Voltage regulation circuit 12V to 5V in 5A range

[Ioannis]

Switching to MosFet from bipolar, as Richard noted, it will introduce MORE noise because they are faster.

So, do add capacitors (100nF plus 10uF) as close as possible to the Mosfet power supply, taking care of ground loops at the same time.

Ioannis

[richard]

So, do add capacitors

a waste of time until he address' the correct current limiting resistors for each display

if its really 90mA per display then a 1000uF might help a little.
The peak current as it stands could be very high depending on led vf , could be amps , who knows

[Ioannis]

OK, but having a 4.000uF on the 5V rail is too much, isn't it?

Ioannis

[richard]

You seem to be moving the goal posts. One 1000uF at the pnp tranny emitter since all four back lights are parallel driven from that source

[Ioannis]

By "if its really 90mA per display then a 1000uF might help a little" seemed to me that you meant 1000uF per display.

In any case though, the 1084 or even the humble 7805, do not have any problem with large capacitance.

I bet a reverse biased diode, across output/input pin, would be needed to protect the regulator, in case the Reg. input is grounded for whatever reason while the outuput cap is still charged.

Ioannis

[Demon]

...
I bet a reverse biased diode, across output/input pin, would be needed to protect the regulator, in case the Reg. input is grounded for whatever reason while the outuput cap is still charged.

Ioannis

Yup, I saw that in the datasheet.

Haven't done any of the suggestions for the LCDs yet. I'm doing voltage regulator heat tests for now; looking for the best heatsink setup.


This is how I'm running the LM1084-ADJ now:




Black is from the datasheet, red is my adjustments.

[richard]

Haven't done any of the suggestions for the LCDs yet. I'm doing voltage regulator heat tests for now; looking for the best heatsink setup.

if you solve the backlight issue then you will most likely find the wall warts simple smps are not the problem and the regs and heatsinks are unnecessary

[Ioannis]

The LCD datasheets note that the backlight is 5v at 90mA, isn't it?

So I understand that no current liminting resistor is necessary, as it is included on the LCD board.

Ioannis

[richard]

So I understand that no current liminting resistor is necessary, as it is included on the LCD board

you may be correct but that does not explain why the backlights cause so much noise.
it would be a 2 minute job to apply 5v to the backlight and measure the current .[i would used a cc regulated ps just in case]
i have never come across an lcd of that type with anything onboard to limit led current.