JPH0138995Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a delay switch having a delay circuit and a power control element.

BACKGROUND ART Conventionally, a delay switch that can turn off power to a load after a certain period of time has elapsed after an operation switch is turned off has been widely used, for example, as a switch for turning on and off a ventilation fan for hand washing. FIG. 1 is a circuit diagram showing the configuration of such a conventional automatic delay switch, and its external connection terminal 1
A series circuit of an AC power supply V _s and a load L is connected to a and 1b. A neon lamp Ne is connected to the external connection terminals 1a and 1b via a resistor _R1 , and lights up when the triac 2, which is a power control element, is off. Also, ZNR is a noise prevention element made of nonlinear resistance. 3 is a current transformer, and when a push button type operation switch SW is turned on, an alternating current voltage is generated on the secondary side of the current transformer 3. This alternating voltage is a diode bridge
After being full-wave rectified by DB ₁ and voltage clipped by resistor R ₂ and Zener diode ZD ₁ , it is charged to large capacitor C ₁ via diode D ₁ . A variable resistor 4 is connected in parallel to both ends of this capacitor _C1 , and constitutes a time constant circuit of an electronic timer. The voltage across capacitor _C1 is a switching element.
A reverse bias is applied between the source and gate of FET 5, and FET 5 is turned off while this reverse bias is sufficiently large. The transistor _Q3 , which together with the thyristor 6 forms the switching element, is therefore turned on, which turns on the triac ₂ via the diode bridge DB2, causing it to conduct and turning on the load L. When the charge in the capacitor C ₁ gradually discharges through the variable resistor 4 and the reverse bias of the FET 5 becomes smaller, a current flows through the resistor R ₁₀ and the resulting voltage drop turns on the transistor Q ₄ . _Q5 also turns on, the charge in capacitor _C1 is rapidly discharged, and FET5 turns on all at once. This turns off the transistor _Q3 and turns off the thyristor 6, so that the triac 2 becomes non-conductive and the load L is turned off. Therefore, the load L is turned off after a certain period of time determined by the resistance value of the variable resistor 4. By the way, when using such a delay switch to turn on and off a load L such as a fluorescent lighting fixture, the impedance of the load L is high during standby, and if a voltage of approximately 63V or more is applied to both ends of the load L. Since the glow lamp tube with built-in load L will discharge, the impedance of the switch side circuit viewed from the external connection terminals 1a and 1b must be kept high during standby. On the other hand, when the load L is on, the thyristor 6 must be turned on, and the circuit impedance must be lowered to provide this on signal. The impedance switching circuit 7 in Figure 1 performs this impedance switching, and this circuit is comprised of FET5
When turned on, the capacitor _C3 is charged through the Zener diode _ZD2 and the first transistor
Q ₁ is turned on, the second transistor Q ₂ is turned off, and conversely, when FET 5 is turned off, the transistor Q ₁ is turned off, the transistor Q ₂ is turned on, and the first resistor R ₇ and the second The impedance is switched by inserting a resistor _R6 into the circuit and setting _the resistance value in advance such that the relationship _R7≫R6 holds. Note that R ₃ and R ₄ are current limiting resistors.

However, in the case of this conventional circuit, there is a risk that malfunctions may occur due to the following noise. In other words,
If there is noise such as power supply superimposition, such noise is generally higher than the power supply voltage. Further, in FIG. 1, the power supply voltage waveform for the negative electrode at point x (point y in the figure) has a waveform as shown in FIG. Therefore, when the load L is in the standby (off) state, e
When noise ns is superimposed at a point, the power supply voltage is near its peak and transistor Q ₁ remains on, so transistor Q ₂ does not turn on and the impedance switching circuit 7 operates normally. However, if noise ns is superimposed at point f (near the zero cross point) in Fig. 3, transistors Q ₁ and Q ₂
are both off, and the base current of transistor Q ₁ flows through resistor R ₈ and Zener diode ZD ₂ to the base of transistor Q 1 and turns on transistor Q ₁ only after capacitor C ₃ is charged to a specified voltage or _higher . Therefore, the above noise ns is f
When the points overlap, a problem arises in that transistor Q ₂ turns on before transistor Q ₁ and as a result, transistor Q ₃ turns on, and thyristor 6 also turns on, turning on the load L.

The present invention has been devised in view of the prior art, and its purpose is to provide a delay switch that prevents malfunctions due to noise.

This will be explained below using examples. FIG. 4 shows a circuit according to an embodiment, and this embodiment differs from the conventional circuit shown in FIG. 1 in that a third resistor Rx is inserted into the base of the transistor _Q1 of the impedance switching circuit 7. In other words, during standby, when the power supply voltage reaches the zero cross point, the charge stored in the capacitor _C3 is discharged through the base and the edge of the transistor _Q1 via the resistor Rx, and _Rx ,
transistor depending on the time constant determined by C ₃
Keep Q ₁ on, and the noise ns will be f in Figure 3.
Even if they overlap at points, it is possible to prevent transistor Q ₂ from turning on.

According to the present invention, in the delay switch configured as described above, a resistor is inserted in series between the base of the first transistor of the impedance switching circuit and the second capacitor, so that the electric charge of the second capacitor can be discharged. Since the time is delayed by the resistor, the first transistor continues to turn on even near the zero-crossing point of the AC voltage. Therefore, even if noise is superimposed near the zero-crossing point of the AC power supply voltage during standby, the second transistor The transistor can be prevented from turning on, resulting in the effect that malfunction will not occur.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram of a conventional example, Figs. 2 and 3 are waveform diagrams for explaining the operation of the above, and Fig. ₄ is a circuit diagram of an embodiment of the present invention. is the operating switch, DB ₁ is the first diode bridge,
DB ₂ is the second diode bridge, C ₁ is the first capacitor, C ₂ is the second capacitor, Q ₁ is the first transistor, Q ₂ is the second transistor, Q ₃ is the transistor, R ₇ is the A first resistor, _R6 is a second resistor, _Rx is a third resistor, L is a load, 2 is a triac, 3 is a current transformer, 5 is an FET, 6 is a thyristor, and 7 is an impedance switching circuit.

Claims (1)

[Scope of utility model registration request] A bidirectional power control element is interposed between the AC power supply and the load, a series circuit consisting of an operating switch and the primary winding of the current transformer is connected to both ends of the power control element, and the secondary winding of the current transformer is A first diode bridge for rectifying the secondary output is connected to the line, and a first capacitor for time constant and a first capacitor for discharging are connected between the DC output terminals of the first diode bridge via a charging resistor. A parallel circuit is connected between the pair of DC output terminals of the second diode bridge so that the control current of the power control element can be turned on and off between one electrode of the power control element and the control pole. A series circuit of a current limiting resistor and a switching element is connected, and a series circuit of a second resistor and a second transistor with a low resistance value is connected in parallel to a series circuit of a first resistor and a first transistor with a high resistance value. Along with connecting,
The collector of the first transistor is connected to the base of the second transistor, and a second capacitor charged via the third resistor is connected to the series circuit of the first resistor and the first transistor. A voltage across the capacitor is applied between the base and emitter of the first transistor, and if the voltage across the capacitor is equal to or higher than a predetermined level, the first transistor is turned on, and the second transistor is turned on.
A series circuit of a two-terminal impedance switching circuit that turns off the transistor and a switching element is connected between the DC output terminals of the second diode bridge, and a voltage across the first capacitor is applied in a reverse bias direction. In the delay switch, the switching element is turned on when there is no charge in the first capacitor, and the switching element is turned on when the voltage level at the connection point between the impedance switching circuit and the switching element is equal to or higher than a predetermined level. A delay switch comprising a third resistor inserted in series between the base of the first transistor and the second capacitor of the impedance switching circuit.