Electronics > Beginners
Picking a transistor.
paulca:
I only have NE2222 and BC548's, but I have a project that needs more current than they can handle.
Basically switching a 12V line using a 3.3V PWM pin on an MCU. It's driving some 5050 LEDs, 12V with groups of 3 in series. Power is meant to be 14.4W/m, so call that 15W/m, I have 2 meters, so that's 30W or 10W per colour, so 10W / 12V ~= 1 Amp per transistor.
Would these do:
https://uk.rs-online.com/web/p/bjt-bipolar-transistors/7390347/
BTW, these are the LEDs with GND, RED, GREEN, BLUE connections, not the digital WS8212s
MagicSmoker:
That's a PNP BJT optimized for audio amplifiers, so probably not the correct polarity and otherwise not ideal.
Can you post the schematic you are working off of?
paulca:
Basically this.
https://randomnerdtutorials.com/10-diy-wifi-rgb-led-mood-light-with-esp8266-step-by-step/
But with 2 x 1 meter of strips of LEDs.
A thought did occur to me. These are to light a fish tank that contains plants. I could need it to power 4 strips. 60W, 20W per colour.
ledtester:
The typical solution for low side switching with a microcontroller is a logic-level N-channel MOSFET.
Get one that will fully turn on at 3.3 volts. Searching for "arduino 3.3v logic level mosfet " should bring up plenty of discussions and suggestions.
David Hess:
1 amp will require say 20 milliamps of drive current at a forced beta of 50 for a bipolar transistor which is marginal for most logic outputs. That means either using some sort of driver to provide higher base current, a Darlington bipolar transistor, or a MOSFET.
So bipolar transistors could be used but the higher cost of a power MOSFET is probably worthwhile for simplicity. Or a higher gain higher current bipolar like the KSD5041 could mange a forced beta of 100 for 10 milliamps of drive current. For suitable bipolar transistors, look for higher current devices so that they maintain their gain at higher currents.
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