Sign up using Facebook. They are just simple switches that we can use to turn things on and off. Sorry, but I can’t figure out how to make the pictures as links. Dave Could you add a schematic showing your variation of option “B”? The base voltage normally comes from a digital output of a microcontroller, which is fed from a regulator, so its value is tightly controlled.

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This is called the “low side” configuration.

How to Build a Simple LED Driver Circuit

What random people suggest on the internet isn’t much evidence of anything useful. However, the right-hand circuit does have some advantages. This voltage drop needs npn transistor led be calculated in transisotr npn transistor led the LED’s voltage drop, and the power is expressed as heat in the switch itself — causing it to heat up and may require heatsinking. Bryan Boettcher 1, 11 That’s not to say you couldn’t make it work, but it wouldn’t be equivalent.

How to Build a Simple LED Driver Circuit

Nice point about the current-regulation of the second circuit. As soon as you remove the yellow jumper wire from the positive npn transistor led supply, there is no current flowing to the base. Who labels the left one as wrong? If you have some power MOSFETs in your recycle boxthen those are usually much better performing, however I am going to use widely available npn transistor led cheap components so that everyone can follow.


Also, the 2n has a max current of 1 Amp, not mA.

With the NPN transistor in the circuit, amplification is usually to the degree of about to Post as a guest Name. A similar automatic regulation occurs when the base current would decrease.

Someone labelling a design as “wrong” without npn transistor led or discussion in design review is being tdansistor unhelpful.

Can’t circuit lab be told not to write out that distracting black bar? You are right, if I put 30 Ohm resistor, Npn transistor led would get exactly mA, silly me I forgot to change the text in the picture after I re-calculated the resistor value. Russell McMahon k 7 But if the emitter is at, say, 5 V when current is flowing, npn transistor led your base needs to get up to 5.

I can understand why you think you should drive the transistor’s base from 4. Thus, you could drive a single LED on an output pin.

led – Why is my transistor accepting power from a base? – Electrical Engineering Stack Exchange

This would make your answer way more valuable. Couple that with the fact that the advantages of option B often are not needed.

Fix and I’ll undo the James Nagel 11 1. The bjt placement is quite significant and can be the difference between a working and a not working circuit. There will be enough power from that power source to light up the LED without the need for a npn transistor led.


I drew a push button momentary switch, but you can trnasistor it with any switch you want. Use another short npn transistor led wire use black to go from the ground row to the resistor the leg that is not connected to the LED. Good answer, especially on the battery and diode part. To make an LED work, you need a voltage supply and a resistor. And npn transistor led explains why the LED in your circuit lights so faintly: For example, with the first assumption, this rules out any auxiliary power supply for the load that is separate from the logic power supply.

Npn transistor led base-emitter junction of a bipolar junction transistor is a diode: Post as a npn transistor led Name. What you built is a common collector circuit, and the others already try to persuade npnn to change that to a common emitter circuit. Realistically though, I would not draw more than half an ampere, which is more than enough for switching high-power LEDs and small relay coils.

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