JPH06100940B2 - DC stabilized power supply circuit - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a stabilized DC power supply circuit, and more specifically, when a load on the output side is short-circuited, the outflow current is limited to form an IC (integration). IC that can protect the built-in circuit
DC stabilized power supply circuit.

[Prior Art] A conventional DC stabilized power supply circuit used as a three-terminal regulator in the form of an IC is a differential amplifier circuit (or an operational amplifier, and the operational amplifier is included in the differential amplifier circuit. And a constant current circuit such as a current booster circuit.

[Problems to be Solved] Generally, in the IC-type three-terminal regulator having the above-described configuration, it is preferable that the minimum input / output potential difference between the input voltage on the power supply side and the stabilized output voltage is small. In order to protect the IC from a short circuit on the output side, a protection resistor is inserted in series between the output terminal of the current booster circuit and the power supply line, which limits the output current and prevents a large current from flowing to the IC. So that the circuit is protected.

As a result, the IC three-terminal regulator has a drawback that the minimum difference between the input voltage and the output voltage becomes large. Also, IC
In this case, the current limit value fluctuates due to fluctuations in the protection resistance value, etc., and it is necessary to devise a circuit to form a layout that does not cause such fluctuations.

The present invention solves such a problem of the conventional technique, can suppress the minimum difference between the input voltage and the output voltage to a small value, and limits the output without variations due to the ground short circuit of the output terminal. It is an object of the present invention to provide a stabilized DC power supply circuit.

[Means for Solving the Problems] A configuration of the present invention for achieving such an object is a direct connection between a differential amplifier circuit having a constant current circuit section and a differential circuit section, and an output of the differential circuit section. A DC amplification circuit having a DC current amplification circuit that receives this output and amplifies the current, and outputs a part or all of the voltage generated in the load of the DC current amplification circuit to one input of the differential circuit section. In a stabilized direct current power supply circuit that feeds back to the other input and applies a constant voltage to the other input to output one end of the load to a constant reference voltage, the base is connected to one end of the load, and the emitter and collector have a differential circuit section. Is connected to the supply side to which the operating current is supplied and the sink side that sinks the operating current from the differential circuit section, respectively, and when one end of the load drops near the short-circuited voltage or drops below a predetermined voltage corresponding to it. From "OFF" state to "ON""Transistor that puts the supply side and the sink side in a short-circuited state to stop the operation of the differential circuit section, and" OFF "at startup
And a start-up circuit for applying a voltage to be applied to one end of the load.

[Operation] When the load side is short-circuited or short-circuited in this way, the switch circuit is turned “ON” to short-circuit both ends of the differential circuit section, thereby inputting to the current amplification circuit side. The value of the output signal can be suppressed and the output current of the DC stabilized power supply circuit can be controlled so as not to be generated.

Further, the transistor is switched so that the operating current supply side and the operating current sink side of the differential circuit section are directly short-circuited when a short circuit or the like is detected, and it is directly controlled by the control signal from the output terminal of the load. Since it is configured to operate, the response when the load side is short-circuited is fast, and there is almost no malfunction. Therefore, the circuit on the load side is more reliably prevented from being destroyed than that of the conventional one.

As a result, it becomes unnecessary to insert a protection resistor in the output stage, and the minimum difference between the input voltage and the output voltage can be suppressed to a small value. In addition, it is possible to make a circuit that limits the output current without variation even if the output terminal is ground shorted, and even if the load side is short-circuited, the output current of the DC stabilized power supply circuit will be limited, and peripheral circuits and The IC is never destroyed.

[Embodiment] An embodiment of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a block diagram of a DC stabilized power supply circuit to which the present invention is applied, and FIG. 2 is a circuit diagram of a specific example thereof.

In FIG. 1, 1 is an IC three-terminal regulator, which has an input power terminal (Vcc) 2a and a ground terminal (GND) 2b,
It also has an output terminal (OUT) 2c. Note that 3a
Is the power supply line connected to the input power supply terminal 2a, and 3b
Is a ground line connected to the ground terminal 2b.

Reference numeral 4 denotes a differential amplifier circuit section, which includes a differential circuit section 4a and a constant current source circuit 4b (current value I) that supplies a constant current to the differential circuit section 4a. Reference numeral 5 is a current booster circuit as a DC current amplifier circuit that receives the output signal of the differential amplifier circuit 4, and has a transistor Tr ₁ . Transistor Tr
₁ , the collector is the power line 3a (input voltage terminal 2a)
Connected to the output of the differential circuit section 4a and receiving the output signal at its base, and between the emitter and the ground line 3 (ground terminal 2b), feedback resistors R ₁ and R are connected.
₂ is inserted. The voltage at the connection point of the feedback resistors R ₁ and R ₂ is fed back to the (−) side input of the differential circuit section 4a.

Reference numeral 6 is a reference voltage generating circuit, which supplies a constant voltage as a control reference to the (+) side input of the differential circuit section 4a.

Reference numeral 7 is a switch circuit inserted in parallel with the differential circuit section 4a, and has a transistor Tr ₂ which is set to an "OFF" state in a normal operation state. The emitter of the transistor Tr ₂ is a connection point on the constant current source circuit section 4b side of the differential circuit section 4a.
4c, the collector of which is connected to the output terminal 2c, receives the emitter output of the transistor Tr ₁ at its base, and the emitter is connected to the ground line 3 (ground terminal).
2b) is connected.

Reference numeral 8 denotes a starter circuit inserted between the output terminal 2c and the ground line 3, which is a switch circuit 8a and a reference voltage of 1Vf or more connected in series with it (however, 1Vf is a voltage between the base and the emitter). And a constant voltage source 8b that generates a forward drop voltage.

Here, considering the conditions for setting the transistor Tr ₂ to the “OFF” state, the differential circuit section 4a is always composed of one or more transistors and operates unless a voltage of 1 Vf or more is applied. do not do. On the other hand, because the transistor Tr ₂ is in the "OFF" state in the steady state, the connection point 4c
And the potential difference between the output terminal 2c and 1Vf or more,
In addition, the output terminal 2c side must be set to a high potential.

Therefore, in the steady state, the voltage at the connection point 4c needs to be at least 1 Vf or more. Under these conditions, the transistor Tr ₂ will be "OFF" in normal operation.
Maintained at. However, under such a condition, at the time of startup, the output terminal 2c is at the ground potential, so that the transistor Tr ₂ is in the “ON” state, and the circuit does not operate at the time of startup. To avoid this, the starting circuit 8 is provided.

Starting circuit 8 is for the switch circuit 8a is in "ON" keep transistor Tr ₂ reverse bias to it to "OFF" state at startup. If this transistor is in the "OFF" state at start-up, the regulator circuit that follows is composed of a differential amplifier circuit, and the transistor Tr ₁ is directly connected to this differential amplifier circuit. The potential relationship in the state is maintained as it is, and the transistor Tr ₂ is "OFF".
The transistor is allowed to generate a regular regulator output voltage in the "OFF" state while maintaining a steady state.

That is, in order to set the transistor Tr ₂ to the “OFF” state, it is sufficient that the potential of the output terminal 2c is set higher than the potential of the connection terminal 4c in the normal operating state. Since 1 Vf or more is required to operate the transistor of the differential circuit section 4a of the dynamic amplification circuit 4, the potential of the connection terminal 4c in the steady state is 2 Vf or more. Under this condition, if a short circuit occurs in the load connected to the output terminal 2c, or if a short circuit occurs, and the potential of the output terminal 2c drops to 1 Vf or less, the potential of the connection terminal 4c is 2 Vf or more. The transistor Tr ₂ is in the “ON” state at this time.

When the transistor Tr ₂ is in the “ON” state, both terminals of the differential circuit section 4a are short-circuited, so the voltage applied to it is 1 Vf
Falls below. Thus, the differential circuit section 4a stops the operation at this point, the output is not generated, almost no input current of the transistor Tr ₁ of the current booster circuit 5, there is no current flowing through the output terminal 2c.

FIG. 2 is an example of a specific circuit thereof, which includes a regulator amplifier including a differential amplifier circuit 10 and a current booster circuit 11, a switch circuit 12, a starting circuit 13, and a reference voltage generating circuit 14.

Switch circuit 12 includes transistors Q _8, the reference voltage generating circuit 14 is a power supply for generating a reference voltage 1.2V applied to one input of the differential amplifier circuit. Reference numeral 15 is a power supply line to which the power supply Vcc is applied, 16 is a ground line, and 17 is a regulator output terminal. Here, the power supply voltage Vcc is set to a voltage of 5 Vf or higher. Further, the regulator output in the steady state at this time is set to 3 Vf or more.

The differential amplifier circuit 10 has a differential amplifier 10a and a constant current source 10b (its current value I) of the differential amplifier 10a inside, and as a load of the current booster circuit 11, the feedback resistors R ₁ , R. ₂ series circuit is inserted.

PNP type transistors Q ₁ and Q ₂ are driving transistors in which constant current circuits 10c and 10d are inserted on the emitter side, respectively, and a reference voltage of 1.2V is applied to the base of the transistor Q _{1 so} that the transistor Q ₂ The base receives the voltage fed back from the output side of the current booster circuit 11. The PNP transistors Q ₃ and Q ₄ are a pair of transistors that form a differential amplifier 10a whose bases are coupled to the emitters of the transistors Q ₁ and Q ₂ .

Transistors Q ₁₁ , Q ₁₂ , and Q ₁₃ are transistors that form the circuit of drive stage 11b of current booster circuit 11,
For the transistors Q ₁₁ and Q ₁₂ , the resistor R ₃
It is a circuit connected in Darlington type, inserted as a bias resistor in the base of ₁₂ , and is an NPN type transistor that drives the transistor Q ₁₃ . The base of the transistor Q _{11 in} the preceding stage is driven by receiving the output from the collector of the transistor Q _{4 in} the amplification stage of the differential amplifier circuit 10.
Then, the PNP transistor Q ₁₃ is driven through its base via the collector of the transistor Q _{12 in} the subsequent stage and the voltage divider circuit of the resistors R ₆ and R ₇ connected in series to this. The collector of the transistor Q ₁₃ is the NPN of the current output stage 11b.
Type transistor Q ₅ is connected to the base and drives it.

The emitter of the transistor Q ₅ is connected to the output terminal 17,
Further, it is grounded via the feedback resistors R ₁ and R ₂ , the collector is connected to the power supply line 15, and the transistor Q ₅ is connected to the output terminal 17 without a protection resistor. A bias resistor R ₅ is inserted between the base and the emitter.

Here, the terminal voltage of the feedback resistor R ₂ is fed back to the base of the transistor Q ₂ of the differential amplifier circuit 10, so that the terminal voltage generated in the feedback resistor R ₂ matches the reference voltage 1.2V. The differential amplifier circuit 10 operates to generate a constant voltage V ₀ at the output terminal 17.

This constant voltage V ₀ is V ₀ = (r ₁ + r ₂ ) · Vref (1.2V) / r ₂ . However, r ₁ is the resistance value of the feedback resistor R ₁ , and r ₂ is the resistance value of the feedback resistor R ₂ .

The starting circuit 13 is a constant current source circuit connected to the power line 15.
And 13a, consisting of a constant voltage generating circuit 13a composed of five transistors D ₁ to D ₅ of connected diodes connected in series between the ground line 16 which includes a switch circuit 13b which is driven thereby. The switch circuit 13b includes a transistor Q ₆ which are current-mirror connected to the base of the transistor D _1, which is diode-connected, the bias resistor R ₈ inserted between the collector side and the power supply line 15 of the transistor Q _6,
It comprises a protection resistor R ₉ inserted on the emitter side thereof, and a diode-connected transistor D ₆ which receives the output on the emitter side of the transistor Q ₆ via the protection resistor R ₉ .

This starting circuit 13 is such that, at the time of starting when the power supply voltage is supplied, the transistor Q ₆ is driven by the diode-connected transistor D ₁ to be in the “ON” state, and the diode-connected transistor D _{6 has} a voltage of 1 Vf. The above voltage, in this example, (3Vf / R ₉ ) × (R ₁ × R ₂ ) is generated and applied to the base of the transistor Q ₈ of the switch circuit 12. Therefore, when starting the regulator circuit has its base the voltage of the transistor Q ₈ of the switch circuit 12 (3Vf /
Receive R ₉ ) × (R ₁ + R ₂ ). On the other hand, the voltage of the constant current source circuit 10b of the transistor Q ₈ is in a steady state, the reference voltage generating circuit 14 is not made from it is a 1.2V (1.2V + 2Vf) above, the regulator output voltage at the output terminal 17 , 3Vf
It is set above. Thus, in a steady state, the transistor Q ₈ is in "OFF" state.

Here, when the output terminal 17 which is the output of the regulator amplifier is short-circuited, this terminal falls to the ground, so that the transistor Q ₈ that is "OFF" in the normal state is "ON" and the constant current source 10b it absorbs a current value I, the entire regulator amplifier is turned "OFF" state by the differential circuit part 4a "OFF", no longer supply current from the transistor Q _5. At this time, the current flowing from the output terminal 17 to the ground is the transistor Q ₆ , the protection resistor R ₉ , and the diode-connected transistor D ₆
Flowing through the transistor, and its current is determined by the sum of the resistance values of the internal resistance of these transistors and the protection resistance R ₉ , and is a value limited by the resistance value of these sums. The condition that the transistor Q ₈ as the switch circuit 12 turns “ON” is when the output terminal 17 becomes smaller than 1 Vf below the ground.

On the other hand, at the time of start-up, since the regulator amplifier is in the “OFF” state and the output terminal 17 is at the ground potential, the transistor Q ₈ remains “ON”. By applying a voltage of 1 Vf or more, it is possible to maintain the "OFF" state and generate the regulator voltage.

Note that, here, the protection resistor R ₉ determines the amount of current flowing into the output load at the time of startup. Also, the transistor Q ₁₃
Prevent a large current from flowing to the output terminal 17 when the resistance R ₇ connected to the base of the output terminal 17 also becomes abnormal during operation in the steady state and the output terminal 17 is in a short-circuit state where it does not fall below 1 Vf. It plays the role of a current limiting resistor.

As described above, in the embodiment, the power supply voltage is + Vcc and the (+) power supply is used for operation. However, the PNP transistor is an NPN transistor, and the NPN transistor is a PNP transistor.
Of course, each type transistor may be replaced and driven by a (-) power source.

Further, the number of coupling stages of the transistors of the drive stage of the current booster circuit may be one stage or two stages, and is not limited to the number of stages, and a plurality of stages may be connected. The same applies to the configuration of the transistors of the differential amplifier circuit.

[Effects of the Invention] As described above, according to the present invention, when the load side is short-circuited or at the time of short-circuiting, the switch circuit is turned "ON" to short-circuit both ends of the differential circuit section. Suppresses the value of the output signal of the differential amplifier circuit input to the side,
The output current of the DC stabilized power supply circuit can be controlled so as not to be generated.

Further, the transistor is switched so that the operating current supply side and the operating current sink side of the differential circuit section are directly short-circuited when a short circuit or the like is detected, and it is directly controlled by the control signal from the output terminal of the load. Since it is configured to operate, the response when the load side is short-circuited is fast, and there is almost no malfunction. Therefore, the circuit on the load side is more reliably prevented from being destroyed than that of the conventional one.

As a result, it becomes unnecessary to insert a protection resistor in the output stage, and the minimum difference between the input voltage and the output voltage can be suppressed to a small value. Also, it is possible to make the circuit that the variation of the limiting current with respect to the maximum output current is small, and even if the load side is short-circuited, the output current of the DC stabilized power supply circuit is limited, and the peripheral circuit and IC are destroyed due to heat generation. It will not be done.

[Brief description of drawings]

FIG. 1 is a block diagram of a DC stabilized power supply circuit to which the present invention is applied, and FIG. 2 is a circuit diagram of a specific example thereof. 1 …… Three-terminal regulator, 2a …… Input power supply terminal (Vc
c), 2b …… Ground terminal (GND), 2c …… Output terminal (OU
T), 3a ... Power line, 3b ... Ground line, 4 ...
… Differential amplifier circuit, 4a …… Differential circuit section, 4b …… Constant current source circuit section, 5 …… Current booster circuit, 6 …… Reference voltage generation circuit, 7 …… Switch circuit.

Claims (1)

[Claims] 1. A differential amplifier circuit having a constant current circuit section and a differential circuit section, and a direct current amplifier circuit which is directly connected to the output of the differential circuit section and which receives the output and current-amplifies it. A direct current amplifier circuit having a part of or all of the voltage generated in the load of the direct current amplifier circuit is fed back to one input of the differential circuit section, and a constant voltage is applied to the other input of the load. In a stabilized direct current power supply circuit having one end as an output of a constant reference voltage, a base is connected to one end of a load, and an emitter and a collector supply an operating current to the differential circuit section and a supply side and the operating current. Connected to the sink side for sinking from the differential circuit section, respectively, and when one end of the load drops near the voltage in the short-circuited state or drops below a predetermined voltage corresponding to the short-circuited state, the state changes from “OFF” to “ON”. Becoming the supply side and the thin DC stability, comprising a transistor that short-circuits the power supply side to stop the operation of the differential circuit section, and a starter circuit that applies a voltage to the "OFF" state to one end of the load at start-up. Power circuit.