The protection circuit is composed of 555 as the core, and has the advantages of small volume, low cost, high reliability of delay protection and the like. Its circuit is composed of step-down rectifier circuit, incoming delay circuit and relay control circuit. As shown in the figure, the step-down rectifier circuit is composed of step-down capacitors C1 and R1 and full-bridge circuits QD and C2. After R2 and DW are regulated, a DC voltage of +9V is output for the latter circuit to operate as the operating voltage.
555 and C4, R3, etc. form a monostable delay circuit. When the refrigerator is powered off and then called, the charge on C4 will not be abrupt, so the +9V voltage is applied to the one-shot circuit, and the 555 pin 2 is high, so that the 555 is in the reset state. Thereafter, as C4 is charged by R3, when the lower capacitor plate of C4 is charged to 1∕3VDD, the one-shot circuit is triggered by the low level and turned over, the output of the 3 pin turns to the high level, and the VT1 is saturated. The relay K is sucked, its normally open contact K1-1 is closed, the refrigerator socket is energized, and the refrigerator starts running. The delay of the refrigerator from the time of the call to the run, and the delay of the monostable circuit, the size depends on the charging time constant of the R3C4.
RF is any frequency within the electromagnetic spectrum associated with the propagation of radio waves. When RF current is supplied to the antenna, an electromagnetic field is created, which is then able to propagate or propagate through space. Many wireless technologies are based on radio frequency field propagation. These frequencies form part of the electromagnetic radiation spectrum.
RF coaxial cables are cables that transmit electromagnetic energy in the radio frequency range. Radio frequency cables are indispensable components in various radio communication systems and electronic equipment. They are widely used in wireless communication and broadcasting, television, radar, navigation, computers and instruments.
RF coaxial cable is the most commonly used construction type. Because the inner and outer conductors are in concentric positions, the electromagnetic energy is limited to propagate in the medium between the inner and outer conductors, so it has significant advantages such as small attenuation, high shielding performance, wide operating frequency bandwidth and stable performance. Typically used to transmit radio frequency energy from 500 kHz to 18 GHz. At present, there are two types of commonly used RF coaxial cables: 50Ω and 75Ω RF coaxial cables. The characteristic impedance of 75Ω RF coaxial cable is often used in CATV network, so it is called CATV cable, and the transmission bandwidth can reach 1GHz. At present, the transmission bandwidth of commonly used CATV cable is 750MHz.
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