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I'm trying to find a transistor that can power up to 1A (1000mA) on an animated LED strip lighting circuit. From this thread I found the BC517 darlington:

Choosing the right transistor for a switching circuit

Since I'm trying to switch off as much passive power consumption in the circuit as possible when sleeping, I need to know how much power the transistor will draw when it is off. Is there a name for this characteristic on the datasheet?

I heard that a typical low power transistor (like 2N3904) might "sleep" around 50 nanoamps, but since I'm using a higher power transistor I thought it might use more than that when off. Even a consumption of 1mA takes the sleep time from months or years to mere days.

Thanks for any suggestions!

Edit: The voltage of the circuit is 3-5v dc.

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capsid
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2 Answers2

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No, there is no such parameter. At most there will be off state current, ususally called "leakage current" or "cutoff current". The power has to do with applied voltage, which only you can know.

However, the leakage currents of normal transistors are so low as to be irrlevant in virtually all cases. If the issue is switching 1 A LED lights on and off, then the off current will definitely be irrelevant.

If you are worried about power consumption, then darlingtons are probably not the way to go. These have significantly higher on-state voltage drop than a bare bipolar, and a FET can have even lower than that.

It would be a good idea to explain more your overall problem and ask how to solve that instead of asking details about a possibly inappropriate solution.

Olin Lathrop
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  • Thanks :) I will look into bare bipolars and FETs.

    The consumption of the transistor is irrelevant when the circuit is on, but I would need it to be well below 1ma when the circuit as a whole is sleeping, which it looks like it is :)

     – capsid Feb 06 '13 at 20:45
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    @capsid: The power consumption of the switch when the LEDs are on could be significant. That is the issue. That is why a darlington may not be appropriate. And again, current is not power. The off-state current of any normal transistor will be irrelevantly small compared to running the 1A of LED current for even a short while. 10 seconds of 1 A averaged over a whole year is 317 nA, which will be significantly more than the off-state current of most transistors. You are worrying about the wrong problem. – Olin Lathrop Feb 06 '13 at 20:54
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From this datasheet:

Collector-Base cutoff current = 100nA.

But note that this BC517 is rated to 500mA, not 1A so there may be differences between makers.

JYelton
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