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Topic: Is it safe to run a motor from this voltage regulator without a diode? (Read 555 times) previous topic - next topic

scswift

Hey guys,

I had some voltage regulators made which use the first circuit in this datasheet:
http://www.ti.com/lit/ds/symlink/lm27313.pdf

And I'd like to drive a vibration motor like this off it:
https://catalog.precisionmicrodrives.com/order-parts/product/324-401-24mm-vibration-motor-13mm-type

I had a mosfet module with a flyback diode on it to use with 5V motors, but I had 100 of my 12V modules made and I only really needed 50 and I was thinking maybe I could upgrade the vibration motor in my project to a 12V one of the same size and use those spare 12V modules instead of spending hundreds of dollars getting more of the mosfet modules made.

The 12V modules don't have that flyback diode in them though.  They do however have a diode that would protect the switch pin and inductor, and there's a path to ground through R1 and R2.  So I thought maybe it might be okay.  Plus it's not a very large motor. 

I'd solder a diode across the pins on the motor, but there aren't any, just a couple wire leads, so it would be a bit of a pain and there's no really good place to put a diode on the module itself and I cant' trust the end user won't get the altered and unaltered modules mixed up.

So what do you think?  Will I fry the regulator quickly?  Will it survive?  And is there any chance at all of damaging my microcontroller?

joe mcd

Why are you running your motors off a voltage regulator?   The normall practice is too feed 'raw' power to the motors BEFORE any regulation.

MarkT


Hey guys,

I had some voltage regulators made which use the first circuit in this datasheet:
http://www.ti.com/lit/ds/symlink/lm27313.pdf

And I'd like to drive a vibration motor like this off it:
https://catalog.precisionmicrodrives.com/order-parts/product/324-401-24mm-vibration-motor-13mm-type

I had a mosfet module with a flyback diode on it to use with 5V motors, but I had 100 of my 12V modules made and I only really needed 50 and I was thinking maybe I could upgrade the vibration motor in my project to a 12V one of the same size and use those spare 12V modules instead of spending hundreds of dollars getting more of the mosfet modules made.

The 12V modules don't have that flyback diode in them though.  They do however have a diode that would protect the switch pin and inductor, and there's a path to ground through R1 and R2.  So I thought maybe it might be okay.  Plus it's not a very large motor. 

I'd solder a diode across the pins on the motor, but there aren't any, just a couple wire leads, so it would be a bit of a pain and there's no really good place to put a diode on the module itself and I cant' trust the end user won't get the altered and unaltered modules mixed up.

So what do you think?  Will I fry the regulator quickly?  Will it survive?  And is there any chance at all of damaging my microcontroller?


You need a flyback diode across an inductive load otherwise you'll toast all the semiconductors...
[ I won't respond to messages, use the forum please ]

scswift


Why are you running your motors off a voltage regulator?   The normall practice is too feed 'raw' power to the motors BEFORE any regulation.


Well, the motor I was using before requires 5V and my voltage source could be anything, but typically is an 11-12V battery that also drives an audio amplifier.  It was controlled with a mosfet and powered from the 5V regulator that also powered my boards.

I ran out of the mosfet boards I was using for said motors though and it would cost something like $600 to get more made.  So I was hoping to use these boards I already have to drive them and just get 12V motors since I have to restock on the motors as well anyway.

I can't just use a relay either because I use PWM to control the speed of the vibration. 


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