Secondary power supply switch

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#1
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Hello!

The situation is this: I have an electronic door lock, that needs a bigger voltage kick to open, but after the kick, it can hold open with much less power.

The initial power needed to open is 9V @ 1,125A, but after that an 1V8 225mA is more than enough to hold the lock open.
I need to reduce power consumption (and heat generation), because after a few minutes the lock would overheat.

For this I tried using a huge capacitor (10 000uF) which deliveres the kick, and after that i reduce the voltage with a resistor (100Ohm, 5W). This works, but generates very much heat (the resistor dissipates around 0,8W, become really hot, even in open air, cannot put the circuit in a box with no ventillation.)

I would like to build a switching power regulator that generates 1V8 voltage, I could do this using for ex. a maxim MAX5035D.

But I would need a circuit that automatically switches between the power source once the capacitor has depletet its energy. (voltage drops below a certain voltage, not necessarily 1V8).

Can anyone help me with any links tips, or schematics on this?

Regards,

axos88

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two diodes, cathodes together go to the lock, one anode to the regulator, the other anode to the capacitor.

CAP --|>|----|
             +-------> lock
1V8 --|>|----|

The diodes will drop around 0.7V so the 1V8 need to be higher to account for this.

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Something like this?

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axos88