Society of Robots - Robot Forum
Electronics => Electronics => Topic started by: Conscripted on January 06, 2011, 07:12:38 AM
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Good morning all.
I'm working on a small line follower using a pair of pager motors. They are rated to have a stall current of 260mA @3vdc. I don't think they will ever stall since it will be running on a table top. I'll be using a transistor to turn them on and off. Do I need to put in protective diodes? I have them if I need but I'm trying to keep the part count down as much as possible.
Thanks.
Conscripted
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Yes you need them, your current may be small but it is the short switching time which is mostly responsible for high back-emf.
You could look at using a darlington transistor, they often have protection diodes included and should be available as a drop in replacement.
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Hi,
They are rated to have a stall current of 260mA @3vdc. I don't think they will ever stall since it will be running on a table top. [...] Do I need to put in protective diodes?
Yes, you need the diodes.
Diodes have nothing to do with the stall current. It's the flyback voltage spikes that they're protecting against.
Use fast diodes if at all possible, a 1N400x is too slow and can let short spikes through.
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Thank you for the replies. I've got a couple of SD103B Schottky Diodes that I purchased for this reason. I was hoping not to use them.
Conscripted
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Sorry to say but I wouldn't got with a Schottky diode, just for batteries shake... They tend to have ugly reverse current drain ratings... which current would be loaded on the transistor/mosfet and deprived from your motor...
Go p-n junction style... I just don't know a model to suggest...
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Hi,
[...] They tend to have ugly reverse current drain ratings... which current would be loaded on the transistor/mosfet and deprived from your motor...
Datasheet says:
Maximum Reverse Current 5.0 uA
SD103A @ VR= 30V
SD103B @ VR= 20V
SD103C @ VR= 10V
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Use fast diodes if at all possible, a 1N400x is too slow and can let short spikes through.
What are your favorite model numbers?
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Hi,
Use fast diodes if at all possible, a 1N400x is too slow and can let short spikes through.
What are your favorite model numbers?
That depends on current and the application in general. I always keep a stock of BYV27 (3A and 25ns max. RRT), for fairly low currents, signal diodes like 1N4148 and 1N914 are aces (both about 4ns RRT).