Electronics > Beginners

Power sequences

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Chasm:
Posting in Beginners since this should be simple without my mental block.

A device uses different auxiliary voltages.
They have to be activated in sequence on power up and deactivated in reverse order on power down. No Nothing new there. The device is quite dumb, no special requirements other than the order.

How to realize this, cheap?

tyblu:
What does it need to do, specifically? (What voltages and timing?)

Chasm:
It's a GLCD, it has no strict timing requirements for the sequence.

Vcc -> Vgl -> Vgh (-> Data -> Backlight)
Vcc 3.3V
Vgl -10V
Vgh 15V
Backlight 20V

Psi:
Quick and dirty solution.
You could have a chain of relays so one provides power for the next.
Extra contacts on each relay can switch things on in order.
The time between them will be small, just as long as the contacts take to move state.

Ideally you'd want to switch each power connection on with a transistor or fet using different resistor+capacitor changing rates, or a mcu.

Chasm:
Too much current. =)

The LCD should draw less than 300 micro A on Vgl and Vgh. I want to spec the bost/buck converter quite close and as cheap as possible.
That is the plan, for some reason one implementation uses a LT1172CS8 - very nice but a 1.25A 5€ regulator is a mite excessive.

I can also switch the voltages with the MCU, another 3 I/O is not a problem but I wanted to get rid of more parts.

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