Here I have given you guys my simple ckt. I couldn't find out the fault.

The problem is that it doesn't work. This ckt is interfaced with the computer, when I have given the appropriate signal to the input the motor doesnt work. I'm using a parallel port interface from MATLAB, and wiring pin 2 and 3 for the input to the ckt.


I have used 5V as a Vcc, and Q3 and Q5 and SL100 and Q4 and Q6 SK100, coz I dont want to fry my computer using high voltage Darlington Amplifiers.

So what am I missing here???? :? :?:

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Using the transistor emitters to feed the motor isn't a good idea, you lose far too much voltage - as the transistors are darlingtons each one drops a minimum of 1.4V in that mode, so with your 5V supply you only have around 2V or so to feed the motor. A simple solution would be to increase the voltage to 12V or so - you can easily test it without connecting to the computer, but it shouldn't affect the computer anyway.

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It looks like when Q1 is on, there is nothing limiting the base current of Q4.
Similarly when Q2 is on, there is nothing limiting the base current of Q6.

Bye bye Q4, Bye bye Q6.

JimB

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Q4 and Q6 are emitter followers. Emitter followers don't need base current limiting resistors. The base current will equal the emitter current (which is determined by the load resistance and the supply voltage) divided by (beta+1).

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Ron

 

Agreed.
My mistake.
JimB

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