H-Bridge - diodes (or rather the lack of)

  • Thread starter Dixo
  • Start date
  • Tags
    Diodes
In summary: So if it's just a one off, you're not going to damage anything.But if you keep making them, and they start failing, then you're definitely in trouble.Thanks for the heads up.definitely ones I have never heard of beforeThe part numbers are H772 and H882. They are Chinese semi-manufacturer part numbers and they are not very common.will be interested in seeing how well they last for youI'm not sure how long they will last, but I'll be interested to see how they do.you could put diodes across the transistors if you wanted to ... it would give some peace of mindThat
  • #1
Dixo
18
1
G'day all!

I've got an H-bridge here from an old motorised toy.. as I want to use it for something else and the RF receiver is no use to me for this project i figured i' strip the H and stripboard it.

I noticed though that there are no diodes to protect the four transistors (yes they are transistors - looked up the part numbers).

Now I thought this wasn't supposed to work.. but this toy has survived years.

Any ideas?

Thanks,

Dixo
 
Engineering news on Phys.org
  • #2
Dixo said:
I noticed though that there are no diodes to protect the four transistors (yes they are transistors - looked up the part numbers).

what is the type # of the transistors ?

I have seen the occasional bipolar transistor H-bridges without diodes ... it is surprising that they don't fail

if they are mosfets, then they have built in diodes by default and don't require external diodes eg ...

h_bridge_cd4011b.gif


I should qualify that by saying that not all MOSFETS have built in diode, many do
 
  • #3
davenn said:
what is the type # of the transistors ?

Hi dave

They are H772 and H882 - bog standard npn and pnp basically.

davenn said:
I have seen the occasional bipolar transistor H-bridges without diodes ... it is surprising that they don't fail

Yes I was quite surprised too because i understood that without diodes they were guaranteed to fail.
 
Last edited by a moderator:
  • #4
Dixo said:
They are H772 and H882 - bog standard npn and pnp basically.

never heard of them ... can't be very standard

do you have a link to a datasheet please ?
 
  • #6
Dixo said:
cheers :smile:

definitely ones I have never heard of before
appear to be a Chinese semi manufacturer

will be interested in seeing how well they last for you

you could put diodes across the transistors if you wanted to ... it would give some peace of mind :wink:

H-Bridge-6.gif


they used 1N4148 ... I would prefer to see 1N4001 series diodes in there as they are much more robust and commonly used for that and similar purposes
1N4001 - 4007Dave
 
  • #7
davenn said:
I have seen the occasional bipolar transistor H-bridges without diodes ... it is surprising that they don't fail

I think it's a case of getting away with sloppy design.
Remember that a bipolar transistor when polarity is reversed will still act like a transistor, just with poor gain.

HbridgeReversed.jpg
 
  • Like
Likes davenn

1. What is an H-Bridge and what is its purpose?

An H-Bridge is an electronic circuit that allows for the control of the direction and speed of a motor. It is commonly used in robotics and other applications where precise motor control is needed.

2. What role do diodes play in an H-Bridge?

Diodes are used in an H-Bridge to prevent backflow of current, also known as "back EMF", which can damage the circuit and the motor. They act as one-way valves, allowing current to flow in only one direction.

3. Can I use an H-Bridge without diodes?

It is not recommended to use an H-Bridge without diodes. The back EMF generated by the motor can cause damage to the circuit and the motor itself. Diodes are necessary to protect the components and ensure proper functioning of the H-Bridge.

4. Are there different types of diodes that can be used in an H-Bridge?

Yes, there are several types of diodes that can be used in an H-Bridge, including standard silicon diodes, Schottky diodes, and Zener diodes. The type of diode used may depend on the specific application and the voltage and current requirements.

5. How can I troubleshoot issues with diodes in an H-Bridge?

If you are experiencing problems with your H-Bridge, it is important to first check the diodes. Make sure they are connected correctly and are not damaged. You can also use a multimeter to test the diodes for proper functioning. If the diodes are found to be faulty, they should be replaced with new ones to ensure the proper functioning of the H-Bridge.

Similar threads

  • Electrical Engineering
Replies
10
Views
5K
  • Electrical Engineering
Replies
8
Views
2K
Replies
21
Views
6K
Replies
11
Views
6K
  • Electrical Engineering
Replies
1
Views
2K
  • Electrical Engineering
Replies
9
Views
11K
  • Electrical Engineering
Replies
4
Views
1K
  • Electrical Engineering
Replies
7
Views
13K
Replies
22
Views
1K
  • Mechanical Engineering
Replies
8
Views
8K
Back
Top