JPS63207096A - Discharge lamp lighter - 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 that uses a separately excited inverter circuit to light a discharge lamp at high frequency.

(Background technology) FIG. 8 is a circuit diagram of a conventional discharge lamp lighting device.

The power supply voltage of the alternating current power supply AC is rectified by a diode bridge DB, smoothed by a capacitor Co, and made into a direct current voltage. This DC voltage is applied to a series circuit of the primary side of the oscillation transformer ○T and the semiconductor switch element Q. A discharge lamp DL is connected to the secondary side of the oscillation transformer OT via a capacitor C1, A beam actance element (capacitor C2) is connected to the non-power side of the discharge lamp DL, and a preheating circuit for the discharge lamp filament is configured. A diode D is connected in antiparallel to the semiconductor switch element Q1.

Further, a capacitor CI exhibiting a resonant core with the inductance component of the circuit is connected in parallel to both ends of the switching element Q1. The capacitor C1 may be connected to both ends of the primary coil of the oscillation transformer OT.The output of the oscillation circuit 1 is input to the control pole of the semiconductor switch element Q1 via the gate circuit 2 and the drive circuit 3. has been done.

FIG. 9(a) shows a separately excited signal (Hi
gl+“Separately excited ON signal when at ° level,” L.

When the semiconductor switching element Q1 is turned on by a separately excited ON signal, which indicates a separately excited OFF signal when the level is 4", the signal shown in FIG.
The current Ic as shown in b) is the semiconductor switch element Q.
, flows to. Semiconductor switch element Q1 with separately excited off signal
is turned off, the oscillating transformer OT resonates with the capacitor C1 due to the energy stored in the LC component of the circuit, a resonant capacitor current flows, and the semiconductor switch element Q
, a resonant voltage as shown in FIG. 9(c) is generated at both ends of . When this resonant voltage becomes zero, the resonant current flows through the diode D, and when the diode current becomes zero, the separately excited ON signal causes the semiconductor switch element Q to flow.
1, the current Ic flows in the same way as in the previous cycle (Fig. 9 (b)), and in this way, oscillation continues, and
The voltage generated on the secondary side of the oscillation transformer OT due to this resonance is applied to the discharge lamp DL via the cage inductance of the oscillation transformer OT and the capacitor C1.
lights up. Note that 9th U2 (d) and (e) indicate the primary voltage and primary current of the oscillation transformer OT, respectively.

This one-stone inverter circuit consists of a first resonant circuit consisting of an inductance and a capacitor C2 as seen from the primary side of the oscillation transformer OT, and a one-cage inductance and a capacitor C3 and C2 as seen from the secondary side of the oscillation transformer OT. It has two resonant circuit systems with a second resonant circuit, and also has two resonant circuit systems.
It has a feature that the oscillation waveform of the element voltage VCH changes depending on the state of the next circuit. In other words, when there is no load, the secondary current of the oscillation transformer OT stops flowing, so its primary inductance increases, and as a result, the oscillation period determined by the capacitor C3 and the inductance seen from the primary side of the oscillation transformer OT increases. As a result, the width of the voltage across the semiconductor switch element Q, which is 70 days, increases.

In this way, even if the natural vibration period of the primary side circuit becomes long when there is no load, in a separately excited inverter circuit, the semiconductor switching element Q is turned on according to the period of the separately excited signal. As shown in (b), the semiconductor switch element Q1 is turned on when the voltage across the semiconductor switch element Q, that is, the voltage of the resonant capacitor CI is high, and the rush current from the capacitor CI is transferred to the semiconductor switch element Q. , and may cause large power loss and damage to the semiconductor switching element Q1.

Therefore, the circuit shown in FIG. 8 is provided with an element voltage detection circuit 4 that detects the voltage across the semiconductor switching element Q.
When the voltage across the semiconductor switching element Q is high, the gate circuit 2 prevents the separately excited ON signal from passing through the semiconductor switching element Q.

conduction is prohibited. Therefore, under no load, as shown in FIGS. 10(a) and 10(b), the width of the voltage VCH across the semiconductor switching element Q1 is longer than the period T3 of the separately excited off signal of the oscillation circuit 1. Also, as shown in FIG. 10(C), conduction of the semiconductor switching element Q can be prohibited by prohibiting the drive signal during the period of E>0 in (2). This gate circuit 2 can be constructed simply by taking the logical product of the inverted signal of the element voltage detection signal and the separately excited ON signal. By providing such a gate circuit 2, it is possible to safely and stably oscillate even when there is no load.

However, in this conventional example circuit, when the discharge lamp DL is attached from a no-load state, an overvoltage is applied across the semiconductor switch element Q1, and the semiconductor switch element Q
, pressure breakdown may occur.

(Object of the invention) The present invention has been made in view of the above-mentioned points,
The purpose of this is to reduce the voltage applied to the semiconductor switch element when the discharge lamp is attached under no-load conditions, and to enable safe and stable lighting without compromising the reliability of the semiconductor switch element. To provide electric light lighting devices.

(Disclosure of the Invention) The discharge lamp lighting device according to the present invention will be described with reference to the embodiment shown in FIG. a diode D1 connected in parallel to the semiconductor switch element Q1 in the opposite direction; an inductance element (oscillation transformer OT) connected in series to the semiconductor switch element Q1; and a capacitor C1 forming a first resonant circuit together with the inductance element. The oscillation circuit 1 generates a separately excited signal for repeatedly turning on and off the semiconductor switching element Q, and during a period when the semiconductor switching element Q1 has a voltage across both ends, the separately excited signal is applied to the conduction control pole of the semiconductor switching element Q1. A discharge lamp DL is connected to a circuit that prohibits input (gate circuit 2) and a stabilizing element (oscillation transformer OT glue cage inductance and capacitor C3) to which the resonant voltage generated by turning on and off the semiconductor switch element Q1 is applied. and a second one with a stabilizing element, a discharge lamp DL, and a preheating control reactance (capacitor CZ) connected in parallel with the discharge lamp DL.
In an inverter circuit that forms a resonant circuit in which the resonant frequency of the first resonant circuit during no-load is lower than when the discharge lamp is lit, at least when the discharge lamp DL is attached from a no-load state, the OFF period of the separately excited signal The lamp includes an on-period control circuit 6 that controls the oscillation circuit 1 so that the length of the on-period is shorter than the rated lighting time of the discharge lamp DL.

In the conventional circuit, as described above, when the discharge lamp DL is attached from a no-load state, an overvoltage is generated across the semiconductor switch element Q. When investigating the mechanism of this overvoltage generation, it was found that this phenomenon occurs because the frequency of the separately excited signal operates near or below the resonant frequency in the secondary circuit of the oscillation transformer OT.

The equivalent circuit for the main circuit of the inverter circuit is shown in Figure 2, where L is the excitation inductance seen from the primary side of the oscillation transformer OT, and L2 is the cage inductance seen from the secondary side of the oscillation transformer OT. And −L+>L
It becomes x. C2" is the value obtained by converting the combined value of the capacitors in the secondary circuit of the oscillation transformer OT to the primary side, and R is the filament equivalent resistance. When it is on, the inductance L2, capacitor C2', and resistor R form j:, f, and when the semiconductor switching element Q and diode D+ are off, the inductance L2, capacitor C2', capacitor CI, and resistor are formed. It is composed of bT and R.The resonant frequency of the secondary circuit referred to here is the frequency determined by the inductance 2, the capacitor 02°, and the resistor R.

The width of the separately excited off signal is as shown in Figure 9.
It is set to be constant so that it is longer than the period T, which is o, and shorter than the period T2 until the primary current of the i-oscillating transformer OT commutates. At no load, the element voltage vcI
! As the oscillation period becomes longer, the gate circuit 2 is provided to control the conduction period as described above, so that the semiconductor switching elements Q,
Even if the on-period is set to the maximum, the drive signal as shown in FIG. 10 will be obtained, and stable oscillation will occur.

However, when the discharge lamp DL is connected from a no-load state, the discharge lamp DL has not started discharging.
A capacitor C2 is connected through the filament of
Create a closed circuit on the secondary side of the oscillation transformer OT. The oscillation period of this closed circuit is short, and at this time, the resonance frequency in the secondary circuit of the oscillation transformer OT is higher than the frequency of the separately excited signal. The operating waveforms at this time are shown in Figure 0 in Figure 4.
In the period , the on period of the semiconductor switch element Q (the fourth
(see figure (c)), a gradually increasing collector current flows,
The current waveform has a waveform that once reaches a peak and then decreases due to the resonance current on the secondary side. During the period (2), if the lighting is normal, phase a, in which the primary current of the oscillation transformer OT (Fig. 4 (b)) commutates from negative to positive, should come after the element voltage Vca becomes zero. However, commutation occurs before the element voltage Vc (FIG. 4(a)) becomes zero. This current is due to the resonant current in the circuit between the secondary circuits of the oscillation transformer OT, and flows in the direction of arrow A when the semiconductor switching element Q1 is off in the circuit shown in FIG. A voltage (see FIG. 4(d)) is induced in the winding, charging the capacitor C1, and increasing the element voltage ccE of the semiconductor switching element Q1. Due to the presence of the gate circuit 2 described above, conduction of the semiconductor switching element Q is prohibited while the element voltage VCE is generated.
The element voltage VCE rises, and an overvoltage occurs across the semiconductor switch element Q1.

In this way, when the discharge lamp DL is installed from a no-load state, an overvoltage is transiently applied to the semiconductor switch element Q.
The reliability of the semiconductor switching element Q1 was impaired. At this time, the frequency of the separately excited signal of semiconductor switching element Q1 is lower than the resonance frequency of the secondary side of oscillation 1 to lance ○T, and is lower than the generation of secondary voltage in commutation phase a in Fig. 4. Such a high voltage was generated before because the charging current of the capacitor C2° in the secondary circuit was in a phase advance mode.

Note that when the discharge lamp DL lights up, a damping resistor is connected to the secondary circuit of the oscillation transformer ○T, so the resonance frequency decreases as shown in Figure 5, so when the discharge lamp DL lights up, the frequency of the drive signal decreases. Since fd is controlled in a state higher than the resonant frequency of the secondary circuit, stable oscillation can be performed without causing the above-mentioned overvoltage.

In this way, the present invention provides a single-stone inverter circuit that has a resonance system on the secondary side in addition to the primary side resonance system of the oscillation transformer OT, at least when the discharge lamp DL is installed from a no-load state. The frequency of the drive signal is set higher than the resonance frequency of the secondary side resonance system, so that the inverter circuit oscillates in a slow phase mode.

The frequency of the separately excited signal is determined by the semiconductor switching element Q.

Since the off period is set to a fixed period, it changes by changing the on period. Therefore, increasing the frequency of the separately excited signal means that the semiconductor switching element Q
This means shortening the on period of . When the discharge lamp DL is connected from a no-load state, even if there is a resonance system on the secondary side of the oscillation transformer OT, it will be driven at a frequency sufficiently higher than the resonance frequency, as shown in Figure 6. ,
The primary side of the oscillation transformer OT has a lagging current (Fig. 6 (b)) with respect to the secondary voltage of the oscillation transformer OT (Fig. 6 (c)).
) flows, and the collector current of the semiconductor switching element Q1 during the on period is cut off before reaching its peak, and oscillation occurs safely and stably without overvoltage occurring.

Examples of the present invention will be described below.

Figure 1 is a circuit diagram of a discharge lamp lighting device according to an embodiment of the present invention, showing the secondary winding of the zero oscillation transformer OT and the discharge lamp DL.
A current transformer CT for current detection detects the current (combined value of filament current and lamp current) flowing through the discharge lamp DL, and thereby it is possible to detect whether the discharge lamp DL is attached. The outputs of current 1 to lance CT are rectified by diode D2, and resistors R@,
The voltage is divided by the voltage dividing circuit consisting of R1, and the capacitor C6
, and is input to inverter I2, which serves as an output buffer. The above circuit constitutes the no-load detection circuit 5.

In the oscillation circuit 1, Lllll is a general-purpose timer IC (
NEC'! ! As is well known, this timer ICtm, which is a JμPD15555), is triggered when the trigger terminal (terminal 2) becomes l / 3 V cc or less, and the output terminal (terminal 3) becomes Higl+'' level, and the discharge terminal (Terminal 7) has high impedance. Also,
When the threshold terminal (terminal No. 6) becomes 2/3 Vcc, the output terminal (terminal no. 3) becomes a "Low" level, and the discharge terminal (terminal No. 7) also becomes a "Low" level.

The control unit power supply voltage Vcc is applied to the series circuit of the resistor R1, the resistor R1, and the capacitor C7, and the connection point between the resistor R6 and the resistor R3 is connected to the discharge terminal (7) of the timer ICt+a.
The connection point between resistor R9 and capacitor C7 is the trigger terminal (terminal 2) of the timer ICt+a.
and the threshold terminal (terminal 6). A resistor R3 is connected to both ends of the resistor R1 via a transistor Trs.
゜ is connected. The base of the transistor Trz is connected to the transistor Tr through a resistor, and when the transistor Tr4 is turned on, the transistor Tr3 is also turned on. The base of the transistor Tr is connected to the detection output of the no-load detection circuit 5 via a resistor. The transistors T r 2 , T r and the resistor R10
An on-period control circuit 6 is configured.

Timer ICLm constitutes an astable multivibrator, and its oscillation frequency is determined by resistors R@, R@ and capacitor C7 when transistor Tr= is off.
It is determined by the time constant of At this time, the period during which the output (terminal 3) of the timer jcL song is at the “High+” level (width of the separately excited ON signal) is determined by (Ra + R*) Ct, and the period when it is at the “Low” level. (The width of the separately excited OFF signal) is determined by RBCt. When the transistor Tr3 is turned on, the resistor R1° is connected in parallel to the resistor R8, so the width of the separately excited ON signal is (ns//R1o
*) It is determined by Ct, and is shorter than when the transistor Tr3 is off. Therefore, the oscillation frequency of the oscillation circuit 1 becomes high.

The output of the oscillation circuit 1 is connected to one input of an AND gate G1 in the gate circuit 2.

The logic of the detection output of the element voltage detection circuit 4 is inverted by the inverter 1 and input to the local input of the AND gate G. Here, as the element voltage detection circuit 4,
A voltage divider circuit with resistors R+ and R2 is used. A Zener diode ZD for regulating the output of the element voltage detection circuit 4 is connected in parallel to the resistor R2. AND
The output of the gate G1 is the transistor T r 1 in the drive circuit 3.

It is connected to the input of a complementary operation type emitter follower consisting of Tr2. The output of the complementary emitter follower is
In this embodiment, a bipolar transistor is used as the semiconductor switching element Q1. There is. Note that the control unit power supply voltage Vcc is obtained by a capacitor C4 connected to a smoothing capacitor C0 via a resistor R1. The other configurations are the same as the conventional circuit.

The operation of this embodiment will be explained below.

As mentioned above, the oscillation circuit 1 includes a transistor Tr3 that switches the ON period of the separately excited signal, and when the transistor Tr= is on, the resistor R1° is connected in parallel with the resistor R, and when the separately excited signal is turned on, the resistor R1° is connected. The period becomes shorter and the oscillation frequency can be increased. This transistor Tr3 is driven by the detection output of the no-load detection circuit 5, and when there is no load, the secondary winding current of the oscillation transformer OT does not flow, so the current l.
The output voltage of the lance CT becomes zero, the output signal of the inverter I2 becomes the "Iligb" level, turns on the transistor Tr3 of the oscillation circuit 1, and increases the frequency of the separately excited signal.

When the discharge lamp DL is attached from a no-load state, current flows to the secondary winding of the oscillation transformer OT, but the current transformer C
Due to the time constants of the resistors R@, R7, and capacitor C6 that rectify and smooth the output of T, the rise of the smoothed voltage is delayed for a certain period of time, so the separately excited signal is output at a high frequency during that time, causing resonance in the inverter circuit. The inverter circuit is driven at a frequency sufficiently higher than the frequency. after that,
Even if the smoothed voltage by the capacitor C6 of the no-load detection circuit 5 rises, the output of the no-load detection circuit 5 becomes Low" level, the transistor Tr= is turned off, and the oscillation frequency of the oscillation circuit 1 decreases, the oscillation frequency of the oscillation circuit 1 decreases. At this point, discharge lamp D
Since L is already lit, the inverter circuit operates in a state where the resonance frequency on the load side of the inverter circuit is lower than the oscillation frequency of the Q oscillation circuit 1.

Further, as another embodiment of the present invention, a method may be considered in which the frequency of the separately excited signal is kept constant and only the duty is lowered.

In this case, as shown in FIG. 7, the ON period is narrow, so the stored energy of the oscillation transformer OT is small, and 2
Since the resonant current in the resonant loop of the next circuit becomes smaller, 2
Even if a resonant current flows in the next circuit, overvoltage will not be applied to the semiconductor switch cord Q1. However, at this time, the oscillation output of the inverter circuit will be The waveform becomes a damped oscillation, exhibiting a vibration different from the period of the drive signal, and depending on the duty setting, the oscillation may not continue.

(Effects of the Invention) As described above, the present invention is a resonant single-stone separately excited type that protects the semiconductor switch element during no load by prohibiting conduction of the semiconductor switch element when the element voltage is high. In the inverter evening circuit, at least when the discharge lamp is installed from a no-load state, the length of the on-period with respect to the off-period of the externally excited Accordingly, it is possible to suppress transient overvoltage applied to the semiconductor switch element when the discharge lamp is attached, and there is an effect that the reliability of the semiconductor switch element is not impaired.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram of an embodiment of the present invention, Fig. 2 is an equivalent circuit diagram of the main circuit of the above, Fig. 3 is a circuit diagram for explaining the operation of the above, and Fig. 4 is the operation waveform of the same. 5 is an explanatory diagram of the same operation as above, FIG. 6 is an operation waveform diagram of the same as above, FIG. 7 is an operation waveform diagram of the embodiment of the pond of the present invention, FIG. 8 is a circuit diagram of the conventional example, and FIG. This figure and FIG. 10 are operation waveform diagrams of the same as above. 1 is an oscillation circuit, 2 is a gate circuit, 4 is an element voltage detection circuit, 5 is a no-load detection circuit, 6 is an on-period control circuit, E is a DC power supply, Ql is a semiconductor switch element, D is a diode, C,... C2 is a capacitor, OT is an oscillation transformer, DL
is a discharge lamp, and Tr= is a transistor.

Claims (3)

[Claims] (1) A DC power supply, a semiconductor switching element in the forward direction with respect to the DC power supply, a diode connected in parallel to the semiconductor switching element in the reverse direction with respect to the DC power supply, and an inductance element connected in series with the semiconductor switching element. , a capacitor that forms a first resonant circuit together with an inductance element, an oscillation circuit that generates a separately excited signal to repeatedly turn on and off the semiconductor switch element, and a separately excited The circuit includes a circuit that prohibits a signal from being input to the conduction control pole of the semiconductor switch element, and a discharge lamp that applies a resonance voltage generated by turning on and off the semiconductor switch element via a stabilizing element. In the inverter circuit, a second resonant circuit is formed by a preheating control reactance connected in parallel to the electric lamp and the discharge lamp, and the resonant frequency of the first resonant circuit during no-load is lower than when the discharge lamp is lit, at least in the no-load state. The lamp is characterized by being equipped with an on-period control circuit that controls the oscillation circuit so that when the discharge lamp is installed, the length of the on-period with respect to the off-period of the separately excited signal is shorter than the rated lighting time of the discharge lamp. Discharge lamp lighting device. (2) The on-period control circuit is a circuit that controls the frequency of the separately-excited signal to be higher than the resonant frequency of the second resonant circuit by keeping the off-period of the separately-excited signal constant and shortening the on-period. A discharge lamp lighting device according to claim 1, characterized in that: (3) The on-period control circuit is a circuit that controls the separately-excited signal so that the frequency of the separately-excited signal is kept constant and the length of the on-period of the separately-excited signal is shorter than the off-period. The discharge lamp lighting device according to item 1.