# PWM positive to negative

#### guiwarriors

Joined Nov 16, 2021
3
Hello I am new here, I need you regarding a montage that I have to make. I have an input PWM signal which varies from 0 to + 15V. I have to find an electronic assembly in order to obtain at output a PWM signal varying from 0 to -10V. I have a -10V power supply. However, I have the constraint of only use bipolar transistors. Did you know a montage allowing me to do this? thanks in advance

#### AlbertHall

Joined Jun 4, 2014
11,704
How much current do you need from the output PWM?
What frequency is the PWM?

#### crutschow

Joined Mar 14, 2008
28,551
I have an input PWM signal which varies from 0 to + 15V. I have to find an electronic assembly in order to obtain at output a PWM signal varying from 0 to -10V.
Are you referring to the variation in the PWM duty-cycle or the variation in its averaged DC voltage?

For the former you could use a PNP transistor.
For the latter, you could use an op amp.

#### ronsimpson

Joined Oct 7, 2019
1,752
Most power supplies do not work near 0V. Most will not work below 2.5V.

Please state input voltage range. (+10 or -10?)
Output voltage range? 0 to -10V
Output current?

#### crutschow

Joined Mar 14, 2008
28,551
Most power supplies do not work near 0V
I think the -10V supply is just for power, not that he wants to control it.

#### Papabravo

Joined Feb 24, 2006
17,615
Hello I am new here, I need you regarding a montage that I have to make. I have an input PWM signal which varies from 0 to + 15V. I have to find an electronic assembly in order to obtain at output a PWM signal varying from 0 to -10V. I have a -10V power supply. However, I have the constraint of only use bipolar transistors. Did you know a montage allowing me to do this? thanks in advance
Does "montage = assembly", and is that the same thing as a circuit?

#### guiwarriors

Joined Nov 16, 2021
3
Thanks a lot for your answers and sorry for my mistakes in english,
I will try to be more precise, I am currently looking for an electronic function allowing me to invert a square wave. I do not have any precision on my input frequency nor on my necessary output current as well as on my input / output impedances. The only thing I know is that it is a square wave varying from 0 to + 15V. Thus, I must obtain a square signal at the output varying from 0 to -10V (level of my power supply) or a little below. So naturally I would have gone for an inverting amplifier but unfortunately my condition is to only use bipolar and mosfet transistors. I have a voltage of -10V as a power supply to help me. Do you think this function is achievable with only negative supply voltage? If yes, do you know a circuit to do this? Thank you very much for your help

Recapitulation :
Input voltage range : 0 to +15V
Signal shape: square
Input frequency : ?
Input impedance : ?

Ouput voltage range : 0 to -10V
Signal shape: square + no dephasage between entry and exit
Output frequency : same frequency as input
Output impedance : ?

#### AlbertHall

Joined Jun 4, 2014
11,704
When the input is 15V should the output be 0V or -10V?

#### Irving

Joined Jan 30, 2016
2,422
Like this?

#### guiwarriors

Joined Nov 16, 2021
3

#### Irving

Joined Jan 30, 2016
2,422
Exactly, thank you very much Irving ! I still need to learn a lot of things.
You're welcome.

It may need tuning for your specifics, eg frequency, driving source, output load, etc. but feel free to shout out when you know more.

#### crutschow

Joined Mar 14, 2008
28,551
Below is a slightly simpler alternate design using a PNP transistor in a grounded-base configuration:

Last edited:

#### Irving

Joined Jan 30, 2016
2,422
Below is a slightly simpler alternate design using a PNP transistor in a grounded-base configuration:

View attachment 252915
Nice, but it does a phase inversion that the TS didn't want. He wanted +15v -> -10v, yours does +15v -> 0v, 0v -> -10v, though it might be OK if his eventual need is edge driven.

#### absf

Joined Dec 29, 2010
1,968
Cool. Two ways of doing it to one problem. How would you do it with a LM393?

#### crutschow

Joined Mar 14, 2008
28,551
How would you do it with a LM393?
Why would you want to use an LM393 when you can do it with one transistor?