Simple transistor switch

Techno10 said:

This project is using the parts from a recordable greeting card to drive two motors that can run off a 9v battery. This greeting card also has a moving part that is a small flat motor, so I cut the motor off and measured the voltage 1.2v. I need that voltage to turn on a transistor which will turn on the 9v for the motors. So I practice with a 1.5v AA battery connected to the base of a transistor and it works, but only turns the motors slowly, if I hook up a 9v to the base then the motors will turn fast like they should. The transistor is a NPN NTE47. Is this the wrong transistor or what?

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Mike odom said:

The NTE47 is a good transistor. Very high gain. But it only has a 200mA collector current.

If you're trying to sink the motor( -) to ground, then maybe you have too big a resistor on the gate input to the transistor (especially if it works with 9v). Since you hooked up 6x (9v vs 1.5v) the voltage and it worked, try 1/6 the resistor with the 1.5v input.

Your base current will be (1.5v - .7v) / R. This current needs to be about 1/10 your collector current.
If you can get it to run, let it run for a while and see how hot the transistor gets.

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Techno10 said:

I don't have a resistor on it, maybe if I used a different transistor with a higher collector current?

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