JPH076503Y2 - Overheat protection circuit - Google Patents

Description

[Detailed Description of the Invention] Industrial field of application The present invention relates to a device which needs protection from heat generation.
The present invention relates to an overheat protection circuit, and more particularly to an overheat protection circuit that stabilizes the operation of the device by providing a hysteresis in order to eliminate unstable operation of the device near the heat generation temperature at which the overheat protection works.

2. Description of the Related Art Conventionally, as shown in FIGS. 3 and 4, this type of overheat protection circuit has a heat detection circuit 1c, 1 for detecting heat generated in the device.
d and the protection circuits 2c and 2d that perform protection operation due to the activation of heat detection.When the heat generated in the device reaches the detection temperature determined by the circuit configuration, the heat detection circuit 1
c, 1d outputs a detection output, and thereby the protection circuits 2c, 2d operate to lower the temperature of the device. That is, the thermal detection circuit 1c, 1d, the transistors Q _4, Q _5, Zener diode D _Z,
Is a resistor R ₃ to R _5, taking into account the temperature coefficient of each constituent element, the transistor Q _4, usually in a non-operating state, is designed to be the operating state during thermal detection. Protection circuit 2c of FIG. 3 is constituted by transistors Q _2, Q _3, the thermal detection circuit 1
When the transistor Q ₄ is activated by the heat detection of c,
A bias voltage is applied between the emitters and bases of the transistors Q ₂ and Q ₃ to put them in an operating state, thereby performing a protective operation. The protection circuit 2d of FIG. 4, the transistors Q _2, Q
₃ , a resistor R ₆ and R ₇ connected between the collectors of the transistors Q ₂ and Q ₃ and the ground, and a transistor whose base is connected to the collectors of the transistors Q ₂ and Q _{3 and} whose emitter is connected to the ground It is composed of Q ₆ and Q ₇ . This protection circuit 2
d is the heat detection circuit 1d detects heat as described above,
When the transistor Q ₄ is activated and the transistors Q ₂ and Q _{3 of} the protection circuit 2d are activated accordingly, the transistor Q ₄ is activated.
_A bias is applied between the base and emitter of ₆ and Q ₇ to activate them.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention By the way, the above-mentioned conventional overheat protection circuit includes the heat detection circuits 1c and 1d that detect heat generated in the device and the protection circuit 2c that starts the protection operation when the heat detection works. , 2d only, so when the device self-heats due to its operation, or the temperature rises due to the surrounding environment and reaches the detection temperature determined by the circuit configuration, the heat detection circuits 1c, 1d Due to the detection, the protection circuits 2c and 2d are operated, and as a result, the device temperature decreases, but due to the decrease in the device temperature, the heat detection circuits 1c and 1d and the protection circuits 2c and 2d stop their operation, and therefore, The device temperature rises again and the heat detection circuit 1c, 1
d, because the protection circuits 2c and 2d operate again, it has an unstable configuration that repeats normal operation and overheat protection operation of the device body near the detection temperature set by the circuit configuration of the device. There is a drawback that an external device connected to this device may malfunction or be damaged.

Means for Solving the Problems The overheat protection circuit of the present invention includes a heat detection circuit that detects heat generated in a device, a protection circuit that performs a protection operation by the operation of the heat detection circuit, and a hysteresis in the protection circuit operation. It has a hysteresis circuit.

Action According to the above configuration, when the device self-heats due to its operation, or when the temperature rises due to the ambient environment and reaches the detection temperature set by the circuit configuration of the device, the protection circuit is detected by the heat detection circuit. Is activated and the overheat detection state is maintained to lower the temperature of the device and prevent the device from overheating. Furthermore, once the protection circuit operates, the hysteresis circuit also starts operating, and the detection temperature set by the device is reset to a lower temperature, so the device continues the overheat protection operation and the hysteresis circuit is released. Continue until Therefore, near the originally set detection temperature of the device,
Without returning to normal operation and overheat protection operation of the device repeatedly, when returning to normal operation, since it recovers from a temperature lower than the detection temperature set by the device, normal operation of the device can be maintained, The external device connected to the device can operate stably without causing malfunction or damage.

Embodiment Hereinafter, the present invention will be described with reference to the drawings.

FIG. 1 is an overheat protection circuit diagram having a hysteresis circuit according to an embodiment of the present invention. 1a is an overheat detection circuit in the overheat protection circuit, 2a is a protection circuit, and 3a is a hysteresis circuit. That is, the thermal detection circuit 1a, FIG. 3 is interposed a second resistor R ₂ between the fourth view of the heat sensing circuit 1c, the emitter and the third resistor R ₃ of the fifth transistor Q ₅ in 1d The points are different. The protection circuit 2a is the protection circuit of FIG.
Since it is the same as 2d, its description is omitted. Furthermore, the hysteresis circuit 3a includes a first transistor Q ₁ and an eighth transistor Q1.
And Q _8, is composed of a eighth resistor R _8, the first transistor Q ₁ and the eighth resistor R ₈ are connected in series between V _CC and ground, the collector emitter of the eighth transistor Q ₈ is thermal detection It is connected in parallel to the second resistor R ₂ of the circuit 1a and its base is connected to the collector of the first transistor Q ₁ . The first resistor R ₁ is
It is a resistor for preventing leakage of the first transistor Q ₁ in the hysteresis circuit 3a and the second transistor Q ₂ and the third transistor Q _{3 in} the protection circuit 2a.

Next, the operation of the overheat protection circuit will be described. Thermal detection circuit 1a, setting the fourth transistor Q ₄ for overheat detection at room temperature T ₀ inoperative. At this time, the fourth transistor
The base potential of Q ₄ (V _BE4OFF ) is the Zener diode D
_Z , the fifth transistor Q ₅ , the second resistor R ₂ , the third resistor
It is determined by R ₃ and the fourth resistance R ₄ , and is expressed by the following equation.

Here, V _BE5 is the potential between the base and emitter of the fifth transistor Q ₅ at room temperature T ₀ , and V _Z is the Zener voltage of the Zener diode D _Z. 4th transistor Q ₄ , 5th transistor Q ₅ ,
The Zener diode D _Z , the second resistor R ₂ , the third resistor R ₃ , and the fourth resistor R ₄ are usually arranged in a place sensitive to the heat generation of the device, and generally the potential between the base and emitter of the transistor is The zener diode has a negative temperature coefficient a of about 2 ^mv / ° C, and the zener diode has a positive temperature coefficient b of about 3 ^mv / ° C. Further, the resistance has a positive or negative temperature coefficient c of about 300 PPM / ° C. to 3000 PPM / ° C. depending on its type, and the overheat detecting circuit 1a is configured by utilizing these characteristics.

The base potential V _BE4ON when the device temperature rises and the heat detection fourth transistor Q ₄ operates is V _BE4ON = V _BE4OFF -a (TT ₀ ).

Here, (TT ₀ ) is the temperature rise of the device. Also, from the formula, when the device temperature rises, V _BE4ON = {V _Z + b (TT ₀ ) -V _BE5 + a (TT ₀ )} × (R ₄ + ΔR ₄ ) / (R ₂ + Δ
R ₂ ) + (R ₃ + ΔR ₃ ) + (R ₄ + ΔR ₄ ) ... Where ΔR is the temperature change of the resistance, and ΔR
= R · c (TT ₀ ). The formula is a straight line that decreases with temperature, and by making the formula a straight line that increases with temperature,
The expressions intersect at a certain temperature, and this temperature is the heat detection circuit.
1a is the temperature at which the operation starts. Here, the fifth resistor R ₅ is a bias resistor of the heat detection circuit 1a.

Next, the operation of the heat detection circuit 1a causes the first transistor Q ₁ of the hysteresis circuit 3a and the second transistor Q ₂ and the third transistor Q ₃ of the protection circuit 2a to be in the operating state, and the protection circuit 2a the second transistor Q _2, the operation of the third transistor Q ₃ sixth transistor Q ₆ and the seventh transistor Q ₇ is an operational state, the sixth transistor Q _6, 7
The collector of the transistor Q ₇ shuts off the circuit or element that is the heat source of the device, and cuts off the heat generating part of the device, thereby working to lower the temperature of the entire device. Here, the sixth resistor R ₆ and the seventh resistor R ₇ are base bias resistors of the sixth transistor Q ₆ and the seventh transistor Q ₇ .

Protection circuit 2a, while the fourth transistor Q ₄ for thermal detection is operating and running with the eighth transistor Q ₈ also operates by receiving the first transistor to Q ₁ drives in this case the hysteresis circuit 3a , The second resistor R ₂ is short-circuited. Therefore, even if the reduction temperature of the operation by the device of the protection circuit 2a is, the cut-off voltage of the fourth transistor Q ₄ for thermal detection is not determined by the equation equation is determined by the following equation.

V _BE4OFF = V _BE4ON + a (T-T ₀ ) = {V _Z + b (T
−T ₀ ) −V _BE5 + a (T−T ₀ )} × (R ₄ + Δ
R ₄ ) / (R ₃ + ΔR ₃ ) + (R ₄ + ΔR ₄ ) + γ _SCQ8
≈ {(V _Z + b (T-T ₀ ) -V _BE5 + a (T-
T ₀ )} × (R ₄ + ΔR ₄ ) / (R ₃ + ΔR ₃ ) + (R ₄ + ΔR
₄ ) It becomes. Comparing the formulas and wherein for term (R ₂ + ΔR ₂₎ is not the expression, V _BEOFF equation it is understood that the higher potential relative to V _BEON equation. When the heat detection circuit 1a is released, the base potential of the heat detection fourth transistor Q ₄ has a negative temperature characteristic of about 2 ^mv / ° C. The recovery is delayed by the amount by which the base potential represented by the equation is larger than the base potential of the heat detection fourth transistor Q ₄ at which the overheat protection circuit represented by (4) has started its operation. That is, the temperature is restored at a temperature lower than the temperature at which the heat detection circuit 1a operates, and the temperature detection has a hysteresis.

With this circuit configuration, for example,
In the audio power amplifier manufactured by IC, the IC operation does not repeat on-off at the temperature around the heat detection circuit 1a operates, that is, the annoying situation that sound is emitted or cut off is eliminated. Also, in various other devices, it is possible to prevent damage to the connected external equipment.

FIG. 2 is a circuit diagram of a second embodiment of this invention.

In this embodiment, the second resistor R ₂ of the overheat detection circuit 1a of the first embodiment is omitted and the zener diode D _Z is connected in series with the diode D _I to form the heat detection circuit 1b.
The protection circuit 2b is the same as the protection circuit 2c shown in FIG.
Further, the hysteresis circuit 3b, tenth transistor Q ₁₀ that the ninth transistor Q ₉ which connect the base to the first collector of the transistor to Q ₁ FIG. 1, the base to the collector of the ninth transistor Q ₉ is connected When, V _CC - consists of a ninth resistor R ₉ and a tenth resistor R ₁₀ connected in series between ground and the emitter of said ninth transistor Q ₉ is connected to the ground, the collector and the ninth resistor R ₉ 10 It is the same as the first embodiment except that it is connected to the connection point of the resistor R ₁₀ , and the collector-emitter of the tenth transistor R ₁₀ is connected in parallel to the diode D _I of the overheat detection circuit 1b. The same parts are designated by the same reference numerals and the description thereof will be omitted.

In this embodiment, the tenth transistor Q ₁₀ of the hysteresis circuit 3b is usually located in the operating state to an inactive state by the thermal detection circuit 1b is operated. That is, by thermal detection circuit 1b operates the fourth transistor Q ₄ operates, in the same manner as described above, results the base potential of the first transistor Q ₁ is lowered, the first transistor Q ₁ is operated, depending on the 9 Transistor Q ₉ operates by increasing the base potential. as a result,
The collector potential of the ninth transistor Q ₉ , that is, the base potential of the tenth transistor Q ₁₀ decreases,
₁₀ , the diode ₁₀ becomes inactive, the diode D _I is inserted in series with the Zener diode D _Z , the base potential of the fifth transistor Q ₅ rises, and the detected temperature of the heat detection circuit 1b has hysteresis. Therefore, the temperature at which the device is restored is set to a low temperature as in the case of the first embodiment, and the above-mentioned effect is obtained.

Effect of the Invention As described above, the present invention allows the overheat protection circuit to have a hysteresis so that the temperature at which the overheat protection circuit operates can be set lower than the temperature at which the overheat protection circuit operates. , The device with built-in overheat protection circuit can be operated stably against temperature, so that there is an effect that it can prevent damage such as malfunction and damage to external devices connected to the device. .

[Brief description of drawings]

1 and 2 are circuit diagrams showing different embodiments of the overheat protection circuit according to the present invention, and FIGS. 3 and 4 are circuit diagrams showing different concrete examples of the conventional overheat protection circuit. Q _{1 to} Q ₁₀ ... 1st to 10th transistors, R _{1 to} R ₁₀ ... 1st
~ 10th resistance, D _Z ...... Zener diode, D _I ...... Diode, 1a ~ 1d ...... Heat detection circuit, 2a ~ 2d ...... Protection circuit, 3a ~
3d: Hysteresis circuit.

Claims (1)

[Scope of utility model registration request] 1. An overheat comprising: a heat detection circuit for detecting heat generation; a protection circuit for starting a protection operation when the heat detection works; and a hysteresis circuit for giving a hysteresis to the protection circuit operation. Protection circuit.