JPH03141590A - High frequency lighting apparatus for incandescent lamp - Google Patents

Abstract

PURPOSE:To detect over load condition at a terminal period of a lamp or during lighting when excessive current runs so as to protect a device from breaking and prevent error operation owing to rush current at the initial stage of electric power application by constructing a protection circuit in the way so that a high frequency inverter is stopped when the number of the times at which a lamp current surpasses the threshold value is counted synchronously with alternating current power source and the counted number reaches a prescribed number. CONSTITUTION:A high frequency inverter 1, to which a branched electric power source is supplied and which lights an incandescent lamp by a high frequency power source, and a protection circuit 2, which stops the high frequency inverter when the number of the times at which lamp current surpasses a prescribed threshold value is counted synchronously with alternating current power source and the counted value reaches a prescribed number, are installed. If the counted number is set not to reach a prescribed value in the case that a lamp current damps gradually like a rush current, the rush current is not detected and over current only at that time of secondary short-circuit or the time of over load can be detected. Further, the counted number is set to come up close to the prescribed number by the rush current, the period during stress is applied to the circuit of the high frequency inverter becomes short and high protection function is achieved at the time of secondary short-circuit and the time of over load.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to a high frequency lighting device for an incandescent light bulb.

[Conventional technology]

In recent years, there has been a demand for smaller lighting fixtures and simpler light distribution control, and to meet these demands, compact, high-efficiency, low-voltage compact halogen light bulbs have come into wide use. The rated voltage of this type of halogen light bulb is, for example, 12V, and since it cannot be turned on by being directly connected to a commercial power source, a step-down means is required. A step-down transformer compatible with the frequency of the commercial power source can be considered as a step-down means for the commercial power source, but since the step-down transformer is relatively large, it cannot satisfy the demand for downsizing of lighting equipment. In order to solve these problems, it has been proposed to light an incandescent light bulb, such as a halogen light bulb, with high-frequency power. A lighting device for lighting an incandescent light bulb with high-frequency power is basically constructed as shown in FIG. In this lighting device, a commercial power source AC is full-wave rectified by a rectifier circuit Re to be used as a power source for a high frequency inverter 1, and the high frequency inverter 1 is configured to be an automatic half bridge system. Between the output terminals of the rectifier circuit Re,
A series circuit of resistor R3 and capacitor C1 is connected, and when power is turned on, capacitor C is charged via resistor R3. A pair of capacitors C, , C, which are connected in series and inserted between the output terminals of the rectifier circuit Re, are also charged. When the voltage across the capacitor C3 reaches the breakover voltage (for example, about 8V) of the trigger element Q3 made of SBS, the trigger element Q is turned on and the transistor Q is turned on. When transistor Q is turned on,
The charge in the capacitor CI is discharged through the primary winding of the step-down transformer T1, the primary winding of the current transformer T2, the transistor Q1, and the emitter resistor R. That is, current flows through the incandescent lamp connected to the secondary winding of the step-down transformer T1. Here, the step-down transformer T is a non-saturated type, and the current transformer T2 is a saturated type. However, when the transistor Q is turned on from off, a voltage is induced in the secondary winding of the current transformer T2 in the direction of forward biasing the transistor Q1, and then either the current transformer T2 is saturated or the primary winding of the current transformer T2 is When the change in the current flowing through the line decreases, the voltage induced in the secondary winding becomes zero, and after the accumulation time of transistor Q1 has elapsed, transistor Q1 turns off. At this time, the current transformer T
Since the current flowing through the primary winding 2 rapidly decreases, a voltage is induced in the secondary winding that reverse biases the transistor Q1 and forward biases the transistor Q2. Thus, transistor Q1 is completely turned off and transistor Q2 is turned on. When the transistor Q2 is turned on, the charge in the capacitor C6 is discharged through the transistor Q2, the emitter resistor R2, the primary winding of the current transformer T, and the primary winding of the step-down transformer T. That is,
A voltage that forward biases transistor Q2 is induced in the secondary winding of current transformer T2, and then transistor Q,
Similarly to the case, transistor Q2 is turned off,
Transistor Q is turned on. By repeating this operation, the high frequency inverter 1 performs an oscillation operation of several tens of kHz, and during the zero oscillation operation when high frequency power is supplied to the incandescent light bulb, the high frequency inverter 1 performs an oscillation operation at several tens of kHz, and during the zero oscillation operation when high frequency power is supplied to the incandescent light bulb, the voltage between both ends of the primary winding of the step-down transformer T is The output voltage of the rectifier circuit Re (approximately equal to the voltage of the commercial power supply)
Since one-half of the voltage will be applied, the step-down transformer T1 will be
Moreover, since the step-down transformer T is for high frequency use, the number of turns is reduced and the transformer is made smaller. By the way, it has been known that when an incandescent lamp is connected to a commercial power source and turned on, when the lamp is about to break at the end of its life, arc discharge occurs and the lamp becomes almost short-circuited. In the case of low-voltage halogen light bulbs, the applied voltage is low, so it is thought that arc discharge is unlikely to occur at commercial power frequency; however, with the high-frequency inverter 1 as described above, high-frequency power of several tens of kHz is supplied. ,
A minute arc discharge tends to continue, and at the end of the life, a state close to a short circuit may continue for about 1 second or less (hereinafter referred to as a secondary short circuit). When a secondary short circuit occurs, an excessive current flows through the transistors Q and Q2, which may cause them to be destroyed. To solve this problem, transistors Q,,Q
2 and detects the excessive current flowing through transistor Q +
, it is possible to stop the oscillation operation before Q- reaches destruction. For example, as shown in FIG. 5, it is conceivable to add a protection circuit 2 to the high frequency inverter 1 shown in FIG. 4. This protection circuit 2 monitors the current flowing through the transistor Q1 by detecting the voltage across the emitter resistor R1 of the transistor Q, and stops the oscillation operation if an excessive current flows through the transistor Q. It is. In other words, the voltage across the emitter resistor R+ is the voltage across the rectifier circuit R
The output voltage of e is compared with a reference voltage obtained by dividing the output voltage by a series circuit of a pair of resistors R4 and Rs by a comparison element Q consisting of a PUT. When the voltage across the emitter resistor R1 becomes higher than the reference voltage, the comparison element Q4 is turned on, a trigger is applied to the gate of the switching element Q, which is a thyristor, and the switching element QS is turned on, and the transistor Q,
is turned off. When the transistor Q is turned off in this way, the impedance of the load to the rectifier circuit Re becomes larger than during the oscillation operation, so the voltage across the series circuit of the capacitors C, C2, which had many pulsating current components in the oscillation action, is smoothed out. will be made into That is, the switch element Q
Since the voltage across , does not become zero and remains on,
Transistor Q cannot be turned on, and in order to restart the zero-oscillation operation in which the oscillation operation stops, the power must be turned off and then on again. On the other hand, the filament used in incandescent lamps has a positive resistance temperature characteristic. Immediately after lighting, the temperature of the filament is low and the resistance is low, so a large lamp current flows, and then the filament When the temperature of the lamp increases, the resistance value also increases and the lamp current settles to a predetermined value. This large lamp current that flows immediately after lighting is called rush current. It is known that the rush current reaches 5 to 10 times the lamp current during steady lighting. In other words, even with the circuit shown in Figure 5, for several tens to hundreds of milliseconds after the power is turned on,
A rush current will flow.

[Problem to be solved by the invention]

When the protection circuit 2 as described above is installed, if the protection circuit 2 detects the rush current when the power is turned on,
The lighting device cannot oscillate, and incandescent lamps cannot be lit. Therefore, the judgment level of protection circuit 1 (potential at the connection point of resistors R, R8) must be set to a level that detects excessive current at the end of the life of an incandescent lamp, but does not detect rush current. It won't happen,
That is, since the determination level of the protection circuit 2 must be set relatively high, if an incandescent lamp with a large power rating is used, the lighting device will continue to be overloaded. However, considering variations in the characteristics of each part of the lighting device and incandescent lamps, as well as changes in environmental conditions, the determination level must be set accurately, which requires the use of high-precision parts and increases costs. Problems may arise, such as the need for adjustment and increased work. The present invention aims to solve the above-mentioned problems.It protects elements from destruction by detecting overload conditions at the end of life or during lighting when excessive current flows, and also protects elements from destruction due to rush current at the initial power-on. It is an object of the present invention to provide a high-frequency lighting device for an incandescent light bulb that prevents malfunctions.

[Means to solve the problem]

In order to achieve the above object, the present invention includes a high-frequency inverter that is supplied with AC power and lights an incandescent light bulb with high-frequency power, and a high-frequency inverter that is supplied with AC power and that counts the number of times the lamp current exceeds a predetermined threshold in synchronization with the AC power. A protection circuit is provided that stops the high frequency inverter when the value reaches a predetermined value.

[Effect]

According to the above configuration, the protection circuit is configured to count the number of times the lamp current exceeds the threshold value in synchronization with the AC power supply, and to stop the high frequency inverter when the counted value reaches a predetermined value. When the lamp current gradually attenuates, such as rush current, if the count value is set so that it does not reach the predetermined value, the rush current will not be detected and will not be detected in the event of a secondary short circuit or overload. It can be set to detect only such excessive currents. In addition, if the rush current causes the count value to approach the predetermined value above, the count value will reach the predetermined value in a short time in the event of a secondary short circuit or overload, causing stress on the circuit elements of the high-frequency inverter. This reduces the amount of time it takes to protect the skin and provides a high degree of protection.

【Example】

As shown in FIG. 1, the protection circuit 2 includes a power supply section 3, an overcurrent detection section 4, a counter 5, a latch circuit section 6, and an oscillation stop circuit section 7. The power supply section 3 obtains a DC power source for the protection circuit 2 by applying the output of the rectifier circuit Re across a Zener diode ZD via a diode D and a resistor R1, and smoothing it with a capacitor C4. . The overcurrent detection section 4 detects the voltage induced in the secondary winding of the current transformer T2 in the high frequency inverter 1, and charges the capacitor C3 via the diode D2 and the resistor R7 when the Zener diode ZD2 breaks over. It looks like this. Further, a resistor R- is connected in parallel to the capacitor Cs. The voltage across the capacitor C3 is input to the clock terminal of the counter 5. The counter 5 is a ternary counter consisting of a pair of flip-flops FF, FF, an OR circuit, and an AND circuit AN.
D, and is configured so that when two pulses are applied, the output rises at the fall of the second pulse. The latch circuit section 6 detects the voltage across the emitter resistor R1 connected to the transistor Q1 of the high frequency inverter 1, and when the Zener diode ZD breaks over,
resistors R*, R+ through diodes D,. A clock is input to the flip-flop FF3 from the connection point. Further, the output of the counter 5 is input to the J terminal of the flip-flop F F s. counter 5
The output of counter 5 is the inverted output of flip-flop FF3, so when the input of the J terminal is "H" and the tarok is input, the output of counter 5 becomes "L", and then when the clock stops, the output is The state of is maintained. The oscillation stop circuit section 7 turns on the transistor Q6 and turns off the transistors Q? and Q- when the output of the latch circuit section 6 is "H". When the transistors Qy and Qa turn on, , high frequency inverter 1
Since the capacitor C3 is discharged and the base-emitter of the transistor Q is short-circuited, the oscillation operation of the high-frequency inverter 1 is stopped. Next, the operation will be explained. Under normal conditions, the output voltage of the secondary winding of the current transformer T2 gradually attenuates after the power is turned on, as shown by the solid line in FIG. 2(a). Here, due to rush current, the Zener diode Z
The number of times the breakover voltage of D2 (indicated by the dashed line) is exceeded is set to 1 or less. In this way, the voltage across capacitor C1 rises only once as shown in Figure 2 (b). Only. Counter 5 is capacitor C3
When the voltage across both ends of FF rises, the output of the flip-flop FF rises as shown in Figure 2(e), and a clock is input to the flip-flop FF through the OR circuit OR, but as shown in Figure 2(d). As shown, the output of flip-flop FF2 does not rise, while the resistor R
At the connection point of 1°R9°, as shown in Fig. 2(e),
A pulse signal synchronized with the oscillation of the high frequency inverter 1 is generated, and this pulse signal is input to the clock terminal of the flip-flop FF. However, since the output of the counter 5 input to the J terminal of the flip-flop FF3 is "L", the inverted output of the flip-flop FF is kept at "H" as shown in FIG. 2(f). dripping As a result, the transistor Q6 of the oscillation stop circuit section 7 is
The transistors Q, , Q, are turned off as shown in Fig. 2(h), i.e., the high frequency inverter 1 continues to oscillate, and the transistor Q, remains on as shown in Fig. 2(h). A collector current as shown in (i) flows. In this way, the number of times that the rush current exceeds the breakover voltage of the Zener diode ZD is small, and the counter 5 does not count up, so the high frequency inverter 1 continues its oscillation operation. On the other hand, when excessive current occurs such as during a secondary short circuit, as shown in Figure 3 (
As shown by the solid line in a), the output voltage of the secondary winding of the current transformer T2 is not attenuated and exceeds the breakover voltage of the Zener diode ZD2 (indicated by the dashed line) many times, so the voltage across the capacitor Cs A plurality of clocks to the counter 5 are obtained as voltages, as shown in FIG. 3(b). As shown in Figure 3(c), the output of the flip-flop FF becomes "H" at the falling edge of the second input pulse.
As shown in FIG. 3(d), the output of flip-flop FF rises at the fall of the output of flip-flop FF. Therefore, the inverted output of the flip-flop FF of the latch circuit section 6 is as shown in FIG. 3(f).
Clock input immediately after counter 5 counts up (3rd
(e)), the transistor Q of the oscillation stop circuit section 7 turns off as shown in Fig. 3(g), and the transistors Q, , Q, turn on as shown in Fig. 3(h). Become. That is, the oscillation operation of the high frequency inverter 1 is stopped, and the collector current of the transistor Q becomes as shown in FIG. Therefore, when an excessive current flows due to a secondary short circuit or the like, the counter 5 immediately counts up and stops the oscillation operation of the high frequency inverter 1. Therefore, stress on the circuit elements of the high frequency inverter 1 can be kept to a minimum. In each of the above embodiments, a so-called automatic half-bridge configuration is shown as a high-frequency inverter.
Of course, other configurations may also be used.

【Effect of the invention】

As described above, the present invention includes a high-frequency inverter that is supplied with AC power and lights an incandescent light bulb with high-frequency power, and a high-frequency inverter that is supplied with AC power and counts the number of times the lamp current exceeds a predetermined threshold value in synchronization with the AC power supply until the counted value reaches a predetermined value. A protection circuit is provided that stops the high-frequency inverter when the lamp current reaches the specified value, so if the lamp current gradually attenuates like a rush current, the count value can be set so that it does not reach the predetermined value. This has the advantage of being able to be set to detect only excessive currents such as those occurring during secondary short circuits or overloads, without detecting rush currents. In addition, if the rush current causes the count value to approach the predetermined value above, the count value will reach the predetermined value in a short time in the event of a secondary short circuit or overload, causing stress on the circuit elements of the high-frequency inverter. It has the advantage that the time required is shortened and a high protective effect can be obtained.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing an embodiment of the present invention, Figs. 2 and 3 are explanatory diagrams of the same operation as above, and Fig. 4 shows the basic configuration of a high-frequency inverter used in a high-frequency lighting device for an incandescent lamp according to the present invention. FIG. 5 is a circuit diagram showing a conventional example. 1...High frequency inverter, 2...Protection circuit, 3...
・Power supply section, 4... Overcurrent detection section, 5... Counter,
6... Latch circuit section, 7... Oscillation stop circuit section.

Claims (1)

[Claims] (1) A high-frequency inverter is supplied with AC power and lights up an incandescent bulb using high-frequency power, and the high-frequency inverter counts the number of times the lamp current exceeds a predetermined threshold value in synchronization with the AC power supply, and when the counted value reaches a predetermined value, the high-frequency inverter turns on the incandescent bulb. A high-frequency lighting device for an incandescent light bulb, comprising a protection circuit for stopping the lamp.