darlington question

haunteddansion

If the Darlington array has 3 volts from low current logic, is it posible to control a solenoid on the other side with a different power source like 12 volts, basically use the darlington as a very low current set of relays. If not how would I do this. I am trying to use the pins that control an led matrix to go through the darlington so I can control multiple solenoids, in essence have an LED matrix but instead of leds I will have a matrix of solenoids. This is my senior thesis so I know it is hard to understand but any help will be greatly appriciated, Many thanks!

-Dan

KenM

Yes,
In the attached schematic, assume the transistor is a darlington. There is a 5 volt source driving it, but the transistor is switching (providing ground) for a 12 volt load.
And, there is about 1.4 volts across the b-e junction since there are two b-e junctions on a NPN darlington.

haunteddansion said...
If the Darlington array has 3 volts from low current logic, is it posible to control a solenoid on the other side with a different power source like 12 volts,

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Ken

haunteddansion

Then how does the darlington array fit into the schematic with two power sources? Thanks again

LoopyByteloose

AS KEN NOTEED - That particular transistor is not a darlington array, but the schematic would work the same way.

The first power source is the BasicStamp which turns the Darlington on and off.

The second power source is connect to the device [noparse][[/noparse]selinoid or motor] which is connected to the Darlington, and then the Darlington's other side is to group.

Also, at 3 watts switching, you need a discrete Darlington, the ULN2803 IC is rated for only 0.5 watts total. It will burn up.

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"When all think alike, no one is thinking very much.' - Walter Lippmann (1889-1974)

······································································ Warm regards,····· G. Herzog [noparse][[/noparse]·黃鶴 ]·in Taiwan

Chris Savage

I believe some of these questions were already answered in your other thread.· Please keep the messages of the same subject in the same thread.

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Chris Savage
Parallax Tech Support
csavage@parallax.com

Paul Baker

I would not use a darlington array to switch multiple solenoids, most solenoids require a considerable amount of current to power, much greater than a DIP package device could provide, you'll likely need to get individual darlingtons in a TO-220 package. Then just wire them as Ken has shown in his schematic.

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·1+1=10

KenM

This application may be a overkill for your solenoid, but it is a simple and easy solution to switch several amps directly with your stamp.

Also (not shown) the ground for the stamp and the other power source (12v in this case) must be tied together.

I will fix my schematic later to include this important point.

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Ken

Genesis

Is the advantage of this over something like a L293 the lower voltage-drop between supply and load?· The L293 looks attractive as it can sink 1A, has 4 channels, and internal clamping diodes.....· If you don't need more than 1A (many solenoids fall within this range as do most if not all relays) it appears to be a nearly-ideal solution....

Newzed

The 293 can only handle 600ma per channel.· The L298, a much stronger brother, will handle 2A per channel or a total of 4A for all channels.· I have a Solarbotics L298 Compact Motor Driver kit I built up but never used that is available if you are interested.

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Sid Weaver
Do you have a Stamp Tester yet?
http://hometown.aol.com/newzed/index.html

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