When you turn on power supplies amplifiers, laboratory and other BP occurs in the network interference caused by inrush currents transformers, the charge currents electrolytic capacitors and start themselves PDS.
Outwardly, this interference manifests itself as "blink" light, clicks and sparks in network sockets, electrically - drawdown mains voltage, which can lead to failure and unstable other devices that are powered from the same network. In addition, these inrush currents cause the erosion of the switch contacts, network sockets. Another negative effect of inrush current rectifier diodes in then start working with a current overload and can fail. To example, the inrush current to charge the capacitor 10000mkf 50V can reach 10 and more amps. If the diode bridge is not rated to handle the current, such conditions work can bring the bridge down. Particularly hard starting current visible with the power of more than 50-100W. For these power supplies offer the softstarter.
When turning on the power supply starts in current limiting resistor R4. After a time required for its start, charge the capacitor and start the load resistor shunted relay contacts and the power supply output at full capacity. Time inclusion is determined by the capacitance of the capacitor C2. Elements C1D1C2D2 are transformerless power source for the circuit control relay. The Zener diode D2 is playing a purely defensive role, and when healthy control scheme may be missing. Relay BS-115C-12V, used in the diagram can be replaced by any other relay current contacts not less than 10A, with the selection of the Zener diodes, capacitor C1 and the selection transistor VT1 at a voltage greater than the voltage the relay. The Zener diode D3 provides hysteresis voltage between included and off relay. In other words, the relay turns on abruptly and not gradually.
The capacitor C1 determines the current to activate the relay. In the case of insufficient current capacity of the capacitor must be increased (0,47 1uf… 400…630V). Defensively the capacitor is advisable to wrap electrical tape or put on the heat shrink tubing. Fuses are selected at twice the rated current PSU. For example, the power supply 100W fuses shall be current 2*(220/100)=5A. If necessary, the scheme can be supplemented with a network of symmetric/asymmetric filter included after the fuses. The body connection that is present in the diagram, could be viewed as a common wire to connect the tester. No never connected with the chassis of the device, bring it to a total wire-line filters, etc.
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