JPH0272597A - Control circuit of power tungsten lamp - Google Patents

Abstract

PURPOSE:To prevent surge currents at turning-on of a lighting switch by inserting two fixed voltage diodes in series to a tungsten lamp into a power source circuit, and connecting the way between these both diodes with the output terminal for voltage changeover of a controller. CONSTITUTION:Two fixed voltage diodes 7 and 8 as power sources for stabilization are inserted in series to a tungsten lamp 2 into a power source circuit 3, and the way between these both diodes 7 and 8 and the output terminal 6 for voltage changeover of a miscrocomputer 4 are connected by wiring 9, and specified voltage is applied to both ends of both diodes 7 and 8 through a transformer 10 connected to commercial power source. And at turning-on of a lighting switch 1 the output terminal 6 for voltage changeover is switched on and currents flow to one diode 7 alone, so at A point low voltage arises. Hereby, it can prevent surge currents from flowing to the microcomputer 4 at burning on of the lighting switch 1.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a circuit for controlling power supplied to a tungsten lamp for a display.

2. Description of the Related Art For example, in a typical microwave oven, as shown in FIG. 4, a cooking selection key 21 is arranged on a front panel 22, and this cooking selection key 21 is provided with a tungsten lamp. As shown in FIG. 5, in the control circuit for this tungsten lamp, a lighting switch (corresponding to a cooking selection key) 26 for lighting a tungsten lamp 25 is connected to an input terminal 24 of a microcomputer 23. When turned on, the input signal is Microcombi! - Tungsten is inputted from the input terminal 24 of the lamp 23 and judged in the microcomputer 23, and is disposed between the output terminal 27 of the microcomputer 23 and the cathode side of the Zener diode 28 of the stabilized power supply circuit for the lamp. When a lighting signal is output to the lamp 25 via the output terminal 27, a current is supplied from the Zener diode 28, which is a stabilized power source for the lamp, and the tungsten lamp 25 is turned on.

By the way, according to the above control circuit, as shown in FIG. 6(b), when the lighting switch 26 is input, at point A, for about several ms@e (as shown by B in FIG. 6(a)). ) There is a drawback that a surge current flows through the microcomputer 24 and may destroy the microcomputer 24. For this reason, conventionally, as shown in FIG. 7, the tungsten lamp 25 and the output terminal 27 of the microcomputer 24
By inserting a transistor buffer 29 between the microcomputer 24 and the microcomputer 24, surge current is prevented from flowing.

Problems to be Solved by the Invention According to the above configuration, the number of transistor buffers 29 equal to the number of tungsten lamps 25 is required, so when a plurality of tungsten lamps are used.

The problem was that it was expensive.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to prevent a surge current at a low cost when a lighting switch of a tungsten lamp is input.

Means for Solving the Problems In order to solve the above problems, a control circuit for a power supply for a tungsten lamp according to the present invention includes one lighting switch.

A control circuit consisting of a tungsten lamp, a power supply circuit for the tungsten lamp, and a control device that inputs a signal from the lighting switch to open and close the 8 circuits of the tungsten lamp. Two constant voltage diodes are inserted in series with the lamp, and the voltage switching output terminal of the control device is connected between the two constant voltage diodes.

Effect In the above configuration, when the lighting switch is input, the voltage switching output terminal of the control device is turned on and a low voltage is applied to the tungsten lamp by one of the constant voltage diodes, so that surge current is also suppressed. Further, when the resistance value of the tungsten lamp becomes large, the voltage switching terminal is turned off and a predetermined high voltage is applied by both constant voltage diodes.

EXAMPLE Hereinafter, one example of the present invention will be explained based on FIGS. 1 to 3.

FIG. 1 shows a control circuit for a tungsten lamp power supply provided in a cooking selection key in a microwave oven. In the diagram of the rod 1, 1 is a lighting switch (equivalent to one cooking selection key), %2 is a tungsten lamp, and 3 is a power supply circuit for the tungsten rande 2.

Reference numeral 4 denotes a microcomputer (control device) which inputs signals from the lighting switch 1 and also opens and closes the power supply circuit 3. The microcomputer 4 is provided with a voltage switching output terminal 6 in addition to a plurality of output terminals 5 connected to the tungsten rande 2, and the power supply circuit 3 is connected in series to the tungsten rande 2. Two Zener diodes (constant voltage diodes) 7 and 8 are inserted as a stabilizing power supply, and a wiring 9 is connected between these Zener diodes 7 and 8 and the voltage switching output terminal 6 of the microcomputer 4. connected by. Of course, a predetermined voltage is applied to both ends of the Zener diode 7.8 via a transformer 10 connected to a commercial power supply.

In the above configuration, when the lighting switch 1 is input, the voltage switching output terminal 6 of the microcomputer 4 is turned on as shown in FIG. 3, and current flows only through one Zener diode 7. As shown in Figure 2, a low voltage v1 is generated at point A, and the surge current is also suppressed as shown in Figure 2 (1).This state is called the preheat state. Therefore, if the preheat state is continued until the temperature reaches a point where the resistance value of the tungsten lamp becomes sufficiently large, and when the resistance value becomes large, the voltage switching output terminal 6 is turned off.
As shown in FIG. 2(b), at point A, there is a large voltage V! generated in both Zener diodes 7.8! However, since the resistance value of the tungsten lamp 2 has increased at this time, the current flowing to point A does not increase even if a high voltage is applied. Therefore, it is possible to prevent a surge current from flowing into the microcomputer 4 when the switch 1 is turned on and the switch 1 is turned on.

Effects of the Invention As described above, according to the configuration of the present invention, two regulated voltage diodes are provided in the power supply circuit of the tungsten lamp, and the voltage switching output terminal of the control device is connected between the two regulated voltage diodes. By doing this, the voltage of the tungsten lamp power supply circuit is controlled, so there is no need to provide a transistor buffer like in the past, and the surge current that occurs when the lighting switch is input can therefore be prevented at low cost. .

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a control circuit in an embodiment of the great invention,
Figure 2 (sl and 'b) is a graph showing the current and voltage at point A of the same control circuit, Figure 3 is a graph showing the on/off state of the voltage switching output terminal in the same control circuit, Figure 4 is a front view of a microwave oven, FIG. 5 is a circuit diagram of a conventional control circuit, and FIGS. 6 (a) and (b) are graphs showing the current at point A of the same control circuit and the on/off state of the lighting switch. 8...Zener diode source circuit, 4...Microcomputer, 6...[Pressure cut] Fig. 2 Fig. 3 Fig. 4 Fig. 6 Fig. 7

Claims (1)

[Claims] 1. A control circuit consisting of a lighting switch, a tungsten lamp, a power supply circuit for the tungsten lamp, and a control device that inputs a signal from the lighting switch to open and close the power supply circuit for the tungsten lamp, the control circuit comprising: A control circuit for a power supply for a tungsten lamp, in which two constant voltage diodes are inserted in series with a tungsten lamp, and a voltage switching output terminal of the control device is connected between the two constant voltage diodes.