Toggle LOW on +12v for sleep circuit - PNP vs NPN

Using Arduino General Electronics
1

I have a pin on this amplifier on a chip, that must be toggled low, to engauge sleep / energy conserve state. The voltage on the amplifier "sleep" pin is 12v. I do not want to connect this to my controller pins, fear of damage.

I can use a 2n2222 NPN transistor to toggle a ground to that circuit, and cause the amp-chip to enter energy conserve mode. I feel - that by using power to toggle a sleep circuit defeats the purpose of saving energy.

So I try 2N3906 PNP transistor (I really have little experience with PNP). I can't understand how that circuit pulls the energy to ground. If I 10k resistor SLEEP-TO-GND, it enter sleep mode (which is what I want it to do). This line is connected to "E" and the "C" +12V. Once I put any value resistor from base to ground (or to +5v) - the PNP toggles the circuit ON (collector pin is HIGH +12V).

I hope I described my issue, I know to someone else it's probably an easy answer, but I'm frustrated now after hours and can use some advice, please.

2

The sleep pin should be an input, that is, high impedance. If it was low impedance, it would cause a short circuit if you pulled it LOW, regardless how. Connect it to ground over a 1kOhm resistor. That would limit the current to <20mA even if it had 12V. If you meassure a significant voltage over the resistor, than something is wrong anyway and no transistor will help you with that. If not, go ahead. Still, leave the resistor in. It shouldn't hurt and protect your MCU if there where ever real 12V on that pin. If your MCU has clamping diodes (which it probably has), that is always enough. If not, you might still run into problems if the amp suddenly became an output and your MCU pin was set to input.

3

I am trying to do my best to learn how to make my circuits safe.

I ended up triggering ground through an opto isolator, and pull pin to ground. Probably more circuit than I needed, but it works.

4

Corrected

DocStein99:
Probably more circuit than I needed, but it works.

5

DocStein99:
I am trying to do my best to learn

Then learn about the impedances and what could happen ...

how to make my circuits safe.

... instead of randomly throwing useless components onto the board.