JPH0635538Y2 - Voltage amplification circuit with current limiting circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION "Industrial application field" The present invention relates to a voltage amplification circuit with a current limiting circuit used as a power supply for supplying a stabilized DC voltage to various devices.

“Prior Art” FIG. 2 shows the configuration of a conventional voltage amplifier circuit with a current limiting circuit.

In the figure, A ₁ is a preamplifier, A ₂ is a voltage amplifier, and R _L is the resistance of the power supply circuit of various devices as a load.

Preamplifier A ₁ and voltage amplifier A ₂ is a voltage E _i of the voltage source 1 through the input resistor 2 from the voltage source 1 to the inverting input terminal of the preamplifier A ₁ operational amplifier of the differential input type is used, respectively Given.

The input resistor 2, the resistor 3 and the capacitor 4 connected to the feedback circuit form a circuit for performing the entire phase compensation.

The gain A _{2g of the} voltage amplifier A ₂ is defined by the input resistor 5 and the feedback resistor 6. A feedback circuit 7 is connected between the output of the voltage amplifier A ₂ and the non-inverting input terminal of the preamplifier A ₁ . The feedback circuit 7 is a preamplifier and the output terminal of the voltage amplifier A _2.
A resistor 7A connected between the non-inverting input terminal of A _{1 and} the non-inverting input terminal of the preamplifier A ₁ and a resistor 7B connected between the common potential point.

The feedback circuit 7 defines the overall gain. That is, the relationship between the input voltage E _i and the output voltage V _o is expressed by the following equation, where the resistance values of the resistors 7A and 7B forming the feedback circuit 7 are R ₆ and R ₅ , respectively. Becomes

FIG. 3 shows the internal structure of the voltage amplifier A ₂ . Transistor
A differential input circuit is composed of Q ₁ and Q ₂ , and a transistor Q ₃
The voltage is amplified by and the power is amplified by the output transistors Q ₄ and Q ₇ .
The output voltage V _o is applied to the load resistance R _L.

The transistors Q ₅ and Q ₆ form a current limiting circuit 10 for the output transistors Q ₄ and Q ₇ . That is, the resistor 8 or 9 detects that the current flowing through the output transistors Q ₄ and Q ₇ is excessive, and the detection signal turns on the transistor Q ₅ or Q ₆ to flow into the output transistor Q ₄ or Q ₇ . It bypasses the base current, which limits the collector current of the output transistor Q ₄ or Q ₇ .

“Problems to be solved by the device” When an overcurrent flows in the output transistor Q ₄ due to a sudden decrease in the value of the load resistance R _L when a positive voltage is output to the output voltage V _o , The overcurrent is detected by the resistor 8, the transistor Q ₅ is turned on, and the current limiting operation state is set.

When the transistor Q ₅ turns on and enters the current limiting operation state, the output voltage V _o drops to V _{LM as shown} in FIG.
When the output voltage V _o drops to the voltage V _LM , the preamplifier A ₁ is informed by the feedback circuit 7 that the output voltage V _o has dropped and operates in a direction to return the output voltage to V _o . Therefore, the output voltage of the preamplifier A ₁ drops to around the negative power supply voltage −V _SS , and the voltage is input to the voltage amplifier A ₂ . As a result, both the preamplifier A ₁ and the voltage amplifier A ₂ are saturated.

If the value of the load resistance R _L suddenly returns to the original value in this state, the transistor Q ₅ is returned to the off state. At this time, since the output voltage of the preamplifier A ₁ is in the vicinity of −V _SS , the output voltage of the voltage amplifier A ₂ rises to the vicinity of the positive power supply voltage V _DD as shown at time points cd in FIG. This voltage increase continues until the whole loop of the preamplifier A ₁ and the voltage amplifier A ₂ starts operating (point e).

Even when the output voltage is negative voltage −V ₀ , the value of the load resistance R _L suddenly decreases and an overcurrent flows through the output transistor Q ₇ , which turns on the transistor Q ₆ and enters the current limiting operation state. And the output voltage −V ₀ is −V _LM | −V as shown in FIG.
₀ |> | -V _LM | (section gh in FIG. 5).

When the value of the load resistance R _L suddenly returns to the original value in this current limit state, the transistor Q ₆ returns to off. At this time, since the output voltage of the preamplifier A ₁ has risen to around + V _DD , the output voltage of the voltage amplifier A ₂ is -V as shown in FIG.
_It decreases to around _SS .

This voltage drop continues until the entire loop of the amplifiers A ₁ and A ₂ starts operating (point j).

As described above, in the conventional voltage amplification circuit with current limiting circuit, the load condition returns to the original state or the value of the load resistance R _L increases in the current limiting operation state, and the transistor Q ₅ or When Q ₆ is turned back off, an overshoot or undershoot occurs in the output voltage of the voltage amplifier A ₂ . This overshoot or undershoot may damage the elements of the electronic circuit network connected as a load.

An object of the present invention is to provide a voltage amplifier with a current limiting circuit that can suppress overshoot or undershoot that occurs when canceling the current limiting operation and prevent damage to the load.

"Means for Solving the Problem" In this invention, in a voltage amplifier with a current limiting circuit, a detection circuit for detecting that the current limiting circuit has operated, and a detection circuit for detecting the start of operation of the current limiting circuit, the detection circuit A saturation prevention circuit for preventing the saturation of the preamplifier by the output is provided.

With this configuration, the preamplifier and the voltage amplifier do not saturate even when the current limit circuit operates, and as a result, the load returns to the normal value and the current limit circuit does not operate in the current limit operating state. Then, the occurrence of overshoot or undershoot in the output voltage of the voltage amplifier is prevented.

Therefore, it is possible to provide the voltage amplifier with the current limiting circuit which does not damage the load by the current limiting operation.

"Embodiment" FIG. 1 shows an embodiment of the present invention. 1 in FIG.
Is a voltage source, A ₁ is a preamplifier, A ₂ is a voltage amplifier incorporating a current limiting circuit, R _L is a load resistor, and 7 is a feedback circuit, which is the same as the conventional structure described above.

The characteristic structure of this invention is that the input point B of the voltage amplifier A ₂ is
Detection circuit that compares the voltage V _B of the circuit with the set voltages V _C and V _D, and detects that the current limiting circuit has operated based on the comparison result.
11 and the detection output of the detection circuit 11 causes the preamplifier A ₁
And a saturation prevention circuit 12 for preventing the voltage amplifier A _{2 from} being saturated.

In this example, the detection circuit 11 and the saturation prevention circuit 12 respond to the current limiting operation on both the positive side and the negative side by detecting circuits 11A and 11A.
The result of providing B and the saturation prevention circuits 12A and 12B is shown.

That is, 11A is a detection circuit that detects that the current limiting circuit has operated when the output voltage V ₀ of the voltage amplifier A ₂ is a positive voltage, 11A
B indicates a detection circuit for detecting that the current limiting circuit operates when the output voltage V ₀ of the voltage amplifier A ₂ is a negative voltage.

The detection circuits 11A and 11B have exactly the same structure. The different point is that the voltage applied to the voltage dividing circuit constituting the voltage setting circuit is −V _SS in the detection circuit 11A, whereas + V _DD is applied in the detection circuit 11B. Due to this difference, the comparison voltage applied to the voltage comparator A ₃ forming the detection circuit 11A becomes −V _C ,
The comparison voltage applied to the voltage comparator A ₄ forming the detection circuit 11B is + V _D. These comparison voltages −V _C and + V _D are applied to the inverting input terminals of the voltage comparators A ₃ and A ₄ .

The non-inverting input terminals of the voltage comparators A ₃ and A ₄ are commonly connected and connected to the inverting input terminal (point B) of the voltage amplifier A ₂ , and when the current limiting circuit operates, the potential V _{B at} this point _B is Detect the state of being biased to the negative or positive side.

Saturated blocking circuit 12A, the input point of 12B preamplifier A _1, that is a diode D _3, D ₄ connected between the output terminal of the A point and each voltage comparator A _3, A _4, the diode D ₃ , D ₄ and resistors 13A and 13B connected in series.

The diode D ₃ has an anode connected to the point A and a cathode connected to the output terminal side of the voltage comparator A ₃ . Also diode D ₄
Connects the anode to the output terminal side of the voltage comparator A ₄ and the cathode to the point A.

With this configuration, the potential at the point B is normally maintained at 0V, which is equal to the common potential. Therefore, during normal operation, the reference voltage −V _C is applied to the inverting input terminal of the voltage comparator.
A ₃ outputs a positive voltage, and the voltage comparator A ₄ supplied with the comparison voltage + V _D outputs a negative voltage. This results in diodes D ₃ and D ₄
Are both turned off and kept disconnected from the preamplifier A ₁ .

When the output voltage V ₀ is set to a positive voltage,
When the voltage amplifier A ₂ enters the current limiting operation, the input voltage of the preamplifier A ₁ becomes insufficient because the feedback voltage fed back through the feedback circuit 7 is insufficient for the voltage E _i given from the voltage source 1 to the preamplifier A _1. Becomes an unbalanced state in which the inverting input terminal side becomes higher.

Due to this unbalanced input state, the preamplifier A ₁ outputs a negative voltage and pulls in the potential V _B at the point _B in the negative direction. Detection circuit 11A, 11
Comparison voltage -V _C and + V _D is set to B is set to a very small voltage close to the common potential. By setting in this way, when the potential V _{B at the} point _B is pulled in the negative direction, the comparison voltage −
V _C can be easily exceeded and the current limiting operation can be reliably detected.

When the potential V B at the point _B exceeds the comparison voltage −V _C and is biased in the negative direction, the output voltage of the voltage comparator A ₃ is inverted to the negative voltage. By inverting the output voltage of the voltage comparator A _{3 to} a negative voltage, the diode D ₃ forming the saturation prevention circuit 12A is turned on,
Intake current from point A.

This current sink prevents preamplifier A ₁ from reaching saturation. That is, when the diode D ₃ is turned on, the preamplifier A ₁ , the detection circuit 11A, and the saturation prevention circuit 12A form a negative feedback loop, and this negative feedback loop operates so that V _B = −V _C Suppresses saturation of amplifier A ₁ . Since the saturation of the preamplifier A ₁ is suppressed, the potential at the point B is prevented from being largely biased in the negative direction, so that the saturation of the voltage amplifier A ₂ is also suppressed.

In this state, I _S : Current flowing through the load resistance R _L when the current control circuit of the voltage amplifier A ₂ is operating V _B : Potential at B point V _C : Potential at C point V _E : Potential at E point (A ₁ output ) R _3: the resistance of the input resistor 5 of the voltage amplifier a ₂ R _4: the resistance value R ₁₄ of the feedback resistor 6 of the voltage amplifier a _2, R _15: a comparison voltage divider for partial generation provided to the detection circuit 11A The resistance value of the resistor is shown.

If the value of the load resistance R _L is returned to the normal value in this state, the output voltage V ₀ of the voltage amplifier A ₂ rises to return to the original voltage. The rise in the output voltage V ₀ is fed back to the point B through the feedback resistor 6, and the potential at the point B rises. By this feedback operation, the potential at point B rises to the voltage 0V before the current limiting operation.

The output voltage V ′ ₀ of the voltage amplifier A ₂ at this time is Becomes

Therefore, the overshoot generated at the output of the voltage amplifier A ₂
V _0V is Can be suppressed to.

When the potential at the point B returns to the common potential 0V, the output voltage of the voltage comparator A ₃ that constitutes the detection circuit 11A is inverted to a positive voltage.

As a result, the preamplifier A ₁ , the detection circuit 11A, and the saturation prevention circuit 1
The negative feedback loop composed of 2A is cut open and eliminated. At the same time, the potential at the point A returns to the potential before the current limiting operation, the feedback voltage by the feedback resistor 7A also returns to the normal value, and the output voltage V ₀ also returns to the original potential.

Next, when the current limiting operation is started while the output voltage V ₀ of the voltage amplifier A ₂ is outputting a negative voltage, the potential at the point B is fed back through the feedback resistor 6 of the voltage amplifier A _2. In addition to the feedback voltage changing from the negative potential side toward the common potential, the output voltage of the preamplifier A ₁ tends to saturate toward the positive V _DD .

Therefore, the potential V B at the point _B becomes a positive potential. Detection circuit 11B
Since the comparison voltage + V _D set to 1 is selected as a voltage very close to the common potential 0 V, the potential at the point B can easily exceed the comparison voltage + V _D. As a result, the output voltage of the voltage comparator A ₄ is inverted to a positive voltage, and the voltage is biased to reach + V _DD .

As a result, the diode D ₄ forming the saturation prevention circuit 12B is turned on, the detection circuit 11B and the saturation prevention circuit 12B are connected to the preamplifier A ₁ , and a negative feedback loop is formed.

The formation of this negative feedback loop prevents the preamplifier A ₁ from reaching saturation.

In this state V _D : Potential at point _D R ₁₈ , R ₁₉ : The resistance value of the resistor that constitutes the voltage dividing circuit is satisfied.

Next, when the current limiting operation of the voltage amplifier A ₂ is released, the output voltage V ₀ decreases in the negative direction due to the operation of the voltage amplifier A ₂ .
Trying to return to the original voltage.

This change in the output voltage V ₀ is fed back to the inverting input terminal of the voltage amplifier A ₂ through the feedback resistor 6, so that the potential V _{B at the} point _B decreases in the negative direction and returns to the original common potential 0V.

The undershoot V _0V generated at the output of the voltage amplifier A _{2 at} this time is given by the fifth equation.

[Advantage of Device] As described above, according to this device, the current limiting circuit operates, and the overshoot and the undershoot that occur when the current limiting operation is released can be suppressed to a small voltage. Even if the load resistance R _L fluctuates due to the abnormal condition, an overshoot or undershoot having a large peak value does not occur in the power supply voltage supplied to the load.

Therefore, even if a device such as a semiconductor integrated circuit that uses an element that is weak against overvoltage is connected as a load, damage to the load can be avoided, and a highly reliable device as a whole can be configured.

In the above description, as an example of the current limiting circuit, a current limiting circuit of a type in which the current flowing through the output transistor is detected by the resistor, the transistor is turned on by the detection signal, and the current flowing through the output transistor is limited by this transistor is illustrated. However, it can be easily understood that the present invention can be applied not only to this type of current limiting circuit but also to other various types of current limiting circuits.

Further, in the above description, an example in which two sets of the detection circuit and the saturation prevention circuit are provided for the positive electrode and the negative electrode has been described. However, when the output voltage is used only in one polarity, it corresponds to the polarity of the output voltage. It can be easily understood that it is sufficient to provide one set of the detection circuit and the saturation prevention circuit.

[Brief description of drawings]

FIG. 1 is a connection diagram showing an embodiment of the present invention, FIG. 2 is a connection diagram for explaining a conventional technique, and FIG. 3 is a connection diagram for explaining a concrete example of a current limiting circuit. FIG. 4 and FIG. 5 are waveform charts for explaining the inconvenience of the conventional technique. 1: Voltage source, A ₁ : Preamplifier, A ₂ : Voltage amplifier with current limiting circuit, 7: Feedback circuit, 11: Detection circuit, 12: Saturation prevention circuit

Claims (1)

[Scope of utility model registration request] 1. A preamplifier, which is composed of a differential input type operational amplifier, is provided with a constant DC voltage as a reference of a constant voltage to be applied to a load at one input terminal, and a preamplifier is provided after the preamplifier. In a voltage amplifier circuit with a current limiting circuit, comprising a voltage amplifier connected to the output stage to which a current limiting circuit is added, and a feedback circuit for feeding back the output voltage of the voltage amplifier to the other input terminal of the preamplifier, A detection circuit that compares the voltage input to the voltage amplifier with a preset setting voltage and detects that the current limiting circuit has operated when the input voltage exceeds the setting voltage, and this detection circuit is the current limiting operation. And a saturation prevention circuit for preventing the saturation of the preamplifier by forming a negative feedback loop in the preamplifier by controlling the switching diode to be turned on in the state of detecting A voltage amplifier circuit with a current limiting circuit.