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Principle and Implementation of Current Relay with Time Limit

With time limit current relay, when the time zone time current relay coil is energized, the delay contacts act instantaneously, and after the coil is powered off, the contacts are set to work in a delayed state. When the set delay is reached, the delay contact The head returns to its original state. Power-off delay type due to its working state (no external working power is required during the delay process) and the control contact pulls in the contact during the power-off delay process (the normally open contact should be turned on and should remain connected) State; the normally closed contact becomes open, and should be kept open.) The speciality of conversion (as opposed to the normal working state of the time-delayed time-band current relay contact of the conventional power-on delay) to meet its control requirements. Power-off delay time-band current limit relay is composed of early separation devices (low delay accuracy, short delay time); corresponding programmable timing integrated circuits or CMOS counting frequency division integration are used to complete the delay, compared with It has the characteristics of high delay accuracy and long delay time. This meets the control occasion of power-off long delay.


Typical circuit


The overall composition of the time-limited current relay includes the time-limited current relay power supply (stepped down, rectified, and filtered) to provide a time-limited current relay with a built-in instantaneous electromagnetic band time-limited current relay and a 2-winding latching R reset coil. Part (for powering off the delay part and 2 windings blocking type S setting coil to work); delay working part (programmable timing integration or CMOS counting frequency division integration); driving part;


The power-off delay type time-limited current relay composed of V2 P-channel field effect transistor, V3, V4 triode and time-limited current relay is shown in Figure 2. As follows: After the terminal is connected to the working power, C1 ~ C5 all complete the charging process according to their circuits (the charging time should refer to the time specified by the product). At the same time, the internal 2 windings are latched with the time limit current relay R and the reset coil is energized (the switching contacts 4 and 6 in the virtual frame are turned from the power to the off state and 4 and 8 are connected), and the corresponding external contacts are switched and terminated. Communication, delay working state).


When the working power of the terminal is cut off, the corresponding current relay with time limit enters the delayed working state. For the V2 P-channel field effect transistor, as C4 is discharged through R6 and RP2, its source S voltage is continuously reduced (in the power-on state, because the UGS is small, ID is zero, and V2 is the off-state), According to the corresponding transfer characteristics of the FET (the relationship between the drain current ID and the gate-source voltage VGS), when the VGS voltage reaches VGS (Th) (the turn-on voltage), V2 is turned on. As V2 is turned on, the leakage current ID generates a corresponding voltage drop through R4, so that the V3 transistor is turned on, and eventually V4 is also turned on. When V4 is turned on, the energy storage on the C5 capacitor will energize the winding winding of the winding winding with a time limit current to set the coil to work, so that the time-delay contact is restored to the original state, thereby completing the power-off time-delay work.


The disadvantage of this circuit is that the delay parameters are not easy to set. Usually, RP2 is adjusted (controls the C4 discharge loop), RP1 is adjusted (determines the V2 gate voltage), and the C4 and C3 capacitor capacity parameters are calculated, plus the device. The discreteness makes the delay error larger and the adjustment is inconvenient. It is basically rarely used now.


The delay circuit composed of integrated CD4060 is shown in Figure 3. The core delay of this circuit is composed of CD4060, and the delay setting is set by RP1 and the configured C3. The internal 2-winding latching time-limiting current relay uses DC24V (the time-limiting current relay with a higher working voltage can reduce its driving current and make the driving part simpler). A working power supply is added to the terminal, and the V1 triode works to make its R reset coil suck and work, and the internal contacts return to the original state. C2 and C4 complete the charging work.


When the power supply of the terminal is powered off, it enters the corresponding power-off delay working state. IC ○ 12 pin generates a level at R3 due to C1 discharge. R4 is added to ○ 12 pin to clear the pin to clear it to make it start delay. Drive V2 to work and wait for the delay to stop the oscillation by VD7. According to the time-delay situation, the C2 capacitor can be increased or decreased accordingly (the C2 capacity can be increased or decreased by parallel connection). The C4 capacitor can complete the work of the S setting coil.


This line is characterized by convenient delay setting, high delay accuracy, simple product adjustment, and is currently widely used.