12VDC UPS Project

Hello People,

I try to outline a 12V UPS for my router. The commercial things I see are either to complicate, means have to much functions or they use a relay. I want to build a solid state switch that is faster than a relay. I have a first sketch. What do you think thats the right direction?

The battery has her own BMS it's not in the circuit here. The comparator is the watchdog who activates the switch in case of a power outage. There are a few diodes to prevent return current. A few resistor to adjust the components margins. R4 is a trimm-pot. Works as a pull-down resistor and adjust the threshold for the comparator.

PS: I know. The input voltage has to be higher than 12V.

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dang74 3 days ago

I think you will need second resistor connected to R1 to form a voltage divider. Otherwise I think your comparator will always select the battery. The comparator should also have a bypass capacitor connected to its supply pin.
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dang74 3 days ago

I think you will need second resistor connected to R1 to form a voltage divider. Otherwise I think your comparator will always select the battery. The comparator should also have a bypass capacitor connected to its supply pin.
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JWx 3 days ago in reply to dang74

I think there should be also some current limiting during battery charging - now, when battery voltage is < (12V - Vd4), it would be charged through D4 with possibly big current (even creating fire hazard in case of - for example - battery cell shortage and powerful PSU), but maybe BMS would protect against it?
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