# Simple circuit transistor tester

Discussion in 'General Electronics Chat' started by lordeos, Nov 27, 2015.

1. ### lordeos Thread Starter Member

Jun 23, 2015
33
1
Hi all,

currently we are learning how to analyze and understand the working of electronic schema's. I got scheme " simple transistor tester circuit" (as an attachment in this post) which i have hard to figure it out how it works. I can identify and explain some parts of the scheme but the greater picture battles my mind.

If both transistor works (first one "npn" and second one pnp") the LED should flash (alternate between on and off).

- I believe that both transistors should be conducting before the LED goes on; Since the PNP transistor needs to get current out of the base the NPN transistor must be turned on, otherwise the base current from the PNP can't find his way to ground, correct ?
- I don't understand what the capacitator is doing at the bottom; The only thing i can think of is that the - plate of the ELCO charges up to 0.7 V trough the resistor of 330K and then the npn transistor switches on and the + plate of Elco = voltage emitter of the pnp = 3 - 2 (LED) = 1V
- the values of the resistors, especially the 330k is a mystery to me.

Thanks for the help

File size:
1.2 MB
Views:
12

Jun 22, 2012
5,138
767
3. ### lordeos Thread Starter Member

Jun 23, 2015
33
1
Thank you for the help

When i read the article on oscilators at a certain section the autor states "the rise of voltage on the capacitator is being reflected"

Does this mean :

- If the voltage on the + plate rises , the same amount of voltage is also raised on the - plate.
- If the voltage on the + plate goed down , the same amount of voltage also goes down on the - plate.

thx

4. ### lordeos Thread Starter Member

Jun 23, 2015
33
1
To clarify my previous post ...i mean sudden voltage changes