JPH06176883A - Fluorescent lamp lighting device - Google Patents

Abstract

PURPOSE:To make circuit protection for an over-current in a switching element or an abnormal current in lighting load circuit of a fluorescent lamp lighting device in inverter system. CONSTITUTION:Lighting load circuits 21 in (n) pieces are parallel connected with the switching output terminals out1, out2 of a high frequency inverter circuit 51. An abnormal current sensing/control circuit 1 having a current sensing point X is provided on the source side of a swithing element Q2 which is connected with the negative side DC input B. The source current is flowing in the switching element Q2 is monitored at all times, and thereby the mentioned circuit 1 embodied in a single piece senses failure both in case where abnormal current flows out to the lighting load circuits 21 for a time in excess of the specifiallowable duration and in case where an over-current exceeding the allowable value has flowed in the switching element Q2. The high frequency output of the inverter circuit 51 is shut off immediately after failure occurrence in any case of the above-described.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to protection of a high frequency inverter lighting device against an abnormal current of a lighting load circuit or an overcurrent of a switching circuit generated in a lighting device for a plurality of fluorescent lamps. When an abnormal state of the lighting load circuit including abnormal current at the end of life is detected and at least one load has a non-transient abnormal state, or when an overcurrent flows through the switching element of the high frequency inverter circuit, one of the The present invention relates to a fluorescent lamp lighting device configured to prevent and protect the entire fluorescent lamp lighting device from damage and abnormal heat generation by detecting both abnormal states in the abnormality detection circuit and shutting off the output of the high frequency inverter circuit. is there.

[0002]

2. Description of the Related Art Generally, an inverter type fluorescent lamp lighting device has a filament FL of a fluorescent lamp 20 as shown in FIG.
A series resonance circuit composed of a current limiting coil L and a capacitor C is used as a lighting load circuit 21, and a high frequency inverter circuit using a commercial power supply of 50/60 Hz is used to generate a single frequency fn (several tens) near the resonance frequency of the lighting load circuit. KHz) is output (E), and a high voltage is generated by the resonance action, so that the fluorescent lamp 2
0 is turned on, and after being turned on, it is dumped by the tube current iR and is in a steady lighting state at a low voltage.

The resonance phenomenon will be described below with reference to a specific measurement example of the series resonance circuit 21 shown in FIG.

In the figure, the inductance L of the coil
= 910 μH, capacitance C of capacitor = 0.0
082 μF, input voltage E = 130 V, operating frequency fn =
In the case of 50 kHz and fluorescent tube FL32S, the current iL flowing through the coil during normal lighting is 0.43 A.

However, at the end of the life of the fluorescent tube, the tube current iR decreases and approaches the series resonance state, resulting in the current iL.
Rises to about 1.06A.

Generally, at such a current value, the current limiting coil L
However, due to the increase in current, the core loss increases and the temperature of the current limiting coil rises. As a result, the DC superimposition characteristic of the core is deteriorated, and the current iL is further increased.

Although the allowable superposed DC current is set in the core, when it exceeds the allowable value, the core is completely saturated and the current limiting capability is lost (Ts period) as shown in FIG. Occurs.

When the above-mentioned state is reached, the coil is destroyed due to a rapid temperature rise, and the high frequency inverter circuit is overloaded and is in a dangerous state. In addition, the filament of the fluorescent lamp may be broken, which may lead to an unusable state of the entire apparatus or a dangerous state leading to a fire.

At present, an inverter type fluorescent lamp lighting device having a detection circuit for detecting an abnormal current generated in the lighting load circuit 21 has been devised, and the circuit configuration shown in FIG. 5 is a typical one. is there.

FIG. 5 shows an inverter type fluorescent lamp lighting device for lighting a plurality of n fluorescent lamps, which comprises coils and capacitors (Lo1, Co1) to (Ln, Con).
Each form a series resonance circuit, and the fluorescent lamps FL1 to FL
While Ln is lit, a normal synthetic current of each fluorescent lamp is flowing through the ring core 25 at the detection point Y.

Next, due to the end of life or failure of the fluorescent lamp,
When an abnormally high high-frequency current is generated in at least one fluorescent lamp, the abnormal high-frequency current component included in the combined current is picked up by the ring core 25, and the abnormal current detection circuit 26 controls the abnormal current detection circuit 26 only when the current value exceeds a specified current value. A shutoff signal 28 is sent to 27 to shut off the output of the high frequency inverter circuit. At this time, the detection voltage is integrated by the integrating circuit within a predetermined time, and the control circuit is configured to operate only when the comparator exceeds a certain threshold value. A detection circuit having a structure that prevents the value from being exceeded and can be distinguished from a continuous abnormal state has been devised.

Further, as a protection circuit for the abnormal current generated in the other lighting load circuit 21, it is considered that the current waveform flowing through the switching element of the high frequency inverter circuit is out of phase with respect to the normal state in the case of an abnormal current. Instead of discriminating values, a method has been devised in which the phase shift is detected by a pulse width discriminator, and the control circuit is activated in the event of an abnormal state, particularly an abnormal current at the end of the life of the fluorescent lamp.

Next, a circuit failure of the switching circuit in the high-frequency inverter circuit, in particular, an overcurrent flowing in the switching element due to defective switching timing and a protection circuit therefor will be described.

The cause of the above-mentioned overcurrent is that the gate potential of a switching element (generally a power MOSFET is often used) connected in series with the inverter output at normal times is alternately applied at a cycle of several tens of kilocycles to turn on. The off state is alternately realized to generate a high frequency AC voltage as an inverter output.In this case, when the switching elements connected in series between the DC power supplies are simultaneously turned on, the power supply is short-circuited and an overcurrent occurs. Is flowing to the switching element.

In the above-mentioned state, the element is destroyed, and further heat is generated.
This can lead to a condition that can trigger a fire.

In general, however, there is a pause period in which both of them are in the off state while they are alternately turned on and off, and normally, the above-mentioned state does not occur. However, it cannot be said that there is a risk of the occurrence of the abnormal state due to the intrusion of extraneous noise and the rapid fluctuation of the power supply voltage.

Conventionally, as a countermeasure against the above-mentioned overcurrent, it is general that each switching element is provided with a protection circuit separately.

As the protection circuit 12 for the conventional switching element, as shown in the fluorescent lamp lighting device of FIG. 6, switching elements (for example, power MOSFETs) Q1 and Q2 connected in series between DC inputs A and B are provided. In general, a so-called through-short protector which is inserted between the gate and the source and prevents the switching element from being in the ON state at the same time and the overcurrent continues to flow has been generally used.

In this circuit operation, when an overcurrent flows through the detection resistor Rx having a small value (about 0.1Ω) while Q1 and Q2 are on, the voltage across Rx rises and the resistance Rc of the branch path is increased. The potential increases, and current flows through the gates of the thyristors (SCR; silicon controlled rectifying elements) CR1 and CR2, turning on the thyristors. The threshold value is set by each resistor so that the thyristor does not turn on under normal switching current.

When the thyristors CR1 and CR2 are turned on, the gate potential of the switching element is not given and Q1
And Q2 are fixed to the off state and the high frequency output is cut off. Further, once the thyristors CR1 and CR2 are turned on, the on state is maintained until the power is turned off.

In the circuit of FIG. 6, the ring core 25 inserted between the switching output and the lighting load circuit 21 serves as a protection circuit against the abnormal states of the plurality (n) of lighting load circuits 21 described above. Detect the current,
The abnormal current detection / control circuit 29 is also configured to cut off the output of the high frequency inverter circuit. On this occasion,
The output can be cut off by, for example, turning off the auxiliary power supply circuit 30 or stopping the oscillation of the oscillation / pulse shaping drive circuit 31.

[0022]

However, in the configuration of the abnormal current detection circuit 26 in the conventional lighting load circuit 21, the detection point is one point Y, and the abnormal current in the lighting load circuit is detected. Only. Therefore, it is not possible to detect an overcurrent that flows when two switching elements connected in series in the switching circuit that alternately turn on and off are turned on at the same time for some reason.

On the other hand, as shown in the figure, the protection circuit 12 for the overcurrent of the switching element is composed of a diode CR1 with a gate, a capacitor, a resistance element and a diode, and CR1 is normally open. It operates when an abnormal current flows to the source side and a voltage is applied to the gate, and operates so as to destroy the drive pulse applied to the gate of the switching element. At this time, since the earth point potential of the protection circuit is different in each switching element, the control is independent from the primary side via the insulating transformer T.

Therefore, the conventional protection circuit requires two protection circuits, which is disadvantageous in terms of space and cost.

As described above, in the inverter type fluorescent lamp lighting device 100, the high frequency switching elements Q1, Q
Since 2 is operated, the circuit configuration is extremely complicated as compared with the conventional method, and several protection circuits are required when an abnormal state occurs.

The present invention has been made in view of the above circumstances, and protects a switching element in the case of a failure including an inverter control system with one detection circuit, and protects the device from damage or fire due to an abnormal current on the lighting load circuit side. (EN) Provided is a fluorescent lamp lighting device which can both prevent dangers and can completely separate a switching unit and an inverter control system, and which simplifies the protection circuit design.

[0027]

The present invention comprises a fluorescent lamp, a current limiting coil connected in series to the fluorescent lamp, and a capacitor connected in parallel to the non-power supply side of the filament of the fluorescent lamp. In a fluorescent lamp lighting device configured by connecting a plurality of lighting load circuits in parallel to switching output terminals of a high frequency inverter circuit, a current detection point is provided on a source side of a switching element connected to a negative side DC input of the high frequency inverter circuit. An abnormality detection / control circuit having the above is provided, and by constantly monitoring the source current flowing through the switching element connected to the negative side DC input, at least one circuit of the plurality of lighting load circuits has a higher operating frequency than that at lighting. If an abnormal current containing high-frequency components has flown out for longer than a specified allowable time, or if there is a direct current between the DC inputs of the high-frequency inverter circuit, When the two connected switching elements are simultaneously turned on and an overcurrent exceeding a predetermined allowable value flows into the switching element, both abnormalities are detected by the one detection / control circuit, The above object is achieved by providing a fluorescent lamp lighting device characterized in that the output of the high frequency inverter circuit is cut off immediately after the occurrence of the abnormality.

[0028]

In the inverter type fluorescent lamp lighting device according to the present invention, when an abnormal current is generated in at least one of the plurality of lighting load circuits by the integrating circuit and the comparator inside the detection / control circuit, the abnormalities are detected by the high frequency inverter. All lighting in the circuit is detected as an anomaly in the combined current flowing into the load circuit, and whether the anomaly is due to transient noise, the terminal symptom of the fluorescent tube, the circuit failure, or other failure, the anomalous current is permitted Distinguish by whether or not it leaked over time.

Then, only in the latter case, the protection circuit provided in the high frequency inverter circuit is activated to send a cutoff signal to the high frequency inverter output circuit to cut off the output. The switch circuit for this interruption is a holding circuit that does not automatically recover, and keeps the output interruption state.

On the other hand, the detection / control circuit also detects when an overcurrent flows through the switching element at the time of malfunction / failure in the high frequency inverter circuit, and outputs the high frequency inverter output as in the case of the abnormality of the lighting load circuit. It acts to cut off the output by sending a cutoff signal to the circuit.

Therefore, in one detection / control circuit, protection of the switching transistor at the time of failure including the inverter control system and damage of the lighting device due to abnormal current on the load side,
Since it is possible to prevent a danger such as a fire, it is not necessary to individually provide a protection circuit or a detection / control circuit, and the overall circuit configuration is simplified.

Since the detection section is an insulated type current sensor (for example, a ring core) and is insulated from the source line of the negative side switching element, the ground point of the detection / control circuit can be separated from the AC line.

Therefore, the control signal (cutoff signal) output from the control circuit can be directly connected directly to the target circuit, which increases the degree of freedom in circuit design.

[0034]

EXAMPLES According to the research conducted by the present inventor, the abnormal current generally contains a high frequency component in various abnormal states (for example, end of life and poor contact) in the fluorescent tube lighting device. The high frequency component is the operating frequency of the fluorescent lamp inverter that is currently most often used (approximately 50K).
It is confirmed that they are far apart from each other.

Therefore, if any abnormality occurs, if the high-frequency component of the abnormal current is focused and selected and detected, the abnormal state can be identified regardless of the frequency of the steady state, and it is simply transient. It is possible to identify the case due to noise or the like and distinguish it from the abnormal state so that the protection circuit does not operate unnecessarily.

Based on the above, a concrete example of the fluorescent lamp lighting device according to the present invention will be described in detail with reference to FIGS. 1 and 2 (the same components as those of the conventional fluorescent lamp lighting device 100 use the same reference numerals). ).

FIG. 1 is a block circuit diagram of a fluorescent lamp lighting device 50 including an abnormal current detection / control circuit 1 according to the present invention. The fluorescent lamp 20 and a current limiting coil Lo1 connected in series to the fluorescent lamp. And a lighting load circuit 21 composed of a capacitor Co1 connected in parallel to the non-power source side of the filament of the fluorescent lamp and a plurality of switching output terminals OUT1 and OUT2 of the high frequency inverter circuit 51 are connected in parallel. In the fluorescent lamp lighting device, the abnormal current detection / control circuit 1 having a current detection point X is provided on the source side of the switching element Q2 connected to the negative side DC input B of the high frequency inverter circuit 51, and the negative side DC By constantly monitoring the source current is flowing in the switching element Q2 connected to the input B, at least one of the plurality of lighting load circuits 21 is When an abnormal current containing a high frequency component higher than the operating frequency fn at the time of lighting flows out over a predetermined permissible time due to the end of life or poor contact in the circuit, or between the DC inputs A of the high frequency inverter circuit 51. -B
When the two switching elements Q1 and Q2 connected in series at the same time are turned on at the same time and an overcurrent exceeding the allowable value flows into the switching element Q2, both abnormalities are detected by the one abnormality detection / control circuit 1. In addition, the high frequency output of the high frequency inverter circuit 51 is cut off immediately after any one of the abnormalities occurs, and the conventional switching element protection circuit 12 (in FIG. 6) is deleted.

The main point of interest of the present invention is that the negative side of the high-frequency inverter circuit 51 is designed so that a single detection circuit can be used as a protection circuit for the generation of an abnormal current, which is conventionally provided individually. In the current path on the source side of the switching element Q2 connected to the DC input B, the current detection point X
Is set and the current value of the abnormal current is detected.

Regarding this point, regarding the abnormality that occurs in the lighting load circuit 21, the conventional detection point Y in FIG. 6 is set in the current path between the output OUT1 of the inverter circuit and the lighting load circuit 21, and each switching element The reciprocating current iout is picked up at the detection point by the alternating operation, but at the detection point X in FIG. 1, the unidirectional source current is is picked up only when the switching element Q2 is turned on. Is halved compared to the conventional case.

However, according to the experiment, it has been confirmed that the detected current in the abnormal state can be sufficiently detected with the half current value, and the abnormality of the lighting load circuit 21 can be surely detected.

On the other hand, even if the overcurrent of the switching elements Q1 and Q2 is abnormal, it is picked up in the current path of the detection point X as a rapid change of the source current is of Q2. Is the switching element Q
It also works effectively as a protection circuit for 1 and Q2.

Next, a concrete example of the abnormal current detection / control circuit 1 is shown in FIG.

In the figure, reference numeral 2 is an abnormality detection sensor section for picking up an abnormal current, which is composed of a ring core 25. The induced voltage on the secondary side of the ring core 25 is selectively passed by the band elimination filter 3 due to the high frequency abnormal current of the lighting load circuit and due to the overcurrent of the switching element (low frequency range). Next, after rectifying at D1 of the rectifying / smoothing circuit 4, a capacitor C3 and a resistor R
The signal is smoothed by 1 and then passed through the differentiating / clamping circuit 5 in order to extract only the abrupt change amount, and a voltage signal having a required pulse width is obtained.

The integrator circuit 6 is intended to prevent malfunction of the circuit as described above, has an integrating function by a capacitor, and has a low risk by properly selecting an integrating time constant (C5, R3). The integrated value becomes low for the intrusion of extraneous noise or a temporary short-time abnormality, while the integrated value becomes large in an abnormal state having a high-frequency component, and both can be distinguished.

The threshold value setting circuit 7 is an IC circuit that operates by generating a voltage equal to or higher than a certain set value (threshold value), and the set value is determined depending on how dangerous the integrated value is. Set to the value to be set in R5.

When the threshold value setting circuit 7 is activated, the output is input to the switch circuit 8. The circuit is a latch circuit that holds the state once an input signal is input, and the cutoff signal 10 is sent to the auxiliary power supply circuit 30 or the oscillation pulse shaping drive circuit 31 of the high frequency inverter circuit to cut off the switching output. It will be.

The fluorescent lamp lighting device 50 according to the present invention.
The circuit configuration of is not limited to the above embodiment, and the abnormal current detection point X of the fluorescent tube lighting device 50 is set to the source side of the switching element Q2 connected to the negative side DC input B of the high frequency inverter circuit 51. Other circuit configurations may be used as long as an abnormal current detection / control circuit for picking up the abnormal currents in the two abnormal states of the different causes is provided as a protection circuit.

The switching output circuit of the present inverter type fluorescent lamp lighting device 50 is the same as that used in the conventional high frequency inverter circuit. To shut off the output, for example, the output of the auxiliary power supply circuit is used as described above. It goes without saying that it can be easily implemented by a method such as turning off or a method of stopping oscillation.

In this respect, since the detection unit is an insulated type current sensor (for example, a ring core) and is insulated from the source line of the negative side switching element, the ground point of the abnormal current detection / control circuit 1 is connected to the AC line. The control system circuit can be configured separately from the switching circuit.

Therefore, the control signal (cutoff signal) output from the control circuit can be directly connected directly to the target circuit, which increases the degree of freedom in circuit design.

[0051]

Since the fluorescent lamp lighting device according to the present invention is constructed as described above, it has the following effects.

(1) An excellent effect that one detection circuit can both protect switching elements at the time of failure including the inverter control system and prevent damage such as equipment damage or fire due to abnormal current in the load lighting circuit. Have.

(2) The switching circuit of the high-frequency inverter circuit and the control system circuit can be completely separated, which simplifies the circuit.
This has the excellent effect that the degree of freedom in selecting control points is expanded.

(3) The protection circuit between the gate and the source of the switching element is not required, which has the excellent effects of simplifying the circuit structure and reducing the cost.

[Brief description of drawings]

FIG. 1 is a block circuit diagram of a fluorescent lamp lighting device according to the present invention.

[Fig. 2] Circuit diagram of abnormal current detection / control circuit

[Figure 3] Lighting load circuit

[Figure 4] Abnormal current waveform

FIG. 5 is a block circuit diagram of a conventional fluorescent lamp lighting device including an abnormal current detection circuit for a lighting load circuit.

FIG. 6 is a block circuit diagram of a fluorescent lamp lighting device including a conventional switching element protection circuit and an abnormal current detection / control circuit for a lighting load circuit.

[Explanation of symbols]

1 Abnormal current detection / control circuit 2 Abnormality detection sensor section 3 Band elimination filter 4 Rectification / smoothing circuit 5 Differentiating / clamping circuit 6 Integrating circuit 7 Threshold setting circuit 8 Switch circuit 9 DC power supply 10 Cutoff signal 12 Switching element protection circuit 20 Fluorescent lamp 21 Lighting load circuit 25 Ring core 26 Abnormal current detection circuit 27 Control circuit 29 Abnormal current detection / control circuit 30 Auxiliary power supply circuit 31 Oscillation / pulse shaping drive circuit 50 Fluorescent light lighting device 51 High frequency inverter circuit 100 Fluorescent light lighting device A DC Input (positive side) B DC input (negative side) C, Co1, C1, ... Capacitor Lo1, ... Current limiting coil L1, ... Coil OUT1, OUT2 Switching output end Q1 Positive side switching element Q2 Negative side switching element Rx Detection resistance R , R1, ... Resistor CR1, ... Siri Motor; source current X of (SCR silicon controlled rectifier) is Q2, Y detection point

Claims (1)

[Claims] 1. A high frequency inverter circuit comprising a lighting load circuit comprising a fluorescent lamp, a current limiting coil connected in series to the fluorescent lamp, and a capacitor connected in parallel to a non-power source side of a filament of the fluorescent lamp. In the fluorescent lamp lighting device configured by connecting a plurality of switching output terminals in parallel, an abnormality detection / control circuit having a current detection point is provided on the source side of the switching element connected to the negative side DC input of the high frequency inverter circuit. By constantly monitoring the source current flowing through the switching element connected to the negative side DC input, at least one circuit of the plurality of lighting load circuits has an abnormal current containing a high frequency component higher than the operating frequency at lighting. Two switches connected in series if they flow out for longer than a predetermined allowable time or between the DC inputs of the high frequency inverter circuit. When both the switching elements are turned on at the same time and an overcurrent exceeding a predetermined allowable value flows to the switching element, both abnormalities are detected by the one abnormality detection / control circuit, and immediately after any one of the abnormalities occurs. A fluorescent lamp lighting device, which is configured to cut off the output of the high-frequency inverter circuit.