When you switch power supply amplifiers, laboratory and other PS in the network there is interference caused by triggering currents of transformers, charge currents of electrolytic capacitors and the start of powered devices themselves. Outwardly, this interference manifests itself as a “blinking” light pops and sparks to an electrical outlet and electrically – this drawdown line voltage, which can lead to failure and instability of other devices that are powered from the same network.
In addition, these inrush currents cause burning of contacts of switches, power outlets. Another negative impact of inrush current – rectifier diodes at the start of this work by the current overload and could be damaged. For example, the inrush current charging the capacitor 10000uF 50V can reach more than 10 amps. If the diode bridge is not designed for this current operating environment may bring the bridge down. Especially strong inrush currents seen at a power 50-100W. For these power units offer the starter.
When you enable the network adapter current limiting resistor starts through R4. After some time needed for its start, capacitor charging and starting load resistor shunted by relay contacts and the power supply output to full capacity. Closing time is determined by the capacitance of the capacitor C2. C1D1C2D2 elements are transformerless power supply for control circuit relay. Zener diode D2 plays a purely defensive role, and an intact control scheme may be missing. Relay BS-115C-12V, was used in the scheme may be replaced by any other relay contacts with a current of at least 10A, with the selection of diodes, a capacitor C1 and the choice of transistor VT1 on voltages, high voltage relay. Zener diode D3 provides hysteresis between the voltage on and off switch. In other words, the relay will turn sharply, but not smoothly.
The capacitor C1 determines the current of the relay. In case of insufficient current capacity of the condenser must be increased (0.47 … 400 … 630V 1uF). In protective wrap for the capacitor is desirable to put on tape or shrink it up. Fuses are selected on the two-times the rated current of power supply. For example, for a 100W power supply fuses must be current on 2 * (100/220) = 1A. If necessary, the scheme can be complemented by a network balanced / unbalanced filter on after the fuses. Connection with the case, which is present in the scheme can be regarded only as a common wire to connect the tester. In no case can it connect to the chassis device, display it on the general wire-line filters, etc.