JP2005198384A - Electronic transformer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electronic transformer which can restart a power supply to a load without reclosing an ac power supply when it becomes a normal load after operating by an unloaded condition. <P>SOLUTION: The electronic transformer 1 includes a resetting means 4 which reduces the connecting point potential of a resistor R1 for a trigger and a capacitor C3 for a trigger at the zero crossing point of the output voltage of the ac power supply AC. The current flowing to a trigger element Q3 at the zero crossing point of the output voltage of the ac power supply AC is reduced smaller than a holding current which holds the trigger element Q3 in a conductive state. Even after operated by the unloaded condition, since the trigger element Q3 is once turned off at the zero crossing point of the output voltage of the ac power supply AC and again conducted, the switching element Q2 is turned on at the timing for conducting the trigger element Q3, and the oscillation of the inverter circuit 2 is started. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an electronic transformer that converts an output of an alternating current power source into a high frequency, further converts a voltage, and applies it to a load.

  As this type of electronic transformer, as shown in FIG. 5, power is supplied from an AC power source AC such as a commercial power source, and a high frequency output is stepped down to, for example, 12 V and applied to a lamp La such as an incandescent lamp as a load. What turns on the lamp La is provided. In general, a large number of lighting fixtures that use such an electronic transformer 1 to turn on the lamp La are used in museums and stores.

  The electronic transformer 1 shown in FIG. 5 starts the oscillation of the rectifier circuit DB1 for full-wave rectification of the AC power supply AC, the self-oscillation type inverter circuit 2 connected between the output terminals of the rectifier circuit DB1, and the inverter circuit 2 Trigger circuit 3 to be provided.

  The inverter circuit 2 is a half-bridge type, and includes a series circuit of two capacitors (for inverter) C1 and C2 connected between the output terminals of the rectifier circuit DB1 and two switching elements Q1 and Q2. A series circuit of a primary winding P2 of a load transformer T1 composed of a step-down transformer and a primary winding P1 of a feedback transformer CT1 that alternately turns on and off each switching element Q1, Q2 by self-excited oscillation. It has the structure connected between the connection point of C1, C2 and the connection point of switching element Q1, Q2. In the illustrated example, bipolar transistors are used for the respective switching elements Q1 and Q2.

  The feedback transformer CT1 includes a first secondary winding S1 connected between the base and emitter of one switching element Q2, and a second secondary coil connected between the base and emitter of the other switching element Q1. A secondary winding S2. Both the secondary windings S1 and S2 of the feedback transformer CT1 are configured so that only one of the switching elements Q1 and Q2 is turned on when a current flows in one direction of the primary winding n1. One end of a different pole is connected to the base of Q2. A lamp La is connected to the secondary winding S3 of the load transformer T1.

  The trigger circuit 3 includes a trigger element Q3 that is turned on when the voltage between both ends reaches the trigger voltage, a trigger resistor (hereinafter simply referred to as a resistor) R1 that is connected between the output ends of the rectifier circuit DB1, and a trigger circuit. The detection circuit 30 is composed of a series circuit with a capacitor (hereinafter simply referred to as a capacitor) C3, and the capacitor C3 is charged via the resistor R1 by the output of the rectifier circuit DB1, and the trigger element Q3 includes the resistor R1 and the capacitor C3. Connected to the base of one of the switching elements Q2. Once the trigger element Q3 is turned on, the trigger element Q3 is held in a conductive state until the current flowing between both ends falls below the holding current (see, for example, cited document 1).

  The operation of the above-described electronic transformer 1 will be described below. When the AC power supply AC is turned on, the output voltage of the rectifier circuit DB1 is applied to the trigger circuit 3, and the capacitor C3 is charged via the resistor R1. When the output voltage of the rectifier circuit DB1 rises and the voltage across the capacitor C3 reaches the trigger voltage of the trigger element Q3, the trigger element Q3 becomes conductive and current flows through the base of the switching element Q2. When a current flows through the base of the switching element Q2, the switching element Q2 shifts from an off state to an active state (a state where the switching element Q2 operates in the active region), and thus the primary winding P1 of the feedback transformer CT1 and the load transformer T1 from the capacitor C3. Current flows through the primary winding P2 and the switching element Q2. Here, when a current in the forward bias direction of the switching element Q2 flows through the first secondary winding S1 of the feedback transformer CT1, the switching element Q2 rapidly shifts to the complete ON state (ON state in the saturation region).

  When the switching element Q2 is in the fully ON state, the magnitude of the current flowing through the primary winding P1 of the feedback transformer CT1 is not changed, so that the current flowing through the first secondary winding S1 of the feedback transformer CT1 does not flow. Element Q2 transitions to the off state. As a result, the current flowing through the primary winding P1 of the feedback transformer CT1 is interrupted, and the current due to the counter electromotive force flows through the second secondary winding S2, so that the switching element Q1 is forwarded to the base of the other switching element Q1. A current in the bias direction flows. When a current flows through the base of the switching element Q1, the switching element Q1 shifts from the off state to the active state, and therefore the primary winding P1 of the switching element Q1, the feedback transformer CT1, and the primary winding of the load transformer T1 from the capacitor C2. A current flows through the line P2, and the switching element Q1 rapidly shifts to the fully on state in the same manner as the switching element Q2.

  The electronic transformer 1 repeats the above-described operation to alternately turn on and off the switching elements Q1 and Q2, and by passing an alternating current through the primary winding P2 of the load transformer T1, the secondary winding of the load transformer T1. A high frequency output is applied to the lamp La connected to S3 to light the lamp La.

In the vicinity of the zero cross point of the output voltage of the AC power supply AC, the output voltage of the rectifier circuit DB1 becomes substantially zero, so that neither of the switching elements Q1 and Q2 can be turned on and the oscillation of the inverter circuit 2 stops. However, since the switching element Q2 is turned on by the trigger circuit 3 and the oscillation of the inverter circuit 2 is restarted in the same manner as when the AC power supply AC is turned on, the high-frequency output is continued.
Japanese Patent Laying-Open No. 2003-151792 (page 2-3, FIG. 8)

  By the way, the electronic transformer 1 described above cannot continue the oscillation of the inverter circuit 2 because a large current does not flow through the primary winding P2 of the load transformer T1 in a no-load state such as a broken lamp of the lamp La. . If power supply from the AC power supply AC is continued in a state where the oscillation of the inverter circuit 2 is stopped, the output voltage of the rectifier circuit DB1 is smoothed by the capacitors C1 and C2 to become a DC voltage, so that the capacitor C3 is maintained in a saturated state. Thus, the switching element Q2 is continuously maintained in the on state. In this state, even if the broken lamp La is replaced with a normal lamp La, the capacitor C3 is maintained in a saturated state and the switching element Q2 is maintained in a fully on state, so that the inverter circuit 2 oscillates. Can't start.

  That is, in the electronic transformer 1 described above, once the lamp La is operated in a no-load state such as a broken bulb, the inverter circuit 2 oscillates only by returning the lamp La to a normal load state. It cannot be resumed. In order to resume the oscillation of the inverter circuit 2, it is necessary to turn off the AC power supply AC and turn it on again.

  However, when many lighting fixtures that use the electronic transformer 1 to turn on the lamp La are used, the AC power supply AC is cut off when the lamp La is replaced due to a broken bulb, etc. It is not desirable to turn off the light up to La. Therefore, there is a demand for an electronic transformer 1 that can turn on the lamp La without switching on the AC power supply AC when the lamp La is replaced.

  It can be considered that by setting the resistance value of the resistor R1 large, the current flowing through the trigger element Q3 in the no-load state is made smaller than the holding current of the trigger element Q3 to turn off the switching element Q2. However, since the holding current of the trigger element Q3 is very small and varies, when the resistance value of the resistor R1 is set so that the current flowing through the trigger element Q3 in the no-load state is smaller than the holding current of the trigger element Q3, the trigger circuit 3 may make it impossible to turn on the switching element Q2.

  The present invention has been made in view of the above-described reasons, and provides an electronic transformer that can resume power supply to a load without re-turning on an AC power supply when returning from a no-load state to a normal load state. For the purpose.

  In the first aspect of the present invention, a rectifier circuit for full-wave rectification of an AC power supply, a series circuit of two inverter capacitors, and a series circuit of two switching elements are connected in parallel between the output terminals of the rectifier circuit. Between the connection point of the capacitor and the connection point of the switching element, a load transformer in which a load is connected on the secondary side and a feedback transformer that alternately turns on and off each switching element by self-excited oscillation are connected in series. A detection circuit consisting of an inverter circuit and a series circuit of a trigger resistor and a trigger capacitor, and the trigger capacitor is charged via the trigger resistor when power is supplied from an AC power source, and a connection point between the trigger resistor and the trigger capacitor One switching element is connected to the control terminal of the switching element and becomes conductive when the voltage at the connection point reaches the trigger voltage. A current flowing in the trigger element by lowering the potential at the connection point of the trigger resistor and the trigger capacitor at the zero-cross point of the output voltage of the AC power supply, and a trigger circuit having a trigger element that turns on the element and starts oscillation of the inverter circuit And reset means for making the trigger element smaller than a holding current for holding the trigger element in a conductive state.

  According to this configuration, the reset means turns off the trigger element at the zero cross point of the output voltage of the AC power supply, and when it returns to a normal load state after operating in a no-load state, immediately after the zero cross point of the AC power supply. When one of the switching elements is turned on, the oscillation of the inverter circuit can be resumed. As a result, even after operating in a no-load state, the power supply to the load can be resumed without turning on the AC power supply again.

  According to a second aspect of the present invention, in the first aspect of the invention, the reset unit includes an auxiliary rectifier circuit that is connected in parallel to the rectifier circuit with respect to the AC power source and rectifies the AC power source in a full wave, and is connected between output terminals. The detection circuit is connected.

  According to this configuration, the invention of claim 1 can be realized with a simple circuit configuration in which an auxiliary rectifier circuit is added to the conventional configuration.

  According to a third aspect of the present invention, in the first aspect of the present invention, the detection circuit is connected between the output terminals of the rectifier circuit, and the reset means is a capacitor for the inverter between the detection circuit and the inverter circuit. It is characterized by comprising reverse flow blocking means for blocking current flowing from to the detection circuit.

  According to this configuration, since the backflow blocking means only needs to block current in one direction, the invention of claim 1 can be achieved with a simple circuit configuration in which only one diode is added to the conventional configuration. Can be realized.

  According to a fourth aspect of the present invention, in the first aspect of the present invention, the detection circuit is connected between output terminals of the rectifier circuit, and the reset means is connected in parallel to the rectifier circuit with respect to the AC power source. An auxiliary rectifier circuit that performs full-wave rectification and a voltage divider circuit in which two voltage dividing resistors are connected in series between the output terminals of the auxiliary rectifier circuit. The connection point of the voltage dividing resistors is the trigger resistor and the trigger. It is connected to the connection point of the capacitor for use.

  According to this configuration, the output voltage of the auxiliary rectifier circuit is pulled down by the voltage dividing circuit and applied to the trigger element, so that the reset means can reliably detect the zero cross point of the AC power supply.

  According to a fifth aspect of the present invention, in the fourth aspect of the invention, a current flows toward the connection point of the voltage dividing resistor between the connection point of the voltage dividing resistor and the connection point of the trigger resistor and the trigger capacitor. A discharge diode provided as described above is inserted.

  According to this configuration, the trigger element can be prevented from conducting due to the voltage divided by the voltage dividing circuit.

  According to a sixth aspect of the present invention, in the first aspect of the present invention, the detection circuit is connected between output terminals of the rectifier circuit, and the reset means is connected in parallel to the rectifier circuit with respect to the AC power source. An auxiliary rectifier circuit for full-wave rectification, a voltage divider circuit in which two voltage dividing resistors are connected in series between the output terminals of the auxiliary rectifier circuit, a collector-emitter is connected between both ends of the trigger capacitor, and a base is And a pnp-type transistor connected to a connection point of a voltage dividing resistor through a discharge diode having an anode connected to the base.

  According to this configuration, the trigger capacitor is discharged through the pnp transistor, and the electric charge charged in the trigger capacitor is discharged by amplifying the current by the pnp transistor. Even if the value is set relatively large, the trigger capacitor can be discharged, and the power consumption by the voltage dividing circuit can be made relatively small.

  According to a seventh aspect of the present invention, in the fifth or sixth aspect of the present invention, the trigger capacitor and the connection point of the trigger resistor in a period in which a current flows from the trigger capacitor toward the connection point of the voltage dividing resistor, A Zener diode having a Zener voltage equal to or higher than a voltage difference between the voltage dividing resistor and a connection point is connected in series with a trigger element.

  According to this configuration, the trigger element can be reliably turned off by turning off the Zener diode.

  The invention according to claim 8 is the invention according to claim 1, wherein the detection circuit is connected between output terminals of the rectifier circuit, and the reset means is connected in parallel to the rectifier circuit with respect to the AC power supply. An auxiliary rectifier circuit for full-wave rectification, a voltage divider circuit in which two voltage dividing resistors are connected in series between the output terminals of the auxiliary rectifier circuit, and a drain-source connected between both ends of the trigger capacitor, and a gate And a depletion type MOSFET connected to the connection point of the voltage dividing resistor.

  According to this configuration, the depletion type MOSFET operates even if the resistance values of both voltage dividing resistors are set to be relatively large, so that the power consumption by the voltage dividing circuit can be made relatively small.

  According to a ninth aspect of the present invention, in any one of the first to eighth aspects, the trigger element is selected from a silicon bidirectional switching element and a trigger diode.

  According to this configuration, since a general and easily available trigger element is used, the inventions of claims 1 to 8 can be realized at a relatively low cost.

  According to the present invention, the reset means turns off the trigger element at the zero cross point of the output voltage of the AC power supply. When the reset means returns to a normal load state after operating in the no-load state, the trigger is immediately after the zero cross point of the AC power supply. By making the element conductive, one of the switching elements can be turned on and the oscillation of the inverter circuit can be resumed. As a result, even after operating in a no-load state, there is an advantage that the power supply to the load can be resumed without turning on the AC power supply again.

  The best mode for carrying out the present invention will be described below with reference to the drawings. In addition, about the structure similar to a conventional structure, description is abbreviate | omitted using the same code | symbol.

(Embodiment 1)
As shown in FIG. 1, the electronic transformer 1 of the present embodiment is provided with an auxiliary rectifier circuit 40 for full-wave rectifying the output voltage of the AC power supply AC separately from the rectifier circuit DB1 as a reset means 4 compared to the conventional configuration. The difference from the conventional configuration is that the detection circuit 30 is connected between the output terminals of the auxiliary rectifier circuit 40 in place of the output terminals of the rectifier circuit DB1. As the trigger element Q3, SBS (silicon bidirectional switching element) or diac (trigger diode) is used.

  The auxiliary rectifier circuit 40 includes two diodes D1 and D2. The anodes of the diodes D1 and D2 are connected to the respective poles of the AC power supply AC, and the cathodes of both the diodes D1 and D2 are connected to each other. And the negative output terminal of the rectifier circuit DB1 is used as the negative output terminal.

  In the electronic transformer 1 of the present embodiment, even when power is supplied from the AC power supply AC in a no-load state, the output voltage of the auxiliary rectifier circuit 40 is not smoothed by the inverter capacitors C1 and C2, but is a DC voltage. Therefore, it becomes substantially zero at the zero cross point of the output voltage of the AC power supply AC. Therefore, at the zero-cross point of the output voltage of the AC power supply AC, the voltage flowing across the capacitor C3 decreases, so that the current flowing through the trigger element Q3 becomes smaller than the holding current, and the trigger element Q3 is turned off. Thereafter, when the output voltage of the AC power supply AC rises and the output voltage of the auxiliary rectifier circuit 40 rises, the voltage across the capacitor C3 reaches the trigger voltage of the trigger element Q3 and the trigger element Q3 becomes conductive, so the switching element Q2 is turned on. Then, a pulse current large enough to start the oscillation of the inverter circuit 2 can be supplied to the gate of the switching element Q2.

  In short, even if the electronic transformer 1 described above operates in a no-load state, if the load becomes normal, the trigger element Q3 is turned on without interrupting the AC power supply AC and turning it on again. The oscillation of the inverter circuit 2 can be restarted by the same operation as that described in the conventional configuration. Therefore, in the lighting fixture using the electronic transformer 1, even if the lamp La is replaced without shutting off the AC power supply AC, the lamp La can be turned on without turning on the AC power supply AC again.

(Embodiment 2)
As shown in FIG. 2, the electronic transformer 1 of the present embodiment includes two voltage dividing resistors (hereinafter referred to as “detection circuit 30”) between the output terminals of the auxiliary rectifier circuit 40 in the electronic transformer 1 of the first embodiment. A voltage dividing circuit 41 composed of a series circuit of R2 and R3 is simply connected, and the auxiliary rectifier circuit 40 and the voltage dividing circuit 41 constitute the reset means 4. The detection circuit 30 is connected between the output terminals of the rectifier circuit DB1, and the connection point between the resistor R1 and the capacitor C3 is a discharge diode (hereinafter simply referred to as a diode) D3 whose cathode is connected to the connection point between the resistors R2 and R3. Connected to the anode.

  In the electronic transformer 1 of the present embodiment, the potential at the connection point of the resistors R2 and R3 becomes substantially zero in the period when the absolute value of the output voltage of the AC power supply AC is small as well as the zero cross point of the AC power supply AC. The potential at the connection point of the resistors R2 and R3 can be reliably reduced to zero at the zero cross point. The diode D3 compares the connection point potential of the resistor R1 and the capacitor C3 with the connection point potential of the resistors R2 and R3, and the connection point of the resistor R1 and the capacitor C3 during a period when the connection point potential of the resistor R1 and the capacitor C3 is higher. Current from the resistor R2 to the connection point of the resistors R3 and R3. That is, when the potential at the connection point of the resistors R2 and R3 becomes substantially zero while the capacitor C3 is charged, the capacitor C3 is discharged through the diode D3.

  Further, when a current flows through the diode D3, a forward loss occurs due to a forward voltage drop between both ends of the diode D3. Therefore, the capacitor C3 is a diode even if the potential at the connection point between the resistors R2 and R3 is zero. The forward loss of D3 cannot be discharged, and charge remains in the capacitor C3. In the present embodiment, a Zener diode ZD1 is provided between the trigger element Q3 and the base of the switching element Q2. By setting the Zener voltage of the Zener diode ZD1 to be larger than the forward loss of the diode D3, the capacitor C3 When discharged through the diode D3, the Zener diode ZD1 is turned off to turn off the trigger element Q3.

  Further, in the present embodiment, a startup acceleration capacitor C4 is connected in parallel with the resistor R1. This capacitor C4 is required when a general incandescent lamp dimmer (not shown) is connected as an external dimmer. According to the configuration of the present embodiment, even if this capacitor C4 is provided, the output voltage of the auxiliary rectifier circuit 40 is not smoothed, and the output voltage of the auxiliary rectifier circuit 40 is substantially reduced at the zero cross point of the output voltage of the AC power supply AC. Can be zero. Other configurations and functions are the same as those of the first embodiment.

(Embodiment 3)
As shown in FIG. 3, the electronic transformer 1 of the present embodiment is different from that of the second embodiment in that a pnp transistor (hereinafter simply referred to as a transistor) Q4 connected between both ends of a capacitor C3 is added to the reset means 4. Different from the electronic transformer 1. The transistor Q4 has a base connected to the anode of the diode D3, an emitter connected to the connection point between the resistor R1 and the capacitor C3, and a collector connected to the negative output terminal of the rectifier circuit DB1.

  In the electronic transformer 1 of the present embodiment, when the potential at the connection point of the resistors R2 and R3 becomes substantially zero with the capacitor C3 being charged, the capacitor C3 is discharged between the emitter and base of the transistor Q4 and through the diode D3. To do.

  In the present embodiment, the Zener voltage of the Zener diode ZD1 is set to be larger than the voltage obtained by adding the base-emitter voltage necessary for turning on the transistor Q4 to the forward loss of the diode D3. When discharging through Q4 and the diode D3, the Zener diode ZD1 is turned off to turn off the trigger element Q3.

  Furthermore, in the present embodiment, the current flowing through the discharge of the capacitor C3 is amplified by the transistor Q4, so that the capacitor C3 can be discharged even if the resistance value of the resistor R3 is set relatively large. Other configurations and functions are the same as those of the second embodiment.

(Embodiment 4)
As shown in FIG. 4, the electronic transformer 1 of the present embodiment includes a diode D4 (backflow prevention means) inserted between the positive output terminal of the rectifier circuit DB1 and the inverter circuit 2, and the output terminal of the rectifier circuit DB1. The present embodiment is different from the conventional configuration in that it includes a reset means 4 including a voltage dividing circuit 41 connected in between and a depletion type MOSFET (hereinafter simply referred to as MOSFET) Q5 connected between both ends of a capacitor C3.

  The diode D4 has an anode connected to one end of the voltage dividing circuit 41 and a cathode connected to one end of the resistor R1, thereby preventing current flowing backward from the capacitors C1 and C2 for the inverter to the voltage dividing circuit 41. . The voltage dividing circuit 41 is a series circuit of resistors R2 and R3 similar to those shown in the second and third embodiments. MOSFET Q5 is off during the period when the voltage across resistor R3 exceeds the threshold voltage of MOSFET Q5 by connecting the gate to the connection point of resistors R2 and R3, and the voltage across resistor R3 is the threshold voltage. It is turned on during a period equal to or lower than the voltage to form a discharge path for the capacitor C3.

  In the electronic transformer 1 of this embodiment, even when power is supplied from the AC power supply AC in a no-load state, no current flows from the inverter capacitors C1 and C2 to the voltage dividing circuit 41, and the voltage dividing circuit 41 Since the both-end voltage does not become a DC voltage, the connection point potential of the resistors R2 and R3 becomes substantially zero at the zero cross point of the output voltage of the AC power supply AC. Therefore, at the zero crossing point of the output voltage of the AC power supply AC, the MOSFET Q5 is turned on and the capacitor C3 is discharged. Therefore, the voltage across the capacitor C3 decreases, the current flowing through the trigger element Q3 becomes smaller than the holding current, and the trigger element Q3 Turn off. Thereafter, the output voltage of the AC power supply AC rises and the potential at the connection point of the resistors R2 and R3 rises, so that the MOSFET Q5 is turned off. As in the first embodiment, the capacitor C3 is charged and oscillation of the inverter circuit 2 is started. can do.

  Further, since the MOSFET Q5 is employed in the present embodiment, the resistance values of both resistors R2 and R3 constituting the voltage dividing circuit 41 can be set relatively large, and the power consumption by the voltage dividing circuit 41 is relatively small. can do.

  On the other hand, it is conceivable to use an enhancement type MOSFET Q5 (not shown). In this case, the circuit configuration is described above so that the MOSFET Q5 is turned on when the potential at the connection point of the resistors R2 and R3 is substantially zero. There is a need to change things. In addition, the enhancement-type MOSFET has a narrower depletion layer than the depletion-type MOSFET and is unstable in operation, and is generally used by connecting a capacitor (not shown) or an inductor (not shown) in parallel with the resistor R3. . On the other hand, in the present embodiment, by using a depletion type MOSFET, a capacitor and an inductor connected in parallel with the resistor R3 are unnecessary, and an increase in the number of components is suppressed.

  Further, in the present embodiment, a startup acceleration capacitor C4 is connected in parallel with the resistor R1, as in the second and third embodiments. According to the configuration of the present embodiment, even if this capacitor C4 is provided, the voltage across the voltage dividing circuit 41 is not smoothed, and the resistors R2 and R3 are made substantially zero at the zero cross point of the output voltage of the AC power supply AC. be able to.

It is a circuit diagram which shows Embodiment 1 of this invention. It is a circuit diagram which shows Embodiment 2 of this invention. It is a circuit diagram which shows Embodiment 3 of this invention. It is a circuit diagram which shows Embodiment 4 of this invention. It is a circuit diagram which shows a prior art example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Electronic transformer 2 Inverter circuit 3 Trigger circuit 4 Reset circuit 30 Detection circuit 40 Auxiliary rectifier circuit 41 Voltage dividing circuit AC AC power supply C1, C2 Capacitor CT1 Feedback transformer C3 (For trigger) Capacitor D3 (For discharge) Diode D4 Diode (Backflow prevention) means)
Q1, Q2 Switching element Q3 Trigger element Q4 Pnp type transistor Q5 Depletion type MOSFET
R1 (for trigger) resistance R2, R3 (for voltage division) resistance T1 Load transformer ZD1 Zener diode

Claims (9)

  A rectifier circuit for full-wave rectification of an AC power supply, a series circuit of two inverter capacitors and a series circuit of two switching elements are connected in parallel between the output terminals of the rectifier circuit, and the connection point of the capacitor and the An inverter circuit in which a load transformer whose load is connected to the secondary side between the connection points of the switching elements and a feedback transformer that alternately turns on and off each switching element by self-excited oscillation; and a trigger resistor And a detection circuit in which the trigger capacitor is charged via the trigger resistor when power is supplied from the AC power supply, and the connection point between the trigger resistor and trigger capacitor and the control terminal of one switching element When the voltage at the connection point reaches the trigger voltage, the switch is turned on to turn on one of the switching elements. The trigger circuit having a trigger element that starts oscillation of the data generator circuit and the trigger element is configured to reduce the current flowing through the trigger element by lowering the potential at the connection point of the trigger resistor and the trigger capacitor at the zero crossing point of the output voltage of the AC power supply. An electronic transformer comprising: reset means for making the current smaller than a holding current held in a conductive state.   The reset means includes an auxiliary rectifier circuit that is connected in parallel to the rectifier circuit with respect to the AC power source and rectifies the AC power source in a full wave, and the detection circuit is connected between output terminals. The electronic transformer according to 1.   The detection circuit is connected between the output terminals of the rectifier circuit, and the reset means includes backflow prevention means for blocking current from the capacitor for inverter to the detection circuit between the detection circuit and the inverter circuit. The electronic transformer according to claim 1.   The detection circuit is connected between the output terminals of the rectifier circuit, the reset means is connected in parallel to the rectifier circuit with respect to the AC power source, and an auxiliary rectifier circuit for full-wave rectification of the AC power source, and an output of the auxiliary rectifier circuit The voltage dividing circuit includes two voltage dividing resistors connected in series between the ends, and a connection point of the voltage dividing resistor is connected to a connection point of the trigger resistor and the trigger capacitor. The electronic transformer according to claim 1.   A discharge diode provided so that a current flows toward the connection point of the voltage dividing resistor between the connection point of the voltage dividing resistor and the connection point of the triggering resistor and the trigger capacitor; The electronic transformer according to claim 4.   The detection circuit is connected between the output terminals of the rectifier circuit, the reset means is connected in parallel to the rectifier circuit with respect to the AC power source, and an auxiliary rectifier circuit for full-wave rectification of the AC power source, and an output of the auxiliary rectifier circuit For voltage division through a voltage dividing circuit in which two voltage dividing resistors are connected in series between the ends, and a discharge diode in which a collector-emitter is connected between both ends of the trigger capacitor and an anode is connected to the base. 2. The electronic transformer according to claim 1, further comprising a pnp transistor connected to a connection point of the resistor.   A trigger capacitor in a period in which current flows from the trigger capacitor toward the connection point of the voltage dividing resistor, and a Zener voltage equal to or higher than a differential voltage between the connection point of the trigger resistor and the connection point of the voltage dividing resistor 7. The electronic transformer according to claim 5, wherein a Zener diode is connected in series with the trigger element.   The detection circuit is connected between the output terminals of the rectifier circuit, the reset means is connected in parallel to the rectifier circuit with respect to the AC power source, and an auxiliary rectifier circuit for full-wave rectification of the AC power source, and an output of the auxiliary rectifier circuit A voltage dividing circuit in which two voltage dividing resistors are connected in series between the ends; a depletion type MOSFET in which a drain-source is connected between both ends of the trigger capacitor and a gate is connected to a connection point of the voltage dividing resistor; The electronic transformer according to claim 1, comprising: The electronic transformer according to any one of claims 1 to 8, wherein the trigger element is selected from a silicon bidirectional switching element and a trigger diode.

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