Want to sleep with the music, without fear that the network adapter radio or player will remain plugged in all night? Then manufacture described in the article the power supply, automatically turning off from network when you turn off the load. Or modify the available network the adapter...
When using the apparatus whose power source is made in the form single unit (adapter) inserted into the wall outlet, always comes up the disadvantage is that at the end of use of the apparatus have to get up, to go to the outlet and pull out the power supply. But if you like bedtime to listen to the radio or a tape recorder next to the bed, there the risk to fall asleep and leave the PSU plugged in all night, even if the tape works hitchhiking. While it is not safe - it may happen that you Wake up in the middle of the burned-out apartment.
We offer our readers the power supply will not allow it: the moment when the load will stop consuming current, he will disconnect from the network. If, for example, from it eats the tape with the hitch, then you can safely go to sleep, and if the connected device without hitchhiking or radio, they are just to turn off the power switch unit, and in this case will turn off itself. Agree, it is much more convenient than getting up half asleep and approach outlet.
Schematic diagram samootkryvayuschiesya power supply shown in the figure. It based on a classic stabilized rectifier consisting of step-down transformer T1, rectifier bridge VD1-VD4 and integrated stabilizer voltage DA1. The device is a switch SA1. If you leave it in closed condition, the unit will operate in normal mode all the time. If while running his load switch in position "Off", the unit the power will stay on only as long as the load is drawing current.
As can be seen from the diagram, the load current passing through the silicon diode VD6, creates the a voltage drop of about 0.6...0.7 V. This voltage is sufficient to opening of the transistor VT1 in the collector circuit of which includes a relay K1. Actuating its contacts K1.1 bypasses the switch SA1, and the power supply stay connected to the network. If the load (for example, switch) the current through the diode VD6 is terminated, the transistor is closed and the switch, letting go, unplug the unit from the mains. Diode VD5 compensates for the loss of output voltage due to the input in the output circuit of the diode VD3. HL1 led - indicator connect the device to the network.
In the rectifier unit, you can use any diodes that are suitable for direct current and reverse voltage. Diode VD6 - any silicon that is able to skip (preferably stock) load current, VD5 and VD7 - any silicon thin. Relay K1 - with voltage of not more than 7...8 V, operating current not exceeding the maximum allowable for the transistor VT1 and contacts, designed for switching AC voltage of 220 V. the Switch SA 1 - any compact, capable of switching a voltage of 220 V.
The auto power off function can be given any power supply by typing only three of the diode VD5-VD7), transistor and relay.
Author: S. Kosov, Ryazan