Router UPS
It can be handy to have your phone and Internet router continue working for a while after a power failure for example, if they provide access to a security system. This requires a backup power supply for the router. The version described here consists of a 12-V lead-acid battery and a voltage converter capable of supplying an output voltage in the range of 15 to 30 V. It has built-in protection to prevent excessive battery discharge. This DIY uninterruptible power supply (UPS) operates in standby mode as long as the mains voltage is present. Circuit diagram : Router UPS Circuit Diagram The UPS consists of four parts: a backup detector circuit that monitors the supply voltage from the AC mains adapter, a battery circuit that monitors the battery voltage to prevent it from dropping below 11.8 V, a FET switch between the battery and the voltage converter, and a voltage doubler (inside the dashed outline). To understand how it works, first consider the situation with ...