A practical novel electronic load-limiting automatic controller

Electronic load-limiting automatic controller (hereinafter referred to as the controller) applies to AC 50Hz, operating voltage AC22OV control circuits, so that the system according to a predetermined power supply. When the electrical load exceeds the specified range of values, the controller automatically cut off the load power. When the load is restored to the set power value, the load power can be automatically connected, thus realising the automatic monitoring and control of the electrical load. The appearance of the controller adopts the DZ47 similar structure, and with the DZ47 small circuit breaker parallel installation supporting the use of. The panel is equipped with light-emitting diodes to indicate the monitoring of the controller’s working status: when the indicator is green, it means that the load power supply is connected to the operating state; when the indicator is red, it means that the load has been cut off, and the load limiting controller has been started to work.

Working Principle

Due to the small external size of the controller, coupled with the small internal load, RC resistor-capacitor buck is used to provide power to the controller. The capacitance parameter values are mainly determined according to the internal load of the controller. The main loads inside the controller include: internal high-power conversion relay (DC24V, P = O.93W), dual-colour LEDs, Ul55 chips, transistors and other devices. The high power relay has the highest load when it closes, and the relay closes with a current of 38mA when the load limiter is in operation. Plus light-emitting diodes and chips and other workload current 12mA, so the power supply to provide 50mA current can meet the normal operation of the controller.

The buck capacitor in this circuit mainly plays the role of capacitance XC to reduce the voltage and provide load current. The value of the capacitance XC can be obtained from (220V-24V)/50xIO3A =39200; where XC = l/ 2 πfC, the capacitance value C = l / 2πfX C is 0.81 μF, and according to the capacitance parameter series can be selected as 0.82 μF. When the controller is not in use, the drain resistor connected in parallel with it mainly serves as a drain channel for the capacitor. Resistance value is usually selected in 100 KΩ a 1M Ω, power 1W or more.

Here, 555 circuits can be generally summarised into three categories: monostable circuits, unstable circuits and bistable circuits in terms of application and mode of operation. The controller internal 555 circuit monostable to complete the work of load limiting. Usually in the 2-pin terminal for the “high level”, 3-pin terminal V uT = 0 is a steady state; when the 2-pin terminal for the “low level”, 3-pin terminal VOUT = 1 is a transient steady state, and transient steady state time t = 1.1x R12xC5 to determine.

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