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Principle and Implementation of Current Relay with Time Limit

With time limit current relay, when the time 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 contacts are restored again. Is the initial 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) conversion characteristics (as opposed to the normal power-on delay type time relay contact working state) to meet its control requirements. The power-off delay time relay is composed of early separation devices (low delay accuracy and short delay time); the corresponding programmable timing integrated circuit or CMOS counting frequency division integration is used to complete the delay. Compared with this, it has a delay High time 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 relay and a 2-winding latching type R reset coil. After power-off, the delay part works with the 2-winding latching S setting coil); the delay work part (programmable timing integration or CMOS counting frequency division integration); the driving part;

The power-off delay type relay composed of V2 P-channel field effect transistor, V3, V4 triode and relay as the main components 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 winding latching relay R reset coil is energized to work (the conversion contacts 4 and 6 in the virtual frame are turned from the power to the off state, and 4 and 8 are connected). Delay work status).

When the terminal working power is cut off, the corresponding relay 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 2 winding latching relay set coil to work, so that the delay contact will return to its original state, thereby completing the power-off 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 relay adopts DC24V (relay with 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.