I have a few Toshiba C5242 BJT's.... probably not going to do much for pwm.
looking for opinions on suitability of the BJT(s) for the light bar.
I have about 5 of the C5242 so using a couple to spread the load is a possibility.
Well given a BJT needs about 5 to 10% of the output current to the base, you'll need another
transistor to drive a 2SC5242 (C5242 is the marking, the device code is 2SC....)
Much easier to use a logic-level MOSFET surely?
And as the 2SC5242 is designed for linear operation its switching performance is probably awful (long
turn off delay from saturation).
Having said that its a transistor, it has gain, drive it properly and don't exceed its maximum
ratings and it will work.
Did I miss something? What light bar? I assume you didn't build it yourself?
Typically an LED light bar has a built-in constant-current power supply. If you PWM it, it's going to try holding constant current (and constant brightness) and who-knows what's going to happen...
the LED light bar is powered by 12vdc. (automotive application)
this car has a seperate 5vdc power supply that can push upto 25 amps
i was planning on using a switch and a heavy duty resistor to activate the gates.
a relay is not out of the question. but i already have the BJTs and the relay would have to handle 10 amps and i would probably buy a 15 amp rated relay.
like i said... parts i have vs. parts i need
LandonW:
**the LED light bar is powered by 12vdc. ** (automotive application)
this car has a seperate 5vdc power supply that can push upto 25 amps
i was planning on using a switch and a heavy duty resistor to activate the gates.a relay is not out of the question. but i already have the BJTs and the relay would have to handle 10 amps and i would probably buy a 15 amp rated relay.
like i said... parts i have vs. parts i need
5V supply to 12V LED strip?????????
Tom.... :o :o :o
5V into the base and 12V through the collector/emitter? Doesn't sound wrong to me.
LandonW:
the LED light bar is powered by 12vdc. (automotive application)
Car lighting is usually switched high-side, with the metal of the car as negative/ground/return.
Leo..
TomGeorge:
5V supply to 12V LED strip?????????
Tom.... :o :o :o
no, two power supplies. the 12vdc (14vdc charging system) and the regulated 5vdc.
the 5vdc controls more than just these lights.
I also have a full engine monitoring system and remote start / fuel pump control / electric radiator fan control
its a 71 dodge dart with a 360
probably not going to do much for pwm.
I don't know what you're trying to say, but like I said it's probably not going to work with PWM. I guess you could try it with your 5V supply and if it "dims nicely" at 5V then PWM might work.
A relay would be the most foolproof way to turn it on & off, but a MOSFET could work too.
110W @ 12V = 9.2A.
Typical voltage drop at saturation is 0.4V so power dissipation is just under 4W. That's not too bad.
However to get to saturation you need to provide about 1 A of base current (datasheet mentions IC/IB = 10) much more than an Arduino can deliver, so you need a second transistor in darlington configuration to provide this base current.
As an Arduino pin can not deliver more than 20 mA, and typical gain is about 100 times, so to go from 20 mA to 1A is 50 times gain. That second transistor is also going to need a heat sink.
Much easier: replace it with a MOSFET. An n-channel one such as the IRLZ44N doesn't need a driver transistor, and at 0.022Ω on resistance produces just 1.9W of heat. You can probably find MOSFETs with even lower on resistance.
thank you all for your comments and time... I'm gonna start with two transistors and go for smoke.
With those transistors probably best chance of success (and no smoke) is to use two darlington pairs, so four transistors total.