JPS6367767B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention operates in a steady state of operation of a circuit, and when an output terminal contacts one end of a power supply, a detection circuit is activated to limit or suppress the base drive current of a transistor to be protected. This provides a protection circuit that prevents the transistor from being destroyed by an abnormally large current when the output terminal contacts one end of the power supply.

FIG. 1 shows a conventional amplifier circuit without a built-in protection circuit. In Figure 1, R ₂₁ , R ₂₂ , R ₂₃ are resistors, D ₂₁ , D ₂₂ , D ₂₃ are diodes, Q ₂₁ , Q ₂₂ ,
Q ₂₃ , Q ₂₄ , Q ₂₅ are transistors, a is a signal input terminal, I _B is a constant current source whose current is I _B , and V _cc2 is a voltage
Indicates the voltage source of V _cc2 . Now, if we consider the case in which the circuit goes from a normal operating state to an abnormal state in which the output terminal b contacts the negative power supply in Fig. 1, the upper Darlington connected transistors Q ₂₂ and Q ₂₄ continuously become I _B current driven transistor
Abnormal excessive current flows through Q ₂₄ , resulting in excessive power consumption and destruction.

As described above, the present invention provides a protection circuit that prevents a transistor from being destroyed in an abnormal state in which an output terminal of an amplifier circuit according to the prior art comes into contact with a power supply terminal.

The principle of the present invention is shown in FIG. In Figure 2, R ₇ and R ₉ are resistors D ₄ , D ₅ , and D ₆ are diodes, and Q ₄ ,
Q ₅ , Q ₈ , Q ₁₁ are transistors, ZD ₁ is a Zener diode, c is a terminal connected to one end (positive voltage side in this case) of the power supply of the circuit including the transistor to be protected (transistor indicated by a dotted line), d is a terminal connected to the base current supply circuit of the transistor to be protected, e is a terminal connected to the base of the transistor to be protected, f is a terminal connected to the output terminal of the circuit including the transistor to be protected, g is a terminal to be protected It shows a terminal connected to the other end (here, negative or reference potential) of a circuit including a transistor. In FIG. 2, when the terminal f connected to the output terminal of the circuit including the transistor to be protected comes into contact with the terminal g connected to the negative side of the power supply of the circuit including the transistor to be protected, the transistor to be protected Current begins to flow at (shown by the dotted line).

Since the terminals e and f are connected between the base and emitter of this transistor, the transistor Q ₈
A large bias voltage is instantaneously applied between the base and emitter of the transistor, and a current proportional to the large current flowing through the transistor to be protected (the transistor indicated by the dotted line) flows. As a result, transistor Q ₄ is driven, causing a voltage drop across diodes D ₅ , D ₆ and resistor R ₇ , and forward bias voltage is applied between the base and emitter of transistors Q ₅ and Q ₁₁ .
_Q5 becomes conductive, collector current flows to terminal d, and the base drive current of the transistor to be protected connected to terminal d is cut off or the operation of the base drive current supply circuit is stopped. Furthermore, if the collector-emitter voltage of the transistor to be protected is high, the collector current in the safe operating area of the transistor to be protected will decrease.
In order to limit the collector current even further, the Zener diode ZD ₁ conducts and the transistor
Collector current flows through Q ₁₁ , which together with the collector current of transistor Q ₄ increases the voltage across resistor R ₇ and diode D ₅ , so that the base-emitter of transistor Q ₅ resists the abnormal current flowing to the transistor to be protected. , lower values result in forward bias (within the safe operating area). And the transistor
When _Q5 becomes conductive, the base drive current of the transistor to be protected connected to the terminal d is limited or cut off, or the operation of the base drive current supply circuit is stopped, thereby preventing destruction of the transistor to be protected.

Note that although the diode _D5 is not necessary in principle, an example in which it is added to compensate for the temperature of the base-emitter voltage V _BE of the transistor _Q5 is explained here. Also, did you replace diode _D6 with a resistor?
In this case, it is particularly effective when setting the drive ratio of transistor _Q11 to a small value.
Furthermore, even if the terminals g and f are connected in common, the voltage across the resistor _R7 can be detected by the transistor _Q5 , so that a protective operation against abnormal current of the transistor to be protected can be performed.

Next, one specific embodiment of the present invention is shown in FIG. In Figure 3, R ₁ , R ₂ , R ₃ , R ₄ , R ₅ ,
R ₆ , R ₇ , R ₈ , R ₉ are resistances, D ₁ , D ₂ , D ₃ , D ₄ , D ₅ ,
D ₆ is a diode, Q ₁ , Q ₂ , Q ₃ , Q ₄ , Q ₅ , Q ₆ ,
Q ₇ , Q ₈ , Q ₉ , Q ₁₀ , Q ₁₁ are transistors, R _L is a load, C ₁ , C ₂ , C ₃ are electrolytic capacitors, ZD ₁ is a Zener diode, a is a signal input terminal, b is a signal output terminal, H is the base potential of transistor _Q5 , I _p
indicates a constant current source whose current is I _p , and V _cc1 indicates a voltage source whose voltage is V _cc1 . In FIG. 3, the output stage has a generally known class B single-ended pushable configuration. Now, in the steady state of operation of this circuit, for example, when a sine wave input signal a shown in Fig. 4 is input to input terminal a, a sine wave output signal b shown in the figure is output to output terminal b, but at this time V _cc1 The upper waveform with respect to /2 occurs when transistor Q ₉ is conducting, and the lower waveform occurs when transistor Q ₁₀ is conducting. Here, when transistor Q ₉ is conducting, the base-emitter voltage V _BEQ9 of transistor Q ₉ becomes large, and similarly, if the base-emitter voltage V _BEQ8 of transistor Q ₈ is set, the current shown in the following equation is
I ₁ flows into the collector of transistor Q ₈ .

I ₁ = V _BEQ9 −V _BEQ8 /R ₈ ... Now, when a current I ₁ flows through the collector of transistor Q ₈ , the mirror circuit of diode D ₄ and transistor Q ₄ will cause h _FE of transistor Q ₄ to be large enough. Thinking about it, a current _I1 flows through the collector of transistor _Q4 . The voltage drop across diode _D5 is V _D5
Then, a voltage drop of (I ₁ R ₇ +V _D5 ) occurs at point H, but at the same time, as mentioned above, output terminal b shows an upper waveform, so the potential at point H is always lower than the potential Vb at the output terminal. Set it to keep it low. That is, if the resistors R ₇ and R ₈ are adjusted so that I ₁ R ₇ +V _D5 < Vb + V _BEQ5 , the transistor Q ₅
Since the emitter, that is, the output terminal b, and the base of the transistor _Q5 , that is, the potential at the point H are always reverse biased, this protection circuit does not operate during normal steady operation.

If an abnormal state occurs in which the output terminal b contacts the negative terminal (-terminal) of the power supply, the output terminal b becomes the lowest potential and the upper Darlington connected transistors Q ₆ and Q ₉ are continuously driven with a current of I ₀ . Ru. Therefore, a large current begins to flow through the transistor _Q9 , but at the same time, a current _I1 proportional to this large current also flows through the collector of the transistor _Q8 . This current is caused by the mirror circuit of diode D ₄ and transistor Q ₄ , and if h _FE of transistor Q ₄ is large enough, current I ₁ flows to the collector of transistor Q ₄ and resistor R ₇ .
A voltage drop occurs across diodes D ₅ and D ₆ . Then, a forward bias voltage is applied between the base and emitter of transistor _Q5 , causing transistor _Q5 to operate, absorbing the base drive current of transistor _Q6 with its collector current, and injecting the drive current into the base of the final stage transistor _Q9 . to refuse. That is, the transistor Q ₉ is not operated to prevent the transistor Q ₉ from being destroyed by an abnormally large current. With the current I ₁ flowing through transistor Q ₄ depending on the current in transistor Q ₉ , I ₁ R ₇ +V _D5 > Vb +
When V _BEQ5 , transistor Q ₅ operates, and the collector current (emitter current) of transistor Q ₉
to limit and protect. Furthermore, such an output terminal b
In an abnormal condition where V cc1 contacts the negative terminal (one terminal) of the power supply, the voltage V _cc1 is connected to the Zener diode
When ZD ₁ is high enough to conduct, transistor Q ₁₁ carries _{a collector current I 2 proportional} to current I 1 and resistor R ₇ diode D ₅ carries a current (I ₁ +
I ₂ ) causes a voltage drop. If the voltage drop that occurs across diode D ₅ at this time is V _D5 ', then (I ₁ +
I ₂ ) When R ₇ + V _D5 ′ > Vb + V _BEQ5 , transistor Q ₅ operates and protects transistor Q ₉ .
Therefore, if the voltage source _Vcc1 is high during the abnormality, the transistor _Q5 operates at a stage where the current _I1 is small, thereby strengthening the protection of the transistor _Q9 . This is an extremely convenient operation considering that the safe operating area of the transistor depends on the collector-emitter voltage and is limited. In this way, during the abnormality, the transistor _Q5 operates depending on the relationship between the current flowing through the transistor _Q9 and the collector-emitter voltage applied to the transistor _Q9 during the abnormality.
The level at which Q ₉ is protected is determined.

As described above, by connecting the protection circuit according to the present invention, it is possible to realize a protection circuit that limits the transistor collector current within the safe operating range and prevents destruction in an abnormal state where the output terminal of the amplifier circuit comes into contact with one end of the power supply.

Next, one of the other embodiments is shown in FIG. Fifth
In the figure, R ₁ , R ₂ , R ₃ , R ₄ , R ₅ , R ₆ , R ₇ , R ₈ ,
R ₉ , R ₁₀ , R ₁₁ , R ₁₂ , R ₁₃ are resistances, D ₁ , D ₂ , D ₃ ,
D ₄ , D ₅ , D ₆ , D ₇ are diodes, Q ₁ , Q ₂ , Q ₃ ,
Q ₄ , Q ₅ , Q ₆ , Q ₇ , Q ₈ , Q ₉ , Q ₁₀ , Q ₁₁ , Q ₁₂ are transistors, ZD ₁ is a Zener diode, R _L is a load, C ₁ , C ₂ , C ₃ is an electrolytic Capacitor, a is the signal input terminal, b is the signal output terminal, V _cc1 is the voltage
Indicates the voltage source of V _cc1 . In FIG. 5, the output stage has a generally known class B single-ended pushable configuration. Now, in the steady operating state of this circuit, when the sine wave input signal a shown in Fig. 4 is input to the input terminal a, the sine wave output signal b shown in Fig. 4 is output to the output terminal b, but V _cc1 The upper waveform with respect to /2 is generated when the transistor Q ₁₀ is conductive, and the lower waveform is generated when the transistor Q ₁₁ is conductive. Here, when transistor Q ₁₀ is conducting, the current flowing through the emitter of transistor Q ₁₀ is
When I ₁ , the base-emitter voltage V _BEQ10 of the transistor Q ₁₀ and the voltage drop I ₁ R ₁₂ across the resistor R ₁₂ become large. Similarly, if the base-emitter voltage of transistor Q ₉ is V _BEQ9 , current I ₂ expressed by the following equation flows to the collector of transistor Q ₉ .

I ₂ = (V _BEQ10 + I ₁ R ₁₂ ) - V _BEQ9 /R ₁₁ ... Now, when the current I ₂ flows, h _FE of transistor Q ₆ is sufficiently large due to the mirror circuit of diode D ₆ and transistor Q ₆ . Considering this, a current I ₂ flows through the collector of transistor Q ₆ . At this time, a voltage drop of (I ₂ R ₁₀ ) occurs at point H, but at the same time, as shown above, output terminal b shows the upper waveform, so the potential at point H is changed to the potential at the output terminal.
Always keep it below Vb, i.e. I ₂ R ₁₀
By adjusting the resistors R ₁₀ , R ₁₁ , and R ₁₂ so that <Vb+V _BEQ5 , the emitter of transistor Q ₅ , that is, output terminal b, and the base of transistor Q ₅ , that is,
Since the potential at point H is always reverse biased,
This protection circuit does not operate during normal steady operation.

Now, if an abnormal state occurs in which the output terminal b comes into contact with the negative terminal (-terminal) of the power supply, the output terminal b becomes the lowest potential and the upper Darlington connected transistors Q ₇ and Q ₁₀ absorb the voltage drop of the diode D ₁ .
V _D1 and the base-emitter voltage of transistor Q ₃ is V _BEQ3 , then the current I ₀ = {(V _cc1 − V _D1 /R ₇ +R ₈ ×R ₇ + V _D1 )−V _BEQ3 } /R ₉ . A large current begins to flow through transistor _Q10 as it is continuously driven. At the same time, a current I ₃ proportional to this large current flows through the collector of transistor Q ₉ , and a mirror circuit of diode D ₆ and transistor Q ₆ causes transistor Q _{6 to}
When h _FE is large enough, a current I ₃ flows in the collector,
A voltage drop occurs across the resistor R ₁₀ and diodes D ₅ and D ₇ . Then, a forward bias voltage is applied between the base and emitter of transistor _{Q5 .}
operates and the collector current increases the voltage drop across resistor _R9 , rendering transistor _Q3 inoperable,
Cut off the base drive current to transistor _Q7 . Therefore, the base drive current of the final stage transistor _Q10 is also cut off, and the transistor _Q10 is not operated. In this way, destruction of transistor _Q10 due to abnormally large current is prevented. That is, when the current I ₂ flowing through the transistor Q ₆ depending on the current of the transistor Q ₁₀ becomes I ₂ R ₁₀ +V _D5 >Vb + V _BEQ5 , the transistor Q ₅ operates and protects the transistor Q ₁₀ . Furthermore, in such an abnormal state where output terminal b contacts the negative terminal (-terminal) of the power supply, the voltage V _cc1 is connected to the Zener diode.
If high enough to make ZD ₁ conductive, transistor Q ₁₂ receives the aforementioned current I ₂ = {(V _BEQ10 +
Collector current I ₃ proportional to I ₁ R ₁₂ ) − V _BEQ9 }/R ₁₁
flows through resistance R ₁₀ and diode D ₅ (I ₂ + I ₃ ).
This causes a voltage drop. Diode at this time
If the voltage drop that occurs across D ₅ is V _D5 ', then (I ₂ + I ₃ )
When R ₁₀ +V _D5 ′ > Vb + V _BEQ5 , transistor Q ₅ operates and protects transistor Q ₁₀ . Therefore, if the voltage source V _cc1 is high during the above abnormality, the transistor Q ₅ operates when I ₂ is small,
Increase the protection of transistor Q ₁₀ . In this manner, during the abnormality, the transistor _Q5 operates depending on the relationship between the current flowing through the transistor _Q10 and the collector-emitter voltage applied to the transistor _Q10 during the abnormality. That is, the level at which transistor _Q10 is protected is determined. that's all,
By connecting the protection circuit according to the present invention, it is possible to prevent the transistor from being destroyed in an abnormal state where the output terminal of the amplifier circuit comes into contact with one end of the power supply, and even when the power supply voltage is high, the protection function can be effectively operated to maintain normal operation. This makes it possible to effectively utilize the safe operating area of the transistor.

[Brief explanation of drawings]

Figure 1 is a circuit diagram of a conventional circuit without a protection circuit, Figure 2 is a circuit diagram showing the principle of the present invention,
FIG. 3 is a circuit diagram of one embodiment of the present invention, FIG. 4 is an input/output waveform diagram showing the operation of the circuits of FIGS. 3 and 5, and FIG. 5 is a circuit diagram of another embodiment of the present invention. FIG. Q ₁ ,…, Q ₁₂ , Q ₂₁ ,…, Q ₂₅ are transistors,
D ₁ ,…, D ₇ , D ₂₁ ,…, D ₂₃ are diodes, ZD ₁
are Zener diodes, R ₁ ,…, R ₁₃ , R ₂₁ ,…,
R ₂₃ is a resistor, C ₁ ,..., C ₃ are electrolytic capacitors, R _L is a load, I _B , I _p are constant current sources, V _cc1 , V _cc2 are voltage sources,
a,...,g indicate terminals.

Claims (1)

[Claims] 1: first and second potential supply terminals, a signal output terminal, a base to which an input signal is supplied, an emitter that is DC-connected to the signal output terminal, and a collector that is DC-connected to the first potential supply terminal. a first transistor having a first transistor, a first means for generating at an output terminal a first current corresponding to the current flowing through the first transistor, an output terminal of the first means and the second potential supply terminal; a second means coupled between the second means for generating a voltage corresponding to the first current with reference to the potential of the second potential supply terminal; and a second means for receiving the voltage generated by the second means. a second transistor having a base and an emitter DC-connected to the signal output terminal and limiting the base current of the first transistor by a collector output when the transistor becomes conductive; voltage drop means connected between the output of the means and said second means; a third transistor having a base-emitter path connected in parallel to said voltage drop means; and a collector of said third transistor. and switching means connected between the first potential supply terminal and the first potential supply terminal, the switching means being electrically conductive when the voltage between the first and second potential supply terminals is equal to or higher than a predetermined value, and the switching means is connected between the first potential supply terminal and the first potential supply terminal. A protection circuit characterized in that when the means is conductive, the third transistor supplies a second current corresponding to the first current to the second means.