JP4534808B2 - Amplifier circuit with current limiter - Google Patents

Description

The present invention relates to an amplifier circuit with a current limiter that can operate quickly and has high output current stability. In particular, the present invention is used in a voltage generator, an LSI (Large Scale Integration) tester, and the like. It is related with the amplifier circuit with the current limiter which makes the value of.

  In general, an amplifier detects an output voltage and applies feedback in order to obtain an accurate gain, and corrects an error from the input voltage. However, once an overvoltage is applied, it is necessary to limit the current value of the output current in order to prevent damage to the components. For this reason, an amplifier to which a current limit function is added is required. As a document of such an amplifier circuit with a current limiter, there is one as disclosed in Patent Document 1.

Japanese Patent Laid-Open No. 07-302125

  Hereinafter, a conventional amplifier circuit with a current limiter will be described with reference to FIG. FIG. 2 is a block diagram showing an embodiment of a conventional amplifier circuit with a current limiter. The amplifier circuit 10 with a current limiter is an amplifier circuit with a current limiter that employs a feedback method, and is connected to a positive power supply VCC and a negative power supply VEE via power supply terminals P1 and P2. The input of the amplifier circuit 10 with current limiter is connected to the input voltage source 20 via the input terminal IN, and amplifies the input voltage Vi generated by the input voltage source 20 with a constant gain. Further, the output of the amplifier circuit 10 with a current limiter is connected to the load 30 via the output terminal OUT.

The current limiter 11 is built in the amplifier circuit 10 with a current limiter, and limits the output current Io to a predetermined current value or less.

Next, the operation of FIG. 2 will be described. First, the operation when the output current Io is small will be described. In this case, the current limiter 11 does not operate, and the amplifier circuit 10 with the current limiter drives the load 30 using the voltage obtained by amplifying the input voltage Vi with a constant gain as the output voltage Vo. At this time, the amplifier circuit 10 with a current limiter detects and feeds back the output voltage Vo in order to make the gain accurate, and corrects and controls an error from the input voltage Vi (feedback loop mode).

  The operation when the input voltage Vi is increased will be described. In this case, the output voltage Vo also increases as the input voltage Vi increases. The output current Io also increases in proportion to the output voltage Vo. However, when the limit current is reached, a current detection circuit (not shown) formed in the current limiter 11 switches the feedback loop mode. Then, the output of the amplifier circuit 10 with the current limiter automatically enters the constant current control mode, and the current limiter 11 operates to limit the output current. That is, when shifting from the feedback loop mode to the constant current control mode, it is necessary to switch the loop that detects the output voltage and feeds back to the input to the loop that detects and feeds back the output current.

  Next, the operation when the input voltage Vi is decreased from this state will be described. When the output current Io is less than the limit current, the current detection circuit formed in the current limiter 11 switches to the feedback loop mode, and the current limiter 11 is turned off.

  However, the conventional amplifier circuit with a current limiter has the following problems. That is, since the operation of switching the loop that detects and feeds back the output voltage to the loop that detects and feeds back the output current is required, the response time of the switching operation of the current limiter is slow. In the limit current limit mode, mode switching occurs periodically, and a complicated design that ensures phase margin in both the feedback loop mode and constant current control mode is required. Io may become unstable.

  The present invention has been made in view of these problems, and does not require a switching operation between the feedback loop mode and the constant current control mode, can operate quickly, and has a high output current stability. The purpose is to provide.

In order to achieve such a problem, the invention described in claim 1
In an amplifier circuit with a current limiter that amplifies an input voltage and applies an output voltage to a load, and limits the output current of the amplifier to a predetermined value,
A floating power supply connected between a positive power supply terminal and a negative power supply terminal of the amplifier;
A diode bridge connected to the floating power supply;
Comprising current supply means for driving the diode bridge;
When the output current reaches the current value of the current supply means due to the fluctuation of the output voltage, the current value of the output current is limited to be equal to the current value of the current supply means by the rectifying action of the diode bridge.

The invention described in claim 2 is an amplifier circuit with a current limiter according to claim 1,
The current supply means includes a first constant current source for supplying a current to the diode bridge;
And a second constant current source for supplying current from the diode bridge.

The invention described in claim 3
An amplifier for supplying an output current by applying an output voltage obtained by amplifying the input voltage to a load;
A floating power supply connected between a positive power supply terminal and a negative power supply terminal of the amplifier;
A first diode having a cathode connected to the floating power source;
A second diode having an anode connected to a connection point of the cathode of the first diode and the floating power supply;
A third diode having an anode connected to an anode of the first diode and a cathode connected to a ground terminal;
A fourth diode in which an anode is connected to a connection point between the cathode of the third diode and a ground terminal, and the cathode is connected to the cathode of the second diode;
A first constant current source for supplying a constant current to a connection point between the anode of the first diode and the anode of the third diode;
And a second constant current source for supplying a constant current from a connection point between the cathode of the second diode and the cathode of the fourth diode, and the maximum value of the output current of the amplifier output current is the first constant current source. It is limited to the current value of one constant current source, and the maximum value of the sink current of the output current of the amplifier is limited to the current value of the second constant current source.

The present invention has the following effects.
When the output current of the amplifier becomes equal to the current value of the current supply means, the current value of the output current is limited to be equal to the current value of the current supply means by the rectifying action of the diode bridge connected to a potential independent from this amplifier. Therefore, there is no switching between the feedback loop mode and the constant current control mode, and an amplifier circuit with a current limiter that can operate quickly and has high stability can be provided.

  Hereinafter, a configuration example of an amplifier circuit with a current limiter according to the present invention will be described with reference to FIG.

FIG. 1 is a block diagram showing an embodiment of an amplifier circuit with a current limiter according to the present invention. The amplifier circuit 100 with a current limiter includes an amplifier 110, floating power supplies 111 to 112, diodes 120 to 123, and constant current sources 124 to 125. The amplifier 110 has an input terminal IN connected to the input voltage source 130 and an output terminal connected to the load 140. The amplifier 110 amplifies the input voltage Vi generated by the input voltage source 130 with a constant gain and drives the load 140. The positive power supply potential V + and the negative power supply potential V− of the amplifier 110 are connected to the positive electrode of the floating power supply 111 and the negative electrode of the floating power supply 112, respectively. The grounds of these power supplies are insulated from the illustrated ground. Shall.

The diodes 120 to 123 constitute a diode bridge. The constant current source 124 is connected to the positive power supply VCC via the terminal P1, and supplies the current to the diodes 120 to 123. The constant current source 125 is connected to the negative power source VEE via the terminal P2, and is connected so as to discharge current from the diodes 120 to 123. The cathode of the diode 120 is connected to the negative electrode of the floating power source 111 and the positive electrode of the floating power source 112 at the connection point P, and the cathode of the diode 122 is grounded via the terminal P3.

Next, the operation of FIG. 1 will be described. When the input voltage Vi is input to the amplifier 110, the output voltage Vo amplified with a constant gain is output to the output terminal OUT, and an output current Io corresponding to the output voltage Vo flows through the load 140. When the input bias current of the amplifier 110 is sufficiently small, the output current Io flows through the floating power supply 111 or 112 via the power supply terminal V + or V− of the amplifier 110, and finally the connection point P in FIG. It becomes the flowing current Ip. That is,
Ip = Io
It becomes.

  An operation when the potential of the input voltage Vi is increased will be described. When the potential of the input voltage Vi increases, the output voltage Vo also increases accordingly. The output current Io also increases in proportion to the output voltage Vo. When the output voltage Vo is a positive voltage, the output current Io is also a positive value (source). When the output voltage Vo further increases and the output current Io becomes equal to the current value I1 of the constant current source 124, the potential Vp at the connection point P starts to decrease due to the operation of the diode bridge. Along with this, the positive power supply potential V + of the amplifier 110 also decreases and approaches the output voltage. In this way, the output stage of the amplifier is saturated on the positive power supply side. Even if the input voltage Vi is further increased, the output voltage Vo does not increase, and the current limit operation is maintained at the output current Io = I1. The

  An operation when the potential of the input voltage Vi is lowered will be described. When the input voltage Vi decreases and becomes a negative value, the output voltage Vo also becomes negative, so the output current Io also becomes a negative value (sink). When the output voltage Vo further decreases and the absolute value of the output current Io becomes equal to the current value I2 of the constant current source 125, the potential Vp at the connection point P starts to rise due to the operation of the diode bridge (120 to 123). As a result, the negative power supply potential V− of the amplifier 110 also rises and approaches the output voltage. In this way, a state in which the output stage of the amplifier 110 is saturated on the negative side is created. Even if the input voltage Vi is further decreased, the output voltage Vo does not decrease, and the current limit operation is maintained at the output current Io = I2.

  As described above, when the output current becomes equal to the current value of the constant current sources 124 to 125 due to the fluctuation of the output voltage of the amplifier 110, the diode bridge (120 to 123) grounded to the ground independent of the amplifier 110. Since the current value of the output current is limited to be equal to the current value I1 or I2 of the constant current sources 124 to 125 by the rectifying action, there is no switching between the feedback loop mode and the constant current control mode, and it can operate quickly and has stability. An amplifier circuit with a high current limiter can be provided.

In the present embodiment, the output current is not detected and fed back, but the power source currents I1 and I2 are directly limited by the diode bridge (120 to 123), so that a complicated mechanism is provided inside the amplifier 110 for the current limiter. It is not necessary to prepare the amplifier 110, and any off-the-shelf amplifier may be used as the amplifier 110. This is particularly optimal when it is desired to limit the output current to a commercially available high-speed monolithic IC or the like.

  Furthermore, if the forward voltage matching of the diodes in the diode bridge (120 to 123) is poor and the power supply potential is slightly shifted, the output voltage accuracy is not affected, and the limit current accuracy is not affected. (120 to 123) is not required to have a particularly high precision, and it is sufficient to select one having a small reverse leakage current.

  In this embodiment, the floating power supplies 111 to 112 are used, but a DC-DC converter may be used instead. Further, the constant current sources 124 to 125 may be controlled by a control program (not shown) using a D / A converter.

The ground potential of the ground terminal P3 does not necessarily affect the accuracy of the output voltage and limit current of the amplifier 110, and therefore does not necessarily have to be the ground potential, and may be connected to an appropriate positive or negative potential. In other words, it is only necessary to be independent of each other so that the ground of the amplifier is not shaken by the operation of the diode bridge (120 to 123).

It is an example of a structure of the amplifier circuit 100 with a current limiter by this invention. It is a structural example of the conventional amplifier circuit 10 with a current limiter.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Amplifier circuit with current limiter 110 Amplifiers 111-112 Floating power source 120-123 Diode 124-125 Constant current source

Claims (3)

In an amplifier circuit with a current limiter that amplifies an input voltage and applies an output voltage to a load, and limits the output current of the amplifier to a predetermined value,
A floating power supply connected between a positive power supply terminal and a negative power supply terminal of the amplifier;
A diode bridge connected to the floating power supply;
Comprising current supply means for driving the diode bridge;
When the output current reaches the current value of the current supply means due to the fluctuation of the output voltage, the current value of the output current is limited to be equal to the current value of the current supply means by the rectifying action of the diode bridge. Amplifying circuit with current limiter. The current supply means includes a first constant current source for supplying a current to the diode bridge;
The amplifier circuit with a current limiter according to claim 1, further comprising: a second constant current source that supplies current from the diode bridge. An amplifier for supplying an output current by applying an output voltage obtained by amplifying the input voltage to a load;
A floating power supply connected between a positive power supply terminal and a negative power supply terminal of the amplifier;
A first diode having a cathode connected to the floating power source;
A second diode having an anode connected to a connection point of the cathode of the first diode and the floating power supply;
A third diode having an anode connected to an anode of the first diode and a cathode connected to a ground terminal;
A fourth diode in which an anode is connected to a connection point between the cathode of the third diode and a ground terminal, and the cathode is connected to the cathode of the second diode;
A first constant current source for supplying a constant current to a connection point between the anode of the first diode and the anode of the third diode;
And a second constant current source for supplying a constant current from a connection point between the cathode of the second diode and the cathode of the fourth diode, and the maximum value of the output current of the amplifier output current is the first constant current source. An amplifier circuit with a current limiter, which is limited to a current value of one constant current source, and is configured such that a maximum value of a sink current of an output current of the amplifier is limited to a current value of the second constant current source.

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