JPH077945A - Ac-ac converter - Google Patents

Abstract

PURPOSE:To reduce the loss of a switching element and to obtain a high power factor at low harmonics by a method wherein a high-frequency current provided with a low-frequency component which is nearly proportional to the sine-wave voltage of a commercial AC power supply is supplied to a load circuit from the power supply via a second diode or a third capacitor. CONSTITUTION:The contact of a high-frequency choke TH with a first diode D1 is connected to a switching element Q1 via a series circuit which is composed of a second diode D2 whose anode has been connected to the side of the contact and of a load circuit including an inductance element, and a third capacitor 3 is connected across the contact of the first diode D1 with a smoothing capacitor C2 and the contact of the second diode D2 with the load circuit. Then, a high-frequency current provided with a low-frequency component which is nearly proportional to the sine-wave voltage of a commercial AC power supply AC is supplied to the load circuit from the power supply AC via the second diode D2 or the third capacitor C3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an AC-AC converter, which is applied to, for example, a discharge lamp lighting device.

[0002]

2. Description of the Related Art FIG. 7 is a block diagram of a conventional AC-AC converter having an active smoothing filter AF. In FIG. 7, the active smoothing filter AF is connected to the output terminal of the diode bridge DB that rectifies the voltage of the commercial AC power supply AC, the inverter IV is connected to the output terminal of this active smoothing filter AF, and the output terminal of this inverter IV. A load LD is connected to.

The active smoothing filter AF is composed of a transistor Q2 which switches at high frequency, a drive control circuit BC of this transistor Q2, a harmonic choke TH, a first diode D1 and a smoothing capacitor C2. In FIG. 7, the inverter IV is operated by the smoothing action of the active smoothing filter AF.
The smoothed DC voltage is supplied to.

FIG. 8 is a block diagram of another conventional AC-AC converter using a capacitor input type smoothing circuit. In FIG. 8, the smoothing capacitor C2 and the inverter IV are connected to the output terminal of the diode bridge DB that rectifies the voltage of the commercial AC power supply AC, and the load LD is connected to the output terminal of the inverter IV. In FIG. 8, due to the smoothing action of the capacitor C2, the inverter IV is supplied with a substantially completely smoothed DC voltage.

[0005]

The conventional AC-AC converter of FIG. 7 as described above can make the input current waveform almost sinusoidal, and therefore has a high power factor and few power source harmonics. On the other hand, active smoothing filter AF
There is a problem that the circuit configuration of the transistor Q2 and the drive control circuit BC is complicated, expensive, and large in loss.

On the other hand, the conventional AC-AC converter shown in FIG. 8 has the features that the circuit configuration is simple, the cost is low, and the loss of the switching element of the inverter can be designed to be small, but the input current has a peak phase of a sine wave voltage waveform. Since it has a pulse-like waveform that flows only in the vicinity, the power factor is low and there are many problems with power source harmonics.

The present invention has been made in order to solve such a problem, and it is a circuit system which does not use the above-mentioned active smoothing filter, and the power factor of the conventional example shown in FIG. An object of the present invention is to obtain an AC-AC converter having a combination of a small number of features, a circuit configuration of the conventional example shown in FIG.

[0008]

According to a first aspect of the present invention, an AC-AC converter has a first capacitor connected to an output terminal of a rectifying circuit for rectifying a commercial AC power supply voltage, and also an output terminal of the rectifying circuit. A smoothing capacitor for smoothing the output voltage of this rectifier circuit is connected in series with a harmonic choke connected to the rectifier circuit side and a smoothing capacitor and a first diode in the charging direction.
Connect the resonance circuit and the switch element that turns on and off at high frequency, and connect the harmonic choke and the contact point of the first diode,
This switch is connected to a switch element through a series circuit of a load circuit including a second diode having an anode connected to the contact side and an inductance element, and the contact point of the first diode and the smoothing capacitor, the second diode and the load circuit. The third capacitor is connected between the contact and the contact.

An AC-AC converter according to a second aspect of the invention eliminates the third capacitor of the first aspect of the invention, and a sixth capacitor is provided between the contact of the second diode and the load circuit and the negative terminal of the rectifier circuit. Is connected.

An AC-AC converter according to a third aspect of the invention eliminates the third capacitor of the first aspect of the invention and connects a third diode at the same place as the third capacitor.

An AC-AC converter according to a fourth aspect of the present invention uses a series circuit of a discharge lamp and a ballast choke as a load circuit including the inductance element of the first, second or third aspect of the invention.

In the AC-AC converter according to the fifth aspect of the present invention, the seventh capacitor is additionally connected between the contact of the first diode and the smoothing capacitor and the contact of the discharge lamp and the ballast choke, in addition to the fourth aspect. It was done.

[0013]

In the first invention or the fifth invention, a high-frequency current having a low-frequency component substantially proportional to the sine wave voltage of the power supply is supplied from the commercial AC power supply to the load circuit via the second diode or the third capacitor. Supplied.

In the second invention or the third invention, a high frequency current having a low frequency component substantially proportional to the sine wave voltage of the power supply is supplied from the commercial AC power supply to the load circuit via the second diode.

In the fourth invention, the first or second
Alternatively, the third invention is effectively applied to the discharge lamp lighting circuit.

[0016]

EXAMPLES Examples will be described with reference to the drawings. First Embodiment FIG. 1 is a circuit diagram of an AC-AC converter according to a first embodiment of the present invention. The load is composed of a series circuit of a discharge lamp FL, a parallel circuit of a starting capacitor C4 connected to both ends of the discharge lamp FL, and a ballast choke TB that limits the lamp current of the discharge lamp FL.

In FIG. 1, a first capacitor C1 is connected to the output terminal of a diode bridge DB for rectifying the voltage of the commercial AC power supply AC, and a smoothing capacitor for smoothing the DC output voltage of the pulsating current of the diode bridge DB. C2 is connected to the harmonic choke TH connected to the diode bridge DB side and the smoothing capacitor C2 in the series circuit of the first diode D1 in the charging direction.

Further, a series circuit of a resonance capacitor C5, a resonance circuit composed of a parallel circuit of a resonance choke TO, and a main transistor Q1 of a switching element which is turned on / off at a high frequency is connected to both ends of the smoothing capacitor C2. There is. Further, the contact point of the harmonic choke TH and the first diode D1 is connected to the collector of the main transistor Q1 via a series circuit of the second diode D2 having the anode connected to this contact side, the discharge lamp FL, and the ballast choke TB. is doing. Further, a third capacitor C3 is connected between the contact point between the first diode D1 and the smoothing capacitor C2 and the contact point between the second diode D2 and the discharge lamp FL.

Next, the circuit operation of FIG. 1 will be described. The main transistor Q1 turns on and off at a high frequency of several tens KHz,
The high frequency current loop in each case is shown below.

First, when the commercial AC power supply AC is turned on, a high frequency current flows in the following loop. When the main transistor Q1 is on, loop 1 (ballast choke TB
→ main transistor Q1 → diode bridge DB → commercial AC power supply AC → diode bridge DB → harmonic choke TH → second diode D2 → parallel circuit of discharge lamp FL and starting capacitor C4 → ballast choke TB).

Or loop 2 (ballast choke TB
→ main transistor Q1 → diode bridge DB → commercial AC power supply AC → diode bridge DB → harmonic choke TH → first diode D1 → third capacitor C3 → parallel circuit of discharge lamp FL and starting capacitor C4 → ballast choke TB).

Loop 3 (ballast choke TB → main transistor Q1 → smoothing capacitor C1 → third capacitor C
3 → Parallel circuit of discharge lamp FL and starting capacitor C4 →
Ballast choke TB).

A high frequency current flows through the loop 4 (resonance choke TO → main transistor Q1 → smoothing capacitor C2 → resonance choke TO).

On the other hand, when the main transistor Q1 is off,
Loop 5 (ballast choke TB → resonance capacitor C5
→ smoothing capacitor C2 → diode bridge DB → commercial AC power supply AC → diode bridge DB → harmonic choke TH → second diode D2 → parallel circuit of discharge lamp FL and starting capacitor C4 → ballast choke TB).

Alternatively, loop 6 (ballast choke TB
→ Resonance capacitor C5 → Smoothing capacitor C2 → Diode bridge DB → Commercial AC power supply AC → Diode bridge DB → Harmonic choke TH → First diode D1 → Third capacitor C3 → Discharge lamp FL and starting capacitor C
4 parallel circuit → ballast choke TB).

Loop 7 (ballast choke TB ← → resonance capacitor C5 ← → third capacitor C3 ← → parallel circuit of discharge lamp FL and starting capacitor C4 ← → ballast choke TB).

A high frequency current flows through the loop 8 (resonance choke TO → resonance capacitor C5 → resonance choke TO).

First, when the commercial AC power supply AC is turned on, a high frequency current flows in the above loop (however, in the parallel circuit of the discharge lamp FL and the starting capacitor C4, the current flows only in the starting capacitor C4), and the ballast choke TB. A resonance voltage is generated in the starting capacitor C4 due to the series resonance of the starting capacitor C4, and the discharge lamp FL is lit by the resonance voltage. Even when the discharge lamp FL is lit, high-frequency current flows through the same loop as above,
In the parallel circuit of the discharge lamp FL and the starting capacitor C4, since the impedance of the discharge lamp FL is low, a high frequency current mainly flows in the discharge lamp FL.

FIG. 2 shows high-frequency current and voltage waveforms at various points when the discharge lamp FL in FIG. 1 is turned on. In the figure, (a), (b) and (c) are high frequencies in the peak voltage phase, the intermediate voltage phase and the zero voltage phase of the pulsating voltage waveform V _C1 of the first capacitor C1 connected to the output of the diode bridge DB, respectively. The waveform is shown.

In the figure, I _Q1 is the collector current waveform of the main transistor Q1, V _Q1 is the collector-emitter voltage waveform of the main transistor Q1, I _TH is the current waveform of the harmonic choke TH, and I _D1 is the first diode. Current waveform of D1, I _D2
Shows the current waveform of the second diode D2, I _C3 shows the current waveform of the third capacitor C3, and I _TB shows the current waveform of the ballast choke TB.

From the above, a high frequency current proportional to the voltage value of the harmonic choke TH over the entire phase of the pulsating current voltage waveform V _C1 of the first capacitor C1 is generated in the loop 1 or 2 and the loop 5 or loop 6. Flow in, especially loop 1
It can be seen that, in the loop 5, the current is supplied from the commercial AC power source AC in one direction by the rectifying action of the second diode D2.

Then, the high frequency component is passed by the first capacitor C1, and the input current waveform I ₁ of the AC-AC converter of FIG. ₁ is a sine which is substantially proportional to the voltage waveform V ₁ of the commercial AC power supply AC as shown in FIG. It has a wavy waveform.

Second Embodiment FIG. 4 is a circuit diagram of an AC-AC converter according to a second embodiment of the present invention. In FIG. 4, the third capacitor C3 in FIG. 1 is eliminated, and the sixth capacitor C6 is connected between the contact of the second diode D2 and the discharge lamp FL and the negative terminal of the diode bridge DB.

The circuit operation of FIG. 4 is almost the same as that of FIG. 1, but the loop 7 of the high frequency current when the main transistor Q1 is off is not passed through the smoothing capacitor C2 in FIG. Is different in that it goes through the smoothing capacitor C2.

FIG. 5 shows an AC according to the third embodiment of the present invention.
FIG. 3 is a circuit diagram of an AC converter. In FIG. 5, the third capacitor C3 in FIG. 1 is eliminated and the third diode D3 is connected to the same place as the third capacitor C3 with the anode on the load side. Compared with the third capacitor C3, the third diode D3 is smaller, and it is easier to realize low cost. The circuit operation of FIG. 5 is almost the same as that of FIG. 1, but the third diode D3 is different from the third capacitor C3.
The high-frequency current flows only in one direction.

FIG. 6 shows an AC according to the fourth embodiment of the present invention.
FIG. 3 is a circuit diagram of an AC converter. 6 is different from the embodiment of FIG. 1 in that a first diode D1 and a smoothing capacitor C2 are provided.
The seventh capacitor C7 is connected between the contact of the discharge lamp FL and the contact of the ballast choke TB. This has the advantage of facilitating the circuit design for reducing the power supply harmonics when the discharge lamp FL (for example, a fluorescent lamp of 40 W or more) having a relatively high lamp voltage is lit by the 100 V commercial AC power supply AC.

[0037]

As described above, according to the present invention, as compared with the conventional AC-AC converter using the active smoothing filter, the circuit configuration is very simple, the cost is low, and further, the capacitor input type smoothing is performed. It is possible to realize an AC-AC converter with low harmonics and high power factor in which the loss of switching elements is as small as that of a conventional AC-AC converter using a circuit.

[Brief description of drawings]

FIG. 1 is a circuit diagram of an AC-AC converter according to a first embodiment of the present invention.

FIG. 2 is a high-frequency waveform chart of each part for explaining the circuit operation of FIG.

FIG. 3 is an input waveform diagram for explaining the circuit operation of FIG.

FIG. 4 is a circuit diagram of an AC-AC converter according to a second embodiment of the present invention.

FIG. 5 is a circuit diagram of an AC-AC converter according to a third embodiment of the present invention.

FIG. 6 is a circuit diagram of an AC-AC converter according to a fourth embodiment of the present invention.

FIG. 7 is a block diagram of a conventional AC-AC converter.

FIG. 8 is a block diagram of another conventional AC-AC converter.

[Explanation of symbols]

 AC commercial AC power supply DB diode bridge AF active smoothing filter BC drive control circuit IV inverter LD load circuit TH harmonic choke TO resonance choke TB ballast choke Q1 main transistor Q2 transistor C1 first capacitor C2 smoothing capacitor C3 third capacitor C4 starting capacitor C5 Resonance capacitor C6 Sixth capacitor C7 Seventh capacitor D1 First diode D2 Second diode D3 Third diode

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yasunori Ieshiro 5-1-1 Ofuna, Kamakura-shi Mitsubishi Electric Lighting Co., Ltd. (72) Inventor Kazutaka Shimizu 5-1-1 Ofuna, Kamakura-shi Mitsubishi Electric Lighting Incorporated (72) Inventor Masaomi Asayama 5-1-1 Ofuna, Kamakura-shi Mitsubishi Electric Lighting Co., Ltd.

Claims (5)

[Claims] 1. A first capacitor is connected to an output terminal of a rectifier circuit for rectifying a commercial AC power supply voltage, and a smoothing capacitor for smoothing an output voltage of the rectifier circuit is connected to an output terminal of the rectifier circuit. Connected in series with a harmonic choke connected to the smoothing capacitor and a first diode in the charging direction. An LC resonance circuit and a switching element that turns on and off at high frequency are connected to both ends of the smoothing capacitor. A contact between the harmonic choke and the first diode is connected to a switch element through a series circuit of a load circuit including a second diode and an inductance element whose anode is connected to the contact side, and the first diode and the smoothing capacitor are connected. AC-AC converter characterized in that a third capacitor is connected between the contact of the second diode and the contact of the second diode and the load circuit. . 2. A rectifier circuit for rectifying a commercial AC power supply voltage is connected to a first capacitor, and a smoothing capacitor for smoothing the output voltage of the rectifier circuit is connected to the output terminal of the rectifier circuit. Connected in series with a harmonic choke connected to the smoothing capacitor and a first diode in the charging direction. An LC resonance circuit and a switching element that turns on and off at high frequency are connected to both ends of the smoothing capacitor. The contact between the harmonic choke and the first diode is connected to the switch element through the series circuit of the load circuit including the second diode and the inductance element whose anode is connected to the contact side, and the contact between the second diode and the load circuit. An AC-AC converter, wherein a sixth capacitor is connected between the contact and the negative terminal of the rectifier circuit. 3. A first capacitor is connected to an output terminal of a rectifier circuit for rectifying a commercial AC power supply voltage, and a smoothing capacitor for smoothing an output voltage of the rectifier circuit is connected to an output terminal of the rectifier circuit. Connected in series with a harmonic choke connected to the smoothing capacitor and a first diode in the charging direction. An LC resonance circuit and a switching element that turns on and off at high frequency are connected to both ends of the smoothing capacitor. A contact between the harmonic choke and the first diode is connected to a switch element through a series circuit of a load circuit including a second diode and an inductance element whose anode is connected to the contact side, and the first diode and the smoothing capacitor are connected. The third diode is connected to the load side between the second contact and the contact of the second diode and the load circuit.
C-AC converter. 4. The load circuit includes a discharge lamp connected to the second diode side and a parallel circuit of a starting capacitor connected to both ends of the discharge lamp.
The AC-AC converter according to claim 1, 2 or 3, wherein the AC-AC converter comprises a series circuit with a ballast choke connected to the switch element side. 5. The AC-AC converter according to claim 4, wherein a seventh capacitor is connected between the contact of the first diode and the smoothing capacitor and the contact of the discharge lamp and the ballast choke.