SparkFun Forums

[Woehrle]

Is there such thing as a 3 volt transistor? What I mean by 3 volt is, will it switch if 3 volts is applied to the base?
If this doesn't not exist what could do the same thing?

Thanks

Woehrle

[waltr]

No, there is not such a transistor.
Bipolar transistors are current devices which means that the transistor turns on when current flows from Base to Emitter.

[NleahciM]

Is there such thing as a 3 volt transistor? What I mean by 3 volt is, will it switch if 3 volts is applied to the base?
If this doesn't not exist what could do the same thing?

Thanks

Woehrle

How fast of a transition do you want? Does it need to be all off at 2.999V and all on at 3.000V? Please give a more complete description of your application.

[lyndon]

Not really, but you can get some transistors to switch on with 3V. How much current does the transistor need to switch? Something like a 2N3904 (200mA?) or a 2N2222A (400mA?) will probably work. Use a 470 ohm resistor from the 3V supply to the transistor base with the circuit in a common-emitter configuration (emitter grounded) and it should saturate/cutoff properly.

If that doesn't work, then give us more information about what you're trying to do so we can help you better.

Is there such thing as a 3 volt transistor? What I mean by 3 volt is, will it switch if 3 volts is applied to the base?
If this doesn't not exist what could do the same thing?

Thanks

Woehrle

[dattaway]

Usually about 0.7 volts through the base and emitter, but its all about the current. Bipolars amplify current, not voltage. For voltage amplification, look at mosfets. Or if you want a the best of both worlds with a mosfet gate and bipolar output, try a IGBT transistor.

[60amp_relay]

I'm guessing what you really want is a voltage comparator, like an LM311.

[Woehrle]

Sorry for the lack of information. The full story behind this issue is that I am building a suborbital payload with a spectrometer that cannot be powered before the data logger, other wise the logger gets confused and logs squares only. So, I'm using one of the arduinos on the payload to switch a transistor allowing the spectrometer to power after a certain amount of time. I will try to link a drawing of what I've tried to do, and what I'm going to attempt. Thanks for all your input.

Note: My idea is to create a voltage divider and supply the base with a higher voltage so it doesn't require so much current from the Arduino. Does this work?



Woehrle

[waltr]

Almost. You need to set the current through the base (to emitter) and also limit the current drawn from the processor pin.
This requires a resistor in series with the processor pin an the base. As drawn the npn transistor won't work.

A pnp transistor would be better. Like this.

[Woehrle]

Thanks Waltr! I will try this right away. =]

Woehrle

[waltr]

Forgot to add that the processor output is set low to turn on the transistor.
The 10k pull-up is to keep the transistor off when the processors output is Hi-Z (like during reset).

[n1ist]

Also look into using a pmos fet for lower loss.
/mike