JPH07183083A - Lamp control circuit for cooking apparatus - Google Patents

Abstract

PURPOSE:To extend the life of a lamp without decreasing brightness by decreasing a current flow through the lamp by control of a switching element immediately after the turn-on period of the lamp in which a large rush current flows is started, and passing a stationary current through the lamp thereafter. CONSTITUTION:A switching element 2 connected in series with a lamp 1 for backlighting the control keys of a cooking apparatus such as a microwave oven is controlled by a lamp drive signal S1 outputted from a control circuit 3, to control a current flowing through the lamp 1. The switching element 2 comprises e.g. pnp-type transistors TR, and the control circuit 3 comprising microcomputers outputs the drive signal S1 according to preprogrammed data, and passes a current consisting of pulse signals for a few minutes after the turn-on period of the lamp is started, thereby reducing the current flowing through the lamp 1. After the period of a few minutes has elapsed a predetermined DC-level current is passed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cooking appliance lamp control circuit for controlling lighting of an internal lighting lamp of a cooking appliance such as a microwave oven or a backlight lamp of an operation key.

[0002]

2. Description of the Related Art Conventionally, as a technique for extending the life of a lamp, the filament temperature is lowered by constantly lowering the applied voltage from the rated value, thereby extending the life of the lamp.

[0003]

However, in the above-mentioned conventional technique, the brightness is lowered, so that it is necessary to use a large lamp or increase the number of lamps in order to secure a predetermined brightness. However, there is an inconvenience that the cost of the lamp becomes expensive even though the life of the lamp is improved.

Therefore, an object of the present invention is to provide a lamp control circuit for a cooking appliance which can improve the life of the lamp without lowering the brightness.

[0005]

A cooking appliance lamp control circuit according to the present invention comprises a lamp and a switching element connected in series between both ends of an AC power source or a DC power source, and a current flowing through the lamp by controlling the switching element. The control circuit controls the switching element so that the current flowing through the lamp is reduced immediately after the lamp starts lighting, and the switching circuit switches the current flowing through the lamp into a steady state after a certain period of time. It is configured to control the device.

Further, the control circuit is configured to control the switching element so that the current flowing through the lamp is reduced again after a lapse of a predetermined time after a lapse of a certain time.

[0007]

In the structure of the present invention, the control circuit controls the switching element in order to extend the life of the lamp at the start of lighting when a large rush current flows and reduces the current flowing through the lamp, and after a certain period of time, the lamp In order to ensure the brightness of the lamp, the switching element is controlled to make the current flowing through the lamp a steady current, and after a predetermined time has elapsed, the switching element is controlled so that the current flowing through the lamp is reduced again.

[0008]

1 is a block diagram showing an embodiment of a lamp control circuit for a cooking appliance according to the present invention. The present embodiment is a backlight lamp 1 for operating keys of cooking equipment such as a microwave oven.
Is a circuit for driving and lighting the lamp with a DC power source. By controlling the switching element 2 connected in series with the lamp 1 by the lamp drive signal S1 output from the control circuit 3, the current flowing through the lamp 1 is controlled and the lamp 1 is driven. The lighting is controlled.

As an example, the switching element 2 is composed of a pnp type transistor TR, the emitter terminal of which is connected to the ground potential (0V) and the collector terminal of which is connected to the DC potential of -12V through the lamp 1. Has been done. Further, the control circuit 3 is composed of a microcomputer (hereinafter, referred to as a microcomputer), outputs a drive signal S1 based on preprogrammed data, and secures necessary brightness while reducing the load on the filament of the lamp 1. I am trying. The control circuit 3 is supplied with 0V and -5V as a DC power source.

FIG. 2 is a waveform diagram of the lamp drive signal S1 output from the control circuit 3. As shown in the figure,
The drive signal S1 is formed of a pulse signal composed of a plurality of pulse trains for several seconds (for example, one second) from the lighting start time t1 and becomes a signal of a predetermined DC level from time t2 when several seconds elapse.

In this case, since the transistor TR is of the pnp type, when the drive signal S1 is -5V, the transistor TR is turned on and the lamp 1 is turned on to drive the drive signal S.
When 1 is 0V, the transistor TR is turned off and the lamp 1
Turns off.

For this reason, immediately after the start of lighting, a rush current that greatly affects the life of the lamp flows and the drive signal S
Since 1 is a pulse signal, the transistor TR is intermittently turned on / off and the current flowing through the lamp 1 also becomes a pulse signal. Therefore, an effective current having a lower level than the current flowing in the steady state flows through the lamp 1, and the rush current can be suppressed.

From time t2, the drive signal S1 becomes a signal of a predetermined DC level (-5 V), so that the transistor TR is continuously turned on, the current flowing through the lamp 1 increases, and the lamp 1 reaches a predetermined level. It will light up with brightness.

By the way, when a certain time or more has elapsed from the time t2, it is considered that the user has moved away from the cooking appliance, and in this case, there is no problem even if the brightness of the lamp 1 is lowered, so that the drive signal S1 is again provided. To the pulse signal,
The current flowing through the lamp 1 is reduced to reduce the load on the filament of the lamp 1, and the life of the lamp 1 is extended.

FIG. 3 is a block diagram showing another embodiment of the lamp control circuit for the cooking appliance according to the present invention. This embodiment is a circuit for lighting and driving an internal lighting lamp 11 of a cooking appliance such as a microwave oven by an AC power supply 12, and a switching element 13 connected in series to the lamp 11 is a triac T.
The AC power source 12 is configured by controlling the conduction timing of the triac TA by the trigger circuit 14.
To control the phase angle of the alternating current flowing through the lamp 11 to control the lighting of the lamp 11.

The trigger circuit 14 is composed of a light emitting diode LD and a phototriac PT having a light receiving element structure. When the light emitting diode LD is controlled to emit light by a drive pulse S2 output from the control circuit 15, the phototriac PT is activated. Upon receiving light, it becomes conductive and outputs a pulse signal for turn-on to the gate of the triac TA. This turns on the triac TA, causing current to flow through the lamp 11 until the next zero crossing of the alternating current.

The control circuit 15 is composed of a microcomputer, and outputs a drive pulse S2 based on preprogrammed data to control the conduction timing of the phototriac PT, that is, the phase angle of the triac TA, to control the lamp 11. Control the current flowing through.

FIG. 4 is a waveform diagram for explaining the operation of the lamp control circuit shown in FIG. 3, showing the operation immediately after the start of lighting. As shown in the figure, the drive pulse S2 (FIG. A) has a conduction start phase angle of about 90 ° and about 270 from the AC power supply 12 (FIG. B) for a certain period from the lighting start time t1 for a certain period, for example, 1 second. The pulse signal is output at a timing of 0 °, and the conduction start phase angle of the alternating current is 0 ° (360 °) and 1 from the time t2 after the elapse of a certain period.
The pulse signal is output at a timing of 80 °. The phase control of the drive pulse S2 is performed with reference to the zero cross point of the AC power supply 12.

Therefore, as indicated by the slanted lines in FIG. 4 (b), the alternating current has a phase angle of 90 ° to 1 during the time t1 to t2.
Since the current flows only between 80 °, 270 ° and 360 ° (0 °), an effective current having a lower level than the current flowing in the steady state flows in the lamp 11, and the rush current can be suppressed. Then, from the time point t2, the alternating current flows for all the phase angles, so that a larger current flows to the lamp 11 immediately after the start of lighting, and the lamp 11 is lit with a predetermined brightness.

By the way, when a certain time or more has elapsed from the time point t2, it is considered that the user has left the cooking appliance, and in this case, there is no problem even if the brightness of the lamp 11 is lowered, and therefore, it is shown in FIG. As described above, the phase of the drive pulse S2 is again shifted from the zero cross point of the alternating current from the time point t3 so that the conduction start phase angle of the triac TA becomes about 90 ° and about 270 °. As a result, the current flowing through the lamp 11 is reduced, the load on the filament of the lamp 11 is reduced, and the life of the lamp 11 is extended.

[0021]

According to the present invention, immediately after the start of lighting in which a large rush current flows, the switching element is controlled to reduce the current flowing to the lamp, and thereafter, the switching element is controlled to provide a steady-state current to the lamp. Since the flow is made to flow, it is possible to extend the life of the lamp, and to realize a low-cost cooking appliance lamp control circuit that does not reduce the brightness in the steady state.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of a lamp control circuit for a cooking appliance according to the present invention.

FIG. 2 is a waveform diagram of the lamp drive signal shown in FIG.

FIG. 3 is a configuration diagram showing another embodiment of the lamp control circuit for the cooking appliance according to the present invention.

FIG. 4 is a waveform chart for explaining the operation of the embodiment shown in FIG.

5 is a waveform diagram for explaining the operation of the embodiment shown in FIG.

[Explanation of symbols]

 1,11 Lamp 2,13 Switching element 3,15 Control circuit 12 AC power supply 14 Trigger circuit TR Transistor TA Triac PT Phototriac LD Light emitting diode

Claims (2)

[Claims] 1. A lamp and a switching element connected in series between both ends of an AC power source or a DC power source, and a control circuit for controlling the switching element to control a current flowing through the lamp, the control circuit comprising: Immediately after starting the lighting of the lamp, the switching element is controlled so that the current flowing through the lamp is reduced, and after a certain period of time, the switching element is controlled so that the current flowing through the lamp becomes a steady state. Lamp control circuit for cooking equipment. 2. The control circuit controls the switching element so that the current flowing through the lamp is reduced again when a predetermined time has elapsed after the predetermined time has elapsed. Lamp control circuit for cooking equipment.