JPS62112416A - Load on-off control circuit - Google Patents

Abstract

PURPOSE:To eliminate the need for a large sized power transformer to step down a commercial AC power voltage and to improve the safety by using a multivibrator and a small sized transformer connected to its output so as to make a voltage fed to an operation switch section lower. CONSTITUTION:A commercial AC power supply E is converted into a DC voltage (12V) by a rectifier diode D1, a smoothing capacitor C1 and a Zener diode D2. When an operation switch SW is turned off, a transistor (TR) 3 is turned on/off synchronously with the oscillation output of a multivibrator 1. A pulse voltage appearing at a collector of the TR 3 is smoothed by a smoothing circuit comprising a capacitor C4 and a resistor R5, a DC voltage of nearly 12V is applied to an anode of a PUT Q1, in which a TR 4 is turned on and a gate current is fed to a triac Q2 and a load L being an incandescent lamp is lighted. In turning on the operation switch SW, since the impedance of the primary side of the small sized transformer T is nearly zero, the TR 3, the PUT Q1 and the TR 4 are turned off and no gate current is fed to the triac Q2 and the load L goes out.

Description

Detailed Description of the Invention Ta) Technical Field The present invention relates to a load on/off control circuit that prevents a large voltage from being applied to an operation switch section.

(b) Prior Art and Its Disadvantages In on/off control circuits for lighting equipment used in hospitals, etc., it is necessary to prevent large voltages from being applied to the operation switch section from a safety standpoint. In particular, in the case of lighting fixtures located next to a bed or the like, there is a possibility that the operating switches at hand may get wet due to tea, juice, etc., so even in such cases, it is necessary to prevent electric shock to the human body when operating the lighting equipment.

For this reason, in the past, the commercial AC power supply voltage was directly lowered to a low voltage by a power transformer, and the entire control circuit was operated at that low voltage. However, such a control circuit requires a large transformer to reduce the voltage of the commercial AC power supply to a low voltage, which has the disadvantage of increasing the overall weight and cost.

(C1 Purpose of the Invention The purpose of the present invention is to use a multivibrator and a small transformer connected to its output to reduce the voltage applied to the operation switch section to an extremely low voltage and reduce the commercial AC power supply voltage. An object of the present invention is to provide a load on/off control circuit that does not require a large power transformer for power down.

(d1 Structure of the Invention This invention comprises a rectifying and smoothing circuit for a commercial AC power supply voltage, a Zener diode for setting its smoothed output to a constant DC voltage, a multivibrator driven by the DC voltage, and a circuit for both the multivibrator and the DC voltage). The stage outputs are each connected to a primary side terminal, and the stage output is connected between a small transformer whose number of secondary windings is smaller than the number of windings on the primary side or whose number of windings is approximately equal to the number of windings on the primary side, and the secondary side terminal of the small transformer. An emitter is connected to the primary terminal of the small transformer.
A pulse rectifying and smoothing circuit consisting of a transistor whose base terminal is connected to each other and a smoothing circuit connected to its collector terminal, and a switch that turns on and off a switching element connected in series to a load based on the output of the pulse rectifying and smoothing circuit.・It is equipped with a switching element on/off control circuit.

(8) Embodiment The figure is a circuit diagram of a load on/off control circuit which is an embodiment of the present invention.

The commercial AC power supply E is rectified by a rectifying diode D1, and further smoothed by a smoothing capacitor C1. This smoothed output is set to a DC voltage of 12V by Zener diode D2. A multivibrator 1 is connected in parallel to this Zener diode D2. This multivibrator 1 has two transistors TRI, T
R2゜4 resistors R1 to R4 and 2 capacitors C
The oscillation frequency is set to 3 KHz. Both stage output terminals a and b of this multivibrator 1 are connected to the primary side input terminal of a small transformer T, respectively. Further, an operation switch SW is connected to the secondary side terminal of this small transformer T via a line e. The number of secondary windings of the transformer T is set smaller than the number of primary windings. In this embodiment, the number of secondary windings is one third of the number of primary windings.

The numbers of these windings may be substantially the same. Furthermore, the base terminal and emitter terminal of a transistor TR3 are connected to both primary terminals of the transformer T, respectively, and the collector terminal of this transistor TR3 is connected to a capacitor C4 and a resistor R5.
A smoothing circuit consisting of is connected. Further, this smoothed output is connected to the anode terminal of PUTQI, and the cathode terminal of PUTQl is connected to the power supply side via a resistor R6 and to the base terminal of the transistor TR4. Transistor TR4 supplies gate current to triac 9, which is connected in series to load I- via resistor R7. The gate voltage of PUTQl is set to about 8.times. by a voltage dividing circuit including resistors R8 and R9.

With the above circuit configuration, the circuit including the transistor TR3, the resistor R5, and the capacitor C4 constitutes a pulse rectifying and smoothing circuit that rectifies and smoothes the output pulse of the multivibrator. Also, PUTQl, ) transistor TR4 and resistor R
6 to R9 constitute a switching element on/off control circuit that controls on/off the triac Q2, which is a switching element.

Next, the operation will be explained.

When the operation switch SW is in the off state, the transistor TR3 is turned on when one stage output terminal a of the multivibrator 1 is "H". When the output terminal of the other stage is "I", the transistor TR3 is turned off. Transistor TR3 is multivibrator 1 after all.
Turns on and off in synchronization with the oscillation output. transistor T
When R3 is on, a voltage of approximately 12V is applied to capacitor C4. This results in capacitor C4 and resistor R5
The pulse voltage of approximately 12V appearing at the collector of transistor TR3 is smoothed by the smoothing circuit consisting of PUTQ.
This smoothed DC voltage of about 12 V is applied to the anode terminal of the electrode. A resistor R8 is connected to the gate terminal of PUTQl.
, R9 is applied, so this PUTQI is turned on and the transistor TR4 is also turned on. That is, a gate current is supplied to the triac Q2, and the load, which is an incandescent light bulb, is turned on.

Next, when the operation switch SW is turned on, the impedance on the primary side of the small transformer T becomes almost 0, so even if one stage output terminal a of the multivibrator 1 becomes "H", the transistor TR3 will not be turned on. That is, PUTQI is turned off, transistor TR4 is also turned off, and no gate current is supplied to triac Q2. In other words, the load is turned off. In this way, when the operation switch SW is turned on, the load can be set to the off state, and when the operation switch SW is turned off, the load can be set to the lighted state.

During the above operation, when the operation switch sW is in the OFF state, the voltage appearing between both primary side terminals of the small transformer T has a maximum forward voltage drop (approximately 1 V) between the emitter and base of the transistor TR3. That is, when one stage output terminal a of the multivibrator 1 becomes "H", a voltage of about 1 V is applied to the primary side of the transformer T. When the b terminal is at "H", almost no voltage is generated in the primary winding of the transformer T. As described above, since the maximum voltage applied to the primary side of the transformer T is about 1 V, almost no voltage is generated on the secondary side of the transformer T, where the number of turns is smaller than that on the primary side. Also, the operation switch SW
When is in the on state, the voltage generated in the secondary winding is O■.

(f1 Effects of the invention As described above, according to this invention, the output of the multivibrator is supplied to the pulse rectifying and smoothing circuit via the transformer, so the transformer T can be made very small. In addition, since the base and emitter of the transistor are connected to the primary side of the transformer T, and the operation switch is connected to the secondary side, the voltage applied to the operation switch can be extremely small, and in the unlikely event that a contact occurs. There is no electric shock even if the human body comes into contact with it, making it extremely safe.

[Brief explanation of drawings]

The figure is a circuit diagram of a load on/off control circuit according to an embodiment of the present invention. L-Multi-vibrator, D-Small transformer, SW-Operation switch.

Claims (1)

[Claims] (1) A rectifying and smoothing circuit for the commercial AC power supply voltage, a Zener diode that sets its smoothed output to a constant DC voltage, a multivibrator driven by the DC voltage, and the outputs of both stages of the multivibrator are on the primary side, respectively. a small transformer connected to the terminal and having a smaller number of secondary windings than the number of primary windings or approximately equal to the number of secondary windings; an operation switch connected between the secondary terminals of the small transformer; A pulse rectifying and smoothing circuit consisting of a transistor whose emitter and base terminal are respectively connected to the primary side terminal of a small transformer and a smoothing circuit connected to its collector terminal; and a pulse rectifying and smoothing circuit which is connected in series to a load based on the output of the pulse rectifying and smoothing circuit. a switching element on/off control circuit that turns on and off the switching element;
Off control circuit.