What do you need to create a negative output on a PWM output whenever the device is off?

Thread Starter

Shawn0431

Joined Feb 24, 2020
4
I am wanting to be able to simulate a square wave alternative current where I can change the average output voltage from - 12vDC to +12 vDC. This would be to control 2 white LEDs of different colors temperature hooked in opposite polarity so that I can have complete control of the color temperature
 

jpanhalt

Joined Jan 18, 2008
11,088
If I understand your question, either of these options may do what you want.

Option 1 (switching transistors +RDL):
1582612382896.png

Option 2 (RDL):
You can also eliminate the mosfets to give simple resistor-diode logic (RDL). Input would be at the junction of R1 and R2. The logic would be reversed. That is, INPUT low = LED1 on & LED2 off; INPUT high = LED1 of f& LED2 on.
 

Thread Starter

Shawn0431

Joined Feb 24, 2020
4
If I understand your question, either of these options may do what you want.

Option 1 (switching transistors +RDL):
View attachment 199923

Option 2 (RDL):
You can also eliminate the mosfets to give simple resistor-diode logic (RDL). Input would be at the junction of R1 and R2. The logic would be reversed. That is, INPUT low = LED1 on & LED2 off; INPUT high = LED1 of f& LED2 on.
Thanks, I think this helps, I'm new to electronics so I really appreciate your help
 

Alec_t

Joined Sep 17, 2013
12,160
What are the specifications of the LEDs? Although the arrangements above would be fine for low power LEDs drawing 20mA or so, high power LEDs would require circuit modifications.
 

ebeowulf17

Joined Aug 12, 2014
3,282
Planning on using some prebuilt led strips, so I don't know the exact draw but it would be likely 1-2 amps
Can you upload datasheets for, or just share links to, the strips you have in mind?

For some reason your first post had me imagining that both different kinds of white LEDs were built into the same strip, wired in inverse parallel with each other. Maybe I was misunderstanding, or just adding too many of my own guesses. Anyway, if the two different LED types are in separate strips and can be controlled independently, then you have much simpler options. However, if they're bound together in a single strip in the arrangement I was imagining, then reversing current flow as you originally alluded to would be the only solution, and that requires a more complicated circuit than the one posted above.
 

Alec_t

Joined Sep 17, 2013
12,160
There are numerous PWM-controllable LED drivers available. A couple of those plus a logic inverter would enable progressive dimming of one LED strip and simultaneous brightening of another strip.
 

Thread Starter

Shawn0431

Joined Feb 24, 2020
4
I suspect I was overthinking this project, it sounds like you've simplified it for me, thanks. But I was still wondering about an inverse parallel hookup. But you've helped a lot already, I believe this is all I needed
 
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