JPS59181959A - Chopper circuit - Google Patents

Abstract

PURPOSE:To enable to shorten the rising time of the luminous flux or the like of a lamp by limiting the current reduction for maintaining the power constant in a low voltage range, i.e., large current range, thereby supplying the large current immediately after starting. CONSTITUTION:A clamping circuit which has a diode 11 is connected in parallel with a current detecting resistor 4 of a chopper circuit. In other words, the resistor 4 is clamped by the prescribed voltage value, thereby preventing the peak value of the detected voltage from rising so as not to shorten the ON time of a main transistor 5. Thus, the current value in a low voltage range increases, and the heating of the lamp 3 is accelerated. Since the transistor 5 might damage at a load shortcircuiting time, a current detector 14 made of a current transformer 13 is provided, the output current is dropped by the current detection output to protect the overcurrent.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of the Invention) The present invention relates to a Chung-8 circuit used, for example, as a discharge lamp lighting device for lighting a high-intensity discharge lamp with constant power.

(Background of the Invention) Conventionally, a lighting device for a high-intensity discharge lamp having the configuration shown in FIG. 1 has been known. In the same figure, ■ is a DC power supply (for example, 20V) from this DC power supply to the chopper I! 2
Constant power is supplied to the lamp 3 via the circuit 2. The chopper circuit 2 includes a current detection resistor (RCL) 4 inserted in series with the lamp 3, a main lamp 3, and a duty ratio inversely proportional to the voltage across the resistor 40.

ff to drive the base of transistor 50
! 1 circuit 6 is provided. As this control circuit 6, for example, TL497 manufactured by Texas Innos Tormenot, μA78340 manufactured by Fairchild, etc. can be used. In the figure, the inductor 7 and the connector 8 are used for smoothing the output, and the diode 9 is used for the flywheel. Also,].

is the positive voltage (for example, 10V) for the control circuit.

Figure 2 (al is the voltage VR across resistor 4 in Figure 1)
A waveform diagram of CL is shown. Here, the waveform when the lamp current is small is schematically shown at the top left end of Figure 1, and the waveform when the electric current θIL[direction] is increased in order toward the right. In this chopper circuit 2, the main transistors 1 to 5 are turned on at regular intervals, and when the voltage VRCL across the resistor 4 exceeds a certain value VTH, the main transistor 5 is turned on as shown in the waveform diagram of FIG. 2(b). By shortening the ON time of , the output current or current is reduced, thereby achieving a constant output.

FIG. 3 shows the luminous flux and lamp voltage of the lamp with respect to the elapsed time t after starting the lamp in the lighting device of FIG. 1, and the luminous flux and voltage at constant lighting. This is shown as OO staff. By the way, in the lighting device shown in Fig. 1, as shown in Fig. 3, the luminous flux is 50%, which can be considered as lamp lighting.
There was an inconvenience that it took a long time To to stand up. This is because the output current increases almost linearly as the output voltage decreases, as shown in Figure 4. This is because the output current, that is, the lamp current, is insufficient to heat the lamp electrodes, and it takes time for the lamp electrodes to warm up.

(Object of the Invention) In view of the problems in the conventional type described above, the present invention has been made to
In a chopper circuit that chopper-controls current to generate a constant power output, it supplies a larger current in the low voltage region based on the concept of keeping the chopper circuit's pass period constant when the output current is above a certain value. The purpose is to make it possible.

(Explanation of Examples) Embodiment 1 of the present invention will be described below with reference to the drawings.

FIG. 5 shows a chopper circuit according to one embodiment of the present invention. In other words, by clamping the current detection resistor 4 at a predetermined voltage (i.e., output current) value, the peak value of the detection voltage is prevented from increasing, and the on-time of the main traverse disc 5 is not shortened. As a result, as shown in FIG. 6, the current value increases in the low voltage region, and the wrap 3 is heated quickly.

In addition, since there is a risk of destruction of the Jtri main), lanogistor 5, etc. when the load is short-circuited,
A current detection circuit 14 is provided, and the output current is drooped based on the current detection output to perform overcurrent retention.

Note that the numbers attached to each lead terminal of the control circuit 6 in FIG. 5 indicate connection pin numbers when the above-mentioned TL497 is used as the control circuit 6.

Voltage VRCL across the current detection resistor 4 in FIG.
The waveform and the base 1 drive waveform of the main toranodisk 5 are
As shown in the figure.

FIG. 8 is a circuit diagram showing another embodiment of the invention, and FIG. 9 is a partial circuit diagram showing still another embodiment of the invention. In the circuit shown in Fig. 8, the voltage VRCL across the current detection resistor 40 is set to 1
~The voltage amplified by the ranosdiscs 15 and 16 is applied to the control circuit 6 as a control input, and as in FIG. 5, this control input voltage is clamped by the diode 1-1''11. In FIG. 9, the control input terminal of the control circuit 60 is clamped by a transistor 7 instead of the diode 12 in FIG. In,
main! - Although the lamp disk 5 is connected to the negative side of the lamp 3, the operation is substantially the same as that shown in FIG. 1 or 5.

Figure 10a, O, and b are other parts of the detection device. =g indicates the image side. This detection device uses current transformers (C, T,
) 18 is used, and the secondary winding of this current transformer] 8 is heated at 11℃
The pressure is rectified by a diode 19 to provide a detection output. 1] is a clamping diode similar to that described above.

(Effects of the Invention) As described above, according to the present invention, in the low voltage region, that is, in the large current region, it is possible to carry out the intrusion for constant power. 1 ill is limited, so when using this small 8 circuit to light a high-intensity lamp such as a metal halide lamp, the lamp has constant power control (higher than when the lamp is started) while the lamp voltage is low immediately after starting the lamp. Since current is supplied,
The fissine/1 electrode of the wrap heats up faster, thus reducing the light speed rise time of the wrap.

[Brief explanation of drawings]

Figure 1 is a circuit diagram of a conventional discharge lamp lighting device, Figure 2 is a fal
is a diagram of the voltage waveform across the current detection resistor in Figure 1, Figure 2 (b) is a diagram of the base and drive waveform of the main transistor in Figure 1, and Figure 3 is the elapsed time after starting the lamp in the device of Figure 1. 4 is a graph showing the output current-voltage characteristics of the device in FIG. 1, FIG. 5 is a circuit diagram of a discharge lamp lighting device according to Example J of the present invention, and FIG. Figure 6 is a graph showing the voltage waveform across the current detection resistor in Figure 5 and the base and drive waveforms of the main lance disc in Figure 5. Figure 7 is a graph showing the output current' direct pressure characteristics of the device in Figure 5. A circuit diagram of a discharge lamp lighting device according to another embodiment of the present invention, and FIGS. 9 and 10 are partial circuit diagrams of a discharge lamp lighting device according to still another embodiment of the present invention, respectively. J. DC power #i 2...chono.8 circuit, 3
...Lamp, 4.Current detection resistor, 5.Main 1-Landisk, 6.Control circuit. Patent Applicant Toshiba Electric Materials Co., Ltd. Patent Applicant Tokyo Shibaura Electric Co., Ltd. Representative Patent Attorney Tatsuo Ito (Patent Attorney Tatsuo Ito) Figure 6 Figure 8 Figure 9 Figure 10 Ishikawa

Claims (1)

[Claims] I. A DC power supply, a switching element connected in series with the DC power supply, and a detection device for detecting the value of acid flow flowing through the switching element, and according to the detection value of the detection device. In the chopper circuit, the chopper circuit generates a countercurrent output with substantially linear voltage-current characteristics by controlling the conduction period of the switching element in a negative feedback manner, wherein the detection device detects the value of the current flowing through the switching element. In a range larger than a predetermined value (a chopper circuit patented to keep the detected value d substantially constant. 2. The detection device applies a resistor connected in series with the switching element), and this resistor 2. The chopper circuit according to claim 1, wherein a diode is connected in parallel, and the voltage across the resistor is clamped by the forward voltage drop of the diode, thereby making the detected value substantially constant.