JP2949542B2 - Electronic load device having overcurrent protection circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device under test including various power supply devices and the like, which operates as a constant voltage load of the device under test .
Electronic load device with overcurrent protection circuit to protect against overcurrent
About the installation . Power supply devices having various characteristics are known, and an electronic load device is used to test the characteristics of such a power supply device. Since the maximum current value that can be absorbed by this electronic load device is determined, it is necessary to protect the electronic load device when a current larger than that is passed. Therefore, a protection circuit that has a simple configuration and operates reliably is demanded. I have.

[0002]

2. Description of the Related Art As an electronic load device for testing a power supply device, for example, a configuration shown in FIG. 4 is known. In the figure, 41 is an operational amplifier for control input, 42-1 to 42-2
-N is a transistor, 43-1 to 43-n are operational amplifiers for current balance control, 44 is an input terminal of a reference voltage Vr, 45 is an electronic load device, 46 is a device under test indicating various power supply devices, and RS1 to RSn. Is a current detection resistor.

The control input operational amplifier 41 compares the reference voltage Vr with the output voltage of the device under test 46, and outputs a signal corresponding to the difference between the set reference voltage Vr and the output voltage of the device under test 46. Operational amplifier 43 for output and current balance
Add to + terminals of -1 to 43-n. This operational amplifier 43
Since the current detection values by the resistors RS1 to RSn are input to the-terminals of -1 to 43-n, each transistor 42-1
.About.42-n are controlled so as to shunt the current from the device under test 46 corresponding to the set reference voltage Vr, and to flow the current in a balanced manner. Therefore, the output characteristics of the device under test 46 can be tested by varying or setting the reference voltage Vr and using a voltmeter, an ammeter and the like, not shown.

[0004]

There is no problem if the output capacity of the device under test 46 is smaller than the capacity of the electronic load device 45, but the device under test 46 having an output capacity larger than the capacity of the electronic load device 45 is used. If the connection is made erroneously and control is performed to absorb a current larger than the capacity of the electronic load device 45, the transistors 42-1 to 42-n connected in parallel
Etc. will be damaged by overcurrent.

For example, when the electronic load device 45 has a characteristic as shown by a curve c in FIG. 5, that is, when the maximum input voltage is V ₃ and the maximum input current is I ₃ , the output characteristic of the device under test 46 is but has a constant-voltage characteristic of the voltages V ₁ to the output current I _1, if having an output characteristic shown in curve a output voltage is V ₂ when the current I _2, because the output characteristic of the curve c The test can be performed including the drooping characteristics of the output voltage of the device under test 46 by the electronic load device 45 having the characteristics of the curve c.

However, when the output current reaches I ₄ , the output voltage V ₁
If having a constant voltage characteristic of the relative device under test having an output characteristic shown by the curve b the output voltage is V _2, is controlled so as to reduce the output current I ₅ of the output voltage is V ₂ Then, the electronic load device 45 is damaged by the overcurrent. That is, by passing a maximum current I ₃ or more current electronic load 45, will be damaged.

In order to protect such an overcurrent, it is conceivable to provide a fuse, an overcurrent relay, and the like. The operation speed is not sufficient to protect the data such as 42-n. Accordingly, overcurrent protection cannot be performed at high speed and reliably. An object of the present invention is to provide overcurrent protection with a simple configuration.

[0008]

SUMMARY OF THE INVENTION An overcurrent protection circuit according to the present invention comprises a reference voltage for setting an output current of a device under test and a device under test in an electronic load device operating as a load of the device under test. And a plurality of transistors 2-1 to 2-n for shunting and flowing an output current of the device under test.
Balance control for controlling the transistors 2-1 to 2-n by comparing a detected value of a current corresponding to the plurality of transistors 2-1 to 2-n with an output signal of the operational amplifier 1 for control input. Operational amplifiers 3-1 to 3-n, a reciprocal circuit 4 for obtaining an output voltage of the device under test or a reciprocal of a voltage proportional to the output voltage, and comparing the output signals of the reciprocal circuit 4 with the transistors 2-1 to 2-1. When the detected value of the current flowing through 2-n increases, the output voltage of the device under test input to the operational amplifier 1 for control input or a voltage proportional thereto is forcibly reduced to exceed the maximum load power. Transistor 2
And an operational amplifier 5 for overcurrent protection for controlling the current flowing through 1 to 2-n.

The output signal of the reciprocal circuit 4 is compared with the output signal of the operational amplifier 1 for control input. When the output signal of the reciprocal circuit 4 becomes larger than the output signal of the operational amplifier 1 for control input, the current Operational amplifiers 3-1 to 3-3 for balance control
A control auxiliary operational amplifier 6 (see FIG. 3) forcibly reducing the output signal of the control input operational amplifier 1 to be input to -n.
Reference).

[0010]

The operational amplifier 1 for control input, the plurality of transistors 2-1 to 2-n, and the operational amplifiers 3-1 to 3-n for current balance control are the same as those of the conventional electronic load device. The input current Ii flowing from the device under test 10 is set by setting a reference voltage Vr input to the terminal 7.
n can be controlled. This electronic load device is provided with a reciprocal circuit 4 and an operational amplifier 5 for overcurrent protection. The reciprocal circuit 4 calculates a voltage Vin applied from the device under test 10 or a reciprocal of a voltage proportional thereto. so,
The output signal is input to the + terminal of the operational amplifier 5 for overcurrent protection. Further, since the current flowing through each of the transistors 2-1 to 2-n is detected by the resistors R5-1 to R5-n,
Operational amplifier 5 via resistors R9-1 to R9-n and R11
Connected so as to be input to the-terminal.

Assuming that the resistors R5-1 to R5-n are R, the negative terminal of the operational amplifier 5 receives Iin.R, and the positive terminal receives A / Vin, where A is a constant. Therefore, the operational amplifier 5 controls the input voltage of the + terminal of the operational amplifier 1 for control input via the diode D1 so that Vin · Iin = A / R (constant value), and the current Iin Is increased, the maximum load power (V
The input signal to the + terminal of the operational amplifier 1 for control input is reduced so as not to exceed (in · Iin) (max).
Thus, the transistors 2-1 to 2-n can be protected.

When the output signal of the reciprocal circuit 4 increases, that is, when the output voltage of the device under test 10 decreases due to the drooping characteristic, the operational amplifier 6 for control assistance causes the operational amplifier 1 for control input to output from the operational amplifier 1 for control input. The signals input to the + terminals of the operational amplifiers 3-1 to 3-n for current balance control are forcibly reduced. Thereby, each of the transistors 2-1 to 2-
The increase in the current flowing through n is suppressed. That is, overcurrent protection is performed. In this case, since the output signal of the operational amplifier 1 for control input is controlled, high-speed control is possible as compared with the case where the input voltage is controlled.

[0013]

FIG. 1 is a diagram for explaining an embodiment of the present invention. As described above, an operational amplifier 1 for control input, a plurality of transistors 2-1 to 2-n, and a It has operational amplifiers 3-1 to 3-n, a reciprocal circuit 4, and an operational amplifier 5 for overcurrent protection, and performs a characteristic test of the device under test 10, where R1 to R13 are resistors, C1 to C4 Is a capacitor, D1 is a diode, and 7 is an input terminal for the reference voltage Vr.

The set reference voltage Vr is input to the minus terminal of the operational amplifier 1 via the resistor R1, and
Is input to the + terminal of the operational amplifier 1 via the resistor R13. Therefore, the output signal of the operational amplifier 1 has a value corresponding to the difference between the reference voltage Vr and the input voltage Vin, and is input to the + terminals of the operational amplifiers 3-1 to 3-n corresponding to the transistors 2-1 to 2-n. Is done. The transistors 2-1 to 2-n are connected in parallel to the output terminals of the device under test 10 via the resistors R5-1 to R5-n.

The current Iin input from the device under test 10
Is divided into the transistors 2-1 to 2-n and flows. The operational amplifiers 3-1 to 3-n are connected to the output signal of the operational amplifier 1 and the resistors R5-1 to R5-n. The transistors 2-1 to 2-n are controlled by comparing with the current detection values, and when the current detection values increase, the operational amplifiers 3-1 to 3-n
n is such that transistors 2-1 to
2-n, each of the transistors 2-1 to 2-n
Can be balanced.

When the reference voltage Vr applied to the input terminal 7 is reduced, the output signal of the operational amplifier 1 increases, and the current flowing through the transistors 2-1 to 2-n increases. Conversely, when the reference voltage Vr is increased, the output signal of the operational amplifier 1 decreases, and the current flowing through the transistors 2-1 to 2-n decreases. That is, the test under test
Flow from device 10 through transistors 2-1 to 2-n
Current can be controlled. Then, the device under test 1
When the characteristic of 0 is shown by the curve a in FIG. 5, an arbitrary input current Iin can be set, but when the characteristic is shown by the curve b, it is necessary to control so as not to exceed the curve c . Calculation
The amplifier 5 is designed for such a setting that exceeds the curve c.
To limit the input current Iin.
You.

That is, the input voltage Vin input to the + terminal of the operational amplifier 1 is generated by the reciprocal circuit 4 and the operational amplifier 5.
Is forcibly reduced to limit the input current Iin. The reciprocal circuit 4 calculates the reciprocal of the input voltage Vin from the device under test 10. If the constant at that time is A, the output signal of A / Vin is input to the + terminal of the operational amplifier 5. The resistors R5-1 to R5-1 are connected to the minus terminal of the operational amplifier 5.
When the current detection value by R5-n is equal to the resistance of the resistors R9-1 to R9-
n, R11, and each of the transistors 2-1 to 2-1.
2-n, a current detection value corresponding to the average value of the current flowing through
The signal is input to the negative terminal of the operational amplifier 5.

When the average current detection value is represented by Iin · R, the output signal of the operational amplifier 5 is set so that the input signal Iin is reduced (A / Vin)> (Iin · R).
In the case of the relationship of R), since the polarity is positive, a reverse voltage is applied to the diode D1 and the diode D1 is turned off.
The input voltage Vin from the device under test 10 is input to the + terminal of the operational amplifier 1 via the resistor R13. Also, the input current Iin is set to be large (A / Vin) <
(Iin · R), the output signal of the operational amplifier 5
No. is negative polarity, ing the on-state voltage in the forward direction is applied to the diode D1. In that case, the input voltage Vi from the device under test 10 input to the + terminal of the operational amplifier 1
n will be forcibly reduced .

Therefore, since the output signal of the operational amplifier 1 becomes small, the current flowing through each of the transistors 2-1 to 2-n is maintained such that the relation of Iin.Vin = R / A is maintained.
In other words, the maximum load power (Iin · Vin) (ma
x) will be controlled so as not to exceed. Thus, the device under test having the characteristic of the curve a in FIG. 5 can be tested until the maximum current is reached, but the characteristic of the curve b that exceeds the maximum load power of the electronic load device is obtained. It is possible to control the device under test so as not to exceed the curve c. That is, overcurrent protection can be performed.

FIG. 2 is an explanatory view of the reciprocal circuit, (A), the has an operational amplifier 21 and resistors 22-26 and diodes 27 and 28, the V _cc is applied as a power supply voltage, the When the input voltage Vin from the test apparatus 10 is input and the input voltage Vin is sequentially increased, the diode 2
7, 28 are sequentially turned on in response to the voltage rise. Therefore, the output voltage Vout has the characteristic of the broken line approximation shown by the solid line in (B). That is, the relationship between the input voltage Vin and the output voltage Vout is represented by the output characteristic curve of (B), so that a reciprocal circuit can be configured. Note that by further increasing the combination of the diode and the resistor, the polygonal line can be made closer to the ideal characteristic indicated by the dotted line. Also, as the reciprocal circuit 4, an analog division circuit or the like can be used.

FIG. 3 is an explanatory view of another embodiment of the present invention. The same reference numerals as in FIG. 1 denote the same parts, 6 denotes an operational amplifier for control assistance, and D2 denotes a diode. The output signal of the reciprocal circuit 4 is input to the + terminal of the operational amplifier 6, the output signal of the operational amplifier 1 is input to the-terminal, and a diode D2 is connected between the-terminal and the output terminal.

As in the previous embodiment, the operational amplifier 1
The reference voltage Vr and the input voltage Vin from the device under test 10
Output signal VA corresponding to the difference ₁ To each operational amplifier 3-
Input to the + terminals of 1-3 to n, and output their operational amplifiers 3-
1 to 3-n terminals, transistors 2-1 to 2-n
The flowing current is detected by the resistors R5-1 to R5-n.
Voltage, and the current Iin from the device under test 10
In this case, the flow is divided and passed to the transistors 2-1 to 2-n. So
Then, the operational amplifier 5 calculates (A / Vin) ≧ (Iin ·
Control the maximum load power so that the condition of R) can be maintained
Things. Also, the gain of each operational amplifier 3-1 to 3-n
When it is increased, the output signal VA of the operational amplifier 1 ₁ And current detection
The output value Iin · R will be proportional. That is, the input side
The feedback resistor R3 is compared with the resistors R4-1 to R4-n.
By increasing −1 to R3-n and increasing the gain,
Voltage V generated at resistors R5-1 to R5-n _R5-1 ~ V
_R5-n Is the input voltage of the-terminals of the operational amplifiers 3-1 to 3-n.
And the output signal of the operational amplifier 1 input to its + terminal
Issue VA ₁ The operational amplifiers 3-1 to 3-
n is performed, and the voltage V _R5-1 ~
V _R5-n Is defined as the current detection value Iin · R.
The output signal VA of the operational amplifier 1 ₁ And the current detection value Iin
-R will be proportional. And the operational amplifier 6
Is the output signal VA of the operational amplifier 1. ₁ And the output of the reciprocal circuit 4
The output signal is compared with the force signal A / Vin. ₁ > A / Vin Seki
In the meantime, current can be drawn through the diode D2.
, The signals are input to the + terminals of the operational amplifiers 3-1 to 3-n.
VA ₁ Forcibly reducing the input current IinFast and controlled
Can be limited.

That is, protection of the overcurrent flowing through the transistors 2-1 to 2-n is performed by the operational amplifiers 5, 1, 3-1 to 3-n
However, since the operational amplifier 6 is provided, the input signals of the operational amplifiers 3-1 to 3-n can be forcibly reduced. , The overcurrent can be limited at high speed. Therefore, when the reference voltage Vr is changed so as to flow an input current exceeding the maximum load power of the electronic load device, the output signal of the operational amplifier 1 is reduced by the operational amplifier 6, and the transistors 2-1 to 2-n Can be suppressed from increasing.

In each of the above embodiments, the operational amplifier 1 for control input is configured to input the output voltage of the device under test 10 as the input voltage Vin to the + terminal via the resistor R13. It is also possible to set a voltage proportional to the input voltage Vin by dividing the voltage or the like. Also, the reciprocal circuit 4 can be configured to output the input voltage Vin or the reciprocal of a voltage proportional thereto. Also, transistors 2-1 to 2-n
Can be set in accordance with the current capacity of each transistor, the maximum load power as an electronic load device, and the like. The current flowing in correspondence with the transistors 2-1 to 2-n is detected, and the detected current value as an average value is input to the minus terminal of the operational amplifier 5 for overcurrent control. It is also possible to use the detected current value.

[0025]

As described above, the present invention relates to an overcurrent protection circuit for an electronic load device that operates as a constant voltage load for a device under test such as various power supply devices. A reciprocal circuit 4 for obtaining a reciprocal of a voltage proportional to the reciprocal circuit;
An operational amplifier 5 for overcurrent protection for comparing the detected value of the current flowing in each of the circuits 1-2 to 2-n with an operational amplifier 1 for control input and an operational amplifier 3-1 to 3-n for current balance control
When a current exceeding the maximum load power flows through the transistors 2-1 to 2-n controlled by the above, the output voltage of the device under test 10 input to the operational amplifier 1 for control input is forcibly reduced. The current flowing through the transistors 2-1 to 2-n is limited, and the transistors 2-1 to 2-n of the electronic load device can be protected from overcurrent.

When the input voltage Vin from the device under test 10 drops or the output signal of the operational amplifier 1 increases, the output signal of the operational amplifier 1 is forcibly reduced by the operational amplifier 6 for control assistance. This protects the overcurrents flowing through the transistors 2-1 to 2-n. Even if the operation of the operational amplifier 1 for control input is delayed, the inputs of the operational amplifiers 3-1 to 3-n for current balance control are protected. Since the number of signals can be reduced, overcurrent protection can be performed at high speed.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of one embodiment of the present invention.

FIG. 2 is an explanatory diagram of a reciprocal circuit.

FIG. 3 is an explanatory diagram of another embodiment of the present invention.

FIG. 4 is an explanatory diagram of a conventional example.

FIG. 5 is an explanatory diagram of voltage / current characteristics.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Operational amplifier for control input 2-1 to 2-n transistor 3-1 to 3-n Operational amplifier for current balance control 4 Reciprocal circuit 5 Operational amplifier for overcurrent protection 10 Device under test

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) G01R 31/00 G01R 19/165 G05F 1/10

Claims (2)

(57) [Claims] 1. The device under test operates as a constant voltage load ,
In an electronic load device having an overcurrent protection circuit , a reference voltage for setting an output current of the device under test;
A control input operational amplifier (1) for comparing an output voltage of the device under test or a voltage proportional to the output voltage; and a plurality of transistors (2-1 to shunt the output current of the device under test. 2-n), and comparing a detected value of a current corresponding to the plurality of transistors (2-1 to 2-n) with an output signal of the operational amplifier for control input (1), -1 to 2-n)
Operational amplifiers for controlling the current balance (3-1 to 3-1)
3-n), a reciprocal circuit (4) for obtaining an output voltage of the device under test or a reciprocal of a voltage proportional to the output voltage, and comparing the output signal of the reciprocal circuit (4) with the transistor (2- When the detected value of the current flowing through the first through second-n) increases, the output voltage of the device under test or the voltage proportional to the output voltage input to the operational amplifier for control input (1) is forcibly applied. An operational amplifier (5) for overcurrent protection for controlling the current flowing through the transistors (2-1 to 2-n) so as not to exceed the maximum load power. Electronic load device with overcurrent protection circuit
Place. 2. An output signal of said reciprocal circuit (4) is compared with an output signal of said operational amplifier for control input (1).
When the output signal of the reciprocal circuit (4) is smaller than the output signal of the operational amplifier (1) for control input, the current is input to the operational amplifier (3-1 to 3-n) for current balance control. 2. The overcurrent circuit according to claim 1, further comprising a control auxiliary operational amplifier for forcibly reducing an output signal of the control input operational amplifier.
Electronic load device.