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alternate power source even in power-off condition

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123vincent

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hello sir/mam
i am using 555 timer for a circuit. But the problem is that the 555 ic should remain energized for 4-5 minutes even when the main power goes off. Can u suggest any circuit which can work as alternate power source when the main power goes off???

Thanks in advance!
 

Hi,
How much current are you drawing from 555 circuit ? If it is only logic inputs, then you can reduce the current drawn by the 555 IC itself by using a 7555 IC and probably use a large capacitor for standby. Else you need to use a standby battery.

Regards,
Laktronics
 

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    123vincent

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thanks for the quick reply. I was eagerly waitin for that. I dont want to use any battery for the alternate power source. Capacitor in discharging mode is a good option. I already used capacitor ; but it discharges very quickly as soon as i connect it to 555. I think may be it is getting discharged through the internal of 555.
But can u plz help me out how to connect the capacitor with 555.
 

Hi,
The way to connect the capacitor is simple, isolate the supply pin of 7555 IC and just connect the capacitor across the supply pin and ground pin of the IC and connect a diode from Vcc supply to the supply pin with its anode to Vcc supply. This will reduce the Vcc supply to 555 IC by the diode drop, so, you may need to increase Vcc to that extent. The main problem will be to assess the total current requirement of the IC and fix the capacitor value considering the self leakage of the capacitor also.

Regards,
Laktronics
 

hello laktronics.........
ur idea worked quite well. Thanks for the suggestion. Hoping to get more of ur advices in other circuits.
With regards,
123vincent
 

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