JPS61296695A - Discharge lamp lighting apparatus - 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 [Technical Field] The present invention relates to a discharge lamp lighting device using a separately excited inverter circuit, and relates to a device for dimming a discharge lamp such as a fluorescent lamp by changing the operating frequency.

[Background technology]

As shown in FIG. 12, the discharge lamp lighting device which is the basis of this invention consists of a commercial power source 1. The separately excited inverter circuit 2 is supplied with power from the DC power supply ■ consisting of the diode bridge DB and the capacitor C'.
A series circuit of an inductor L, a capacitor C, and a parallel circuit of a discharge lamp 3 is connected as a load. The separately excited inverter circuit 2 is controlled by a V/F (voltage/frequency) conversion circuit 7. This is carried out by a control circuit 2' consisting of a variable resistor VR, an oscillation circuit 6 and a drive circuit 5.

This discharge lamp lighting device starts the discharge lamp 3 by boosting the high frequency output voltage of the separately excited inverter circuit 2 through an inductor and a series resonant circuit consisting of a capacitor C and applying it to the discharge lamp 3. After starting, the discharge lamp 3 is lit with current limited by an inductor.

And V/F conversion circuit 7. Variable resistance VR, oscillation circuit 6
The operating frequency of the separately excited inverter circuit 2 is periodically switched alternately between a first frequency and a second frequency by a control circuit □■' consisting of a drive circuit 5 and a variable resistance. It is configured to change by adjusting VR, and the discharge lamp 3 is dimmed by adjusting the first frequency.

Further, the second frequency is set to a fixed frequency (for example, the frequency fA in the fully lit state) near the series resonance frequency of the inductor L and the capacitor C, so that the dimming becomes deep and the discharge lamp 3
Even when the lamp goes out, a high voltage is applied across both ends of the discharge lamp 3 to re-ignite it and keep it lit.

FIG. 13 shows the frequency characteristics of the voltage across the capacitor C when the discharge lamp 3 is not lit (no load), where fo is the resonance frequency determined by the inductor L and the capacitor C, and is (2). fA is the frequency of the fully lit state (second frequency),
f8 is the frequency of the lowest level dimming state.

FIG. 14 is a waveform diagram of each part in the lowest level dimming state.

The figure (A) shows the output voltage from the V/F conversion circuit 7, and the level is alternately and periodically repeated in sections TA and TB.
There are different levels. Figure (B) shows changes in the operating frequency of the separately excited inverter circuit 2, and in the section TA, the frequency f
A, and the same wave number fB in section TB. Same figure (C)
shows the waveform of the lamp voltage at that time, and (D) of the same figure shows the waveform of the lamp current.

Note that in the above, the second frequency is f. lower f
Although the frequency is set to A, it may be set to a higher frequency than fo.

However, in such a discharge lamp lighting device, since the interval TA in which the separately excited inverter circuit 2 operates at the second frequency is fixed, when the dimming becomes deep, the discharge lamp 3 operates at the frequency rA in the interval TA. Immediately after re-ignition, the lamp continued to operate at the frequency fA, and the lamp current continued to flow at the frequency fA, so there was a limit to dimming.

[Purpose of the invention]

An object of the present invention is to provide a discharge lamp lighting device that can achieve deep dimming levels.

[Disclosure of the invention]

The discharge lamp lighting device of the present invention includes a series circuit including a DC power source, a separately excited inverter circuit supplied with power from the DC power source, and a parallel circuit of an inductor, a capacitor, and a discharge lamp serving as a load of the separately excited inverter circuit. a restriking detection circuit that detects restriking of the discharge lamp; and switching the operating frequency of the separately excited inverter circuit from a first frequency to a second frequency at regular intervals, and a restriking detection circuit that detects restriking of the discharge lamp; a control circuit that switches the operating frequency of the separately excited inverter circuit from the second frequency to the first frequency in accordance with the restriking detection output, the control circuit varying the first frequency and controlling the operating frequency of the separately excited inverter circuit; The frequency is set to a frequency near the resonance frequency determined by the inductor and capacitor.

In this way, since the operating frequency of the separately excited inverter circuit is switched from the second frequency to the first frequency by detecting the re-ignition of the discharge lamp, the discharge lamp can be dimmed at the same time as the discharge lamp is re-ignited. Instead of the first frequency for performing the operation, the operating interval at the second frequency can be minimized and thus deep dimming levels can be achieved.

Example A first embodiment of this invention will be described based on FIG.

As shown in FIG. 1, this discharge lamp lighting device consists of a DC power source I, a separately excited inverter circuit 2 supplied with power from the DC power source 2, an inductor L1 and a capacitor C3 serving as the loads of the separately excited inverter circuit 2. and a series circuit with a parallel circuit of the discharge lamp 3, a re-ignition detection circuit 4 for detecting re-ignition of the discharge lamp 3, and an operating frequency of the separately excited inverter circuit 2 at a first frequency at regular intervals. a control circuit that switches the operating frequency of the separately excited inverter circuit 2 from the second frequency to the first frequency in accordance with the restriking detection output from the restriking detection circuit 4; (2) The first frequency is varied, and the second frequency is varied by the inductor L,
and a frequency near the resonance frequency determined by the capacitor C3.

DC electricity! ! ! XI is designed to full-wave rectify commercial power ai with a diode bridge DB and smooth it with a capacitor C'. The control circuit (■) includes a drive circuit 5, an oscillation circuit 5. It is composed of a V/F (voltage/frequency) conversion circuit 7 and a variable resistor VR.

This discharge lamp lighting device starts the discharge lamp 3 by boosting the high frequency output voltage of the separately excited inverter circuit 2 using a series resonant circuit consisting of an inductor L1 and a capacitor C3 and applying it to the discharge lamp 3. At the start, the discharge lamp 3 is lit in a state where the current is limited by the inductor L1.

Then, the separately excited inverter circuit 2 is controlled by the control circuit H.
The operating frequency is periodically switched alternately between a first frequency and a second frequency, and the first frequency is configured to be changed by adjusting a variable resistor VR. Discharge lamp 3 by adjusting the frequency of 1
It is designed to perform dimming. In addition, the second frequency is set to a fixed frequency (for example, the frequency fA in the fully lit state) near the series resonance frequency of the inductor L1 and the capacitor C3, so that the discharge can be maintained even when the discharge lamp 3 is turned off due to deep dimming. A high voltage is applied between both ends of the lamp 3 to re-ignite it and keep it lit.

At this time, switching from the first frequency to the second frequency is as follows:
This is performed at regular intervals, and the switching from the second frequency to the first frequency is performed in response to restriking detection by the restriking detection circuit 4.

FIG. 2 shows a specific circuit diagram of the circuit shown in FIG.

However, although the DC voltage B■ is different in circuit from the one in FIG. 1, it is the same in that it obtains a DC voltage, and therefore is given the same reference numeral for convenience.

The configuration and operation of each part will be explained below.

First, regarding the main circuit, the diode D1. D2° and capacitors C, . This separately excited inverter circuit 2 includes a transistor Tr1
．． A so-called separately excited half-bridge configuration is adopted in which high frequency power is supplied to the load (L, C3, 3) by alternately repeating on and off of Tr2. discharge lamp 3
is started and lit by a series resonant circuit consisting of the ink cliff L1 and the capacitor C3, and the transformer T1 is connected to the discharge lamp 3.
It is assumed that the excitation inductance of the transformer T1 is sufficiently larger than that of the inductor L1 and has almost no effect on the resonant circuit formed by the inductor L1 and the capacitor C3. D3. D4 is a diode, and C3 is a capacitor for direct current coupling.

Next, the oscillation circuit 6 and drive circuit 5 will be explained.

IC, is astable multi-high break (IC for general purpose timer)
r555J), and its frequency is determined by resistors R5, R6,
It is determined by the capacitor C6 and the input voltage at the No. 5 terminal. Then, the output from terminal 3 is connected to the D flip-flop I.
C2 (4013) is divided and the Nant gate G3. G, and the transistor Tr3. It is used as the gate input of Tr4.

And trans'r2. On/off control of the transistors Try and Tr2 is performed via 'r3.

That is, when the transistor T r 3 is turned on, a voltage is induced in the transformer T2 in the direction shown by the solid line in the figure, and the transistor T r 1 is turned off. Transistor T r
When transistor Tr3 is turned off, a flyback voltage is generated in the transformer T2 in the direction shown by the dotted line in the figure, and the transistor Tr1 is turned on. After the transistor Tr1 is turned on, the operation of 0 or more in which the collector current is returned to the base current to maintain the on state is the same for the transistor Tr2.

R1-R6 are resistors, D5. D6 is a diode. C
5 is a capacitor, C7 is a capacitor, R7 is a resistor, G1
．． G2 is an inverter.

FIG. 6 is a waveform diagram showing how the oscillation circuit 6 and drive circuit 5 operate. The same figure (A) shows the voltage at the third terminal of the astable multi-by-break ■C1, the same figure (B) shows the C1 voltage and voltage of the D flip-flop IC2, and the same figure (C) shows the 101 voltage of the D flip-flop IC2, the same The figure (D) shows the gate voltage of the transistor T r 4, and the figure (E) shows the gate voltage of the transistor T
The gate voltage of r3, the same figure (F) is the transistor T
The drain voltage of r3, the same figure (G) is the transistor T
The base current of r 1, the figure (H) is the transistor T r
1 collector current.

Next, the V/F conversion circuit 7 will be explained. A transistor T r operated by a signal from the restriking detection circuit 4
If we exclude 6, the operation will be as follows.

The operational amplifier IC is used to obtain a power synchronization signal, and here operates as a comparator. The voltage obtained by rectifying the commercial power supply 1 by the diode bridge DB1 and dividing it by the resistors R, R9 is the voltage that is applied to the operational amplifier IC2.
is applied to the inverting input terminal of On the other hand, a control type 1ji (Vcc is connected to a resistor RI) is connected to the non-inverting input terminal of the operational anti-IC.
The value divided by D and R1+ is added. Therefore, when the non-inverting input terminal voltage>inverting input terminal voltage, the operational amplifier I
C.

The output voltage of is high level, and conversely, it is low level between the non-inverting input terminal voltage and the inverting input terminal voltage. C8 is a small capacitor.

Inverter G6. ANDGATE G6. and grinding force R, □,
The circuit consisting of capacitor C9 is a fall detection circuit, and the high level section of the output voltage of AND gate G6 is determined by resistor R32 and capacitor C9. The output voltage of the AND gate G is applied to the data input terminal (D2) of the D flip-flop lC2, and the transistor T r 4
In synchronization with the on/off of the transistor T r
It is input to gate 5. When the δ2 output is at a low level, the transistor T r 5 is off and the operational amplifier IC
The non-inverting input terminal of 5 is connected to the +
Vcc is applied. IC5 and IC6 are operational amplifiers, and here both operate as so-called voltage followers (also called impedance conversion) in which the voltage at the non-inverting input terminal appears as an output voltage.

That is, the output voltage of the operational amplifier TC5 becomes +Vcc. Then, the diode D7 compares the voltage RIs +R18 determined by the resistor RIS and R111 with the output voltage of the operational amplifier IC5. In this case, R15 + RIl+, so the diode D7 is turned off, and therefore the non-inverting input voltage of the operational amplifier IC6 is I8 □・Vcc R, 5 + R summer 6, and this voltage becomes the No. 5 terminal input voltage of the astable multi-by-break IC.

Next, when the output of the D flip-flop IC2 is at a high level, the transistor T r 5 is turned on and the resistor R
13, R14□Id determined by variable resistor VR! R, 3+ R, 4+ V R is added to the non-inverting input terminal of the operational amplifier IC5, and RIs
When it becomes +R16, becomes the output voltage of the operational amplifier IC6, and becomes the No. 5 terminal input voltage of the astable multivibrator ■C1. here,
D7 (ON) is a voltage for turning on the diode D7, and is about 0.7V. Therefore, when the transistor T r 5 is on, by changing the variable resistor VR, the No. 5 input terminal of the astable multi-by-break IC changes. However, RIs +R16, and the astable multivibrator IG at this time.

The 5th terminal input terminal of I6 □・Vcc RI5+Do IB It remains as it is.

Note that the voltage IB □・■CC RIs ” R18 corresponds to the operating frequency when the discharge lamp 3 is in the rated lighting state, and the voltage becomes smaller as the resistance value of the variable resistor VR is reduced, but this The value corresponds to the operating frequency of the separately excited inverter circuit 2 when the discharge lamp 3 is dimmed by the variable Jffi resistor VR.

The above operation is shown in FIG. 1 using waveforms of each part.

In FIG. 4, (A) shows the value of variable resistor VR. Figure (B) shows the input terminal of the operational amplifier IC.
VZ+ is the inverting input terminal voltage, ■2□ is the non-inverting input terminal voltage, R10+RI+, and (C) in the same figure shows the output voltage of the operational amplifier IC. (D) in the same figure shows the input voltage at the ■ terminal of the AND gate G6. The figure (E) shows the AND gate G6.
The terminal input voltage is shown, and 23 shows the high level maintenance voltage of the AND gate G6. (F) in the figure shows the output voltage of the AND gate C6. The figure (G) shows the voltage at the 5th terminal of the astable multi-by-break IC, and ■24=
Vzs.

VZ & + vzt are (the following margins) R15+R16 RIs +R16, respectively. (H) in the figure shows changes in the operating frequency of the separately excited inverter circuit 2, where fl is the frequency corresponding to the rated lighting state, r2 is the frequency corresponding to the predetermined level dimming state, and f3
is the frequency corresponding to the lowest level dimming state. Figure H
) indicates the lamp voltage, and (J) in the figure indicates the lamp current.

FIG. 5 is an enlarged view of waveforms at various parts in the lowest level dimming state in FIG. 4. The same figure (A) shows the astable multivibrator IC, the 05th terminal voltage, the same figure (B) shows the lamp voltage,
(C) shows the waveforms of the lamp currents. FIG. 2D shows changes in the operating frequency of the separately excited inverter circuit 2.

Note that the operating frequencies r, , r3 of the separately excited inverter circuit 2
1 on the inductor. The resonant frequency of capacitor C3 is r, <r2<r3.

Note that the operation up to this point is the same as that shown in FIG. 12.

Finally, the operation of the restriking detection circuit 4 will be explained.

The transformer T1 is a detection transformer that detects the lamp voltage of the discharge lamp 3, is rectified via a diode bridge DB2, and becomes an input to the operational amplifier IC7. At this time,
The capacitance of the capacitor CIO is selected to be small, so that the voltage across the capacitor CIO changes faithfully as the lamp voltage changes, while the diode D8. The capacitance of capacitor C11 smoothed via D9 is selected to be sufficiently larger than C1o. Resistors R17 and R18 are each connected to a capacitor Cl.
This is the discharge resistance of 02C11. At this time, operational amplifier ■C
The voltage applied to the input terminal of 7 is shown in FIG. In Fig. 7, (A) shows the lamp voltage, (B) is the input voltage of the operational amplifier ■C7, vo is the inverting input terminal voltage, and vtq
is the non-inverting input terminal voltage, V2O is the diode D8. D9
This is the drop due to (C) is the output voltage of the operational amplifier IC7. Note that the lamp voltage waveform at this time is the one shown in FIG. 5 for convenience of explanation (because later, D flip-flop (4013) IC3, transistor T
r3.

(This is because the lamp voltage waveform in the present invention differs from that shown in FIG. 5 due to the functions described in the operation of T r 6, etc.), and the output voltage of the operational amplifier IC7 is as follows: When the high level is 1 and vice versa, the level becomes low, as shown in FIG. That is,
At the moment when the discharge lamp 3 is re-ignited, the non-inverting input voltage becomes greater than the inverting input voltage, and the output voltage of the operational amplifier IC7 becomes high level.

By the way, the operation of the D flip-flop IC3 is as follows. Two D flip-flops (OF/F[11,
Cent terminals (S, S2, respectively) of DF/F (21)
) is connected to the Q2 output of the D flip-flop IC2, and when the ζ2 output is high level, DF, /Fill,
The Q outputs (Q, Q2, respectively) of DF/F (2) both become high level. Also, Q2 of D flip-flop IC2
When the output is at a low level, D In F/F C21, the contents of the data input D2 terminal appear on the Q2 output in synchronization with the clock signal (02 input terminal).

D F ,/F [The clock input at 11 is the output voltage of the operational amplifier IC7, and the clock input at 21 is the output voltage of the astable multi-by-break IC. The data input of F+21 (contents of D2 terminal) is D F / F (
11 and the Q2 output of the D flip-flop IC2. D F / F (21 Q
2 outputs turn on/off transistor T r6
I wholesale. C7 is an or gate.

The above contents are shown in FIG. 8 using waveforms of each part.

FIG. 8(A) shows 62 outputs of the D flip-flop IC2,
That is, it shows the 81°82 manual power of the D flip-flop IC3. The same figure (B) shows the output of the operational amplifier IC7,
In other words, it shows 01 manual power of D flip flop IC3. (C) of the same figure shows the Q1 output of the D flip-flop IC3. The figure (D) is a D flip-flop IC.
3 D2 shows human power. The same figure (E) shows 02 manual power of D flip-flop IC3. The figure (F) is D
It shows the Q2 output of the flip-flop IC3, that is, the gate input voltage of the transistor T r 6, and the operating range at the frequency f1 is narrowed by Pl by restriking detection. The figure (G) shows the gate input voltage of the transistor T r 5. (H) in the figure shows the voltage at the fifth terminal of the astable multi-by-break IC, and (1) in the figure shows changes in the operating frequency of the separately excited impark circuit 2. (J) in the same figure shows the lamp voltage, and (K) in the same figure shows the lamp current.

As is clear from FIG. 8, by detecting the re-ignition, the period in which the separately excited inverter circuit 2 is operating at the operating frequency f1 after the discharge lamp 3 is re-ignited is eliminated;
This further reduces the section through which the lamp current flows, achieving deeper dimming.

In this embodiment, since the operating frequency of the separately excited inverter circuit 2 is switched from the second frequency to the first frequency by detecting the re-ignition of the discharge lamp 3, the operating period at the second frequency is minimized. Note that in this embodiment, the separately excited inverter circuit 2
Although it has a half-bridge configuration, it goes without saying that a full-bridge, push-pull, or other configuration may also be used. In addition, the DC power source is connected to diodes D11 D21 in Fig. 2.
Although voltage doubler rectification and smoothing is performed using capacitors C, C2, rectification and smoothing may be performed using a diode bridge or the like. Furthermore, in the embodiment of FIG. 2, as can be seen from the waveform shown in FIG. 8, the output voltage of the operational amplifier ■C7 and the gate voltage of the transistor T r 6 have the same waveform, so The operational amplifier IC7 may directly drive the transistor T r 6 without going through it.

A second embodiment of the invention will be described based on FIGS. 9 to 11. As shown in FIG. 9, this discharge lamp lighting device uses a control circuit "■" in place of the control circuit "■" in FIG. 2, and the rest is the same as in FIG. 2.Control circuit "■"
' is the same as the control circuit (2) except for the V/F conversion circuit 7'. That is, resistor R12, capacitor C
9, Inverter G5. There is no falling detection circuit consisting of AND gate G6, but resistor RI9. A series circuit of capacitor CI2 is connected in parallel to resistor RI6.

In this discharge lamp lighting device, the operating frequency is set as shown in FIG.

Next, the operation of the resistor R19=capacitor C1□ section will be explained. Again, for convenience of explanation, the transistor T
The behavior of r6 shall not be taken into account.

The on/off state of the transistor T r 5 depends on the state a (high or low level) of the Q output of the D flip-flop IC2. When the transistor T r 5 is off, the operational amplifier IC
, the output voltage becomes approximately Vcc, and the diode D7 is off. At this time, the capacitor CI2 has a resistor RIS
, the charging current flows through R11+, and the operational amplifier ■C6
The non-inverting input terminal voltages of resistors RIll, RIs,
It gradually increases due to the time constant determined by R16 and capacitor C9, and this value is also related to the period in which transistor Tr5 is off, but it should rise to RIs + R18 (before that, transistor T
When r5 is turned on, it does not rise to this value).

Next, when the transistor T r 5 is turned on, the output voltage of the operational amplifier C5 becomes R, 3+ R, 4+ V R , which is the voltage of the dimming state set by the variable resistor VR. At this time, diode D7 connects both this voltage and resistor R11+ #i! The voltages are compared, and if the output voltage of the operational amplifier IC is low, the diode D7 is turned on.

When the diode D7 turns on, the charge in the capacitor C8 is rapidly discharged through the resistor RI9, and the operational amplifier ■C
The non-inverting input terminal voltage of 6 is Habo R, , + R, 4 + V
It becomes R.

By the way, as explained in the embodiment shown in FIG. 2, the transistor T r 6 is turned on immediately after the re-ignition is detected, thereby switching the operating frequency of the separately excited inverter circuit 2 to the frequency set by the variable resistor VR. do the work.

The above operation is shown in waveforms as shown in FIG. (A) in the figure shows the resistance value of the variable resistor VR.

In the figure (B), V31 is the inverting input terminal voltage, and ■3□ is the non-inverting input terminal voltage in the input voltage of the operational amplifier IC.

The same figure (C) is the output voltage of the operational amplifier IC, the same figure (D)
is the gate voltage of transistor T r 5. Same figure (
E) is the lamp voltage, and (F) is the lamp current. (G) in the figure shows the input voltage of the operational amplifier ■C7, where V33 is the inverting input terminal voltage and v34 is the non-inverting input terminal voltage.

The same figure (old is the output voltage of operational amplifier IC7, the same figure (1) is the S, S2 voltage of D flip-flop IC3, the same figure (J
) is the Q1 output voltage of the D flip-flop IC3, and the figure (
K) is the input voltage of D2 of the D flip-flop IC3, ie the gate voltage of the transistor T r 6. The figure (L) is the output voltage of operational amplifier IC5, V35+
v3. are each. The figure (M) shows the voltage at the 5th terminal of the astable multi-by-break IC1, ■3ff+
V3B is RIs + RIs R, 3 + R14 + VR (min) + I)7 (ON), respectively, and the slope of the W part is the resistance RIs, RIll l
Determined by RIs and capacitor C+Z. Then, the operating frequency of the separately excited inverter circuit 2 changes continuously according to this slope, and the lamp voltage increases until the discharge lamp 3 is re-ignited.

In this embodiment as well, similarly to the embodiment shown in FIG.
Since the operating frequency is switched, deep dimming is possible. Furthermore, according to this embodiment, when re-igniting the discharge lamp 3, the frequency is gradually changed to increase the re-ignition voltage, so the lamp voltage waveform becomes smooth and this is effective in reducing noise. Become.

In the embodiments shown in FIGS. 2 and 9, a method of detecting lamp voltage is used as a means for detecting re-ignition of the discharge lamp 3, but for example, lamp current, light output waveform, etc. , any means capable of detecting lamp re-ignition.
Either method may be used.

〔Effect of the invention〕

The discharge lamp lighting device of the present invention detects the re-ignition of the discharge lamp and switches the operating frequency of the separately excited inverter circuit from the second frequency to the first frequency, so that at the same time as the discharge lamp is re-ignited. Instead of the first frequency for dimming the discharge lamp, the operating interval at the second frequency can be minimized and thus deep dimming levels can be realized.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram of the first embodiment of the present invention, Fig. 2 is a specific circuit diagram thereof, Figs. 3 to 5 are waveform diagrams for explaining its operation, and Fig. 6 is a capacitor voltage. FIG. 7 and FIG. 8 are waveform diagrams for explaining the operation, FIG. 9 is a circuit diagram of the second embodiment of the present invention, and FIG.
The figure is a frequency characteristic diagram of the capacitor voltage, Figure 11 is a waveform diagram for explaining its operation, Figure 12 is a circuit diagram of the discharge lamp lighting device that is the basis of this invention, and Figure 13 is a diagram of the capacitor voltage. The frequency characteristic diagram, FIG. 14, is also a waveform diagram. ■...DC power supply, ■, ■''...control circuit, 2...
Separately excited inverter circuit, 3... discharge lamp, 4...
Re-ignition detection circuit Fig. 1 Fig. 3 Fig. 6 Fig. 7 Fig. 10 ＼■' Fig. 12

Claims (1)

[Claims] A series circuit consisting of a DC power supply, a separately excited inverter circuit supplied with power from this DC power supply, a parallel circuit of an inductor, a capacitor, and a discharge lamp serving as a load of this separately excited inverter circuit, and detection of re-ignition of the discharge lamp. a restriking detection circuit that switches the operating frequency of the separately excited inverter circuit from a first frequency to a second frequency at regular intervals, and a restriking detection circuit that switches the operating frequency of the separately excited inverter circuit from a first frequency to a second frequency in response to a restriking detection output from the restriking detection circuit. The operating frequency of the separately excited inverter circuit is set to the second
and a control circuit for switching from a frequency of Device.