Food magically 12V with a different PSU?

The scheme is as follows:
consumer - car (12V) power supply 220V.
The 12V supply from the PSU 300ватт (includes "Assembly" filed phase on an additional device, in our case PSU 220V to 12V - 300ватт). But when turned off unit this PSU is turned off and, accordingly, lost settings, etc. It is necessary to organize constant power and through the control (there is such a + on the radio) give +12 when there is a launch unit. So 2 BP. Whatever one feeds the other switches.
Question - the idea of 2 different BP - we need to unite the earth ? specify if I do not understand.
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*PSU - Power supply Unit.
April 4th 20 at 00:44
2 answers
April 4th 20 at 00:46
Solution
Usually, the power supplies are galvanically isolated from the network. The second PSU that connects to the red wire of the radio (memory) can be very thin. There are 100-200 milliamps high, in the standby mode. Although when connected in the car, for example, yellow wire to turn in the ignition circuit, or in the winter for a couple of days the battery is average, strange plants, so that then not to have. Earth (negative supply) to connect to that voltage was considered from one level of potential.
Thank you! - modesto.Bailey commented on April 4th 20 at 00:49
April 4th 20 at 00:48
For car radios it is convenient to use a computer power supply, computer power supply has a special +5vsb output, there is 5 volts even when power supply is turned off (the main thing that the outlet was plugged).
You can put the boost Converter output 5vsb and raise to 12 volts, those 12 volts on the yellow wire of the radio.
will consider the future, but here again the problem is that input 220V disappears. Ie we need "support" source. And when turning on 220V from the "unit" is the inclusion of music, light and so on. - modesto.Bailey commented on April 4th 20 at 00:51

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