Discussion in 'The Projects Forum' started by yourfriendahsan, Jul 17, 2008.

1. ### yourfriendahsan Thread Starter Member

Jul 5, 2008
11
0
I am a beginner in electronics, i just know about capacitors, diodes, resistors, etc and their working currently i am researching upon transistors.

I am noob about transistors, i have searched many tutorials and everything just to know what transistors are but cant find anything good.

lets come to the point, I wanna know about the working of transistor with reference to the image posted below, i just wanna know what is the transistor doing in this circuit.

plz explain with reference to direction and current and all, and make sure the details should be simplest

http://img401.imageshack.us/my.php?image=car912cp1.gif

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2. ### SgtWookie Expert

Jul 17, 2007
22,201
1,809
It's a voltage follower.

The 560 Ohm resistor supplies current to the Zener diode, which has a breakdown voltage of (approximately) 9.1v. This can vary somewhat from diode to diode.

Unfortunately, Mr. Van Roon is in error about the output voltage. There is a drop of roughly 0.63v to over a volt between the base and emitter of the transistor, depending upon the load at the output. If the voltage at the emitter falls more than about 0.63v below the Zener voltage, it begins to conduct, most of it's current coming from the collector. If there is no load, then the output voltage could actually rise to within perhaps 0.4v of the Zener's voltage, due to very small leakage current.

But if there is a substantial load (say, 100mA) the output voltage will drop as the transistor has to conduct more.

The ECG184 isn't available anymore that I know of. A 2N3055 might be substituted. Better to just use a voltage regulator; it would be lots cheaper and more accurate.

3. ### studiot AAC Fanatic!

Nov 9, 2007
5,003
523
Why do you want to know?

Are you trying to repair something or make something?

Either way this circuit will self destruct if the output terminals are shorted as it has no protection.

Wookie is correct in suggesting that the zener should be closer to 10 volts than 9.

Also there should be a reasonably high value (say 10K) resistor across the output.