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Topic: powering two SMA wires on one power source (Read 388 times) previous topic - next topic

MarkT

Use a logic level MOSFET to switch the SMA wire, then the voltage drop will be tiny.
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CrossRoads

Oh, that diagram is just wrong! If you are wired like that, you have to fix that before proceeding.

http://www.fairchildsemi.com/ds/TI/TIP122.pdf

Problem is TIP120 is not a straight NPN transistor - it is 2 NPN connected in Darlington fashion, where 1st NPN provides extra drive to the 2nd for higher Collector-Emitter current flow. The drawback is higher Collector-Emitter voltage drop, closer to 2V than say 0.5 or 0.7V.

That may work out okay here tho:
(5V - 2V)/(7.8 ohm) = 384mA.

If the 5V is something else, re-do the math and add the appropriate current limit resistor.
Designing & building electrical circuits for over 25 years. Check out the ATMega1284P based Bobuino and other '328P & '1284P creations & offerings at  www.crossroadsfencing.com/BobuinoRev17.
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hilukasz


Oh, that diagram is just wrong! If you are wired like that, you have to fix that before proceeding.

http://www.fairchildsemi.com/ds/TI/TIP122.pdf

Problem is TIP120 is not a straight NPN transistor - it is 2 NPN connected in Darlington fashion, where 1st NPN provides extra drive to the 2nd for higher Collector-Emitter current flow. The drawback is higher Collector-Emitter voltage drop, closer to 2V than say 0.5 or 0.7V.

That may work out okay here tho:
(5V - 2V)/(7.8 ohm) = 384mA.

If the 5V is something else, re-do the math and add the appropriate current limit resistor.



ah, you know what, I am new to schematics so I didn't realize how wrong that looked. I used a generic transistor on my build tool, I guess the pins were flipped (schematic gets build almost automatically from breadboard tool). I do in fact have the digital pins from arduino going to the base, not the collector. For the most part I have exactly what you have in my actual breadboard.

yeah I have 12v on it so the resistor was 14.4ohms.
for(i = 0, i < 820480075, i++){ Design(); Code(); delay(1000); } // hellowoo.com

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