JPS61240597A - Ac-dc conversion circuit - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an AC-DC conversion circuit for passing a DC current from an AC power supply to a load, and more particularly to a discharge lamp lighting circuit for lighting a discharge lamp as a load.

Conventional technology The lighting circuit for lighting a discharge lamp with an AC power supply is as follows:
Lighting circuits using magnetic circuit components such as choke coils and one-cage transformers are most commonly used. However, these were heavy and large, making them undesirable for ceiling mounting. Furthermore, lighting circuits based mainly on magnetic circuit components generate large amounts of heat and power loss, and are considered undesirable from the standpoint of efficiency.

3 bae.

Another type of lighting circuit has been known that mainly uses electronic circuits to flow direct current from an alternating current power source to a discharge lamp. This type of lighting circuit is known, for example, from Japanese Patent Application Laid-open No.
As shown in Japanese Patent No. 25980, the configuration was as shown in FIG.

In FIG. 4, 1 is an AC power supply, 2 is a rectifier circuit, and 3 is a capacitor for smoothing the rectified pulsating voltage. This capacitor 3 and the rectifier 2 constitute a power supply smoothing circuit. A discharge lamp 6 is connected to the output end of the power supply smoothing circuit via a transistor 4 and a choke coil 5. Reference numeral 7 denotes a control circuit for controlling the transistor 4 to turn on and off. Further, 8 is a diode that allows the electromagnetic energy of the choke coil 5 to flow through the discharge lamp 6 while the transistor 4 is off, and 9 is a capacitor that smooths the voltage across the discharge lamp 6.

The output of the AC power supply 1 is rectified by a rectifier circuit 2 and further smoothed by a capacitor 3 to obtain a relatively flat DC ratio. Due to the output of the power supply smoothing circuit composed of the rectifier circuit 2 and the capacitor 3, a current flows into the discharge lamp 6 via the choke coil 6 when the transistor 4 is turned on. The electromagnetic energy stored in the choke coil 5 at this time flows to the discharge lamp 6 via the diode 8 when the transistor 4 is turned off. Further, the on/off control of the transistor 4 is controlled by a control circuit 7 so that the discharge lamp 6 is lit under predetermined electrical conditions. This on/off control performs switching at a high frequency in order to make the lighting circuit lightweight and compact, thereby making it possible to use a choke coil with a small inductance as the choke coil 5.

Problems to be Solved by the Invention In such a conventional discharge lamp lighting device, a capacitor is directly connected to the output terminal of the rectifier circuit 2 to smooth out the ripple voltage.
, the diode 8, the control circuit 7, and the capacitor 9 allow the current to continue flowing through the discharge lamp 6 without interruption.
It is possible to prevent the arc from extinguishing or turning off. On the other hand, since the phase advance chamber 5 page current flows from the AC power supply 1 to the capacitor 3 via the rectifier circuit 2, ■ the input power factor is low, ■ a large inrush current flows when the AC power supply 1 is turned on, and the power switch There were problems such as the possibility of damaging the rectifier circuit.

The present invention has been made in view of the above points, and has a simple configuration that allows current to flow seamlessly through the load, while providing a high power factor and a low inrush current when AC power is turned on. The purpose is to provide a switching circuit.

Means for Solving the Problems In order to solve the above problems, the present invention provides an AC power source, a rectifier circuit that rectifies the AC voltage of the AC power source to output a pulsating voltage, and an output terminal of the rectifier circuit. a series circuit of a connected load, a choke coil, and a controlled semiconductor switch; and a series circuit of the choke coil and the load connected in parallel with the series circuit of the choke coil and the controlled semiconductor switch, and connected in an opposite direction to the controlled semiconductor switch. a first diode, one end of which is connected to the rectifier circuit, the other end of which is connected to a connection point between the load and the choke coil, and the first diode is connected to be charged from the rectifier circuit to the six through the load; a series circuit of a capacitor and a second diode, and a series circuit of the capacitor and a third diode connected to discharge the accumulated charge of the capacitor into a series circuit of the load, a choke coil, and a controlled semiconductor switch. and a control circuit that controls a controlled semiconductor switch to cause current to flow through the load under predetermined electrical conditions. When the voltage is lower than the charging voltage of the capacitor, current is caused to flow from the capacitor to the load via the choke coil and the controlled semiconductor switch.

Effect of the Invention With the above-described configuration, the present invention stores a charge of a voltage equal to the maximum value of the power supply voltage minus the voltage drop caused by the load, and in a voltage range exceeding the voltage of this capacitor, the rectified AC power source is removed from the AC power supply. Without current flowing through the circuit, current flows from the alternating current source over a wide alternating voltage phase range. Therefore, a high input power factor can be obtained.

77, -7 Furthermore, in the present invention, when the AC power is turned on, the current that flows through the capacitor does not flow directly from the rectifier circuit, but through the load. Therefore, the in-rush current is limited by the impedance of the load, and excessive in-rush current can be prevented.

Embodiment FIG. 1 is a diagram showing the configuration of a discharge lamp lighting circuit which is an AC-DC conversion circuit in an embodiment of the present invention. In FIG. 1, 1 is an AC power supply, 2 is a rectifier circuit, 4 is a transistor which is a controlled semiconductor switch, 5 is a choke coil,
6 is a discharge lamp which is a load, 7 is a control circuit, 8 is a diode, and 9 is a capacitor.The above configuration is the same as the conventional example shown in FIG. 4, and the same numbers are given. 10 is a capacitor, 11 is a diode, the positive terminal of capacitor 1° is connected to the positive output terminal of rectifier circuit 2, and capacitor 10
The anode of the diode 11 is connected to the negative electrode of the diode 11, and the cathode of the diode 11 is connected to the connection point between the choke coil 5 and the discharge lamp 6.

Further, 12 is a diode. The cathode of the diode 12 is connected to the connection point between the capacitor 10 and the diode 11, and the anode of the diode 12 is connected to the negative output of the rectifier circuit 2. Note that this lighting circuit is called a step-down chopper circuit.

The operation of the embodiment shown in FIG. 1 will be explained below.

The output of the AC power supply 1 is rectified by a rectifier circuit 2 and becomes a pulsating voltage. The capacitor 1o is charged via the diode 11 and the discharge lamp 6 by the output of the rectifier circuit which becomes a pulsating voltage. At this time, the maximum charging voltage of the capacitor 1° is approximately the maximum value of the pulsating current voltage, that is, the value obtained by subtracting the voltage of the discharge lamp 6 from the maximum value of the instantaneous voltage of the AC power source. Furthermore, capacitor 1
o is connected in parallel with the output terminal of the rectifier circuit 2 by a diode 12, and the charge of the capacitor 1o is transferred to the transistor 4.
, can be supplied to the discharge lamp 6 via the choke coil 5. In this way, since the output terminal of the rectifier circuit 2 and the output terminal of the series circuit of the capacitor 1o and the diode 12 are connected in parallel, the voltage waveform at the output terminal becomes 9 Ω as shown in Fig. 2. . In FIG. 2, the section A is the section where the instantaneous value of the AC voltage exceeds the charging voltage of the capacitor 10. In this section, from the AC power supply 1, the rectifier circuit 2, the transistor
, a current is passed through the discharge lamp 6 via the choke coil 5. Also, during this section A, the capacitor 10 is charged via the diode 11 and the discharge lamp 6. Furthermore, in the section B in FIG. 2, the charging voltage of the capacitor 10 exceeds the instantaneous value of the AC voltage.
A current is passed through.

As mentioned above, when transistor 4 is turned on, the second
In the section shown in FIG. 2, current flows from the AC power source 1, and in the section shown in FIG. At this time, the electromagnetic energy stored in the choke coil 5 is transferred to the transistor 4.
When the voltage is turned off, the current flows through the diode 8 to the discharge lamp 6. Further, the on/off control of the transistor 4 is controlled by a control circuit 7 so that the discharge lamp 6 is lit under predetermined electrical conditions.
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In this way, by charging the capacitor 1o from the AC power supply 1 via the discharge lamp 6, the inrush current generated when the power is turned on can be reduced to a small value. Also,
The capacitor 10 is charged with a voltage obtained by subtracting the voltage of the discharge lamp 6 from the maximum instantaneous voltage of the AC voltage, and only when the voltage of the capacitor 10 exceeds the instantaneous voltage of the AC voltage, the capacitor 1° is discharged. When the instantaneous value of the AC voltage exceeds the voltage , current can flow from the AC power supply 1 to the discharge lamp 6 via the rectifier circuit 2, and the current flows from the AC power supply over a wide AC voltage phase range. Therefore, a high input power factor can be obtained.

Further, FIG. 3 is a diagram showing a discharge lamp lighting circuit according to another embodiment of the present invention. In FIG. 3, a series circuit of a transistor 4, a choke coil 5, and a discharge lamp 6 is connected to a rectifier circuit 2 in the reverse order of the embodiment shown in FIG. Although the connection positions are different, the circuit operation is similar to the embodiment shown in FIG.

11 bases. In the embodiment, the load was a discharge lamp, but other loads such as a resistor or a light bulb may be used. Further, although the controlled semiconductor switch is a transistor, it goes without saying that other controlled semiconductor switches such as SCR and TRIAC may be used.

It goes without saying that the charging voltage of the capacitor 10 can be kept higher than the voltage of the load if the set value of the voltage of the load is set to be less than μ of the maximum instantaneous voltage of the AC voltage.

Effects of the Invention As described above, according to the present invention, it is possible to allow current to flow seamlessly through the load with an extremely simple configuration, while maintaining a high power factor and reducing inrush current when AC power is turned on. A small AC-DC conversion circuit is obtained, which is extremely useful in practice.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the configuration of a discharge lamp lighting circuit which is an AC-DC conversion circuit in an embodiment of the present invention, FIG. 2 is a diagram showing a voltage waveform at the output end of the rectifier circuit of the present invention, and FIG. 4 is a diagram showing the configuration of a discharge lamp lighting circuit, which is an AC-DC conversion circuit in another embodiment of the present invention, and FIG. 4 is a diagram showing the configuration of a discharge lamp lighting circuit, which is a conventional AC-DC conversion circuit. be. 1... AC power supply, 2... Rectifier circuit, 3
... Capacitor, 4 ... Transistor, 5 ... Choke coil, 6 ... Discharge lamp, 7 ... Control circuit, 8 ... ...Diode, 9...Capacitor, 10...Capacitor, 11...Diode, 12...
diode.

Claims (1)

[Claims] an AC power source, a rectifier circuit that rectifies the AC voltage of the AC power source and outputs a pulsating voltage, a series circuit including a load connected to an output end of the rectifier circuit, a choke coil, and a controlled semiconductor switch; a first diode connected in parallel to the series circuit of the choke coil and the load in the series circuit and connected in the opposite direction to the controlled semiconductor switch; one end connected to the rectifier circuit and the other end connected to the a series circuit of a capacitor and a second diode connected to a connection point between the load and the choke coil so as to be charged from the rectifier circuit through the load; a series circuit of the capacitor and a third diode connected to discharge in a series circuit of the controlled semiconductor switch and the controlled semiconductor switch; and a control circuit that controls the controlled semiconductor switch so as to cause current to flow through the load under predetermined electrical conditions. The capacitor is charged from the rectifier circuit through the load, and when the instantaneous value of the AC power supply voltage is lower than the charging voltage of the capacitor, current flows from the capacitor to the load through the choke coil and the controlled semiconductor switch. An AC-DC conversion circuit characterized by the following.