JPS60207294A - Firing device - 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 of invention] The present invention relates to a lighting device having an overvoltage protection function.

Technical background of the invention] Conventionally, for example, an inverter circuit and an error amplifier having a semiconductor switching element are provided, and the semiconductor switching element is subjected to PWM (pulse width modulation) using the output of the error amplifier.
There is a lighting device that controls lighting of a lamp with a constant current. This is a lighting device that detects the average value of the current supplied to the lamp side and variably controls the switching duty ratio of a semiconductor switching element based on this detection signal. However, this lighting device has the disadvantage that, for example, in the event of incorrect wiring or a short circuit in the lamp, a large current will temporarily flow and the circuit will be damaged.

Therefore, the inventor of the present invention has developed a lighting circuit as shown in FIG. 1 which eliminates these drawbacks, that is, has a circuit protection function. This is a DC power supply 1 and an NPN type switching transistor 2 which is a semiconductor switching element.
and a diode 4 via a resistor 3 for current layer detection in series.
are connected to the illustrated polarity, and further connected to a capacitor 6 and a refrigerant 7 via a current limiting coil 5. The switching transistor 2 is operated in response to the voltage across the resistor 3 by a control circuit 8 that controls, for example, its switching duty ratio. The control circuit "-" includes an average value circuit 11 that integrates and averages the voltage across the resistor 3 by applying it to the capacitor 10 via the resistor 9;
The voltage across the capacitor 13 is passed through the diode 12.
a current peak value detection circuit 14 that detects the peak value of the current supplied to the lamp 7 side by applying the current to the lamp 7 side and outputs a detection signal, a reference power supply 15, 16, and an output voltage of the reference power supply 15 that is inverted The output of the average value circuit 11 is input to the input terminal (-), and the output of the average value circuit 11 is input to the non-inverting input terminal (+).
a first error amplifier 18 having a feedback resistor 17 connected between the inverting input terminal (-) and the output terminal;
The output voltage of the reference power supply 16 is input to the inverting input terminal (-), and the output of the current peak value detection circuit 14 is input to the non-inverting input terminal (+), and the output voltage is connected to the inverting input terminal (-) and the output terminal. A second circuit with a feedback resistor 19 connected between
error amplifier 20 and the first and second error amplifiers 18
．． a PWM (pulse width modulation) control circuit 23 which receives the outputs of 20 through diodes 21 and 22, and controls the switching duty ratio of the switching transistor 2 according to the voltage level of each error amplifier 18 and 20; It consists of

Normally, in this circuit, when the current flowing through the lamp 7 increases, the voltage generated across the resistor 3 increases,
The voltage input to the non-inverting input terminal (+) of the first error amplifier 18 increases. Therefore, the first error amplifier 1
The level of the output from 8 increases and the PWM control circuit 2
3, the switching duty ratio of the switching transistor 2 is small, that is, the ON width is narrowed, and the amount of current supplied to the lamp 7 is reduced. Conversely, when the current flowing through the lamp 8 decreases, the voltage generated across the resistor 3 decreases, and the voltage input to the non-inverting input terminal (+) of the first error amplifier 18 decreases. However, the first
The level of the output from the error amplifier 18 becomes smaller and P
The switching duty ratio of the switching transistor 2 by the WM control circuit 23 is large, that is, the ON width is wide, and the amount of current supplied to the lamp 7 is increased.

In this way, the lamp 7 is normally controlled to be lit at a constant current.

In this state, even if the current peak value detection circuit 14 performs a current peak value detection operation, the voltage level supplied to the non-inverting input terminal (+) of the second error amplifier 20 is supplied to the inverting input terminal (-). Therefore, the second error amplifier 20 does not output a voltage signal.

In this state, if the lamp 7 is short-circuited due to incorrect wiring or the like, a large amount of current will flow through the lamp 7. As a result, the level of the detection signal from the current peak value detection circuit 14 increases significantly, and the input level to the non-inverting input terminal (+) of the second error amplifier 20 becomes higher than the input level to the inverting input terminal (-). The output of the second error amplifier 20 causes the PWM control circuit 23 to perform control to narrow the on-width of the switching transistor 2, thereby controlling the current supplied to the lamp 7 to decrease. In this way, when a current with a high peak value such as a short circuit current flows, the switching duty ratio of the switching transistor 2 is immediately controlled to become small even if the average current amount is small, and the circuit is protected against overcurrent. It will be done.

[Problems with Background Art] However, in such a circuit, the second error amplifier 20
The input voltage to the non-inverting input terminal (+) of the second error amplifier 20 changes with the voltage fluctuation of the power supply 1, as shown in the graph (A) in FIG. The input voltage to is obtained from the reference power supply 16 and does not change with respect to voltage fluctuations of the power supply 1, as shown in the graph (b) in FIG.

For this reason, as shown in the load characteristics in Figure 3, if there is a fluctuation in the power supply voltage when an overcurrent is flowing, the current will not be constant and will flow too much or too little, as shown by the dotted line in the figure. was there. Such a problem also occurred when a variable control means was provided to keep the lamp power substantially constant.

[Purpose of the Invention] The present invention has been made to solve such problems, and it is possible to control the lamp current or lamp power to be substantially constant even in the event of an overcurrent despite fluctuations in the power supply voltage. It is an object of the present invention to provide a lighting device that can reliably perform current control or power control against fluctuations in power supply voltage.

L Summary of the invention] This invention provides an inverter circuit having a semiconductor switching element, a lamp connected to the inverter circuit, and a current detecting the average value of the current supplied from the inverter circuit to the lamp side and outputting a detection signal. an average value detection circuit; a variable control means for variably controlling the switching duty ratio or switching period of the semiconductor switching element based on the detection signal so that the lamp power has substantially constant current or substantially constant power characteristics; and an inverter circuit. A current peak value detection circuit that detects the peak value of the current supplied to the lamp side and outputs a detection signal, a reference power supply that generates a reference voltage, and a voltage proportional to the iI power supply voltage from the power supply supplied to the inverter circuit. and a voltage fluctuation detection circuit that outputs a voltage signal obtained by subtracting the reference voltage of the reference power supply from the voltage, and a detection signal from the current peak value detection circuit is input to one end, and the output signal from the voltage fluctuation detection circuit is input to one end. and an error amplifier that outputs a voltage signal according to the magnitude of the input level of one end with respect to the input level of the other end, and the switching circuit of the semiconductor switching element is configured according to the level of the voltage signal from the error amplifier. The output voltage signal of the error amplifier is input to the variable control means so that the utility ratio or switching period is set so that the lamp has substantially constant current or substantially constant power characteristics.

[Embodiments of the Invention] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In this embodiment, only the main parts will be described, and since the other configurations are the same as those shown in FIG. 1, detailed explanation thereof will be omitted. Note that the same parts as in FIG. 1 are given the same reference numerals.

As shown in FIG. 4, a voltage fluctuation detection circuit 27 is constructed by connecting a series circuit of resistors 25 and 26 through a reference power supply 24 and reverse polarity as shown in the figure to a voltage supply source Vin proportional to the voltage. The connection point of the resistors 25 and 26 of the voltage fluctuation detection circuit 27 is connected to the inverting input terminal (-) of the second error amplifier 20.

In the device according to the embodiment of the present invention having such a configuration, the power supply voltage fluctuates and a voltage 8! When V1n changes as shown in FIG. The voltage is determined by -V25 (voltage across the resistor 25) and changes as shown in the graph (b). On the other hand, the voltage input to the non-inverting input terminal (+) of the second error amplifier 20 changes as shown in the graph (A) as in the conventional case. Finally, the reference voltage V24 of the reference power supply 24, the resistance 25.26
By setting the resistance value, the slopes of graphs (a) and (b) can be made the same. In other words, the second
It is possible to make changes in the input voltages to both input terminals of the error amplifier 20 substantially the same. Therefore, the load characteristic is the sixth
As shown in the figure, the current can be controlled to be constant even when there is an overcurrent, and the current can be reliably controlled against fluctuations in the power supply voltage.In the above embodiment, the switching transistor is Although the method for controlling the switching duty ratio has been described, the present invention is not necessarily limited to this, and the method may also control the switching period. Further, although the above embodiments have been described with respect to a device that performs substantially constant current control, the present invention is not necessarily limited to this, and can also be applied to a device that performs substantially constant power control. Furthermore, in the above embodiment, the power supply voltage fluctuation signal is input only to the second error amplifier 20, but it is input to the first error amplifier 18, so that constant current control or constant power control during stable lighting can be performed more accurately. You may do so.

[Effects of the Invention] As detailed above, according to the present invention, it is possible to control the lamp current or lamp power to a constant level even in the event of an overcurrent in response to fluctuations in the power supply voltage; It is possible to provide a lighting device that can more reliably control current or power consumption.

[Brief explanation of drawings]

Figure 1 is a circuit diagram that is the premise of the present invention, Figure 2 is a graph showing changes in the input voltage of the second error amplifier with respect to fluctuations in the power supply voltage in Figure 1, and Figure 3 is a graph showing the load characteristics in Figure 1. 4 is a main circuit diagram showing an embodiment of the present invention, FIG. 5 is a graph showing changes in the input voltage of the second error amplifier with respect to fluctuations in power supply voltage in the same embodiment, and FIG. 6 is a graph showing the same. It is a graph showing load characteristics in an example. 1...Power supply, 2...Switching transistor, 3
...Resistance, 7...Lamp, 11...Average value circuit,
14... Current peak value detection circuit, 18... First error amplifier, 20... Second error amplifier, 23... P
W M IIJ 8 circuits, 24...Reference power supply, 27
...Voltage fluctuation detection circuit. Applicant's agent Patent attorney Takehiko Suzue

Claims (1)

[Claims] an inverter circuit having a semiconductor switching element; a lamp connected to the inverter circuit; a current average value detection circuit that detects an average value of current supplied from the inverter circuit to the lamp side and outputs a detection signal; variable control means for variably controlling the switching duty ratio or switching period of the semiconductor switching element based on the detection signal so that the lamp power has substantially constant current or substantially constant power characteristics; a current peak value detection circuit that detects the peak value of the current supplied to the inverter circuit and outputs a detection signal, a reference power supply that generates a reference voltage, and a voltage proportional to the power supply voltage from the power supply that is supplied to the inverter circuit. a voltage fluctuation detection circuit that outputs a voltage signal obtained by subtracting the reference voltage of the reference power supply from the supplied voltage; and a voltage fluctuation detection circuit that receives a detection signal from the current peak value detection circuit at one end and outputs an output from the voltage fluctuation detection circuit. and an error amplifier that inputs a signal to the other end and outputs a voltage signal according to the magnitude of the input level of one end with respect to the input level of the other end, and the semiconductor switching element according to the level of the voltage signal from the error amplifier. A lighting device characterized in that the output voltage signal of the error amplifier is input to the variable control means so that the lamp has a substantially constant current or substantially constant power characteristic with a switching period of □-Tay ratio or a switching period.