I am designing a circuit where I want a 14M2 to continue to operate after power is lost. I need, as a minimum, to a) sense that power is lost and then b) switch two latching relays, each relay 5VDC and drawing 20ma for a minimum of 3ms in order to switch. The power to switch the two relays is stored in capacitors between the relays and ground, and the 14M2 will need to switch pins from high to low in order to sink the power from those two capacitors.
I'm thinking LP2951 regulator, 5V at 100mA, max 30V in. I want to put the storage capacitance on the regulated side because I need to save physical space (6.3V caps vs 35V caps). What I would like to know is this -- when the power fails/cut off, will the stored energy flow back through the regulator, or will it remain available for the Picaxe to continue to function for a few moments after the power quits, and how much capacitance do I need to keep the 14m2 working for "long enough" to do the job? I have space for up to 2x1000uF@6.3V.
Do I need special regulator protection due to the unusually large capacitance between the regulator and the load?
Or should I use smaller capacitors charged to 24V upstream of the regulator?
I'm thinking LP2951 regulator, 5V at 100mA, max 30V in. I want to put the storage capacitance on the regulated side because I need to save physical space (6.3V caps vs 35V caps). What I would like to know is this -- when the power fails/cut off, will the stored energy flow back through the regulator, or will it remain available for the Picaxe to continue to function for a few moments after the power quits, and how much capacitance do I need to keep the 14m2 working for "long enough" to do the job? I have space for up to 2x1000uF@6.3V.
Do I need special regulator protection due to the unusually large capacitance between the regulator and the load?
Or should I use smaller capacitors charged to 24V upstream of the regulator?
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