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# Transistor problems

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#### EEPS

##### New Member
HI, I am prety new to electronics and whatnot.... I have read all about transistors recently and learned a lot. From what I read, you apply current to the input, then when you apply current to the gate, it lets the input flow through the output. This was great so I went to radio shack and bought some to try and make simple logic gates. After messing around with them, I was getting bad results. Even when I dissconect the current from the input, the current from the gate flows out the output and turns my circuit on! This is not good since my and gate should only turn on when both transistors are on! I have tried both NPN and PNP and neither worked the way I expected! what am I doing wrong? -Thanks :x

It would help us understand you, if you posted a schematic of your circuit. Once we see exactly what you're doing, we can give advice.

There IS notheing else to the circuit it is just the transistor and it turns on when I don't think its supposed to.

transistors

There are different types of transistors. not all of them are based on current. Some transistors are supposed to conduct when there is no voltage applied to the gate, and stop conducting when you apply voltage. Tell us what type of transistor you got (give the number written on it), and we'll tell you how to control it.

EEPS said:
There IS notheing else to the circuit it is just the transistor and it turns on when I don't think its supposed to.

If there's nothing else in the circuit I'm not surprised it doesn't work :lol:

I think you should study the transistor characteristics ,biasing ...etc im not an expert,but I was reading those things b4 I came here and saw ur post hehe...

I have a couple types of transistors that I bought, on them they say:
___
848
2N
4403
___

___
612
MPS
5179
___

___
818
PN
3645
___

2N4403 and PN3645 are general purpose PNP while
MPS5179 is NPN RF Transistor (just use www.google.com
to find datasheets)

And if you are after some digital circuits, don't waste your time
building gates, just buy few chips like 74LS00, few LEDs and resistors and
make sure you have 5V regulated power supply (or use 7805 to
trim it down to +5V)

I am really not, I am only expirementing to understand how these work.

As stated earlier, a schematic would be useful. It is kind of a universally understood method of information sharing among EE's.

Man, if you would post the schematics, maybe I would be able to say something... I'm new to electronics, and without something to look and think on, I can't work it out...

If you are using BJT's , i think you mean something like this

Both switch A AND switch B must be closed to turn on the LED

... and heres another:

Closing either switch A OR switch B ( or both) will turn on the LED.

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