Electronics > Beginners

Power sequences

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Zero999:

--- Quote from: Chasm on January 26, 2011, 06:12:45 am ---The aux. voltages are generated from a 5V supply.
A comparator is also a nice solution, and even cheaper than the power sequencer. ;)

Another transistor, FET or other chicken food is not a problem.
--- End quote ---
Then you need to additional components: connect the emitters to all of the PNP transistors together and connect the 5V input of each regulator to the collector of the appropriate transistor.

The formulae for calculating the timing can be found on Wikipedia under RC circuit and potential divider. I would remove the supply voltage from all the derived equations as it'll make it easier to calculate.

You can of course get power supplies with enable/disable pins and use RC circuits but the LM399 and PNP transistors are so cheap, they might cost less and are certainly cheaper than an additional microcontroller.

Another option is to use an astable multivibrator (couple of logic gates, Schmitt trigger oscillator, 555 timer etc), a CD4017 and some thyristors which is more complicated but you can have up to 10 outputs using only two ICs. The diodes are only requited if the voltage supplying the load is greater than Vdd. This circuit is also better for higher voltages.

Chasm:
While a 555 solution would get me into the contest I think I keep it to something a bit more practical. Especially since I'm not into the run for a lifetime supply of LCD's. ;)

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