recommend me a transistor

Hello all,

I need to control four cold cathode tubes by buttons on a Playstation controller so that when a certain button is pressed, the corresponding cold cathode is illuminated. I'd like to use transistors to switch the cathodes on and off. Can anyone recommend a transistor? Is there anything else I need to add/remove to this circuit to make it work? I'm pretty sure I need a resistor going from the Playstation button/switch to the base of the transistor, but I don't know what value I need. Is the amperage going from the power supply to the cold cathode inverters correct as I have it configured in parallel? Sorry if I'm asking a lot of questions at once but I really want to get this project off the ground. Thanks!

- PrL

Firstly, you need to insert a resistor in series with the base of each transistor, to limit the base current. The value of this will depend on the transistor you use. Usually in the range of 100 ohm - 10kohm (roughly).

There are a lot of general-purpose transistors you could use. Probably the most available one is the BD139. Good for 80V and 1A. You could also try a TIP31, which is rated at 60-100V (depending on the variant) and 3A. Start with a base resistor of about 470 ohm, and experiment with the value, between 100 ohm and 1kohm.

Alright, so I decided to go with the TIP31. I've read the datasheet for it but I still don't know what value resistor to use on the base. Can anyone help?

Datasheet: https://www.fairchildsemi.com/ds/TI/TIP31.pdf

I still don't know what value resistor to use on the base

Click to expand...

For the TIP31, start with 220 ohm.