3 volts.
Then look for suppliers of the parts.

Incidentally, this post might do better in the Electrical Engineering section. There have been a few H Bridge queries there over the last few months.
 
  • #3
The real problem with FETs is getting enough voltage to turn them on. Here is one solution:
http://www.pololu.com/catalog/product/120
This Allegro chip will go down to 1.8 volts, but I don't knoe how to install it.:
http://www.allegromicro.com/en/Products/Part_Numbers/1448/
I usually prefer discrete NPN and PNP collector outputs at 3 volts. Avoid Darlingtons.
[added info] This TI H-bridge DRV592VFP works from 2.8 V to 5.5 V. See
http://www.chipcatalog.com/Datasheet/05E85EF564800B2FB1F1FC107941937B.htm
I have seen some on ebay.
 
Last edited:
  • #5
vk6kro said:
I found this one on Google. It seems like a very good presentation, although I haven't tried it, of course.

http://www.mcmanis.com/chuck/robotics/tutorial/h-bridge/bjt-circuit.html
This looks like a nice choice, until one looks into the details. This H-bridge uses collector outputs (common emitter configuration) which is nice, but the four output transistors are all darlingtons, and VCE sat is about 2 volts or more, so they won't work on a 3 volt power supply. A better choice for 3-volt operation is to drive a discrete NPN common emitter (collector output) with a PNP transistor, and vice versa.
 
  • #6
Not a problem. The motor has to run off 3 Volts, not the H Bridge. Still, the less voltage needed the better.

The circuit was misleading though. The transistors were shown with normal symbols not Darlington ones.

I liked the tutorials in that article.
 
  • #7
Bob S said:
This looks like a nice choice, until one looks into the details. This H-bridge uses collector outputs (common emitter configuration) which is nice, but the four output transistors are all darlingtons, and VCE sat is about 2 volts or more, so they won't work on a 3 volt power supply. A better choice for 3-volt operation is to drive a discrete NPN common emitter (collector output) with a PNP transistor, and vice versa.
Nice tutorial. I liked it too. But actually, i would like my Hbridge be driven by power FET. I have already designed one with BJT but i don't find it more efficient so, as i think FET are the powerful ones, i would like to replace those BJT by FET. Just as hint, how does one chose FET to drive a motor according to its voltage needs?
 
  • #8
FETs are nice. When they are turned on, they look like a low resistance in series with the motor. However, if the voltage across the motor is too high, an external resistance is required between the FET and the motor (which is actually being driven by two FETs in an H-bridge) to limit current. For H-bridges operating on a low voltage power supply, finding a FET that can operate on say 3 volts (2 D cells) can be a problem. The problem is getting enough gate voltage to turn the FET fully on. Thus using a PNP bipolar transistor with emitter tied to Vcc and the collector tied to an N-channel FET gate gives the best voltage swing.
 
  • #9
DeviceCraft has a nice H-Bridge controller.
http://www.devicecraft.com

It is too high a voltage 10 to 50v but
It is pretty much the standard design recommended by IRF plus the microcontroller and Temp/Current protection.
The onboard PIC microcontroller is in a socket and can be reprogrammable.
The device has a lots of cool features like fast hall effect overcurrent protection, thermistor over temperature protection, limit stopping, forward/reverse, 50amp MOSFETS mounted with mica to heatsink, mounting plate, LEDS, and thick copper traces.

There are a zillion uses for this thing.

The part is listed on EBAY now.
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=250498364685&ssPageName=STRK:MESELX:IT [Broken]
 
Last edited by a moderator:

1. How does an H-bridge circuit work?

An H-bridge circuit is a type of electronic circuit that allows for bidirectional control of a motor or other high-powered device. It consists of four switches, typically in the form of power FETs, arranged in a configuration that resembles the letter "H". By turning these switches on and off in a specific sequence, the H-bridge can change the direction of current flow through the motor, allowing it to rotate in either clockwise or counterclockwise direction.

2. What are the advantages of using power FETs in an H-bridge circuit?

Power FETs, or field-effect transistors, are commonly used in H-bridge circuits due to their high power handling capabilities and fast switching speeds. This allows for more efficient control of the motor, reducing heat dissipation and improving overall performance. Additionally, FETs have a lower on-resistance compared to other types of transistors, resulting in lower power losses and improved efficiency.

3. How do I choose the right power FETs for my H-bridge circuit?

When selecting power FETs for an H-bridge circuit, it is important to consider factors such as voltage and current ratings, switching speed, and on-resistance. It is also important to ensure that the FETs can handle the power requirements of the motor being controlled, and that they are properly sized for the circuit's thermal requirements. Consulting a datasheet and seeking expert advice can help in selecting the appropriate FETs for your specific application.

4. Are there any safety considerations when designing an H-bridge circuit with power FETs?

When working with high-power circuits, safety should always be a top priority. It is important to make sure that the FETs are properly rated for the voltage and current levels being used, and that they are mounted and cooled correctly to prevent overheating. Additionally, proper isolation and protection measures should be taken to prevent electrical shocks or short circuits. It is recommended to seek guidance from a qualified professional when designing and implementing an H-bridge circuit with power FETs.

5. Can an H-bridge circuit with power FETs be controlled with a microcontroller?

Yes, an H-bridge circuit can be easily controlled with a microcontroller using pulse width modulation (PWM) signals. By varying the duty cycle of the PWM signal, the speed and direction of the motor can be controlled. This allows for precise and flexible control of the motor, making it a popular choice for robotics and other electronic applications.

Similar threads

Replies
34
Views
2K
  • Mechanical Engineering
Replies
17
Views
3K
  • Mechanical Engineering
Replies
4
Views
1K
  • Mechanical Engineering
Replies
19
Views
609
  • Engineering and Comp Sci Homework Help
Replies
2
Views
1K
  • Mechanical Engineering
Replies
3
Views
1K
  • Mechanical Engineering
Replies
12
Views
2K
  • Mechanical Engineering
Replies
16
Views
2K
Replies
2
Views
1K
Replies
17
Views
822
Back
Top