Making switching NPN with PNP

[crazybuoy]

There is a small circuit schematic attached where I am using voltage regulator 7812. I input 24VDC and 12VDC comes out from OUT pin. I want to make switch off & on NPN transistor with 12VDC buy using PNP transistor before NPN. And I will use PC printer port to provide the 1 & 0 pulse of 5VDC then how I should wire the circuit I want to just get the idea. Or is there any other way to do the same?

 

[ericgibbs]

There is a small circuit schematic attached where I am using voltage regulator 7812. I input 24VDC and 12VDC comes out from OUT pin. I want to make switch off & on NPN transistor with 12VDC buy using PNP transistor before NPN. And I will use PC printer port to provide the 1 & 0 pulse of 5VDC. I want to just get the idea. Or is there any other way to do the same?

hi,
You can use a npn to switch a 12V signal line.
Connect the npn base to the printer port via a 330R resistor and connect for example a 2k2 resistor to the collector to +12V.
Is this what you are asking.?

 

[Boncuk]

As far as I know the parallel port is active with data signals high.

Here are two suggestions for a quick power disconnect using the parallel port.

Boncuk

 

[crazybuoy]

I have tried the following attached circuit in the same structure having fixing the components on a paper card. The real schematic is also attached. I am testing the switching of TIP42 by attaching + probe of voltmeter with collector of TIP142 and – probe of voltmeter with – of power supply. It showing always 24 volt on both switch on & off. I think at switch off, it should show zero volt at voltmeter. Please tell me where I am wiring wrong in paper card. And also tell me the method of testing switching process.

 

[audioguru]

Your new circuit is missing a resistor between the collector of the PNP transistor and the base of the TIP142 darlington transistor.
I wish you kept all your questions about your stepper motor driver circuit in a single thread because in this thread its current is not mentioned.
The value of the missing resistor depends on the stepper motor current in the TIP142 darlington transistor.

 

[crazybuoy]

I have try again it by changing the values of resistors in the following way as changed in attached circuit. I am testing the switching of TIP42 by attaching + probe of voltmeter with collector of TIP142 and – probe of voltmeter with emitter of TIP142. At 0 pulse from parallel port, voltmeter show 24VDC and at 1 pulse it show 12VDC. I want to make it show closer to zero volt at 1 pulse. So how to edit it to do so?

 

[audioguru]

I made a real schematic for you.
A transistor does not work properly if you connect its collector and emitter pins backwards. Its datasheet shows which pin is which.

Simply measure the voltage at the collector of each transistor to see which one is bad.

A voltmeter cannot measure the voltage of pulses.

EDIT: I thought my post didn't work so I posted it again. Then I found that my first post was on the other website. It is a nuisance to see exactly the same thread on two or three different websites.