TIP122 and others

Hi everyone,

I'm looking to control 12V at 5Amps. I have read the specs on the TIPs but i was wondering what peoples' experience has been with this or if they have a suggestion for an appropriate TIP.

I'm worried about over heating and finding a TIP or alternative that is robust enough to stay cool even when running for an extended amount of time. I'm using it on fish tank lighting so id obviously prefer that my apartment stay standing and free of fires :P. (i'm a bit paranoid)

what has your personal experience been like with this method of controlling higher amps? do you have any recommendations you can give me on circuit components or setups?

Thanks

The amount of heat generated is determined by the current and the voltage drop across the transistor. That's going to be about the same for any bi-polar transistor (including the Darlington TIP122). So, it's a question of the ability of the transistor and heatsink to handle and dissipate the heat.

With 5A through a TIP122 you'll probably need a heatsink.

Power dissipation (converted to heat) is calculated as Voltage x Current. (Where voltage is the voltage dropped across the transistor when it's on/conducting.)

A MOSFET will generally have a lower on-voltage, but there's more part-to-part variation. They don't specify the on (or saturation) voltage for MOSFETs, but they specify the on-resistance and you can use Ohm's Law to calculate the voltage drop, and then calculate the power dissipation.

MOSFET is voltage controled saying they have a low on voltage is miss leading. They have a low current turn on but may need 2 to 10 volts to turn on fully. A Darlington is current controled and can turn fully on at much lesser voltage.

The TIP122 is a Darlington transistor. Darlingtons are designed for gain, but have a major problem in that they do not saturate effectively and thus lose something like a volt. They are quite unsuitable for switching substantial current and essentially represent an obsolete technology.

If you wish to use bipolar transistors, then you need to use separate transistors so that you can provide adequate drive to the final transistor via a current-limiting resistor.

If you wish a single device with even better performance and the possibility of operating without a heatsink, then you want a logic-level power FET. Or a non-logic-level power FET with its gate driven by another transistor to the full 12V.

be80be: MOSFET is voltage controled saying they have a low on voltage is miss leading. They have a low current turn on but may need 2 to 10 volts to turn on fully. A Darlington is current controled and can turn fully on at much lesser voltage.

Mosfets have an "on" [u]resistance/u. "Logic" fets must be used with the low voltages of Arduino. A darlington transistor always has a remaining saturation voltage across. So a logic mosfet is the prefered choice for switching.

Personally, I would go for switching constant current LED drivers for aquarium lighting, instead of resistors and mosfets. Leo..

obviously prefer that my apartment stay standing and free of fires :P. (i'm a bit paranoid)

Use a relay just kidding.. If you want something safe you have to supply a lot more info how many leds brand and datasheet. Then you figure the best way to drive them. Safe is not a big transistor be it what ever you use safe is just enough power to get the job done. Then a fuse to trip when you use to much.

That's why all the breakers in your house is not a 100 amp you don't want the wire burning same thing here you don't want a 10 amp driver and 500 mA of leds that's asking for fire.

If you want worry free then you figure what you need based on the facts Fact's being you figure what parts and then how much current, then a chip to drive them or a led driver that let's you use pwm.