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DESCRIPTION JPS55152785

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DESCRIPTION JPS55152785
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a basic circuit diagram of a known protective
circuit, FIG. 2 is a graph showing the temperature characteristic of the electrical resistance of a
positive temperature characteristic thermistor, and FIG. A graph showing the protection
operation characteristic B of the positive temperature characteristic thermistor in a known
protection circuit by a broken line by a solid line, and a protection operation characteristic C of a
positive temperature characteristic by a protection circuit according to the invention by a one-dot
chain line. 1 is a circuit diagram of a protection circuit according to an embodiment of the
present invention, 1 is a speaker, 2 is a positive temperature characteristic thermistor, 3 is a
negative temperature characteristic thermistor, and the same reference numerals denote the
same or corresponding portions in the figure. .
DETAILED DESCRIPTION OF THE INVENTION The present invention relates to the improvement
of a speaker protection circuit using a positive temperature coefficient thermistor. FIG. 1 shows a
known basic circuit of a speaker protection circuit using a positive temperature coefficient
thermistor to protect against excessive input current. In the figure, b (+ l # i is a speaker to be
protected, and ツ is a positive temperature characteristic thermistor. Positive temperature
characteristic thermistor (2) connection type 1 # i, frequency division network circuit and
attenuation (R) path consisting of passive elements in the middle, not directly connected in series
to the speaker ill as described above) ..., +11 mother = '/ 12? Although t may be inserted, the
operation principle as a protection circuit is the same. Next, the operation will be described. As
shown in FIG. 2, the positive temperature characteristic thermistor (2) has a relatively small
change in electrical resistance in a temperature range lower than a certain temperature, but has a
type of increase in electrical resistance rapidly above a certain temperature. In the case of a
thermal resistance element, when current flows, when the temperature rise due to heat
generation reaches the rapid increase in resistance value in Fig. 2, the increase in the calorific
value due to the increase in resistance also contributes to the acceleration of the resistance value.
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It is an element that has an effect of increasing the current and limiting the current flow.
Although the time required to start the current limiting action depends on the element
characteristics, current value, heat radiation conditions of the element, etc., the current limiting
action of the positive temperature coefficient thermistor is a combined result of these factors. An
example of the characteristic is shown by a solid line in FIG. When the allowable input
characteristic of the speaker (1) is indicated by the broken line in FIG. 3, the speaker is protected
in the range of the input current which is on the left side of the solid line on the short side of the
broken line. (2)4−t−スピーカ(! In the circuit inserted between the positive
temperature coefficient thermistor (2) and the positive temperature characteristic thermistor (2),
when the currents of the two do not necessarily match, the above operation is performed
according to the degree of the match. In the known protection circuit described above, operation
#i is performed for the same or substantially the same current as the current flowing through the
operation # i1 speaker 111 of the positive temperature coefficient thermistor (2). Positive
temperature characteristic thermistor (The electric resistance #i at room temperature, the
attenuation of the power to pivot the speaker (1) increased as it became larger), the
electromagnetic control by the amplifier of the speaker (1) Since the power is weakened and a
harmful effect occurs, the speaker (1) is usually cast smaller than the DC resistance value of the
speaker. Therefore, the amount of heat generated by the current is larger in the voice coil of the
speaker 11 than in the positive temperature characteristic thermistor (2).
The speaker ill needs to reduce the mass of the vibration system for high-pitched noise, the case
where the voice coil is made of incoming wires, etc. #i, the thermal capacity of the voice coil is
small, and the voice coil has positive temperature characteristics The temperature rise rate is
greater than the thermistor (3). The electrical resistance value of the voice coil increases
approximately in proportion to the temperature, and in the case of copper O, which is a common
wire, increases at a rate of about IL 43% per 1 ° C. of temperature rise. The electrical resistance
of the voice coil is about twice that of normal temperature at a temperature of about 200 ° C,
which is the heat-resistant temperature of organic materials usually used for insulating coatings
of varnishes and leads, It becomes. In the past, if the voice coil had a faster temperature rise than
the positive temperature coefficient thermistor, the current flow would decrease due to the
increase in the resistance of the voice coil in a conventional series circuit, and the positive
temperature temperature thermistor could start to hold hold As a result, the temperature rise of
the voice coil first exceeds the endurance temperature and the h1 voice coil is thermally
destroyed. As in the case of the prior art, the conventional protection circuit has a drawback that
the speaker having a voice coil with a small heat capacity can not be protected. The present
invention was made to eliminate the above-mentioned drawbacks of the prior art, and the
positive temperature characteristic thermistor was obtained by compensating the current
decrease due to the temperature rise of the voice coil (4) with a negative temperature
characteristic thermistor. The present invention is aimed at providing a speaker holding circuit
capable of promoting the operation of the speaker of the voice coil with a small heat capacity. An
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embodiment of the present invention will be described below with reference to the drawings. In
FIG. 4, (1) a speaker subject to butterfly protection, a positive temperature characteristic
thermistor connected in series between the loudspeaker (1) and the signal source, (31 is a
positive temperature characteristic thermistor (2) Between the speaker + 1 and 1, the speaker (!
Negative temperature characteristic thermistor connected in parallel with Negative temperature
characteristics thermistor Fi, positive temperature characteristics thermistors are also more
common, just mean "thermistor" and mean negative temperature characteristics thermistor,
temperature? The electrical resistance R at ('K), where Q is 1 ambient temperature T. The
resistance Ro (Ω) at (6 K) and the thermistor constant B ('K) determined by the configuration of
the thermistor. R = Roexp (B (-fTO)) (S): It is a thermal resistance element of 1-.zeta. When a
constant voltage is applied to both ends of the negative temperature characteristic thermistor,
the resistance value decreases due to heat generation by the current, and the current increases
cumulatively.
In the circuit of FIG. 4, when the temperature rise of the voice coil of the speaker l + 1 is faster
than that of the direct placement t% thermistor ill and the resistance increase of the voice coil is
faster, the positive temperature characteristic thermistor (2) flows The current decreases, the
voltage drop due to the positive temperature characteristic thermistor a + is small, and the
voltage applied to the speaker (the 110 input voltage increases and the negative temperature
characteristic thermistor 暢) also increases. As a negative temperature characteristic thermistor
(2), one having a resistance value of several 109 at normal temperature is used. Although the
shadow 41 applied to a speaker having a nominal impedance of 89 is small, as described above,
when the temperature of the voice coil of the speaker increases and the input voltage increases,
the current flowing through the negative temperature characteristic thermistor is Cumulatively,
the current flowing through the positive temperature characteristic thermistor (2) increases and
the voltage drop also increases, and the voltage applied to the speaker h1 and the negative
temperature characteristic thermistor (smallest) decreases, and the end 2 (6) --- S Positive
temperature characteristic The time for the thermistor <2) to start the heating operation is
shortened. When the positive temperature characteristic thermistor (2) operates, the voltage
applied to the speaker (1) and the negative temperature characteristic thermistor 0) becomes
very small, and the heat from the voice coil of the speaker fil and the negative temperature
characteristic thermistor (3) stops Return to When the voltage for driving the speaker decreases,
the heat generation of the positive temperature coefficient thermistor (2) also stops, and the
normal state is restored. In the above embodiment, the direct temperature characteristic
thermistor was connected directly to the speaker (11 and the negative temperature characteristic
thermistor body) in parallel, but the positive temperature characteristic thermistor (m and the
speaker 11 and the negative temperature characteristic is shown) In the middle of the thermistor
O), a frequency division network circuit or an attenuation circuit composed of passive elements
such as a coil, a capacitor and resistors may be inserted, and the same effect as the above
embodiment can be obtained. As described above, according to this invention, since the decrease
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in current due to the temperature rise of the voice coil is compensated by the negative
temperature characteristic thermistor connected in parallel, as shown by the one-dot chain line in
FIG. (1)¥)、。 -3- The positive temperature characteristic can accelerate the operation of
the thermistor, and it is possible to protect the speaker of the voice coil having a small heat
capacity from the excessive input.
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