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Old 12th Feb 2005, 21:00   #1
foxx
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PNP NPN and other questions

hey I got a question about this schamatic

If I remove the blue(and replace with a proper five volt power supply from molex) I can remove the green right?
And what is the point of the transister in the red?
and whats the difference between the transister in red and the others?
Isnt it because one is PNP, and the other is NPN?
Couldnt I just use three of the non circled transisters?
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Old 12th Feb 2005, 22:05   #2
alcedes
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Quote:
Originally Posted by foxx
and whats the difference between the transister in red and the others?
Isnt it because one is PNP, and the other is NPN?
Couldnt I just use three of the non circled transisters?
The output of the circuit can be negative or positive instead of just high and low. Both a PNP and NPN transistor are being used so that there is a control mechanism to cause current to flow in either direction.

But you're right, T2 is NPN while T3 is PNP.
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Old 12th Feb 2005, 23:55   #3
foxx
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Ok still confused, but I built the circuite with my modifacations and it worked so thanks enywho.
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Old 13th Feb 2005, 10:17   #4
SteveyG
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The output to pin 1 of the serial lead must be logic high or logic low. The two transistors T2 and T3 do this. If T1 is off, T2 will be on, and T3 will be off. This will make Pin 1 logic high. If T1 is on, T2 will be off, and T3 will be on. This makes Pin 1 logic low.

You cannot replace T3 with an NPN transistor. Doing so would cause a short circuit accross your power supply every time T1 turned off.
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Old 13th Feb 2005, 12:32   #5
cpemma
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That T2/T3 configuration is a common method of sharpening & voltage-raising pulses to drive a non-logic-level power mosfet from logic circuits.
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