Use One Snubber Diode on Multiple Loads

General project help for Adafruit customers

Moderators: adafruit_support_bill, adafruit

Please be positive and constructive with your questions and comments.
Locked
jamilm9
 
Posts: 7
Joined: Fri Dec 25, 2009 1:13 pm

Use One Snubber Diode on Multiple Loads

Post by jamilm9 »

Hi,
I'm using a arduino to control multiple (9) motors. Is it possible to use one snubber diode in parallel with all the motors connected to the positive of the motor and the emitter of the transistors? I have attached part of my schematic which shows using individual diodes in pencil and the proposed single diode in red.

Thank you.
Attachments
Screen Shot 2012-03-04 at 1.26.14 PM.png
Screen Shot 2012-03-04 at 1.26.14 PM.png (246.27 KiB) Viewed 782 times

User avatar
john444
 
Posts: 443
Joined: Sun Mar 04, 2012 2:42 pm

Re: Use One Snubber Diode on Multiple Loads

Post by john444 »

Sorry jamilm9. But the purpose of the diodes across the motors is to absorb the energy in the motor's magnetic field when current to it is interrupted. With only one diode, where you indicated on the schematic, each drive transistor will be subjected to the 'kick-back' from its motor. Diodes are inexpensive and they reduce the chances of blowing the transistors. Also, it is better to catch it at the source so connect each diode as close to the motor as is reasonable. Looks like an interesting project. Good Luck

User avatar
easternstargeek
 
Posts: 347
Joined: Mon Dec 13, 2010 1:39 pm

Re: Use One Snubber Diode on Multiple Loads

Post by easternstargeek »

John444 is right, but you can still simplify things while saving space and money, too!

You don't say how big the motors are, but have you considered using a Darlington transistor array to drive them? The ULN2004A, for example, can control 7 channels at up to 500mA each, and there are built-in snubber diodes which would be perfect for your motors. Like your circuit, that chip uses low-side (NPN) drivers.
http://search.digikey.com/us/en/product ... -ND/599602
http://www.st.com/internet/com/TECHNICA ... 001244.pdf

An 8-channel version is the ULN2803, also with snubber diodes:
http://www.ti.com/lit/ds/symlink/uln2803a.pdf

If you ever need high-side drivers, consider the Allegro UDN2981, which gives you 8 PNP Darlingtons (and a snubber for each):
https://www.jameco.com/webapp/wcs/store ... Id=1762681

Each channel is good for up to 350mA, and your motor voltage supply can be anywhere from 5 to 50 volts.

For even more fun, you can use this chip:
https://www.jameco.com/webapp/wcs/store ... tId=241875

It is a single-channel full H-Bridge that can drive a DC brush motor in either direction up to 1.6A!

Have fun, and do come back to tell us what you are building.
Good luck!

User avatar
philba
 
Posts: 387
Joined: Mon Dec 19, 2011 6:59 pm

Re: Use One Snubber Diode on Multiple Loads

Post by philba »

Yeah, that proposed diode won't do anything at all, assuming it connects voltage source to ground. The collapsing field current would punch through your transistors.

The uln2803 is particularly nice because it has all the resistors you need as well. sweet package.

Phil

Locked
Please be positive and constructive with your questions and comments.

Return to “General Project help”