Can we PWM an LED backlight on LCD module

[Ioannis]

Without knowing the specs of the LED's is not easy to say if it is OK to drive the LED string with 7V instead of with 5V as it was designed initially, even with PWM control.

Besides that PWM may stuck in the ON state and burn everything...

Ioannis

[Demon]

... PWM may stuck in the ON state and burn everything...

That is my biggest concern with this plan.


My design now has 3 enclosures, with power being fed into the center unit. I'm now thinking of using 3 separate voltage regulators; one per unit.

That way each 7805 doesn't get as hot as a single device trying to feed all three. Less complicated (less parts, simpler circuitry) than trying to "cheat the system" so to speak.

[Ioannis]

Why not use SMPS? No heat generated, no heatsink needed.

Unless you need a clean +5V for ADC purposes. In all my cases though, a switching did not make any difference in the ADC.

Ioannis

[Demon]

(post removed, because I can't tell the difference between a circuit that provides power to PIC, and a circuit that provides power while relying on PWM from a PIC)

[Demon]

I'm currently using these buck converters to drop from 12V from wall adapter down to 5V:

https://www.amazon.ca/gp/product/B0B5GQTS64/


These go for $2 each and they are only rated at max 3A with warning to remain under 2.5A.

[Ioannis]

I would not trust those chinese modules for serious projects. Rather design your own based on the TI or Microchip App. Notes for you specific needs.

The modules are just bad copies of western know chips with too cheap inductors and capacitors.

From various module test I did, some were so bad that on power up they just burned(!) others worked ok with a lot of noise and ripple, and all those that worked are way to lower on power output in relation to the advertised power.

Ioannis

[Demon]

...The modules are just bad copies of western know chips with too cheap inductors and capacitors....

A lot of those converter circuits look like they were done in some cave. This one looks surprisingly well done:

https://www.aliexpress.com/item/1005001629723875.html


The 5V pro variety comes down to $0.69ea in packs of 20.

I'm going to look for those app notes.

[Demon]

I would not trust those chinese modules for serious projects. Rather design your own based on the TI or Microchip App. Notes for you specific needs. ...

Well, that's disappointing. I looked only at Mouser, the IC alone is over $6 and most of the discrete components are not available. I don't know enough if I can replace them with components.

8V–24V to 5V/3A Buck Converter, through-hole, Page 7

https://www.microchip.com/content/da.../AN15-APID.pdf


And the SMD designs had a LOT less power (my first choice, to have them fully assembled by JLCPCB). Microchip's app note dates from March 2001, gonna check out TI...