Switching negative voltages with a transistor (revisited)

[etofbsg]

Hi, there is a thread from 2016 (identical headline), which handles my question, but the solutions don't work for me:
I like to switch -12V or -15V with up to1.5A at 50-200Hz.
I've got two power supplies (5V and 12V) and connected 5V-minus to 12V-plus, thus having +5V ... GND ... -12V
2016 suggestion in post 8 by spec was to use BC546 & TIP55. The first one is not at hand while the darlington seems to be discontinued. Hence I used BC547 and TIP120. But it does not work...there is nearly no reaction on the "-12V switched line" when moving the "mcu output" line from GND to +5V and back to GND.

Question to the experts: Is that expectable, because I chose bad replacement parts? Or should that still work with the replacement parts?
Does anybody have an idea for parts with better availability?
PS: The right side of the schematic with the MOSFETs is also difficult to buy, since these parts are only available at industrial suppliers with horrible shipping fees.

Thank you for your support

 

[Nigel Goodwin]

Post a schematic, a picture of how you've built it, plus how it's connected to whatever is feeding it.

 

[etofbsg]

Post a schematic, a picture of how you've built it, plus how it's connected to whatever is feeding it.

Nigel, I've attached the original schematic of 2016 of user "spec". As I said, I replaced BC546 by BC547 and TIP55 by TIP120.

 

[crutschow]

Below is an LTspice sim of the circuit:
As you can see, the output is going between 0V and -12V.
I didn't have models for the transistors you have, but your circuit should operate similarly.

Double check all your wiring.
What load did you have connected to the output?

 

[Nigel Goodwin]

I'm a bit confused by R1 at only 470 ohms?, that seems far too low.

However, the problem is simple and obvious - the BC546 is PNP (which you need), the BC547 is NPN - and completely wrong.

Post #4 used a BC557, which is PNP

 

[crutschow]

I'm a bit confused by R1 at only 470 ohms?, that seems far too low.

Yes, for Q1 being a Darlington.
Okay for my sim without.

the BC546 is PNP (which you need), the BC547 is NPN

Missed that.

 

[Tony Stewart]

Is your load inductive or just 10 Ohms?