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Topic: Problem using a voltage divider to input a voltage to a low impedance line (Read 3 times) previous topic - next topic

Daanii

I had a problem using a voltage divider to input a voltage (between 0 and 12 volts) to a low impedance signal line. I used a potentiometer as the voltage divider, and as I turned the pot the signal voltage would suddenly jump from around 1 volt to over 10 volts. So that did not work.

My new plan is to use a TIP120 transistor to send the voltage signal. I'll use an Arduino analog PWM output to the transistor's gate, and put ground and +12 volts through the transistor. By varying the output from the Arduino from 0 to 255, I hope to get the whole range between 0 and 12 volts. 

Will that give a good voltage signal on the low impedance signal line?

jackrae

For low impedance driving you'll need the transistor in common-emitter mode (resistor between emitter and ground) with output taken from emitter terminal.  This will limit output signal to around 4.3 volts but one major advantage is that the output signal will be in-phase with the arduino PWM output.  The emitter resistance should be the same as your "low impedance" load (50ohms or whatever)

Daanii

Thanks for the reply. I need to get the full 0 to 12 Volt range on the output line. Is there any way to do that?

Magician

how "low" impedance? 500? 50 ? 1 Ohm? how "fast" voltage has to be set?

Daanii


how "low" impedance? 500? 50 ? 1 Ohm? how "fast" voltage has to be set?


About 50 Ohms. Voltage does not have to be set quickly.

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