JPH02165532A - Circuit device - Google Patents

Abstract

PURPOSE:To make it possible to secure the thermal connection and insulating property of a switching element and a temperature fuse with each other by arranging the temperature fuse in a position such that one of its lead wires is longer than the other, and connecting the longer lead wire to that terminal of the switching element which has the same electric potential as that of a heat radiating plate. CONSTITUTION:A temperature fuse 11 is put in proximity to the heat radiating plate 8a of a switching element 8 and in case of abnormalities detects heat radiation from the heat radiating plate 8a. The temperature fuse 11 is also fixed in a circuit substrate 33 while in a position such that one of its lead wires is longer than the other, and besides the former lead wire is connected to that terminal of the switching element 8 which has the same electric potential as that of the heat radiating plate 8a. Even while the former lead wire is put in contact with the heat radiating plate 8a, operation of the circuit will thus not be disturbed. Also, the latter lead wire is connected to the circuit substrate 33 with a short distance therebetween, so that the insulating property of the temperature fuse against the switching element 8 is fully secured.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a circuit device in which a switching element having a heat sink and a temperature fuse are embedded in a circuit board.

(Prior art) For example, a compact fluorescent lamp, in which a fluorescent lamp and an electronic lighting circuit are integrated into a light bulb-shaped casing, has an electronic lighting circuit equipped with an inverter circuit including switching elements such as power transistors and a transformer on a circuit board. It is stored in a sealed space inside the built-in casing.

In such devices, when the discharge lamp reaches the end of its life or the electronic lighting circuit malfunctions, the circuit elements that make up the electronic lighting circuit, especially the switching elements, generate abnormal heat, and the heat is transferred into the casing. It is extremely dangerous because of the heat build-up, and in some cases there is a problem in that smoke is emitted from the circuit elements.

For this reason, in the past, a current fuse was provided in the power supply input section, and the current fuse was blown by increasing the number of input terminals in the event of an abnormality.

However, when using a current fuse, depending on the operating mode of the circuit, it may take a long time for overcurrent to flow after an abnormality occurs. There was a risk that the temperature would become abnormally high and the circuit elements would emit smoke, which was insufficient in terms of safety.

(Problem to be solved by the invention) For this reason, a temperature fuse is used instead of a current fuse,
It is conceivable to use a temperature fuse to detect abnormal heat generation in circuit elements, particularly switching elements, when an abnormality occurs, to shut off the circuit, and to stop the oscillation operation of the inverter circuit within a relatively short period of time.

By the way, when a temperature fuse is used, in order to improve its operating sensitivity, it is necessary to arrange the temperature fuse close to, for example, a switching element to improve thermal coupling. However, when the temperature fuse is placed close to the switching element, there is a problem in that insulation must be ensured.

Therefore, the present invention provides a circuit board in which a switching element is incorporated and a temperature fuse is placed close to the switching element to ensure safety, while ensuring thermal coupling between the switching element and the IR temperature fuse. The present invention aims to provide a circuit device that can ensure insulation.

[Structure of the Invention] (Means for Solving the Problems) The present invention provides a circuit board and a switching device that is installed on the circuit board via a plurality of terminals and that connects a heat sink having the same potential as any of the terminals. In a circuit device having an element and a temperature fuse embedded in a circuit board and placed close to a heat sink of the switching element, the temperature fuse is arranged in such a manner that one lead wire is longer than the other lead wire. At the same time, the longer lead wires are connected to the terminals of the switching elements that are at the same potential as the heat sink.

(Function) In the present invention having such a configuration, since the temperature fuse is arranged close to the heat sink of the switching element, the heat radiation from the heat sink can be reliably detected by the temperature fuse in the event of an abnormality. The temperature fuse is installed on the circuit board with one lead wire longer than the top, and one lead wire is connected to a terminal at the same potential as the heat sink of the switching element, so even if Even if the lead wires come into contact with the heat sink, there will be no problem in circuit operation. Furthermore, since the other lead wire is connected to the circuit board over a short distance, insulation from the switching element is ensured.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings. In this embodiment, the present invention is applied to a self-ballasted fluorescent lamp.

Figure 1 is a diagram showing an electronic lighting circuit, in which a current fuse 1 is connected between input terminals a and b of an AC power supply to a noise prevention capacitor 2, a surge absorbing water -j'-3!11, and a full-wave rectifier circuit 4.
The input terminals of the two are connected to each other.

A smoothing capacitor 6 is connected between the output terminals of the rectifier circuit 4 via a resistor 5 to form a DC power supply circuit.

For example, a self-excited series inverter circuit 7 is connected between the output end of the DC power supply circuit, that is, both ends of the smoothing capacitor 6.

The inverter circuit 7 includes two MO5 type FETs (field effect transistors) 8.9 as switching elements and a feedback transformer 10, and a series circuit of the MOS type FETs 8.9 and a temperature fuse 11 are connected to the smoothing capacitor 6. connected in parallel through That is, the temperature fuse 11 is connected between the drain of the MOS type FET 8 and the positive terminal of the smoothing capacitor 6.

The feedback transformer 10 includes a winding 10a through which a high-frequency output current flows and windings 10b and 10 for feeding back the current to the gates of the MOS FETs 8.9.
It is composed of c.

The winding 10a% inductance coil 12 and capacitor 1 are connected between the drain and source of the MOS type FET 9.
3.14 series circuits are connected.

A series circuit of the -h filament electrode 15a1 of the fluorescent lamp 15, the capacitor 16, and the other filament electrode 15b is connected to the capacitor 13 in parallel.

Note that a series circuit of a constant voltage conduction element 17 such as SSS and a thermistor 18 is connected in parallel to the capacitor 14.

The inverter circuit 7 also includes the winding 10b and the resistor 1.
A drive circuit for the MOS type FET 8 is formed by connecting a constant voltage diode 20 in parallel to the series circuit with the winding 10c and the resistor 21, and a constant voltage diode 2 is connected in series with the winding 10c and the resistor 21.
A drive circuit for the MOS type FET 9 is provided by connecting two MOS FETs 9 in parallel.

The inverter circuit 7 further includes the smoothing capacitor 6.
A starting circuit consisting of a series circuit of a resistor 23 and a capacitor 24 connected in parallel with each other, and a bidirectional switch 25 connected between the connection point of the resistor 23 and capacitor 24 and the gate of the MOS type FET 9. A circuit is provided.

Note that a resistor 26 and a capacitor 2 are connected via the temperature fuse 11 between the drain and source of the MOS type FET 8.
7 are connected in parallel, and a diode 28 is connected between the connection point between the resistor 23 and the capacitor 24 and the connection point between the MOS FETs 8 and 9 with the polarity shown.

As shown in FIG. 2, each of the circuit components constituting the electronic lighting circuit includes a circuit board 33 mounted inside a light bulb-shaped casing 32 having a base 31 at one end and an open end at the other end.
It is arranged above the .

A fixing member 34 for suspending and fixing the U-shaped fluorescent lamp 15 is attached to the opening of the light bulb-shaped casing 32.

Among the circuit components arranged on the circuit board 33, the temperature fuse 11 is insulated and closely fixed to the heat sink 8a of the MO3 type FET 8, as shown in FIG. In this case, the heat sink 8a is at the same potential as the drain terminal 8b, and therefore, the lead wire 11a of the temperature fuse 11 on the side connected to the drain terminal 8b of the MOS type FET 8 is lengthened and placed on the upper side, which is the opposite part of the heat sink 8a. It is bent and fixed to the circuit board 33, and is fixed to the circuit board 33 at a short distance with the lead wire 11b on the opposite side facing downward.

In this case, in order to improve the thermal coupling between the MOS type FET 8 and the temperature fuse 11, a heat shrink tube may be placed between the two.

In this embodiment with such a configuration, when the power is turned on, DC power is supplied to the inverter circuit 7, and the resistor 2
A charging current flows to the capacitor 24 via the capacitor 3. Then, depending on the charging voltage of the capacitor 24, the bidirectional switch 2
5 becomes conductive, current flows to the gate of MOS type FET 9, and MOS type FET 9 performs a switching operation. After that, the inverter circuit 7 alternately switches the MO3 type FETs 8 and 9 to connect the filament electrodes 15a of the fluorescent lamp 15,
The fluorescent lamp 15 is heated by passing a preheating current through the filament electrode 15b and applying a high voltage between the filament electrodes 15a and 15b.
Start and light up.

When the fluorescent lamp 15 is lit normally and there is no abnormality in the lighting circuit, the lamp current is well within the rated range, so the lighting circuit does not generate a large amount of heat. Therefore, the heat trapped inside the casing 32 does not become large.

However, when the fluorescent lamp 15 reaches the end of its life or an abnormality occurs in the operation of the lighting circuit and the lamp current increases, the circuit components of the lighting circuit begin to generate abnormal heat. In particular, since a large lamp current flows through the MOS type FET 8.9, the amount of heat generated is extremely large.

Therefore, a large amount of heat is released to the heat sink 8a of the MO3 type FET 8, and as a result, the temperature fuse 11 is blown out in a short time. When the flat fuse 11 is blown, the operation of the inverter circuit 7 is stopped and the fluorescent lamp 15 is turned off.

When the lighting circuit abnormally heats up like this, the MOS type F
Since the circuit operation is stopped by directly receiving heat from the heat sink 8a of the ET8 through the temperature fuse 11, the circuit operation can be stopped in a short time, and the circuit components do not emit smoke. Safety can be improved.

The heat sink 8a of the MOS type FET 8 is at the same potential as its own drain terminal 8b, and the lead wire 11a of the temperature fuse 11 is connected to the drain terminal 8b of the MOS type FET 8, so the lead wire 11a is connected to the MOS type FET 8. FET8
Even if it comes into contact with the heat sink 8a, there is no problem in circuit operation.

Further, since the lead wire 11b of the temperature fuse 11 is fixed to the circuit board 33 facing downward and at a short distance, there is no risk of deformation of the lead wire 11b, and the lead wire 11b and MO
A distance between the S-type FET 8 and the heat sink 8a and each terminal is always maintained, and insulation is ensured.

In this way, the temperature fuse 11 for the MOS type FET 8
insulation can be ensured.

Although the above embodiments have described the present invention applied to a self-ballasted fluorescent lamp, the present invention is not necessarily limited to this.In short, it can be applied to any type of device as long as a switching element and a temperature fuse are incorporated into a circuit board. It can also be applied to electronic equipment.

[Effects of the Invention] As detailed above, according to the present invention, in a circuit board in which a switching element is incorporated and a temperature fuse is disposed close to the switching element to ensure safety, the switching element and It is possible to provide a circuit device that can ensure insulation while ensuring thermal coupling with a temperature fuse.

[Brief explanation of the drawing]

The figures show an embodiment of the present invention, in which Fig. 1 is a circuit diagram, Fig. 2 is a partial sectional view showing the overall configuration, and Fig. 3 is MO5 type F.
FIG. 3 is a diagram showing a state of connection between an ET and a temperature fuse. 7...Self-excited series inverter circuit, 8...M
OS type FET (switching element), 11... temperature fuse, 33... circuit board. Applicant's agent Patent attorney Takehiko Suzue Figure 1 b (a) Figure 3 Figure 2

Claims (1)

[Claims] a circuit board; a switching element implanted in the circuit board via a plurality of terminals and having a heat sink having the same potential as any of the terminals; and a switching element implanted in the circuit board and having a heat sink of the switching element; In a circuit device having thermal fuses arranged in close proximity to each other, the thermal fuse is arranged in such a manner that one lead wire is longer than the other lead wire, and the longer lead wire is connected to the thermal fuse at the same potential as the heat sink. A circuit device characterized in that it is connected to a terminal of a switching element.