JP2007300722A - Protection circuit, measuring device and electronic device - Google Patents

Abstract

A protection circuit capable of reliably protecting a connected circuit from an overcurrent while reducing its manufacturing cost.
A fuse 21 directly mounted on a circuit board and a fuse holder 22 directly mounted on the circuit board, and a pair of fuse connection terminals 22a and 22b in the fuse holder 22 and a pair of input / output terminals of the fuse 21 are provided. 21a, 21b is a protection circuit 2 connected in parallel, and the fuse holder 22 is configured so that a new replaceable fuse having the same rated current value as the fuse 21 can be mounted.
[Selection] Figure 1

Description

  The present invention relates to a protection circuit having a fuse, a measuring apparatus including the protection circuit, and an electronic apparatus.

An insulation resistance meter disclosed in Japanese Patent Application Laid-Open No. 5-172880 is known as a measuring apparatus provided with this type of protection circuit. This insulation resistance meter is configured by connecting a measurement probe to its line terminal and ground terminal. The line-side measurement probe is provided with a parallel circuit of a fuse that blows when an overcurrent flows and a voltage detector having a warning lamp. In this case, when an excessive voltage that causes dielectric breakdown inside the main body is input to the insulation resistance meter, the occurrence of dielectric breakdown is avoided by fusing the fuse, and the warning lamp is driven to turn on, An excessive voltage input is notified to the measurer.
JP-A-5-172880 (page 2-3, FIG. 1-2)

  By the way, in the conventional measuring apparatus including the above-described insulation resistance meter, generally, as the above-described fuse, a configuration in which a fuse that is blown when an overcurrent flows is mounted on a fuse holder is employed. In this case, when an overcurrent flows and the fuse is blown, the fuse holder is replaced so that the circuit connected to the fuse holder is electrically reconnected between both ends of the fuse holder in a state where the circuit can be protected from the overcurrent. Is possible. However, in the conventional measuring apparatus, generally, after the fuse holder is mounted on a circuit board as a mounting object, the fuse is manually attached to the fuse holder at the time of manufacture. Therefore, the conventional measuring apparatus has a problem that it is difficult to reduce the manufacturing cost due to the necessity of the work of attaching the fuse.

  The present invention has been made in view of such problems, and provides a protection circuit, a measuring device, and an electronic device that can reliably protect a connected circuit from an overcurrent while reducing the manufacturing cost. Main purpose.

  In order to achieve the above object, a protection circuit according to claim 1 includes a fuse directly mounted on a mounting object and a fuse connection device directly mounted on the mounting object, and a pair of fuses in the fuse connection device. The connection terminal and the pair of input / output terminals of the fuse are connected in parallel.

  According to a second aspect of the present invention, there is provided a measuring apparatus comprising: the protective circuit according to the first aspect; and a measuring unit that measures an electrical parameter based on an electric signal input through the protective circuit.

  According to a third aspect of the present invention, an electronic apparatus includes the protection circuit according to the first aspect, and inputs a current for driving power through the protection circuit.

  According to the protection circuit of claim 1, both the fuse and the fuse connection device are electrically connected to each other by providing the fuse directly mounted on the mounting target and the fuse connecting device directly mounted on the mounting target. Since mounting can be performed on the mounting target using an automatic mounting machine for mounting, manual mounting of the fuse can be omitted. For this reason, the manufacturing time can be sufficiently shortened compared with the conventional structure which requires the manual mounting operation of the fuse. In addition, since the pair of fuse connection terminals in the fuse connection device and the pair of input / output terminals of the fuse are connected in parallel, the input and output portions of the protection circuit are electrically connected by the fuse in the initial state. The circuit connected to the protection circuit can be reliably protected from overcurrent by blowing the fuse. In this case, when an overcurrent flows and the fuse is blown, a new replaceable fuse is attached to the fuse connecting device, so that the input / output part of the protection circuit is electrically connected again by the other fuse. be able to. For this reason, in the state where the directly mounted fuse is blown, even if another fuse newly installed in the fuse connection device is further blown, the circuit connected to the protection circuit can be changed by replacing the fuse. It can be restored to a state where it can be protected from overcurrent. Therefore, according to this protection circuit, the circuit connected to the protection circuit can be reliably protected from overcurrent while reducing the manufacturing cost by shortening the manufacturing time.

  According to a second aspect of the present invention, the measuring apparatus includes a protection circuit and a measurement unit that measures an electrical parameter based on an electrical signal input through the protection circuit. In this case, manual fuse installation work can be omitted, so that the manufacturing cost of the protection circuit can be reduced, and thus the manufacturing cost of the entire measuring apparatus can be reduced.

  According to a third aspect of the present invention, the electronic device includes the protection circuit according to the first aspect, and a driving power current is input through the protection circuit. In this case, it is possible to eliminate the work of manually mounting the fuse, so that it is possible to reduce the manufacturing cost of the protection circuit, and thus the manufacturing cost of the entire electronic device.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, best modes of a protection circuit, a measuring apparatus, and an electronic apparatus according to the invention will be described with reference to the accompanying drawings.

  First, the configuration of the measuring apparatus 1 will be described with reference to the drawings.

  The measuring device 1 is, for example, a multimeter, and includes a protection circuit 2, an input unit 3, a control unit 4, a display unit 5, and a pair of probes 10, 11 as shown in FIG. The current value of the current I input (an example of the “electrical parameter” in the present invention) and the voltage value of the voltage V applied between the probes 10 and 11 (another example of the “electrical parameter” in the present invention) ) Is configured to be measurable.

  As shown in the figure, the protection circuit 2 includes a fuse 21 and a fuse holder (corresponding to a fuse connecting device in the present invention) 22. The fuse 21 is a surface mount type chip fuse having a small mounting area, for example, and is automatically soldered after being directly mounted on a circuit board as a mounting target by an automatic mounting machine without interposing a connection device such as a fuse holder. By being soldered by the apparatus, it is mounted on the circuit board in a non-replaceable state. In this case, the fuse 21 electrically connects the input / output units of the protection circuit 2 in the initial state. In addition, the fuse 21 is blown when an overcurrent flows, and protects the circuit connected to the protection circuit 2 (in this example, the input unit 3) from the overcurrent. The fuse holder 22 functions as a connection device for connecting the fuse 23 (see FIG. 2) to a circuit pattern formed on the circuit board, and as an example, a fuse 23 such as a tubular fuse (for example, a glass tube fuse) can be mounted. And mounted directly on the circuit board by soldering using an automatic mounting machine for component mounting. The fuse holder 22 electrically connects the input / output parts of the protection circuit 2 with the fuse 23 mounted. In this case, as shown in FIG. 1, the pair of fuse connection terminals 22 a and 22 b in the fuse holder 22 and the pair of input / output terminals 21 a and 21 b of the fuse 21 are connected in parallel. At the time of factory shipment, no fuse is attached to the fuse holder 22 as shown in FIG. As described above, the measuring apparatus 1 includes the surface mounting fuse 21 and the circuit board mounting fuse holder 22, thereby using both the fuse 21 and the fuse holder 22 by an automatic mounting machine for component mounting. Can be automatically mounted on a circuit board.

  The input unit 3 includes an I / V conversion circuit, inputs a current I (corresponding to an electrical signal in the present invention) flowing between the probes 10 and 11 via the protection circuit 2, and converts the current I into a voltage. The output signal is output to the control unit 4. The input unit 3 inputs a voltage V (corresponding to an electrical signal in the present invention) applied between the probes 10 and 11 via the protection circuit 2, and amplifies or attenuates the voltage V with a predetermined gain. An output signal is output to the control unit 4.

  The control unit 4 constitutes a measurement unit according to the present invention together with the input unit 3, and calculates (measures) measurement values such as the current value of the current I and the voltage value of the voltage V based on the output signal output from the input unit 3. Then, a display signal for displaying the calculated measurement value is output to the display unit 5. The display unit 5 displays measured values and the like based on the display signal output from the control unit 4.

  Next, the overall operation of the measuring apparatus 1 will be described with reference to the drawings.

  For example, when measuring the current value of the current I flowing between the probes 10 and 11, the probes 10 and 11 are respectively connected to the measurement target portions, and the operation unit not shown in the figure is operated to operate each part of the measuring apparatus 1. Let At this time, the input unit 3 inputs the current I flowing between the probes 10 and 11 via the protection circuit 2, generates an output signal based on the current I, and outputs the output signal to the control unit 4. Next, the control unit 4 calculates the current value of the current I flowing between the probes 10 and 11 based on the output signal output from the input unit 3, and displays a display signal for displaying the calculated current value. Output to unit 5. Thereafter, the display unit 5 displays a current value and the like based on the display signal output from the control unit 4.

  Further, when measuring the voltage value of the voltage V applied between the probes 10 and 11, the input unit 3 inputs the voltage V applied between the probes 10 and 11 via the protection circuit 2, An output signal obtained by amplifying or attenuating the voltage V with a predetermined gain is output to the control unit 4. Next, the control unit 4 calculates a voltage value of the voltage V applied between the probes 10 and 11 based on the output signal output from the input unit 3, and displays the calculated voltage value. Is output to the display unit 5. Thereafter, the display unit 5 displays a voltage value and the like based on the display signal output from the control unit 4.

  When an overcurrent exceeding the rated current value of the fuse 21 flows between the probes 10 and 11 during the measurement of the current I and voltage V, the overcurrent is input to the protection circuit 2. In this case, since the fuse 21 electrically connects the input / output parts of the protection circuit 2, the fuse 21 is blown by an inflow of overcurrent, and the electrical connection between the input / output parts is interrupted. Therefore, as a result of the inflow of overcurrent being blocked, the input unit 3 is reliably protected from overcurrent.

  Next, when measuring the current I and the voltage V again, another new fuse 23 having the same rated current value as that of the fuse 21 and replaceable is attached to the fuse holder 22. In this state, as shown in FIG. 2, the pair of fuse connection terminals 22 a and 22 b in the fuse holder 22 (that is, the pair of input / output terminals 23 a and 23 b in the installed fuse 23) is paired with the pair of input / output terminals 21 a in the fuse 21. , 21b in parallel, the fuse 23 connects the input / output parts of the protection circuit 2 electrically again. Next, the current value of the current I and the voltage value of the voltage V are measured in the same manner as described above. In this case, when an overcurrent flows between the probes 10 and 11, the input unit 3 is reliably protected from the overcurrent by blowing the fuse 23.

  As described above, according to the protection circuit 2 and the measuring apparatus 1, the fuse 21 directly mounted on the circuit board as the mounting object and the fuse holder 22 directly mounted on the circuit board are provided. Since both of 21 and the fuse holder 22 can be mounted on the circuit board by using an automatic mounting machine for mounting electrical components, it is possible to omit manual mounting of the fuse. For this reason, the manufacturing time can be sufficiently shortened as compared with the conventional configuration that requires manual fuse mounting work. As a result, the manufacturing cost of the protection circuit 2 and the manufacturing cost of the measuring device 1 as a whole are sufficiently high. Can be reduced.

  Further, since the pair of fuse connection terminals 22a and 22b in the fuse holder 22 and the pair of input / output terminals 21a and 21b of the fuse 21 are connected in parallel, the fuse 21 can be connected between the input and output parts of the protection circuit 2 in the initial state. Are electrically connected, the input unit 3 can be reliably protected from overcurrent by blowing the fuse. In this case, when an overcurrent flows and the fuse 21 is blown, a new replaceable fuse 23 is attached to the fuse holder 22 so that the fuse 23 electrically electrically connects the input / output parts of the protection circuit 2 again. Can be connected. For this reason, in the state where the fuse 21 is blown, even if the fuse 23 newly attached to the fuse holder 22 is further blown, the input unit 3 can be protected from overcurrent by replacing the fuse 23. It can be restored. Therefore, according to the protection circuit 2 and the measuring device 1, it is possible to reliably protect the input unit 3 from overcurrent while reducing the manufacturing costs of the protection circuit 2 and the measuring device 1.

  Further, in this measuring apparatus 1, by using a surface mount type chip fuse having a small mounting area as the fuse 21, an increase in the mounting area on the circuit board can be suppressed to a minimum. Can be avoided.

  In addition, this invention is not limited to said structure. For example, the configuration using the chip fuse as the fuse 21 has been described above. However, for example, a glass tube fuse with a lead that can be directly mounted on the mounting target can be used as the fuse 21. Moreover, although the structure which uses a fuse holder was demonstrated as a fuse connection apparatus, not only this but the fuse metal fixture comprised by the circuit board etc. and comprised by a pair of electrode part which engages with the fuse 21 can also be used. Moreover, although the example which applies this invention to the measuring apparatus 1 which measures an electric current value and a voltage value was demonstrated, this invention is applied also to the various measuring apparatuses which measure various electrical parameters, such as resistance value between the probes 10 and 11. FIG. Of course, it is possible to apply. Furthermore, the mounting target in the present invention is not limited to a circuit board, and includes a housing of an electronic device such as a measuring device.

  In addition, the configuration including the protection circuit 2 that protects the input unit 3 from overcurrent has been described above, but the present invention is not limited to this. For example, the protection circuit 2 and the power supply unit are provided, and the power supply unit inputs a drive power current through the protection circuit 2 and measures the drive power generated based on the current (in the present invention). It is possible to employ a configuration that supplies each part in an example of an electronic device. In this case, the fuse 21 used in the protection circuit 2 is blown when an overcurrent flows from the power supply line to the power supply circuit, thereby protecting the power supply unit from the overcurrent. According to this configuration, it is possible to omit a manual fuse mounting operation, and thus it is possible to reduce the manufacturing cost of the protection circuit 2 and thus the manufacturing cost of the entire measuring apparatus. In addition, the configuration of the electronic device according to the present invention is not limited to the measurement device, but can be applied to various electronic devices such as a display device and an acoustic device.

It is a block diagram of the measuring apparatus 1 in the initial state at the time of factory shipment. It is a block diagram of the measuring apparatus 1 in the state which mounted | wore the fuse 23. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Measuring apparatus 2 Protection circuit 3 Input part 4 Control part 21,23 Fuse 22 Fuse holder I Current V Voltage

Claims (3)

  A fuse directly mounted on the mounting target and a fuse connecting device mounted directly on the mounting target, wherein the pair of fuse connecting terminals in the fuse connecting device and the pair of input / output terminals of the fuse are in parallel Connected protection circuit.   A measurement apparatus comprising: the protection circuit according to claim 1; and a measurement unit that measures an electrical parameter based on an electrical signal input through the protection circuit.   An electronic device comprising the protection circuit according to claim 1 and inputting a current for driving power through the protection circuit.

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