Panasonic Base Power Supply

I have setup a Panasonic KX-TG8424EB 4 set cordless telephone system at home. All telephone Bases use a 6v power supply. 

I have managed not to use the chargers on the phones and instead installed 7v solar panels, which is enough to charge the individual phones during the day. Details can be found here.

However, the Base charger needs to be always on since it needs to receive and transmit the telephone conversation. 

I discovered that the Base station cannot use the same 12v supply rail as the router (through which the telephone system is being received). I therefore needed an isolated power supply for the base station.

I found the below DC Converter isolator online. It receives a maximum of 12.6v and outputs (totally isolated) 12v. This device can handle 250mA working at an efficiency of 75%. I opted to parallel two isolators instead of one to get more current output. 

The below circuit basically needs a 12v-24v input from the house batteries and outputs an isolated 7v supply for the base unit. 

Circuit Description:

The circuit is pretty easy and straightforward. The input is limited to 12v using the U1 7812 voltage regulator. During the day when the 12v batteries are charging, the voltage may even go up to 14v enough to burn the isolators so better safe then sorry! The 7812 voltage regulator will always maintain the input voltage to the isolators at 12v.

Output from the isolators is fed to a 7808 voltage regulator where it is further smoothed and fed to the base unit.

Parts List:

D1, D2 - 1N4001

D3 - Green 3mm LED

D4 - Red 3mm LED

U1 - 7812

U2 - 7805

U3, U4 - HDN3-12S12A1. Isolated Power Supply Module 12.6v In / 12v Out, 250mA.

R1 - 1K

R2 - 1.5K

C1 - 4700uF 25V

C2, C3 - 2200uF 16v

C4, C5 - 0.1uF

The pictures below are showing the finished circuit. Notice that both voltage regulators are fitted to a heatsink.