JP2000124745A - Amplifier circuit and hybrid integrated circuit device mounted with the circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the destruction of Darlington connected elements in a push-pull circuit for constituting the current amplifier circuit of a stereo or the like. SOLUTION: In this amplifier circuit, upon connecting a temperature compensation resistor Rth between the base of a first limit transistor TR5 and the base of a second limit transistor TR6, at the positive signals, a second limit resistor R7 is serially connected to the temperature compensation resistor Rth, and the second limit resistance remains as residual resistance even when the temperature compensation resistance becomes extremely small and a state where limitation does not function is suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an amplifying circuit suitable for use in audio equipment, and more particularly to protection of a power transistor during overload (overcurrent).

[0002]

2. Description of the Related Art Generally, an amplifier composed of a transistor, particularly a current amplifying circuit composed of a push-pull circuit, can break even an expensive speaker when the amplifier fails. Circuit to protect ・ Equipped with a circuit to disconnect amplifier and speaker when DC voltage appears at output.

In particular, if the output is erroneously short-circuited, the load on the power transistor becomes only the emitter resistance (about 0.3Ω), the load line rises, and the ASO (safe operation area)
When a signal enters in this state, a very large output current flows, and the power transistor is instantaneously destroyed.

Therefore, the emitter current of the power transistor is detected, and the power transistor is generally designed so that the emitter current does not exceed a certain limit.

FIG. 4 shows TR1 and TR2, and TR3 and TR4.
Has a push-pull circuit configuration with Darlington connection.

In this circuit, the emitter current IE of the power transistor TR2 flows through the emitter resistor RE, the voltage generated here is divided by R12 and R13, and the voltage generated at R13 is applied between the base and the emitter of TR5. . That is, when the emitter current IE increases, the voltage generated at R13 rises, TR5 is turned on, the inflow current of TR1 is suppressed, and the emitter current IE is suppressed.

In this circuit, when the load Z is short-circuited, the collector current IC flows along the line A in FIG.
And the current is limited so as not to exceed ASO. Therefore, safety is enhanced. However, since the protection line C intersects with the load line B in the normal operation, there is a problem that the thick line portion, that is, the maximum output cannot be taken out.
Circuit has been devised. This is provided with a resistor R14 between the intersection of R12 and R13 and the ground line. By connecting R14, a part of the current flowing to R13 flows to R14, making it difficult to turn on TR5. That is, the protection operation of TR5 is hardly effective.
The protection line at this time is the protection line D after the improvement in FIG. Therefore, the circuit can extract the maximum output described above.

[0008]

However, a circuit such as that shown in FIG.
When mounted on a metal substrate such as l, Cu, etc., the output transistor drives a large current and generates heat, and the metal substrate itself rises in temperature. Then, the temperatures of TR5 and TR6 mounted on the substrate also rise.

However, since the transistor has a negative temperature characteristic of VBE, when the temperature rises, the TR5 limit operation is performed with a smaller VBE, and when the temperature rises in the normal operation, the amplifier circuit restricts the operation. And the output was reduced.

[0010]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and firstly, a first temperature compensating resistor having a negative temperature characteristic and connected in parallel with a first limiting resistor. , Second
And a second temperature compensating resistor having a negative temperature characteristic and connected in parallel with each other.

When the temperature rises, the resistance value of the temperature compensation resistor decreases, so that the bias voltage between the base and the emitter of the transistor decreases, and the limit operation can be suppressed.

Second, the problem is solved by having a temperature compensation resistor connected between the base of the first limiting transistor and the base of the second limiting transistor.

If the temperature rises and the temperature compensating resistance drops extremely in the first means, there is a problem that the limit is not applied at the time of an overcurrent operation in which the protection circuit should operate.

However, when the temperature compensation resistor is connected between the bases of the limiting transistors, the second limiting resistor is connected in series to the temperature compensating resistor when the signal is positive, and the temperature compensating resistor becomes extremely small. Also, it is possible to suppress the state in which the second limiting resistance remains as a residual resistance and the above-mentioned limit does not work.

Third, the problem is solved by using a thermistor as the temperature compensation resistor.

Therefore, even when the amplifier circuit is mounted on a substrate having excellent thermal conductivity, the protection works well by the temperature compensation resistor.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First, a first embodiment of the present invention will be described with reference to FIG. This circuit is a push-pull connection amplification circuit that performs current amplification. The composite transistors S1 and S2 and the transistors TR5 and TR6 may be voltage-controlled power MOSs or IGBTs, but here, the description will be made assuming that they are composed of a PNP transistor and an NPN transistor.

First, the first composite transistor S1 is NP
The N-type transistors TR1 and TR2 are configured by Darlington connection, and the second transistor S2 is
The transistor TR3 and the transistor TR4 of the PNP type are configured by Darlington connection.

Resistors R2 and R3 are connected in series between the current outflow side (emitter side of TR2 in the figure) of the first composite transistor S1 and the current inflow side (emitter side of TR3 in the figure) of the second composite transistor S2. Have been.

The power supply + Vcc is connected to the current inflow side (collector side) of the first composite transistor S1, and the power supply -Vcc is connected to the current outflow side of the second composite transistor S2. The current outflow side of S1 is
The point C is connected to a control electrode (here, a base electrode) of the first limiting transistor TR5 via a first resistor R4. The current inflow side (emitter side) of the second composite transistor S2 is connected to the control electrode (here, the base electrode) of the second limiting transistor TR6 from the point d via the second resistor R6. Further, the current outflow side (here, the emitter electrode) of the first limiting transistor TR5 and the second
Are connected in common to the current inflow side (here, the emitter electrode) of the limiting transistor TR6. The point a of the common connection portion and the middle point b of the first current limiting resistor R2 and the second current limiting resistor R3 are connected by wiring. Then, a first limiting resistor R5 is connected between the control electrode of the first limiting transistor TR5 and the wiring, and a second limiting resistor R7 is connected between the control electrode of the second limiting transistor TR6 and the wiring. It is connected. Further, the current inflow side (here, the collector electrode) of the first limiting transistor is connected to the + side input line via the diode D1. Similarly, a current outflow side (here, a collector electrode) of the second limiting transistor is connected to a negative input line via a diode D2. The resistors R10 and R11 are
Although connected to the control electrode of the composite transistor, it may be omitted. A phase correcting capacitor is connected between the base and the collector of the first and second limiting transistors TR5 and TR6. TR2 and TR
4, the resistors R1a and R1b are connected between the base and the emitter. It is connected. Further, a load Z (here, a speaker) is connected to the point b. Furthermore, a feature of the present invention,
Temperature compensation resistors Rtha and Rthb having negative temperature characteristics are connected to the control electrode of the limiting transistor and the wiring (point a or point b).

When the voltage-amplified positive signal enters X, the first composite transistor amplifies the current according to the positive signal, and the current flows into the load Z via the point b. When the voltage-amplified negative signal enters Y, the second composite transistor amplifies the signal in accordance with the signal, and causes the load Z to output -Vc
Apply current to c. When this circuit is mounted on a substrate having excellent thermal conductivity, for example, a substrate made of copper, iron or Al, a large current flows through the composite transistors S1 and S2, so that the substrate has heat and the first limiting transistor TR5 and the The temperature of the second limiting transistor TR6 also rises due to this heat.

Therefore, in FIGS. 4 and 5, when the temperature rises, the limiting transistors TR5 and TR6 conduct at a smaller VBE, that is, the limiting transistors TR5 and TR6 are current-limited at the time of operation that does not need to be limited, and the output TR Current limit.

However, in FIG. 3, at room temperature, Rtha, Rt
Since the resistance value of hb is much larger than R5 and R7,
When 5 // Rtha ≒ R5 and R7 // Rthb ≒ R7, the limiter values are determined by the limiting resistors R5 and R7, as in FIG.
However, when the temperature rises, for example, by about 100 degrees, the temperature compensation resistors Rtha and Rthb have resistance values of 1 /
The limiter value is determined (R
5 // Rtha) / (R4 + R5 // Rtha) can be made lower than room temperature, and a limiter operation due to temperature rise can be prevented.

However, for example, when a thermistor is used as the temperature compensation resistor Rth, the resistance value decreases exponentially with the temperature rise. In other words, when the substrate is in a higher temperature state (for example, 125 degrees or more), Rth extremely increases.
The ratio that determines the limiter value is too small,
This time, there is a case where the limit operation is desired but the limit is not applied.

FIG. 1 shows a solution to this problem. The difference from FIG. 3 is that the temperature compensation resistor Rt is provided between the points e and g.
The point is that only one h is connected. FIG. 2 shows an equivalent circuit of the first resistor R4, the first limiting resistor R5, and the second limiting resistor R7 when viewed only during a positive signal operation.

As shown in the figure, when the lower end of the temperature compensation resistor Rth is connected to the point g, Rth and Rth connected in series with R5 are connected.
7 are connected in parallel.

That is, the voltage dividing resistors are R4 and R5 // (Rth + R7). Even if the temperature compensating resistor Rth becomes zero at a high temperature, the second limiting resistor R7 remains. That is, R
4, a voltage dividing resistor of R5 // R7. That is, as described above, even if the limit operation is not performed, in FIG. 1, the second limiting resistor R7 remains and the first limiting resistor R5
In addition, since the operation is performed in the direction in which the current flows, it is possible to prevent the limit operation from being stopped.

If the temperature further rises, the limiter operates due to the VBE temperature characteristic of the limiting transistor.
Limit the output as a temperature protection circuit.

Although the limit operation has been described with reference to the first limiting transistor TR5, the same applies to the second limiting transistor TR6, and a description thereof will be omitted.

As described above, the present circuit is particularly effective when mounted on a metal substrate. As a metal substrate,
Copper, iron, Al, and the like are conceivable. Generally, the surface is coated with an insulating resin, and a copper foil pattern is formed thereon. Then, circuit elements are mounted on the copper pattern, and a circuit is realized.

In the embodiment, the substrate temperature is increased due to the heat generated by the composite element. However, the same effect is obtained even if the temperature of the mounting body on which the substrate is mounted rises for some reason.

The same effect can be obtained with a ceramic substrate having excellent thermal conductivity, for example, an alumina substrate.

[0033]

As is clear from the above description, the first
A first temperature compensating resistor having a negative temperature characteristic connected in parallel with the first limiting resistor, and a second temperature compensating resistor having a negative temperature characteristic connected in parallel with the second limiting resistor. Since the resistance value of the temperature compensating resistor decreases as the temperature rises, bias correction can be performed in accordance with the temperature characteristics between the base and the emitter of the limiting transistor. Therefore, limit malfunction due to temperature rise can be suppressed.

Further, when a temperature compensating resistor is connected between the base of the first limiting transistor and the base of the second limiting transistor, the second limiting resistor is connected in series to the temperature compensating resistor. With this configuration, even when the temperature compensation resistance becomes extremely small, the second limiting resistance remains as a residual resistance, and the state where the limit does not work can be suppressed.

Therefore, even if the amplifier circuit is mounted on a substrate having excellent thermal conductivity, more accurate protection can be provided by using the temperature compensation resistor. ,

[Brief description of the drawings]

FIG. 1 is a circuit diagram illustrating an embodiment of the present invention.

FIG. 2 is an equivalent circuit diagram illustrating the operation of FIG.

FIG. 3 is a circuit diagram illustrating an embodiment of the present invention.

FIG. 4 is a circuit diagram illustrating a conventional amplifier circuit.

FIG. 5 is a circuit diagram illustrating a conventional amplifier circuit.

FIG. 6 is a diagram illustrating a protection operation of the amplifier circuit.

[Explanation of symbols]

 S1 first composite transistor S2 second composite transistor R2 first current limiting resistor R3 second current limiting resistor R4 first resistor R6 second resistor TR5 first limiting transistor TR6 second limiting transistor R5 1st limiting resistor R7 2nd limiting resistor

Continued on the front page F term (reference) 5G013 AA16 BA01 CA02 CA10 CA18 5J090 AA02 AA18 AA41 AA51 CA02 CA57 CA89 CN02 CN03 FA08 FA10 FA18 FN06 FN10 HA08 HA19 HA25 HA29 HA39 HA43 HN07 HN11 HN15 HN20 KA12 MA20 KA17 MN01 NN06 NN13 SA05 TA01 TA02 5J091 AA02 AA18 AA41 AA51 CA02 CA57 CA89 FA08 FA10 FA17 FA18 FP05 GP01 GP02 HA08 HA19 HA25 HA29 HA39 HA43 KA12 KA17 KA20 KA28 KA48 KA62 MA06 MA13 MA20 MA24 SA09 TA01 U02

Claims (4)

[Claims] 1. A first composite transistor forming a push-pull circuit and flowing out an output current; a second composite transistor forming the push-pull circuit and flowing in an output current; and the first composite transistor Connected in series between the current outgoing side of the second composite transistor and the current inflow side of the second composite transistor.
A current detection resistor and a second current detection resistor, a first limiting transistor having the current outflow side connected to a base via a first resistor, and controlling a control electrode of the first composite transistor; An inflow side connected to a base via a second resistor, a second limiting transistor controlling a control electrode of the second composite transistor, a current outflow side of the first limiting transistor, and the second limiting transistor A wiring connecting a first midpoint located between the first current limiting resistor and a second midpoint located between the first current limiting resistor and the second current limiting resistor; A first limiting resistor connected between the base of the first limiting transistor and the wiring, a second limiting resistor connected between the base of the second limiting transistor and the wiring, A first temperature compensating resistor having a negative temperature characteristic connected in parallel with the first limiting resistor; and a second temperature compensating resistor having a negative temperature characteristic connected in parallel with the second limiting resistor. An amplification circuit characterized by having: 2. A first composite transistor forming a push-pull circuit and flowing out an output current; a second composite transistor forming the push-pull circuit and flowing in an output current; and the first composite transistor A first current detecting resistor and a second current detecting resistor connected in series between a current outgoing side of the second composite transistor and a current inflow side of the second composite transistor; And a first limiting transistor for controlling a control electrode of the first composite transistor; and a current inflow side connected to a base via a second resistor to control a control electrode of the second composite transistor. A second limiting transistor, and a second limiting transistor located between a current outflow side of the first limiting transistor and a current inflow side of the second limiting transistor. And a wiring connecting a middle point of the first limiting transistor and a second middle point located between the first current limiting resistor and the second current limiting resistor; A first limiting resistor connected therebetween; a second limiting resistor connected between the base of the second limiting transistor and the wiring; a base of the first limiting transistor and the second An amplifier circuit having a temperature compensation resistor connected between the limiting transistor and a base of the limiting transistor. 3. The amplifier circuit according to claim 1, wherein said temperature compensating resistor comprises a thermistor. 4. The hybrid integrated circuit device according to claim 1, wherein said amplifier circuit is mounted on a substrate having excellent thermal conductivity.