PIC: CA 7Seg from 12V

[hantto]

Hello!

In order to save regulator dissipation, would this work? To turn segments on and off the TRIS register would be used. Doesn't that turn the pins from sink/source to high impendace and vice versa?

Anything I didn't think of?

 

[Nigel Goodwin]

Hello!

In order to save regulator dissipation, would this work? To turn segments on and off the TRIS register would be used. Doesn't that turn the pins from sink/source to high impendace and vice versa?

Anything I didn't think of?

Yes, the PIC pins have protection diodes from the pin to Vdd and to Vss, so the bottom of the 330 ohms will never go above 5.7V, so all segments will be permanently lit. You could do it with open-collector driver transistors between the PIC and the resistors.

 

[hantto]

Hello!

In order to save regulator dissipation, would this work? To turn segments on and off the TRIS register would be used. Doesn't that turn the pins from sink/source to high impendace and vice versa?

Anything I didn't think of?

Yes, the PIC pins have protection diodes from the pin to Vdd and to Vss, so the bottom of the 330 ohms will never go above 5.7V, so all segments will be permanently lit. You could do it with open-collector driver transistors between the PIC and the resistors.

Very true. Thanks for pointing that out 8)

 

[eblc1388]

Or fit a 7V zener diode between 7-seg LED CA and +12V.

 

[Roff]

Or fit a 7V zener diode between 7-seg LED CA and +12V.

And shift the dissipation to the zener?

 

[eblc1388]

For a certain amount of LED current, the dissipation has to go somewhere. If it is not in the regulator, then it will be in the transistors, resistors or zener.

So in a sense reducing dissipation is not possible. Or one can try PWM on the output PIC pins.

 

[Roff]

For a certain amount of LED current, the dissipation has to go somewhere. If it is not in the regulator, then it will be in the transistors, resistors or zener.

So in a sense reducing dissipation is not possible. Or one can try PWM on the output PIC pins.

Hantto's original idea was to use 12V instead of 5V on the display, thereby bypassing the regulator. He was going to do this by PWMing the PIC outputs, but Nigel pointed out that they will conduct at 5.7V even when they are tri-stated. I don't think he expects to eliminate the power dissipation - he just wants to keep it out of the 5V regulator.

 

[audioguru]

I use PWM to reduce power dissipation in my Ultra-bright LED Chaser projects. They are very bright but their power dissipation is so lowww that they don't even have on-off switches.
https://www.electronics-lab.com/projects/games/003/index.html
https://www.electronics-lab.com/projects/games/004/index.html