KR101183493B1 - Dc power supply apparatus - Google Patents

Abstract

(assignment)
In the conventional DC power supply, a step-down DC-DC converter is installed at the rear end of the step-up PFC circuit to drive the LED load at low voltage. However, in a DC power supply for LED-loaded lighting, the PFC circuit can be boosted. There is no need.
(Solution)
Step-down converter, in which switching element Q1 and reactor L1 are connected in series with the output of rectifier DB, and current detection for detecting the current of the reactor by a time constant longer than the voltage period of the input alternating voltage AC1. The means R1, the threshold current detecting means CP2 for detecting the timing at which the regenerative current flowing through the reactor became zero, and the regenerative current flowing to the reactor when the regenerative current became 0 were raised to a predetermined inclination. When the triangular wave generating means (CC1, Ct, 3) resets and the regenerative current becomes zero, the switching element is turned on, and the voltage signal Vct generated by the triangular wave generating means has exceeded the current detection signal Vcfb. Turn off the switching element.

Description

DC POWER SUPPLY APPARATUS}

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a direct current power supply device, and more particularly to a direct current power supply device having a power factor improving circuit (hereinafter referred to as a PFC circuit) as a step-down type.

DC power supply which rectifies AC voltage of commercial AC power by rectification smoothing circuit and converts it into DC voltage and converts this DC voltage to DC voltage desired by DC / DC converter and outputs it. The apparatus is conventionally used. When obtaining a DC power rectified by a rectified smoothing circuit from a commercial AC power supply, current flows to the smoothing condensor only near the peak of the sinusoidal AC voltage, so that the power factor deteriorates or harmonics It generates waves and adversely affects the surroundings. In order to solve this problem, a PFC (Power Factor Correction) circuit may be provided.

Generally, this PFC circuit uses more boost type PFC circuits than step-down PFC circuits. A step-down DC-DC converter is connected to the rear end of the step-up PFC circuit to obtain a desired low voltage DC output voltage.

As a prior art using a PFC circuit, Unexamined-Japanese-Patent No. 2002-262563 (patent document 1), Unexamined-Japanese-Patent No. 2010-40878 (patent document 2), etc. are mentioned, for example. In the power factor improving converter disclosed in Patent Document 1, a step-up power factor improving converter is used as a PFC circuit. In addition, a booster chopper (BUC) that performs a boosting operation and a power factor improving operation is used for the light emitting diode lighting device disclosed in Patent Document 2.

Japanese Patent Laid-Open No. 2002-262563 Japanese Patent Laid-Open No. 2010-40878

In the above prior art, a step-up PFC circuit is provided at the front end and a step-down DC-DC converter is provided at the front end to output a desired low voltage DC voltage from the input AC voltage. The DC power supply of the prior art uses a step-up power factor improving converter or a step-up chopper as a PFC circuit at the front end and a step-down DC-DC converter connected to the rear end for the following reasons. By.

(1) Efficiency can be improved by using the PFC circuit of the stage as a boost type PFC circuit. Since the DC voltage obtained by full-wave rectification of the AC voltage of the AC power source is input to the PFC circuit in the preceding stage, the same breakdown voltage is used as the switching element even when the PFC circuit is boosted or stepped. This is required, in other words, it cannot be replaced with a small on resistance as a specification of the switching element. For this reason, the specifications of the on resistance of the switching element are the same in both the boost type and the step-down type. If the power to be handled is the same, when the voltage is reduced by making the PFC circuit step-down, the current increases instead. Therefore, in the step-down PFC circuit, a large current flows through the step-up PFC circuit, so that the loss due to the on resistance of the switching element increases and the efficiency decreases. For this reason, boost type PFC circuits generally have better efficiency.

(2) In addition, when the front end is a step-down PFC circuit, a larger current is input to the later stage DC-DC converter than when the step-up PFC circuit is used, so that the switching current of the DC-DC converter is also increased. As a result, the efficiency of the DC-DC converter is also lowered, thereby reducing the efficiency of the entire power supply system. For this reason, it is advantageous to use a boosted PFC circuit in order to improve the efficiency of the entire power supply system.

(3) By obtaining a boosted voltage using a boosted PFC circuit, it is easy to maintain power for 1 to 2 cycles even in the case of an interruption such as instantaneous power interruption. The reliability as a system can be obtained.

The conventional technique has advantages such as improving the efficiency of the system by boosting the PFC circuit to improve the reliability of the system against instantaneous power failure. However, a light emitting diode (hereinafter referred to as LED) is used as a load for lighting. In order to drive the LED load at low voltage, it is necessary to obtain a low voltage DC output voltage, and a step-down DC-DC converter must be installed at the rear of the boost type PFC circuit. For this reason, the number of components constituting the DC power supply increases, which causes a problem in reducing the size of the device, and lowers the reliability (MTBF). It was also a cause of cost increase. In addition, in the DC power supply for lighting using LEDs, the reliability of the system against instantaneous power failure is not required. Therefore, in the DC power supply for lighting which uses LED as a load, it is not necessary to make a PFC circuit a boost type.

SUMMARY OF THE INVENTION An object of the present invention is to provide a direct current power supply device that solves the problems of the prior art in view of the above problems.

The direct current power supply device of the present invention is a direct current power supply device that converts and outputs energy obtained from an alternating current power source into direct current energy, and converts the AC voltage of the alternating current power source into full-wave rectification. A rectifier for converting the current into a DC voltage, and a switching element and a reactor are connected in series to the output of the rectifier, and the voltage is reduced by ON / OFF control of the switching element. A step-down converter for supplying a DC voltage to the load, a current detecting means for detecting a current flowing through the reactor, and a regenerative current flowing through the reactor are zero. The threshold current detection means for detecting the timing at which the timing has been reached, and the regenerative current flowing through the reactor by the threshold current detection means has become zero. A voltage signal rising at a predetermined inclination is generated starting from the detected timing, and the threshold current detecting means resets the voltage signal to zero at a timing when the regenerative current flowing through the reactor becomes zero. A triangular wave generating means and a gate signal for turning on the switching element when the threshold current detecting means detects a timing at which the regenerative current flowing to the reactor becomes zero, and generates the triangular wave generating means. And a gate signal output means for turning off the gate signal when the voltage signal exceeded the current detection signal detected by the current detection means.

In addition, in the DC power supply device of the present invention, the current detection means includes a filter having a time constant longer than a half period of the AC voltage of the AC power supply for the current detection signal flowing through the reactor. May be output through

Further, constant current control may be performed by controlling the signal of the current detecting means to be a constant signal.

In addition, the DC power supply of the present invention, the threshold current detection means detects that the voltage generated when the regenerative current flowing through the reactor becomes 0 and the free vibration starts to exceed the first predetermined predetermined voltage. You may also do it.

In the DC power supply apparatus of the present invention, the second reference potential of the current detecting means, the triangular wave generating means, and the gate signal output means is equal to the first reference potential on the rectifier output positive electrode side of the rectifier. It may be floating.

In the DC power supply device of the present invention, the current detecting means may detect a current flowing through the reactor by a current detecting resistor provided between the switching element and the reactor connected in series.

In addition, the DC power supply of the present invention, the threshold current detection means, the voltage between the reactor and the output terminal is input to the inverting input terminal of the comparator through a diode, and the predetermined inverting input terminal of the comparator A means for detecting the voltage by inputting the voltage and comparing the voltage between the reactor and the output terminal with the first predetermined voltage by the comparator may be used.

In the DC power supply device of the present invention, the load may be an LED load.

According to the present invention, a power supply device using a LED lighting device or the like as a load can be provided as a step-down power supply device having a power factor improving function by a DC-DC converter unit of a constant current control method. Therefore, since the power factor improvement can be performed by the DC-DC converter alone without combining the power factor improvement circuit and the DC-DC converter or using a multiplier in the control unit of the power factor improvement circuit as in the prior art, the number of parts is greatly reduced. It is possible to provide a reliable power supply device by improving overall efficiency in a small size and low cost. Moreover, since it consists of a step-down DC-DC converter, the inrush current prevention circuit to a smoothing capacitor, etc. are unnecessary, and a compact and inexpensive power supply device can be provided.

1 is a diagram showing a circuit configuration of a DC power supply device 1 according to an embodiment of the present invention.
Fig. 2 is a diagram showing a circuit operating waveform when the AC input voltage of the DC power supply device 1 according to the embodiment of the present invention is 1/2 of the peak value.
Fig. 3 is a diagram showing a circuit operation waveform when the AC input voltage of the DC power supply device 1 according to the embodiment of the present invention is at the peak value time point.
4 is a diagram schematically showing a power factor improvement operation of the DC power supply device 1 according to the embodiment of the present invention.
Fig. 5 is a diagram showing simulations of input voltage waveforms and input current waveforms in the DC power supply device 1 according to the embodiment of the present invention.
Fig. 6 is a measured waveform diagram of input voltage and input current in the DC power supply 1 of the embodiment according to the present invention.
Fig. 7 is a characteristic diagram in which the power factor with respect to the input voltage in the DC power supply device 1 according to the embodiment of the present invention is measured.
8 is a measured waveform diagram of an input voltage and an input current in a DC power supply according to the prior art.

In the prior art described in Patent Literature 1, a slope signal generation unit is required in order to improve the power factor. The power factor is improved only by detecting the current, so that the slope signal is not used, which eliminates the need for the slope signal generation portion, simplifying the circuit configuration, and simplifying the power factor improvement. Since the signal obtained by averaging the current of L1) is fed back, detection of the drain current corresponding to the change from the low voltage of the AC input voltage to the peak voltage is not required as in the prior art described in Patent Document 1. Switching ON even in the detection range of the signal as in the prior art described in Patent Document 1 Since the pulse change width can be large, it is possible to obtain an equivalent power factor even when compared with a power factor improvement circuit using a multiplier.

(Embodiments)

1 shows a circuit configuration of a direct current power supply device 1 according to the embodiment of the present invention.

As shown in FIG. 1, the DC power supply 1 has a full-wave rectification of the AC voltage of the commercial AC power supply AC1 by the rectifier circuit DB. The output voltage is obtained by switching the voltage with the switching element Q1 and stepping down.

The control of the output detects and averages the signal of the current IL1 flowing through the reactor L1, and makes constant current control based on this detection signal. The current IL1 flowing through the reactor L1 is detected by the voltage drop generated in the current detection resistor R1 connected in series with the reactor L1, and the signal IL1 flowing through the reactor L1 is detected. The signal is input to the feedback terminal of the control circuit 2 as a signal of. Here, the signal of the current IL1 flowing through the reactor L1 is averaged by the time constants of the resistor R2, the capacitor C2, and the resistor R3, and the capacitor C3. The signal of the current IL1 flowing through the averaged reactor L1 becomes a constant current control signal voltage.

On the other hand, the timing (the timing at which the regenerative current becomes 0 A) of the threshold current of the current IL1 flowing through the reactor L1 is detected from the voltage input through the diode D2, and the switching element ( The pulse which determines the ON signal start point of the gate signal of Q1) is generated. Starting from this pulse, the capacitor Ct is charged by a constant current of the constant current source CC1 to generate a triangular wave, and the switching element is supplied until the voltage reaches the constant current control signal voltage. When Q1 is turned on, the switching element Q1 is turned off when the voltage of the triangle wave reaches the constant current control signal voltage, and the triangle wave is reset at the timing of generating the pulse of the next threshold current.

When the output current is controlled by turning on / off the switching element Q1 in this manner, the pulse width for turning on the switching element Q1 becomes a constant pulse width in accordance with the constant current control signal voltage and can be switched by the threshold operation. As a result, the input current waveform is approximated to the sine wave shape, and power factor improvement can be performed as shown in FIG.

Next, the circuit configuration of the DC power supply 1 and its circuit operation will be described in more detail.

The circuit configuration of the DC power supply 1 will be described with reference to FIG.

A commercial AC power supply AC1 is connected to ACin1 and ACin2, which are input terminals of the DC power supply 1. The input terminals ACin1 and ACin2 are connected to an AC input terminal of a rectifying circuit DB in which a diode is bridged, and the AC voltage input from the commercial AC power supply AC1 is full-wave rectified and output. A drain terminal of the switching element Q1 is connected to the rectifying output positive terminal (voltage Vin) of the rectifying circuit DB, and a current detection resistor R1 is connected to the source terminal of the switching element Q1. One terminal of) is connected. The other terminal of the current detection resistor R1 is connected to one terminal of the reactor L1, and the other terminal of the reactor L1 is the positive output terminal of the DC power supply 1. It is connected to Pout1. On the other hand, the rectifying output negative terminal of the rectifying circuit DB is connected to the negative output terminal Pout2 (GND1) of the DC power supply 1. The cathode terminal of the diode D1 is connected to the connection point where the source terminal of the switching element Q1 and one terminal of the current detection resistor R1 are connected, and the anode terminal of the diode D1 is connected to the rectifier circuit DB. The rectified output negative electrode terminal and negative output terminal Pout2 are connected to the connected GND1 line. The smoothing capacitor C1 is connected between the positive output terminal Pout1 and the negative output terminal Pout2.

The part shown by 2 of a dotted line frame shows the control circuit which controls the DC power supply device 1. As shown in FIG. In the control circuit 2, the voltage Vin of the rectifying output positive terminal of the rectifying circuit DB is input, and the voltage of the positive output terminal Pout1 is input via the diode D2, and the current detection resistor R1 is input. The voltages at both ends of are smoothed and input by the resistors R2 and R3 and the capacitors C2 and C3. In addition, the ON / OFF signal is output from the control circuit 2 to the gate terminal of the switching element Q1.

The control circuit 2 includes a one shot circuit 3, a start circuit 4, a comparator CP1 and CP2, an operational amplifier OP1, and an operational transconductance amplifier. (OTA1), current source circuit (CC1), buffer circuit (BF), capacitors (Ct, Cfb), resistors (R4, R5), reference voltages (Vref1, Vref2) , Vref3) and the like.

The rectifying output positive terminal (voltage Vin) of the rectifying circuit DB is connected to the starting circuit 4 of the control circuit 2, and the starting circuit 4 is connected to the DC power supply 1 with a commercial AC power supply ( The control circuit 2 is activated at the initial stage when AC1) is connected.

The inverting input terminal of the comparator CP2 is connected to the cathode terminal of the diode D2, and the anode terminal of the diode D2 is connected to the positive output terminal Pout1. The non-inverting input terminal of the comparator CP2 is connected to the positive terminal of the reference voltage Vref3.

The output terminal of the comparator CP2 is connected to the input terminal of the one-shot circuit 3. The output terminal of the one-shot circuit 3 is connected to the connection point to which the inverting input terminal of the comparator CP1, one terminal of the capacitor Ct, and the current output terminal which is one terminal of the current source circuit CC1 are connected. The other terminal of the current source circuit CC1 is connected to the output terminal of the internal regulator Reg (not shown) which is the control power supply circuit of the control circuit 2.

One terminal of the resistor R2 is connected to a connection point where the other terminal of the current detection resistor R1 and one terminal of the reactor L1 are connected, and the resistor R3 is connected to the other terminal of the resistor R2. One terminal of is connected. One terminal of the capacitor C2 and one terminal of the capacitor C3 are connected to a connection point where one terminal of the current detection resistor R1, the source terminal of the switching element Q1, and the cathode terminal of the diode D1 are connected. Is connected, the other terminal of the capacitor C2 is connected to a connection point to which the other terminal of the resistor R2 and one terminal of the resistor R3 are connected, and the other terminal of the capacitor C3 is connected to the resistor. It is connected to the other terminal of (R3). The resistors R2 and R3 and the capacitors C2 and C3 constitute a filter circuit for smoothing the voltage generated at both ends of the current detection resistor R1 and outputting the same to the control circuit 2.

The connection point to which one terminal of the current detection resistor R1, one terminal of the capacitor C2 and one terminal of the capacitor C3 are connected is connected to and controlled with the negative terminals of the reference voltages Vref1, Vref2, and Vref3. The reference potential GND2 of the circuit 2 is set. The potential of the reference potential GND2 is the potential of the connection point where the source terminal of the switching element Q1 and one terminal of the current detection resistor R1 are connected, and the rectifier output negative electrode terminal and the negative side output terminal of the rectifier circuit DB. The potential is floating with respect to the GND1 line to which (Pout2) is connected. The other terminal of the resistor R5, the other terminal of the capacitor Ct, and the other terminal of the capacitor Cfb are also connected to the reference potential GND2.

In addition, one terminal of the resistor R4 is connected to the output terminal of the internal regulator Reg, and the other terminal of the resistor R4 is connected to one terminal of the resistor R5, The other terminal is connected to the reference potential GND2. A connection point to which the other terminal of the resistor R3 is connected to the other terminal of the resistor R3 and the operational amplifier OP1 are connected to a connection point to which the other terminal of the resistor R4 and one terminal of the resistor R5 are connected. The inverting input terminal of is connected.

The non-inverting input terminal of the operational amplifier OP1 is connected to the positive terminal of the reference voltage Vref2, and the negative terminal of the reference voltage Vref2 is connected to the reference potential GND2. The output terminal of the operational amplifier OP1 is connected to the inverting input terminal of the transconductance amplifier OTA1, and the non-inverting input terminal of the transconductance amplifier OTA1 is connected to the positive terminal of the reference voltage Vref1. The negative terminal of (Vref1) is connected to the reference potential GND2.

The output terminal of the transconductance amplifier OTA1 is connected to one terminal of the capacitor Cfb, and the other terminal of the capacitor Cfb is connected to the reference potential GND2. The transconductance amplifier OTA1 converts the difference voltage between the reference voltage Vref1 input to the non-inverting input terminal and the voltage from the output terminal of the operational amplifier OP1 input to the inverting input terminal into current and amplifies and outputs it. . Therefore, the capacitor Cfb is charged and discharged by the output current from the transconductance amplifier OTA1.

The connection point where the output terminal of the transconductance amplifier OTA1 and one terminal of the capacitor Cfb are connected is connected to the non-inverting input terminal of the comparator CP1. The output terminal of the comparator CP1 is connected to the input terminal of the buffer circuit BF, and the output terminal of the buffer circuit BF is connected to the gate terminal of the switching element Q1.

Next, the circuit operation of the DC power supply 1 will be described with reference to Figs. Fig. 2 shows the operating waveform at the point of 1/2 of the peak value of the sine wave pulsating voltage (voltage Vin) output from the rectifying output positive terminal of the rectifying circuit DB. 3 shows the operating waveform at the peak value point of the sine wave pulsating voltage (voltage Vin) output from the rectifying output positive terminal of the rectifying circuit DB.

Each of the waveforms in FIGS. 2 and 3 is a current waveform IL1 flowing from the upper side to the reactor L1, a voltage waveform VR1 generated in the current detection resistor R1, and a voltage waveform Vc2 of the capacitor C2. ), The voltage waveform Vc3 of the capacitor C3, the voltage waveform Vct of the capacitor Ct, the voltage waveform Vcfb of the capacitor Cfb, the output waveform of the one-shot circuit 3, and the buffer circuit BF. The output waveform is shown.

The current IL1 flowing through the reactor L1 is equal to the instantaneous value of the sine wave pulsating voltage of the rectifier circuit DB to the reactor L1 when the switching element Q1 is ON (the output of the buffer circuit BF is H). Since the difference voltage of the output voltage is applied, it increases by the inclination which is approximately proportional to the voltage (referred to as ON current). When the switching element is turned off, the energy accumulated in the reactor L1 is discharged in the closed circuits of the reactors L1 to smoothing capacitors C1 to diodes D1 to Reactor L1, so that the smoothing capacitor C1 is charged. As a result, the current IL1 flowing through the reactor L1 is reduced (referred to as a regenerative current). Therefore, as illustrated in FIGS. 2 and 3, the current IL1 flowing through the reactor L1 flows in a triangular wave current. Each timing indicated by the times t1, t3, ..., t11, t21, t23, ..., t25 is the timing at which the regenerative current becomes 0A and the free vibration starts (critical current )). As will be described later, at each timing t1, t3, ..., t11, t21, t23, ..., t25, free vibration starts by the threshold current, and the reference voltage Vref3 by the free vibration at this time. The voltage exceeding is detected and the triangle wave (voltage VCt of capacitor Ct) generated inside is reset. This reset cycle becomes the ON / OFF cycle of the switching element Q1.

The current IL1 flowing through the reactor L1 is detected by the current detection resistor R1. This detection voltage VR1 has a low voltage at one terminal side of the reactor L1 at the source terminal side of the switching element Q1 when the current flows from the resistor R1 in the direction of the reactor L1. 3, it is detected as a negative voltage.

The voltage VR1 detected by the current detection resistor R1 is integrated by the resistor R2, the capacitor C2, the resistor R3, and the capacitor C3. Here, the time constant of the integral multiplier is set to a time constant equal to or greater than half the frequency of the commercial AC power supply AC1. The output voltage of the first stage filter circuit composed of the resistor R2 and the capacitor C2 is the voltage of the capacitor C2 shown by Vc2 in Figs. 2 and 3, and contains a slightly pulsating component. The output voltage of the second stage filter circuit composed of the resistor R3 and the capacitor C3 is the voltage VC3 of the capacitor C3 shown by Vc3 of Figs. 2 and 3, and the pulsation component is less than that of Vc2. The voltage is approximately constant.

The output voltage of the second stage filter circuit composed of the time constant circuit of the resistor R3 and the capacitor C3 is connected to the inverting input terminal of the operational amplifier OP1. Here, since the other terminal potential of the current detection resistor R1 becomes a negative potential with respect to one terminal potential (reference potential GND2) of the current detection resistor R1, the resistance of the filter circuit R3. ) And the voltage input from the connection point of the capacitor C3 to the point where the output voltage of the internal regulator Reg is divided by the resistor R4 and the resistor R5. Biased to the inverting input terminal of the operational amplifier OP1. Vc3 shown in Figs. 2 and 3 shows a state in which the potential is biased.

The reference voltage Vref2 is connected to the non-inverting input terminal of the operational amplifier OP1. The biased voltage of the filter circuit inputted to the inverting input terminal of the operational amplifier OP1 and the reference voltage Vref2 inputted to the non-inverting input terminal are compared, and the operational amplifier OP1 amplifies these differences to transconductance. Output to the inverting input terminal of the amplifier OTA1.

A reference voltage Vref1 is connected to the non-inverting input terminal of the transconductance amplifier OTA1, compares the input voltage and the reference voltage Vref1 of the non-inverting input terminal, amplifies the difference between the voltages and the current from the voltage signal. Convert it to a signal and output it. Here, the output terminal of the transconductance amplifier OTA1 is connected to the non-inverting input terminal of the capacitor Cfb and the comparator CP1, and the output current of the transconductance amplifier OTA1 charges and discharges the charge of the capacitor Cfb. . Accordingly, the signal input from the output of the transconductance amplifier OTA1 to the non-inverting input terminal of the comparator CP1 can be replaced with a voltage signal.

The inverting input terminal of the comparator CP1 is connected to a connection point to which the output terminal of the constant current circuit CC1, one terminal of the capacitor Ct, and the output terminal of the one-shot circuit 3 are connected. Here, the constant current circuit CC1, the capacitor Ct, and the one-shot circuit 3 constitute a triangular wave oscillator. That is, the inclination of the triangular wave waveform is determined by charging the capacitor Ct with a constant current by the constant current circuit CC1, and the one-shot circuit 3 outputs a pulse signal for determining the reset timing of the triangular wave oscillation. The output waveform of the triangular wave oscillation composed of the constant current circuit CC1, the capacitor Ct, and the one-shot circuit 3 is shown in Figs. 2 and 3 as the voltage Vct of the capacitor Ct.

The voltage at the connection point to which the reactor L1 and the smoothing capacitor C1 are connected is input to the inverting input terminal of the comparator CP2 through the diode D2, and the voltage of the reference potential Vref3 is the ratio of the comparator CP2. It is being input to the inverting input terminal. After the switching element Q1 is turned off, the free vibration starts at the point of time at which the regeneration of the current IL1 of the reactor L1 has finished, and the free potential is applied to the reference potential GND2 of the control circuit 2. A positive voltage exceeding the reference voltage Vref3 is generated. When the voltage of this free vibration exceeds the reference potential Vref3, the output of the comparator CP2 outputs the H level signal to the one-shot circuit 3. The one-shot circuit 3 outputs a pulse signal when this H level signal is input from the comparator CP2 (see the output signal of the one-shot circuit 3 in Figs. 2 and 3). The charge of the capacitor Ct is rapidly discharged by this pulse signal. That is, the one-shot circuit 3 outputs a pulse signal at each timing of the timings t1, t3, ..., t11, t21, t23, t25 of the critical current of the current IL1 flowing through the reactor L1. This pulse signal determines the cycle start timing in the ON / OFF cycle of the switching element Q1.

The output of the buffer circuit BF, in other words, the ON pulse signal of the switching element Q1 is determined by the comparator CP1. As shown in FIGS. 2 and 3, the comparator CP1 compares the triangular wave signal Vct of the inverting input terminal with the Vcfb terminal voltage of the non-inverting input terminal, and the period when the triangular wave signal Vct is lower than the Vcfb terminal voltage. For example, the ON pulse signal is output from the buffer BF in the ton periods t1 to t2 and t21 to t22 shown in Figs. As described above, the OFF period is until the regeneration of the current IL1 of the reactor L1 ends, and the peak voltage of the triangular wave signal of the capacitor Ct is fixed as shown in FIGS. 2 and 3. Instead, the signal is raised to the pulse signal from the next one short circuit 3. 2 and 3, the Toff period of the buffer circuit BF is longer than that in FIG. In this way, the frequency of the triangular wave oscillation is not fixed, but is changed by the pulsation voltage obtained by full-wave rectifying the AC voltage input from the commercial AC power supply AC1.

However, the Ton period of the buffer circuit BF is approximately the same pulse width regardless of the above pulsating voltage. The signal VR1 of the current detection resistor R1 of the current IL1 flowing through the reactor L1 is integrated by the resistor R2, the capacitor C2, the resistor R3, and the capacitor C3. Since the time constant of the integral multiplier is set to a time constant equal to or greater than half the period of the commercial AC power supply AC1, the change in the input voltage of the non-inverting input terminal of the operational amplifier OP1 is small. The voltage of Vc3 of FIG. 2 showing the case where the instantaneous value of the input voltage is 1/2 of the pulsating voltage peak value and the voltage of Vc3 of FIG. 3 showing the case of the instantaneous value of the input voltage of the pulsating voltage peak value are approximately the same voltage. . Accordingly, as shown in Figs. 2 and 3, the ON pulse width in the half cycle period of the frequency of the commercial AC power supply AC1 becomes substantially constant even if the phases are different, so that an input current close to the input voltage waveform flows. do.

4 shows that the operation in the half cycle period of the frequency of the commercial AC power supply AC1 is extremely less than the actual number of switching (for example, 20 kHz) (in the half cycle of Vin in FIG. 4). Number of switching times), which is typically shown clearly. The pulsation voltage obtained by full-wave rectifying the AC voltage input from the commercial AC power supply AC1 is shown as Vin. The triangular wave inside the pulsating voltage Vin indicates the current of the reactor L1. The ton of the triangle wave, painted in black, is the ON current, and the portion shown as Toff following the regenerative current. In FIG. 4, the lower figure is the figure which expands and shows a part of upper figure. A free vibration current is generated immediately after the threshold current at which the current IL1 of the reactor L1 represented by the regenerative current reaches 0A.

When the switching element Q1 is turned on with the threshold current as a starting point, and the pulsating voltage Vin is applied to the reactor L1 and the difference voltage between the voltage (output voltage Vo) of the smoothing capacitor C1 is applied, the reactor L1. The current of is the slope of (Vin-Vo) / L and increases to the value of (Vin-Vo)-Ton / L (L is the inductance value of reactor L1). At this time, since the inductance value L of the reactor L1 is constant and the period Ton is constant, the peak value of the current in the ON current is the instantaneous value of the pulsating voltage Vin at that time and the output voltage. It is proportional to the difference voltage from (Vo). In the regenerative current, instead of the switching element Q1 being turned off, the diode D1 is turned on so that a current caused by induced electromotive force flows in the reactor L1. At this time, the voltage of the smoothing capacitor C1 (output voltage Vo) is applied to the reactor L1. Therefore, the current of reactor L1 is the slope of Vo / L and decreases to 0A (threshold current) (period of Toff). At this time, if the threshold current is detected and the switching element Q1 is turned on again from this point of time, the peak value of the current flowing through the reactor L1 is changed to follow the instantaneous value of the pulsating voltage Vin. It is possible to improve the power factor.

Fig. 5 shows waveforms obtained by simulation of waveforms of the input voltage and the input current of the DC power supply 1 of this embodiment. The simulation condition is to make ON time Ton of switching element Q1 constant, and to turn ON / OFF of switching element Q1 starting from a threshold current. Therefore, the following relation holds for the on / off current.

(Vin-Vo)? Ton / L = Vo? Toff / L

The simulation results show that the voltage and current at the input side of the DC power supply are sinusoidal. That is, the current which charges / discharges the smoothing capacitor C1 connected between the positive output terminal Pout1 and the negative output terminal Pout2 becomes a sine wave. The output current of the DC power supply becomes a constant constant current waveform. That is, constant current control of the signals of the current IL1 of the reactor L1 detected by the current detection resistor R1 with the time constant in the RC circuits of the resistors R2 and R3 and the capacitors C2 and C3 is constant. This means that it is equivalent to detecting the voltage of the smoothing capacitor C1 on the output side in the load resistance.

6 is a measured waveform of an AC voltage and an AC current of an AC power source AC1 connected to the DC power supply 1. 7 shows the actual value of the power factor when the input voltage is changed from 80V to 240V. The measured power factor is reaching 0.98. This satisfies Class C, which is a standard for lighting fixtures of JIS C 61000-3-2.

8 shows the waveforms of the input voltage and the input current of the DC power supply according to the prior art of the condenser input type, and the power factor is about 0.6. In the prior art, since a current flows in the smoothing capacitor only near the peak of the sinusoidal alternating voltage, a large amount of harmonics is included, and the power factor deteriorates or adversely affects the surroundings due to harmonics. On the other hand, according to the DC power supply 1 of embodiment which concerns on this invention, as shown in FIG. 6, it turns out that an input current flows in the wide range, and the power factor is improved.

In the above embodiment of the present invention, the DC power supply 1 is constituted by only one converter so that the smoothing capacitor C1 is provided from the commercial AC power supply AC1 through the rectifier circuit DB, the switching element Q1, and the reactor L1. ). For this reason, the switching element Q1 is connected in series with the smoothing capacitor C1, and becomes an ON / OFF switch when the power supply to the smoothing capacitor C1 is turned on, so that no inrush current flows into the smoothing capacitor C1. There is an advantage. That is, since the connection of the smoothing capacitor C1 is started by the switching ON / OFF operation of the switching element Q1, the inrush current prevention circuit is unnecessary, and there is an advantage that the parts can be reduced as compared with the conventional method.

In the DC power supply 1 according to the present embodiment, the time constant (resistance R2, capacitor C2, resistor R3, and capacitor C3) of the current detection circuit of the step-down chopper is used. The time constant determined) is set to a large time constant equal to or greater than half the period of the commercial AC power supply AC1, and the current detection value is controlled to be equal to or more than the time constant of the time constant and become a substantially constant current value. Therefore, if it is captured in a shorter time than the period of the commercial AC power supply AC1, it becomes a sine wave-shaped current and does not become a constant current. Outputs the set constant current value. Here, by appropriately selecting the capacitance of the smoothing capacitor C1, a constant current with less ripple component of commercial frequency can be obtained.

As described above, the power factor of the conventional step-down chopper of the condenser input type is 0.5 to 0.6. According to the DC power supply 1 of the present embodiment, a power factor of 0.9 or more can be achieved by a simple circuit configuration without a multiplier.

In addition, since the current flowing through the reactor L1 is detected and controlled based on the detected current, the output of the DC power supply 1 becomes constant current control. Since the load current can be controlled constantly by this constant current control, it is also possible to cope with the LED load.

In the DC power supply 1 of the present embodiment, the reference potential GND2 of the control circuit 2 is set on the source terminal side of the switching element Q1. By floating the reference potential GND2 of the control circuit 2 to form a step-down power factor improvement circuit from a commercial power source, even when the switching element Q1 is connected to the step-down side, the control terminal of the switching element Q1 is controlled. The gate drive circuit for driving can be driven without level shifting, so that a general control circuit can be easily configured without providing a level shift circuit as compared with the driving circuit connected to the low voltage side.

In addition, since the step-down power factor improving circuit from the commercial power supply is constituted by one converter, the number of parts can be drastically reduced and the price can be held down.

In addition, the inrush current can be prevented by configuring the step-down power factor improving circuit from the commercial power supply with one converter.

As mentioned above, although this invention was demonstrated by the specific embodiment, it cannot be overemphasized that the said embodiment is an example and can be changed and implemented in the range which does not deviate from the meaning of this invention.

1: DC power supply
2: control circuit
3: One short circuit
4: starting circuit
Q1: switching element
R1: current detection resistor
R2 ~ R5: resistance
C1: smoothing capacitor
C2 ~ C3, Ct, Cfb: Capacitor
D1, D2: Diode
L1: Reactor
DB: Rectifier Circuit
Vin: Output voltage of positive side of RC1
AC1: Commercial AC Power
Vo: Output voltage of DC power supply 1
ACin1, ACin2: Input Terminal
Vin: Voltage of rectifier circuit positive terminal of rectifier circuit (DB)
Pout1: Positive Output Terminal
Pout2: Negative output terminal
OP1, OP2: Operational Amplifier
CP1, CP2: Comparator
OTA1: Transconductance Amplifier
CC1: current source circuit

Claims (6)

In a direct current power supply device that converts and outputs energy obtained from an AC power source into direct current energy,
A rectifier for full-wave rectifying the AC voltage of the AC power source and converting the AC voltage into a DC voltage;
A switching element and a reactor are connected in series with the output of the rectifier, and a step-down converter for supplying a step-down DC voltage to the load by controlling the switching element ON / OFF. Type converter),
A current detecting means for detecting a current flowing through the reactor,
Threshold current detecting means for detecting a timing at which a regenerative current flowing through the reactor becomes zero;
The threshold current detection means generates a voltage signal which rises by a predetermined inclination starting from the timing when the regenerative current flowing through the reactor becomes zero, and the threshold current detection means flows through the reactor. Triangular wave generating means for resetting the voltage signal to zero at a timing when the current becomes zero;
When the threshold current detecting means detects a timing when the regenerative current flowing through the reactor becomes zero, a gate signal for turning on the switching element is output, and the voltage signal generated by the triangular wave generating means is detected by the current detecting means. A gate signal output means for turning off the gate signal when the current detection signal is crossed;
Equipped ,
The current detecting means outputs a current detecting signal flowing through the reactor through a filter having a time constant longer than a half period of the AC voltage of the AC power supply. DC power supply.
delete The method of claim 1 ,
And a constant current control by controlling the signal of the current detecting means to be a constant signal.
The method of claim 1 ,
And the threshold current detecting means detects that a voltage generated when a regenerative current flowing through the reactor becomes zero and free vibration starts has exceeded a first predetermined predetermined voltage.
The method of claim 1 ,
The second reference potential of the current detecting means, the triangular wave generating means, and the gate signal output means is floating with respect to the first reference potential on the side of the rectifying output positive terminal of the rectifier. DC power supply.
The method of claim 1 ,
And the current detecting means detects a current flowing through the reactor by a current detecting resistor provided between the switching element and the reactor connected in series.

Images