Connecting 2 NPN transistors to power the load of a 7555 Timer

Alec_t

Joined Sep 17, 2013
11,650
It would help if you added component designators to the schematic, so that we know which parts of the circuit you're talking about.
 

Reloadron

Joined Jan 15, 2015
5,646
The "example" you posted is just that, it is an example which is why part numbers for TR1 are not called out. The 555 has a limited output current so is not capable of driving any sort of a heavy load. You start with the data sheet for a LM555 timer or if you prefer a ICM7555 timer, whatever you have. You learn the capabilities of the chip and how it works. Then you look at the load you want to drive and what will be needed to drive the load. That is exactly what the image you posted tells you. So again I'll ask what is the load and what exactly are you trying to do? If you don't know what you want it is pretty difficult for anyone to help you.

Ron
 

Thread Starter

Halsey

Joined Mar 4, 2018
30
The "example" you posted is just that, it is an example which is why part numbers for TR1 are not called out. The 555 has a limited output current so is not capable of driving any sort of a heavy load. You start with the data sheet for a LM555 timer or if you prefer a ICM7555 timer, whatever you have. You learn the capabilities of the chip and how it works. Then you look at the load you want to drive and what will be needed to drive the load. That is exactly what the image you posted tells you. So again I'll ask what is the load and what exactly are you trying to do? If you don't know what you want it is pretty difficult for anyone to help you.

Ron
Two LED's and a pair of headphones. I just am uncertain how to connect the transistors. I really would just like any help showing how to connect the transistors as a darlington pair to see if it will be enough to drive the LED's and headphones. They are 2N2222 transisitors.
 

Alec_t

Joined Sep 17, 2013
11,650
Connect the collectors of both transistors to the V+ supply and connect the emitter of the left transistor to the inductor.
 

Reloadron

Joined Jan 15, 2015
5,646
Again, read the data sheet for a 2N2222 transistor. That very popular NPN switching transistor can handle 800 mA of continuous collector current and I doubt you will get close to 800 mA with a few LEDs. Next do a simple Google of 2N2222 LED Circuits which will bring up dozens of circuits like this. Now as to your partial circuit I have no idea what your goal or objective is. What exactly are you trying to do with headphones and LEDs? About anything audible (20 Hz to 20 KHz) in the headphones you will not see in the LEDs unless you want to hear dull clicks in the headphones.

Ron
 
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