JP2013247778A - Electronic load device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electronic load device that allows satisfying harmonic performance and power-factor performance.SOLUTION: An electronic load device 20 having a fluorescent lamp 5 includes: a step-up chopper circuit 2 receiving a DC voltage, converting the DC voltage into a voltage with a predetermined magnitude, and outputting the resultant voltage; a switching circuit 3 converting the DC voltage outputted from the step-up chopper circuit 2 into an AC voltage by switching of switching elements Q2 and Q3; and a load circuit 4 supplying the AC voltage converted by the switching circuit 3 to the fluorescent lamp 5. The step-up chopper circuit 2 includes a transformer T1 having a primary winding P1 to which the input DC voltage is applied, and an adjustment circuit 27 detecting the voltage value of the input DC voltage as a detection value and changing the inductance value of the primary winding P1 on the basis of the detection value.

Description

  The present invention relates to a technology of an electronic load device that turns on a light source as a load, for example.

  As an example of a conventional electronic load device, there is a circuit of an inverter for a fluorescent lamp having a dimming function. The inverter circuit for the fluorescent lamp generates a high-frequency rectangular voltage by turning on and off the boosted DC voltage and a rectifier circuit that rectifies the commercial frequency input voltage, a boost chopper circuit that boosts the rectified pulsating DC voltage A switching circuit and a dimming interface for inputting a PWM (Pulse / Width / Modulation) signal from the outside and generating a dimming command signal are provided.

  The step-up chopper circuit is generally controlled by an IC (Integrated Circuit), and this IC also has a function of suppressing input harmonic current and improving input power factor.

  In order to dim the fluorescent lamp, dimming signals such as PWM are input from the outside to the control circuit of the constant current circuit (switching circuit), and dimming is performed by varying the oscillation frequency of the MOSFET of the switching circuit. There are products that can adjust the dimming rate to 5% or less of the maximum output.

  At present, power-saving LED lamps are becoming the mainstream in place of fluorescent lamps, and since dimming is easier than fluorescent lamps, many products with a dimming rate of 5% or less are in circulation.

  In recent years, the rated input voltage range of such an electronic load device has been widened, and in Japan, for example, there is a product that covers 100V to 254V.

JP-A-8-78171

  However, in electronic load devices with large load fluctuations or a wide rated input voltage range, the inductance value of the transformer mounted in the boost chopper circuit is designed closer to the condition that the load power is maximum and the input voltage is low. There is a need to. As a result, when the load power is minimum or the input voltage is high, there is a problem that the operating frequency of the boost chopper circuit becomes high, the switching operation becomes unstable, and the harmonic current and the power factor are greatly deteriorated.

  Further, in order to solve the above-described problem, there is a method of increasing the inductance value of the transformer of the step-up chopper circuit as long as the operation at the time of maximum load power or minimum input voltage is not impaired. However, as described above, in the case of a power supply device in which the load fluctuation is 100% to 5% or less and the input voltage range is 100 V to 254 V, there is a problem that the ideal harmonic current and power factor performance are often not obtained. There is.

  An object of the present invention is to provide an electronic load device capable of satisfying high frequency and power factor performance in the entire range in an electronic load device having a large load fluctuation and rated input voltage range.

  An electronic load device according to the present invention includes a voltage conversion circuit that inputs a DC voltage, converts the input DC voltage into a voltage of a predetermined magnitude, and outputs the voltage in an electronic load device including a load, and the voltage conversion A switching circuit that converts a DC voltage output by the circuit into an AC voltage by switching of a switching element; and a load circuit that supplies the AC voltage converted by the switching circuit to the load. A transformer including a first winding to which a DC voltage is applied, and a value related to the magnitude of the input DC voltage or a value related to the magnitude of the AC voltage supplied to the load is detected as a detection value; And an adjustment circuit that changes an inductance value of the first winding based on the detected value detected.

  An electronic load device according to the present invention includes a voltage conversion circuit that inputs a DC voltage, converts the input DC voltage into a voltage of a predetermined magnitude, and outputs the voltage in an electronic load device including a load, and the voltage conversion A switching circuit that converts a DC voltage output by the circuit into an AC voltage by switching of a switching element; and a load circuit that supplies the AC voltage converted by the switching circuit to the load. A transformer including a first winding to which a DC voltage is applied, and a value related to the magnitude of the input DC voltage or a value related to the magnitude of the AC voltage supplied to the load is detected as a detection value; And an adjustment circuit that changes the inductance value of the first winding based on the detected value that is detected, so that the load fluctuation / rated input voltage range is large. The electronic load device even when it is possible to satisfy the high frequency and power factor performance over the entire range.

1 is a circuit diagram of an electronic load device 20 according to Embodiment 1. FIG. 2 is a circuit diagram of an electronic load device 201 for comparison with the electronic load device 20 according to Embodiment 1. FIG. 3 is a circuit diagram of an electronic load device 20 according to Embodiment 2. FIG. 6 is a circuit diagram of an electronic load device 20 according to Embodiment 3. FIG.

Embodiment 1 FIG.
FIG. 1 is a circuit diagram of an electronic load device 20 according to the present embodiment. The circuit configuration of the electronic load device 20 according to the present embodiment will be described with reference to FIG.

  The electronic load device 20 includes a commercial power source AC21, a rectifier circuit 1, a boost chopper circuit 2, a switching circuit 3, a load circuit 4, and a fluorescent lamp 5. The electronic load device 20 receives an AC voltage from the commercial power supply AC21. In the electronic load device 20 according to the present embodiment, the fluorescent lamp 5 is used as the light source. However, for example, an LED, an incandescent lamp, a mini halogen lamp, or the like may be used.

  The rectifier circuit 1 rectifies an AC voltage input from the commercial power supply AC21 using a diode bridge, and outputs a pulsating DC voltage. The boost chopper circuit 2 boosts the pulsating DC voltage output from the rectifier circuit 1 and outputs the boosted DC voltage. The step-up chopper circuit 2 is a voltage conversion circuit that receives a DC voltage, converts the DC voltage into a voltage having a predetermined magnitude, and outputs the voltage.

  The switching circuit 3 receives the DC voltage boosted by the boost chopper circuit 2, and converts the input DC voltage by turning on / off (switching) the switching element to generate a high-frequency rectangular voltage (AC voltage). The switching circuit 3 supplies power to the fluorescent lamp 5 connected to the generated high-frequency rectangular voltage via the load circuit 4. The fluorescent lamp 5 is an example of a load. As a load, instead of the fluorescent lamp 5, another light source such as an LED (light emitting diode) light source or a halogen lamp may be used.

  The switching circuit 3 receives a PWM signal 9 (dimming signal) indicating the dimming rate of the fluorescent lamp 5 and controls the magnitude of the AC voltage supplied to the fluorescent lamp 5 based on the input PWM signal 9. A PWM conversion circuit 10 (signal conversion circuit) that outputs a control signal is provided. Further, the switching circuit 3 includes an output control circuit 6 that controls the magnitude of the AC voltage supplied to the fluorescent lamp 5 based on the control signal output from the PWM conversion circuit 10.

  As described above, the switching circuit 3 includes the switching control circuit 8 that controls the oscillation of the switching circuit 3, the PWM conversion circuit 10 that converts the PWM signal 9 (dimming signal) input from the outside into a predetermined DC voltage, And an output control circuit 6 for outputting a signal for changing the oscillation frequency of the switching control circuit 8 based on the DC voltage output from the PWM conversion circuit 10. The PWM conversion circuit 10 may be outside the switching circuit 3. The switching circuit 3 also includes a load current detection resistor R10 that detects a load current flowing through the load circuit 4.

  The output control circuit 6 compares the voltage obtained by the resistor R10 that detects the load current with the DC voltage output from the PWM conversion circuit 10, and outputs a signal that changes the oscillation frequency of the switching control circuit 8.

  The step-up chopper circuit 2 includes pulsating voltage detection resistors R4 and R5, a transformer T1, a MOSFET Q1 (may be a switching element), a current detection resistor R6, a diode D1, an aluminum electrolytic capacitor C1, and an output voltage detection resistor R1. , R2 and a step-up chopper control circuit 7. The transformer T1 (transformer) includes a ferrite core around which a primary winding P1 (first winding), a secondary winding S1 (second winding), and a secondary winding S2 are wound. The resistor R6 is a current detection resistor that detects the current of the switching element Q1.

  The pulsating voltage detection resistors R4 and R5 are connected in parallel to the output terminal of the rectifier circuit 1. The transformer T1 is connected to the MOSFET Q1. The current detection resistor R6 detects a current flowing through the MOSFET Q1.

  The diode D1 (switching diode) has an anode connected to the transformer T1 and a cathode connected to the aluminum electrolytic capacitor C1. The aluminum electrolytic capacitor C1 is connected to the cathode side of the diode D1 and the low potential side of the rectifier circuit 1. The output voltage detection resistors R1 and R2 are connected in parallel to the aluminum electrolytic capacitor C1, and detect the voltage charged in the aluminum electrolytic capacitor C1.

  The step-up chopper control circuit 7 includes a detection signal detected by the pulsating voltage detection resistors R4 and R5, a detection signal detected by the output voltage detection resistors R1 and R2, a detection signal detected by the current detection resistor R6 of the MOSFET Q1, and a transformer T1. The detection signal generated on the secondary winding S2 side is input, and the boost chopper circuit 2 is controlled based on these detection signals.

  The transformer T1 of the step-up chopper circuit 2 includes a primary winding P1 and secondary windings S1 and S2. Connected to one side of the secondary winding S1 is a DC power supply circuit V1 that causes a DC current to flow through the secondary winding S1 via a resistor R7 when the transistor Q5 is turned on. The DC power supply circuit V1 also serves as a power source for turning on the transistor Q5 when the transistor Q4 is turned off. A circuit composed of resistors R4, R5, R7, R8, R9, transistors Q4, Q5, capacitor C2, and DC power supply circuit V1 is an adjustment circuit 27 for causing a DC current to flow through the secondary winding S1. The circuit configuration and operation of the adjustment circuit 27 will be described later.

  The switching circuit 3 includes switching elements Q2 and Q3 and a switching control circuit 8 that generates a signal for alternately switching on and off (switching) the switching elements Q2 and Q3 at a high frequency.

  The load circuit 4 is connected to the fluorescent lamp 5 through a ballast choke L20 from a connection point between the switching element Q2 and the switching element Q3, and a DC voltage component removing capacitor C20 for removing a DC component is connected between the fluorescent lamp 5 and the ground. A series resonance circuit is provided.

  Next, the operation of the electronic load device 20 according to the present embodiment will be described with reference to FIG.

  First, the operation of turning on the fluorescent lamp 5 in the electronic load device 20 shown in FIG. 1 will be described. When an AC voltage from the commercial power supply AC 21 is supplied to the electronic load device 20 (high frequency conversion circuit), the boost chopper circuit 2 operates and a boosted DC voltage is applied to the switching circuit 3.

  The switching control circuit 8 outputs a signal to the switching elements Q2 and Q3 so that the switching elements Q2 and Q3 of the switching circuit 3 are alternately turned on and off. As a result, a high-frequency rectangular wave voltage is generated between the connection point of the switching elements Q2 and Q3 and the low potential side of the DC voltage component removing capacitor C20.

  A rectangular wave high-frequency voltage generated by the switching circuit 3 is applied to the load circuit 4 and the fluorescent lamp 5. The ballast choke L20, the fluorescent lamp 5, and the DC voltage component removing capacitor C20 are a series resonant circuit. A high-frequency current flows through the load circuit 4 and the fluorescent lamp 5, and the fluorescent lamp 5 is lit.

  Next, the operation when the fluorescent lamp 5 is dimmed in the electronic load device 20 shown in FIG. 1 will be described.

  The resistor R10 is connected to the source terminal side of the MOSFET Q3 of the switching circuit 3, and detects the load current of the load circuit 4 while the fluorescent lamp 5 is lit at a high frequency. The voltage generated in the resistor R10 is input to the output control circuit 6 after being smoothed.

  The PWM signal 9 is a dimming signal input from the outside. The PWM conversion circuit 10 converts the PWM signal 9 input from the outside into a DC voltage corresponding to the on-duty of the PWM signal 9. The output control circuit 6 receives a DC voltage from the PWM conversion circuit 10.

  The output control circuit 6 inputs the voltage generated in the resistor R10 and the DC voltage output by the PWM conversion circuit 10. These two voltages (DC signals) are compared by an operational amplifier inside the output control circuit 6, and the following control is performed according to the comparison result.

  For example, when the on-duty of the PWM signal 9 is large, the voltage output from the PWM conversion circuit 10 is high. The output control circuit 6 compares the voltage generated in the resistor R10 with the voltage from the PWM conversion circuit 10. As a result, since the voltage from the PWM conversion circuit 10 is high, the output control circuit 6 controls to increase the output (brighten the light source). To do. That is, the output control circuit 6 outputs a signal so that the oscillation frequency of the switching control circuit 8 is lowered, the current flowing through the load circuit 4 is increased, and the fluorescent lamp 5 is brightened.

  Further, when the on-duty of the PWM signal 9 is small, the voltage output from the PWM conversion circuit 10 is low. The output control circuit 6 compares the voltage generated in the resistor R10 with the voltage from the PWM conversion circuit 10. As a result, since the voltage from the PWM conversion circuit 10 is low, the output control circuit 6 controls the output to be low (darken the light source). To do. That is, the output control circuit 6 outputs a signal so that the oscillation frequency of the switching control circuit 8 is increased, the current flowing through the load circuit 4 is reduced, and the fluorescent lamp 5 is darkened.

  FIG. 2 is a circuit diagram of an electronic load device 201 for comparison with the electronic load device 20 according to the present embodiment. FIG. 2 is a diagram corresponding to FIG. 1, and functional components similar to those in FIG. 1 are denoted by the same reference numerals and description thereof is omitted.

  As shown in FIG. 2, the step-up chopper circuit 22 of the electronic load device 201 has a secondary winding S1 and a circuit configuration connected to the secondary winding S1 (resistors R7, R8, R9, transistors Q4, Q5, The capacitor C2 and the DC power supply circuit V1) are not provided.

  The operation of the step-up chopper circuit 22 when the commercial power supply AC21 fluctuates and the fluorescent lamp 5 is dimmed will be described in the electronic load device 201 shown in FIG. The fluctuation of the commercial power supply AC21 is 100V to 254V, and the dimming rate is 100% to 5%.

  The boost chopper circuit 22 stores energy in the transformer T1 when the MOSFET Q1 is turned on. After that, when the MOSFET Q1 is turned off, the energy stored in the transformer T1 is stored in the aluminum electrolytic capacitor C1 via the diode D1. Rises. The step-up chopper control circuit 7 monitors the voltage divided by the resistors R1 and R2 arranged in parallel with the aluminum electrolytic capacitor C1 in order to maintain the increased voltage at a constant voltage, and varies the switching frequency of the MOSFET Q1. Yes.

  When the commercial power supply AC21 is 100V and the dimming rate is 100%, the input current of the apparatus is the largest. In this case, since it is necessary to store a large amount of energy in the transformer T1, the boost chopper control circuit 7 of the boost chopper circuit 2 makes the on-time of the MOSFET Q1 the longest, and thus the oscillation frequency becomes the lowest.

  When the commercial power supply AC21 is 254V and the dimming rate is 5%, the input current of the apparatus is the smallest. In this case, since it is not necessary to store large energy in the transformer T1, the boost chopper control circuit 7 of the boost chopper circuit 2 minimizes the on-time of the MOSFET Q1, and thus the oscillation frequency becomes the highest. The oscillation frequency also changes along the peak level of the full-wave rectified waveform rectified by the rectifier circuit 1, and is highest near the bottom of the full-wave rectified waveform.

  If the oscillation frequency of the gate voltage for driving the MOSFET Q1 becomes too high, the MOSFET Q1 cannot be turned on. Therefore, the MOSFET Q1 cannot be turned on near the bottom of the full-wave rectified waveform, and as a result, no current flows near the zero cross of the input current, and the power factor deteriorates.

  Next, the operation of the step-up chopper circuit 2 when the commercial power supply AC21 fluctuates and the fluorescent lamp 5 is dimmed will be described using the electronic load device 20 according to the present embodiment with reference to FIG. The fluctuation of the commercial power supply AC21 is 100V to 254V, and the dimming rate is 100% to 5%.

  In the electronic load device 20 according to the present embodiment, the inductance value of the primary winding P1 of the transformer T1 of the step-up chopper circuit 2 is the optimum inductance value when the commercial power source AC21 is 254V and the dimming rate is 5%. It is assumed that it is set. The optimum inductance value is an inductance value at which the harmonic current is lowest and the power factor is high when the commercial power supply AC21 is 254V and the dimming rate is 5%, and the frequency does not become too high. Such an inductance value.

  The step-up chopper control circuit 7 includes a fluctuation detection circuit (adjustment circuit) that detects fluctuations in the input voltage or input current. The voltage dividing ratio of the resistor R4 and the resistor R5 is set to a constant that turns on the transistor Q4 when the commercial power supply AC21 is 254V and turns off the transistor Q4 when the commercial power supply AC21 is 120V or less. That is, when the commercial power supply AC21 is 120V <AC ≦ 254V, the transistor Q4 is on, and when AC ≦ 120V, the transistor Q4 is off.

  In the electronic load device 20, when the commercial power supply AC21 is 254V and the dimming rate is 5%, the voltage that is full-wave rectified by the rectifier circuit 1 is divided by the resistors R4 and R5 of the boost chopper circuit 2, and the divided voltage Is smoothed by the resistor R9 and the capacitor C2 and input to the base of the transistor Q4.

  When the transistor Q4 is turned on, no current flows from the DC power supply circuit V1 to the base of the transistor Q5 via the resistor R8, so that the transistor Q5 is turned off. When the transistor Q5 is turned off, no DC current flows from the DC power supply circuit V1 through the secondary winding S1, the resistor R7, and the transistor Q5 of the transformer T1. That is, when the commercial power source AC21 is 120V <AC ≦ 254V, no direct current flows through the secondary winding S1, so that there is no change in the inductance value of the transformer T1, the commercial power source AC21 is 254V, and the dimming rate is 5 The inductance value that is optimal at the time of% remains unchanged.

  Next, a case where the commercial power supply AC21 is lowered from 254V will be described. When the commercial power supply AC21 is lowered from 254V, the divided voltage of the resistors R4 and R5 decreases. When the commercial power supply AC21 falls below 120V, the transistor Q4 is turned off. When the transistor Q4 is turned off, a current flows from the DC power supply circuit V1 to the base of the transistor Q5 via the resistor R8, and the transistor Q5 is turned on. When the transistor Q5 is turned on, a DC current flows from the DC power supply circuit V1 through the secondary winding S1, the resistor R7, and the transistor Q5 of the transformer T1.

  When a direct current flows through the secondary winding S1 of the transformer T1, the magnetic resistance of the ferrite core of the transformer T1 increases, and the inductance value on the primary winding P1 side of the transformer T1 decreases. That is, when the commercial power source AC21 is AC ≦ 120V, a direct current flows through the secondary winding S1, and the inductance value of the transformer T1 decreases. At this time, the inductance value of the transformer T1 is an optimum inductance value (the lowest harmonic current becomes the highest and the power factor becomes the highest) when the commercial power source AC21 is 100V and the dimming rate is 100%, and the frequency becomes low. The inductance value is not too much. The constant of the resistor R7 is set so that the direct current flowing through the secondary winding S1 has an inductance value that has the lowest harmonic current and a high power factor when the dimming rate is 100% at 100V.

  Note that the on / off switching timing of the transistor Q5 is not necessarily limited to the above range, and may be changed according to the harmonic current and the power factor. For example, when the commercial power source AC21 is 120V <AC ≦ 254V, for example, the optimum inductance value when the commercial power source AC21 is 254V and the dimming rate is 20%, or the commercial power source AC21 is 200V and the dimming rate is 20 It may be an inductance value that is optimal when the value is%. Alternatively, when the commercial power supply AC21 is AC ≦ 120V, for example, the optimum inductance value when the commercial power supply AC21 is 100V and the dimming rate is 80%, or the commercial power supply AC21 is 110V and the dimming rate is 90%. An inductance value that is sometimes optimal may be used.

  As described above, the adjustment circuit 27 including the resistors R4, R5, R7, R8, and R9, the transistors Q4 and Q5, the capacitor C2, and the DC power supply circuit V1 detects and detects the voltage value of the input DC voltage. This is an example of an adjustment circuit that changes the inductance value of the primary winding P1 based on the voltage value. The adjustment circuit includes a DC power supply circuit V1 for applying a DC voltage to the secondary winding S1, and by applying a DC voltage having a magnitude corresponding to the detected voltage value to the secondary winding S1 by the DC power supply circuit V1. The inductance value of the primary winding P1 is changed. Further, the adjustment circuit 27 reduces the inductance value of the primary winding P1 when the detected voltage value (input voltage) is a predetermined value (for example, 120 V) or less, and adjusts so that the frequency does not become too low. .

  As described above, the electronic load device 20 according to the present embodiment includes the rectifier circuit 1 that rectifies the AC voltage of the input commercial power supply AC21, and the booster that converts the voltage rectified by the rectifier circuit 1 into a predetermined voltage. A chopper circuit 2 (voltage conversion circuit), a DC power supply circuit V1 that supplies a DC current to a secondary winding S1 of a transformer T1 provided in the boost chopper circuit 2, and a voltage of the boost chopper circuit 2 according to a load A load circuit 4 for converting the output voltage into a voltage, a switching control circuit 8 (control circuit) for changing the output of a load connected to the load circuit 4, and an adjustment circuit 27 (change detection) for detecting a change in input voltage or input current. Circuit).

  As described above, the electronic load device 20 changes the DC current value of the DC power supply circuit V1 in accordance with the detection value (input voltage) of the adjustment circuit 27, and the transformer T1 of the boost chopper circuit 2 (voltage conversion circuit). The inductance value of the primary winding P1 is varied. The adjustment circuit 27 detects the voltage value of the DC voltage input from the rectifier circuit 1 as a value (detection value) related to the magnitude of the input DC voltage.

  As described above, according to the electronic load device 20 according to the present embodiment, the optimum inductance value of the transformer T1 can be selected according to the input voltage or the like of the commercial power supply AC21. Can be improved.

Embodiment 2. FIG.
FIG. 3 is a circuit diagram of the electronic load device 20 according to the present embodiment. In the present embodiment, components having functions similar to those in FIG. 1 described in the first embodiment are denoted by the same reference numerals, and description thereof is omitted. In FIG. 3, the configuration of the adjustment circuit 271 of the boost chopper circuit 2 is different from that of the adjustment circuit 27 of the first embodiment.

  As shown in FIG. 3, the load current detection resistor R10 of the switching circuit 3 is connected to the transistor Q5 via the resistor R9 of the boost chopper circuit 2. The high-frequency voltage converted by the load current detection resistor R10 is smoothed by the resistor R9 and the capacitor C2 and applied as an average DC voltage to the base terminal of the transistor Q5.

  When a 100% output signal is output from the PWM signal 9, the current flowing through the load current detection resistor R10 is maximized, so that the voltage applied to the base of the transistor Q5 is also maximized. When a 5% output signal is output from the PWM signal, the current flowing through the load current is minimized, so that the voltage applied to the base terminal of the transistor Q5 is also minimized.

  The values of the resistor R9 and the resistor R10 are set so that the transistor Q5 is not turned on when the output is 5% to 90%. When the output exceeds 90%, the transistor Q5 is turned on, and a DC current flows from the DC power supply circuit V1 through the secondary winding S1, the resistor R7, and the transistor Q5. When a direct current flows through the secondary winding S1, the magnetic resistance of the ferrite core of the transformer T1 increases, and the inductance value on the primary winding P1 side of the transformer T1 decreases. Thereby, the frequency of the boost chopper circuit 2 can be maintained in an appropriate range.

  Note that the on / off switching timing of the transistor Q5 at the load output need not be limited to the above output range, and may be changed according to the harmonic current and the power factor.

  As described above, the adjustment circuit 271 (variation detection circuit) of the electronic load device 20 according to the present embodiment detects the load current flowing through the load circuit 4 by detecting the current flowing through the load current detection resistor R10. The DC current value of the DC power supply circuit V1 is changed to vary the inductance value of the primary winding P1. The adjustment circuit 271 detects the load current flowing through the load circuit 4 as a detection value as a value related to the magnitude of the AC voltage supplied to the fluorescent lamp 5 (load).

  As described above, according to the electronic load device 20 according to the present embodiment, the optimum inductance value of the transformer T1 can be selected according to the load power, so that harmonics and power factors can be selected according to the load power. Can be improved.

Embodiment 3 FIG.
FIG. 4 is a circuit diagram of the electronic load device 20 according to the present embodiment. In this embodiment, components having the same functions as those in FIGS. 1 and 3 described in the first and second embodiments are denoted by the same reference numerals, and the description thereof is omitted. In FIG. 4, the connection destination of the adjustment circuit 271 of the boost chopper circuit 2 is different from that of the adjustment circuit 271 of the second embodiment.

  As shown in FIG. 4, the adjustment circuit 271 is connected to the PWM conversion circuit 10. The PWM conversion circuit 10 is connected to the base terminal of the transistor Q5 via the resistor R9.

  The signal output from the PWM signal 9 is input to the PWM conversion circuit 10, converted into a DC voltage (an example of a control signal) corresponding to the on-duty of the PWM signal 9 by the PWM conversion circuit 10, and output. For example, the DC voltage that is output when the on-duty is maximum (load output is 100%) is the maximum, and the DC voltage that is output when the on-duty is minimum (load output is 5%).

  The values of the resistors R9 and R10 are set so that the transistor Q5 is not turned on when the load is output from 5% to 90%. When the output exceeds 90%, the transistor Q5 is turned on, and a DC current flows from the DC power supply circuit V1 through the secondary winding S1, the DC current limiting resistor R7, and the transistor Q5. When a direct current flows through the secondary winding S1, the magnetic resistance of the ferrite core of the transformer T1 increases, and the inductance value on the primary winding P1 side of the transformer T1 decreases. Thereby, the frequency of the boost chopper circuit 2 can be maintained in an appropriate range.

  Note that the on / off switching timing of the transistor Q5 at the load output need not be limited to the above output range, and may be changed according to the harmonic current and the power factor.

  As described above, the adjustment circuit 271 (variation detection circuit) detects the DC voltage (an example of a control signal) corresponding to the on-duty of the PWM signal 9 from the PWM conversion circuit 10 as a detection value, thereby detecting the DC power supply circuit V1. And the inductance value of the primary winding P1 is varied. The adjustment circuit 271 uses a DC voltage (control signal) corresponding to the on-duty of the PWM signal 9 indicating the dimming rate of the fluorescent lamp 5 (load) as a value related to the magnitude of the AC voltage supplied to the fluorescent lamp 5 (load). Is detected as a detection value.

  In addition, the electronic load device 20 according to the present embodiment is characterized in that the load fluctuation is 25% or less with respect to the maximum load output. Alternatively, the fluctuation of the load may be 5% or less with respect to the maximum load output.

  As described above, according to the electronic load device 20 according to the present embodiment, the optimum inductance value of the transformer T1 is selected according to the DC voltage corresponding to the on-duty of the PWM signal 9 from the PWM conversion circuit 10. Therefore, harmonics and power factor can be improved according to load fluctuations.

  As mentioned above, although Embodiment 1-3 was demonstrated, you may implement combining 2 or more among these Embodiment. Alternatively, one of these embodiments may be partially implemented. Alternatively, two or more of these embodiments may be partially combined. In addition, it is not limited to these embodiment, A various change is possible as needed.

  DESCRIPTION OF SYMBOLS 1 Rectification circuit, 2 Boost chopper circuit, 3 Switching circuit, 4 Load circuit, 5 Fluorescent lamp, 6 Output control circuit, 7 Boost chopper control circuit, 8 Switching control circuit, 9 PWM signal, 10 PWM conversion circuit, 20 Electronic load device , 21 Commercial power supply AC, 22 Boost chopper circuit, 27 Adjustment circuit, 201 Electronic load device, 271 Adjustment circuit, R1, R2, R4, R5, R6, R7, R8, R9, R10 resistance, T1 transformer, P1 primary winding Wire, S1, S2 secondary winding, Q1 switching element, D1 diode, C1 aluminum electrolytic capacitor, Q2, Q3 switching element, L20 ballast choke, C20 DC voltage component removal capacitor, V1 DC power supply circuit, Q4, Q5 transistor, C2 Capacitor.

Claims (7)

In an electronic load device with a load,
A voltage conversion circuit that inputs a DC voltage, converts the input DC voltage into a voltage of a predetermined magnitude, and outputs it;
A switching circuit that converts the DC voltage output by the voltage conversion circuit into an AC voltage by switching a switching element;
A load circuit for supplying the load with the alternating voltage converted by the switching circuit,
The voltage conversion circuit includes:
A transformer comprising a first winding to which an input DC voltage is applied;
A value related to the magnitude of the input DC voltage or a value related to the magnitude of the AC voltage supplied to the load is detected as a detected value, and the inductance value of the first winding is determined based on the detected value. An electronic load device comprising: an adjusting circuit for changing the electronic load device. The transformer is
A core around which the first winding and the second winding are wound;
The adjustment circuit includes:
A DC power supply circuit for applying a DC voltage to the second winding, and applying a DC voltage having a magnitude corresponding to the detected value detected for the second winding by the DC power supply circuit; 2. The electronic load device according to claim 1, wherein an inductance value of the first winding is changed. The load is a light source;
The load circuit is
A signal conversion circuit that inputs a dimming signal indicating the dimming rate of the light source, and outputs a control signal for controlling the magnitude of the AC voltage supplied to the load based on the input dimming signal;
The electronic load device according to claim 1, further comprising: an output control circuit that controls a magnitude of an AC voltage supplied to the load based on a control signal output from the signal conversion circuit. The adjustment circuit includes:
The electronic load device according to claim 1, wherein a voltage value of an input DC voltage is detected as the detection value. The adjustment circuit includes:
The electronic load device according to claim 4, wherein when the detected voltage value is equal to or less than a predetermined value, the inductance value of the first winding is reduced. The adjustment circuit includes:
The electronic load device according to claim 1, wherein a voltage value of an AC voltage supplied to the load is detected as the detection value. The adjustment circuit includes:
The electronic load device according to claim 3, wherein a value indicated by a control signal output from the signal conversion circuit is detected as the detection value.

Images