JPH0250595B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to a high-frequency lighting device for an incandescent light bulb, which converts a DC power supply voltage to a high frequency using a self-oscillation type inverter and lights an incandescent light bulb at high frequency.

(Background Art) FIG. 5 is a circuit diagram of a conventional example. A series circuit of capacitors C ₁ and C ₂ and a series circuit of transistors Tr ₁ and Tr ₂ are connected to the DC power supply E.
The emitter of transistor Tr ₁ and the transistor
The connection point with the collector of Tr ₂ and the capacitor C ₁ and
A series circuit of the primary windings of a step-down transformer T ₁ and a current feedback transformer T ₂ is connected to the connection point of C ₂ . One secondary output winding of the current transformer T ₂ is connected to the transistor through the base resistor R ₁
Connected between the base and emitter of Tr ₁ . Further, the other secondary output winding of the power supply feedback transformer _T2 is connected between the base and emitter of the transistor _Tr2 via a base resistor _R2 . DC power supply E
A series circuit of resistor R ₃ and capacitor C ₃ is connected to . Capacitor C ₃ is the trigger element Q
is connected between the base and emitter of transistor Tr ₂ through
The charge in the capacitor _C3 flows through the trigger element Q between the base and emitter of the transistor _Tr2 . Therefore, in the circuit of FIG. 5, after the power is turned on, the transistor Tr ₂ is turned on, and from the DC power source, the capacitor C ₁ , the primary winding of the step-down transformer T ₁ , and the primary winding of the current feedback transformer T ₂ are
Current flows through the next winding, between the collector and emitter of transistor Tr ₂ . At this time, positive feedback is applied to the transistor Tr ₂ due to the voltage generated in the secondary winding of the current feedback transformer T ₂ , and the transistor
Tr ₂ continues to be on. As the change in the collector current becomes smaller, the voltage induced in the secondary winding of the current feedback transformer T ₂ decreases, and eventually the voltage is reversed, so that the transistor Tr ₂ is turned off. At this time, transistor _Tr1 is turned on. transistor
When Tr ₁ is turned on, current flows from the DC power supply E between the collector and emitter of transistor Tr ₁ , to the primary winding of current feedback transformer T ₂ , and to the primary winding of step-down transformer T ₁ .
It flows through the next winding, capacitor C ₂ . From then on,
The transistors Tr ₁ and Tr ₂ are alternately turned on and off, and a high-frequency alternating current flows through the primary winding of the step-down transformer T ₁ . An incandescent light bulb L is connected to the secondary side of the step-down transformer _T1 , and this incandescent light bulb L is lit at high frequency.

However, in such a device, since the load is an incandescent light bulb and the impedance is very low at startup, close to a short-circuit condition, the primary winding current of the step-down transformer _T1 is as shown in Figure 6a. As shown in FIG _.
Similarly, the voltage of the next winding becomes a voltage with a rising peak at the time of starting (see Fig. 6b). The secondary winding voltage of the current feedback transformer T ₂ is the voltage between the transistors Tr ₁ and Tr ₂
The transistors Tr ₁ ,
The base-emitter voltage (V _BE ) of Tr ₂ is
As _{shown in} FIG. There was a risk of deteriorating and destroying Tr ₂ .

The specifications of the current feedback transformer _T2 are designed so that the reverse voltage between the base and emitter of transistors _Tr1 and _Tr2 during steady state is 3 to 5V.・The voltage will be applied between the emitters, completely exceeding V _EBO . In addition, in the conventional example shown in FIG. 5, if an attempt is made to control the secondary voltage of the current feedback transformer _T2 to keep it within V _EBO at startup, the steady state voltage will become low, the reverse bias will become shallow, and The voltage supplied to the base also became low, which caused the disadvantage that the base current decreased.

(Object of the Invention) The present invention has been made in view of the above-mentioned points, and its purpose is to control the reverse voltage between the base and emitter of an oscillation transistor when the power is turned on, and to control the reverse voltage between the base and emitter when the oscillation transistor is turned on. An object of the present invention is to provide a high-frequency lighting device for an incandescent light bulb, which prevents deterioration and destruction of transistors and allows an inverter to smoothly oscillate during normal operation.

(Disclosure of the Invention) As shown in FIGS. 1 to 4, the high-frequency lighting device for an incandescent light bulb according to the present invention converts the voltage of a DC power source E into a high frequency using an inverter to light an incandescent light bulb L at high frequency. In the lighting device, current feedback is used to feed back the load current between the base and emitter so that the oscillation transistors Tr ₁ and Tr ₂ of the inverter turn on and off in the same phase as the load current flowing through the incandescent light bulb L, causing self-oscillation. It has a type control circuit, and a circuit that reduces impedance only in the reverse bias direction is connected between the base and emitter of the oscillation transistors Tr ₁ and Tr ₂ .

Since the present invention is configured in this way, a large load current flows in the initial stage of lighting of the incandescent light bulb L.
Even if a large drive voltage is applied between the bases and emitters of the oscillation transistors Tr ₁ and Tr ₂ , the reverse voltage between the bases and emitters of the oscillation transistors Tr ₁ and Tr ₂ can be prevented from becoming excessive, and the starting This can prevent deterioration and damage of the transistors Tr ₁ and Tr ₂ at times.

Preferred embodiments of the present invention will be described below with reference to the accompanying drawings.

Embodiment 1 FIG. 1 is a circuit diagram of a high-frequency lighting device for an incandescent lamp according to an embodiment of the present invention, and FIG. 2 is an explanatory diagram of its operation. In this embodiment, in the conventional circuit described above, a series circuit of a resistor r ₁ and a diode D 1 is connected between the base and emitter of the transistor Tr 1, and similarly, a series circuit of a resistor r ₁ and a diode D ₁ is connected between the base and emitter of the transistor Tr ₁ . It is a series circuit of resistor r ₂ and diode D ₂ connected, and the polarity of each diode D ₁ and D ₂ is as follows.
The transistors are selected to be in antiparallel to the base-emitter diodes of each transistor Tr ₁ and Tr ₂ .

When the power is turned on, a base current is supplied to the transistor Tr ₂ by a trigger circuit including a resistor R ₃ , a capacitor C ₃ and a trigger element Q, and the transistor Tr ₂ is turned on. A current flows from the DC power supply E through the capacitor C ₁ , the primary winding of the step-down transformer T ₁ , the primary winding n ₁ of the current feedback transformer T ₂ , and the transistor Tr ₂ . At this time, the current feedback transformer
A voltage is induced in the secondary winding n ₂ of T ₂ in the direction of applying positive feedback to the transistor Tr ₂ .
Tr ₂ continues to be on. As the change in the collector current of transistor Tr ₂ decreases, the voltage in the secondary winding n ₂ decreases, and eventually the voltage reverses,
Transistor Tr ₂ is turned off. At this time, the secondary winding n ₃ of the current feedback transformer T ₂ has a transistor
A voltage is induced in the direction of turning on Tr ₁ , and transistor Tr ₁ turns on. Hereafter, capacitors C ₁ and C ₂
Using the power source, the transistors Tr ₁ and Tr ₂ are alternately turned on and off, and the incandescent light bulb L is lit at high frequency with the high frequency voltage obtained at the secondary winding of the step-down transformer T ₁ . In this example, the transistor
Resistor r ₁ and diode between base and emitter of Tr _1
A series circuit of resistor r ₂ and diode D ₂ is connected between the base and emitter of transistor Tr ₂ .
Because they are connected, when the emitter voltage is higher than the base voltage, that is, when the base and emitter are reverse biased, the diode
D ₁ and D ₂ conduct, the secondary winding voltage of the current feedback transformer T ₂ is divided by the resistors r ₁ and r ₂ and the base resistors R ₁ and R ₂ , and this divided voltage is applied to the transistor Tr. ₁ ,
Applied between the emitter and base of Tr ₂ . Therefore, V _BE at startup becomes as shown in Figure 2c, making it possible to suppress the reverse voltage between the base and emitter to below V _EBO . Moreover, when voltage is applied in the forward direction between the bases and emitters of transistors Tr ₁ and Tr ₂ , diodes D ₁ and D ₂
Since the resistors r ₁ and r ₂ do not conduct, the base current is not reduced by the resistors r 1 and r 2 and oscillation is maintained smoothly.

Embodiment 2 FIG. 3 is a main circuit diagram of another embodiment of the present invention. In this embodiment, in Embodiment 1 shown in FIG. 1, a capacitor C is connected in parallel with the resistor r ₂ , and a capacitor C' (not shown) is also connected in parallel with the resistor r ₁ . Other than that, the circuit configuration is the same as that of the first embodiment. In this example, the resistances r ₁ , r ₂
Since a capacitor is connected in parallel to
The circuit that reduces the impedance in the reverse bias direction between the base and emitters of Tr ₁ and Tr ₂ operates only for a certain period of time after the lighting device is started, and does not operate in a steady state. Therefore, it is possible to apply a deep reverse bias to the transistors Tr ₁ and Tr ₂ in a steady state.

Embodiment 3 FIG. 4 is a circuit diagram of still another embodiment of the present invention. In this embodiment, the DC power supply E is connected to the intermediate tap of the primary winding of the oscillation transformer OT via an inductance element _L1 .
A resonance capacitor C ₀ is installed at both ends of the primary winding of OT.
are connected, and transistors Tr ₁ and Tr ₂ are connected to form a push-pull circuit. 1 of the collector currents of transistors Tr ₁ and Tr ₂
The part is taken out by the current transformer T ₃ , and the transistor is taken out by the rectifier circuit Re and the smoothing capacitor C ₃ .
It is used as the base power supply for Tr ₁ and Tr ₂ . oscillation transformer
The current feedback winding of OT is connected to the bases of transistors Tr ₁ and Tr ₂ and turns transistors Tr ₁ and Tr ₂ on and off alternately. Even in this example,
Since the incandescent light bulb L connected to the secondary winding of the oscillation transformer OT has a very low impedance at startup, the collector currents of the transistors Tr ₁ and Tr ₂ increase, and the base bias voltage that feeds back this collector current also increases. Each transistor becomes larger, but
Between the base and emitter of Tr ₁ and Tr ₂ , a series circuit consisting of resistors r ₁ and r ₂ and diodes D ₁ and D ₂ is connected in parallel so as to lower the impedance only in the reverse bias direction. transistor
The reverse voltage between the base and emitter of Tr ₁ and Tr ₂ is reduced. Therefore, the transistor Tr ₁ ,
This can prevent damage to Tr ₂ .

Note that the DC power source E may be a pulsating current power source obtained by rectifying an AC power source.

(Effects of the Invention) As described above, in the present invention, in an incandescent lamp lighting device using a current feedback self-oscillation inverter, only the reverse bias direction is applied between the base and emitter of the oscillation transistor. Since a circuit that reduces impedance is connected, even if a large load current flows during the initial lighting of the incandescent lamp and a large drive voltage is applied between the base and emitter of the oscillating transistor, This has the effect of preventing the reverse voltage of This has the effect that the inverter can oscillate smoothly.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram of one embodiment of the present invention, Fig. 2 is an explanatory diagram of the same operation as above, Fig. 3 is a main circuit diagram of another embodiment of the present invention, and Fig. 4 is a further embodiment of the present invention. FIG. 5 is a circuit diagram of the conventional example, and FIG. 6 is an explanatory diagram of the same operation. L is an incandescent light bulb, Tr ₁ and Tr ₂ are transistors, r ₁ ,
r ₂ is a resistor, and D ₁ and D ₂ are diodes.

Claims (1)

[Scope of Claims] 1. A lighting device for lighting an incandescent light bulb at high frequency by converting a DC power supply voltage to a high frequency using an inverter, in which an oscillation transistor of the inverter is turned on and off in the same phase as a load current flowing through the incandescent light bulb. It has a current feedback type control circuit that feeds back the load current between the base and emitter to cause self-oscillation.
A high-frequency lighting device for an incandescent light bulb, characterized in that a circuit for reducing impedance only in the reverse bias direction is connected between the base and emitter of an oscillating transistor. 2. The high-frequency lighting device for an incandescent light bulb according to claim 1, wherein the circuit for reducing impedance is a circuit that operates only until the current and voltage of the incandescent current are stabilized.