Pn2222 how to#
Pn2222 full#
Pn2222 series#

What Im not confused about is which spec on the sheet I should be looking at in order to figure this out. At this point Im just trying to sort out the math for driving the transistor to saturation. 7 volts which seems to match the value everyone else has been using for transistor voltage drop.

I've also measured the voltage drop from base to emitter and verified that it's right around. Having it in it's own leg on the collector means that I can deal with it separately. If this is the case, I can see how having the LED as part of circuit 2 would impact the power required to drive the transistor. The more I think about this, the more I see that Im dealing with two parallel circuits on the same power supply as I've drawn out.

Pn2222 series#

I've moved the LED and it's series resistor to the collector leg of the transistor. Im really new to this space and still learning so it's been very helpful. Shouldn't this be factored in? What about the voltage drop of the LED? In reality, when I check the voltage drop from collector to emitter and base to emitter I see. 7 volts from voltage since that just seems to be what everyone was doing.

Pn2222 full#

Shouldn't I get the full 46 as I see when the LED and resistor are plugged directly into the power source?Īlso - in the above circuit I subtracted. That gave me 3010 and when I use a 3k resistor I only get about 30 milliamps of current to the LED. From my reading this is important because too much current could open the transistor too far and block the current coming from the collector through to the emitter. I've tried many different formulas to try and figure out what the base resistor should be used and I can't seem to get it right. So my resistor for the LED is 54 ohms and I used a 47 ohm resistor. In this case, I know the LED drops 2.48 volts and draws 46mA. Its my understanding that the resistor for the LED should be calculated much in the same way I would without the transistor.

Pn2222 how to#

That will allow a higher value resistor with less variation due to the LED.I've been continuing to play with small circuits and Im trying to sort out how to calculate the resistor for the base of this transistor. Actually because of device variations, I would not recommend using more than 2 LEDs in series from a 5V supply. If it is for pulse duty such as remote control the duty cycle is low and they can be driven at a higher current.įor continuous duty it looks like 20mA is the maximum.Īlso in your calculation for the LED series resistor you have not taken into account the voltage drop of the 2N7000 (or PN2222). I would use a drive it with 5-10mA of bias current with (that would be good for a collector current of 80mA), for example, a 470-ohm resistor.

The voltage across the device should only be a few hundred millivolts while conducting and 80mA is no problem.Īctually, for this application, I would use a bipolar transistor (such as a PN2222). It really needs 5V to turn on well as can be seen from this datasheet graph: The gate threshold voltage worst case is 3V, but that is not the voltage for full conduction, that is only to pass 1mA. 3.3v may not be enough to drive it enough into conduction for your needs. However, the 2N7000 is not the ideal device to drive from 3.3v. Provided the FET turns on well it won't affect the current through the LEDs or the LED resistor calculation significantly. You can drive the gate directly from the processor. You don't need any resistor at all at Rg.