JP2006084395A - Current limiting circuit, and testing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To carry out current limiting with high accuracy in comparison with a conventional device by applying a semiconductor device operating at high voltage such as an IC for PDP panel drive in a testing device in regard to a current limiting circuit, and a testing device. <P>SOLUTION: A load current is sent through a series circuit of an MOSFET 41 and a current detection circuit 42, a bipolar transistor 46 is turned on by build up of a terminal voltage of the current detection circuit 42 caused by increase of the load current, and a bias voltage retaining the MOSFET 42 in an ON state is lowered. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a current limiting circuit and a test apparatus, and can be applied to a test apparatus for semiconductor elements that operate at a high voltage, such as a PDP (plasma display) panel drive IC. In the present invention, a load current is caused to flow through a series circuit of a MOSFET and a current detection circuit, the bipolar transistor is turned on by a rise in the terminal voltage of the current detection circuit due to the increase in the load current, and the MOSFET is kept in the on state. By lowering the bias voltage, the current can be limited with higher accuracy than in the past.

  Conventionally, in a semiconductor element having an output circuit that operates at a high voltage, such as an IC for a PDP (plasma display) panel drive, the DC characteristics are inspected using a test apparatus having a DC power source capable of generating a high voltage. Japanese Patent Application Laid-Open No. 2004-77166 proposes a configuration that effectively avoids damage to each part even when the test object is short-circuited with respect to such a test apparatus. .

  That is, FIG. 6 is a block diagram showing a configuration relating to the inspection of DC characteristics in such a test apparatus. The test apparatus 1 includes a main body apparatus 3, a test head 2, and cables 6S and 6F that connect the main body apparatus 3 and the test head 2, and the test apparatus 1 is provided with a test power supply apparatus 5 that can generate a high voltage. It is done.

  Here, the test head 2 has a plurality of relays Ss1 to Ssn, Sf1 to Sfn, a probe card or a socket board, and the settings of the relays Ss1 to Ssn and Sf1 to Sfn are switched by a control signal output from the main body device 3. It is done. As a result, in the test apparatus 1, the test voltage or the test voltage output from the test power source 5 and input via the cable 6 </ b> F via each prober held on the probe card or the IC socket attached to the socket board. A current (hereinafter referred to as a driving power source) is selectively supplied to a corresponding terminal of the test object 4.

In the test power supply device 5, a reference voltage V _ref is generated by an analog-digital conversion circuit (not shown), and this reference voltage V _ref is input to a differential amplifier circuit 7 including a power amplifier via an input resistor R 1. The differential amplifier circuit 7 has a positive input terminal grounded, and outputs a differential amplification result to the test head 2 via the current detection circuit 8. Accordingly, the test power supply device 5 applies a drive power supply corresponding to the reference voltage V _ref to the corresponding terminal of the test object 4 via the test head 2.

  In addition, the test power supply device 5 supplies the drive voltage by the test power supply device 5 detected at the terminal portion of the test object 4 to the differential amplifier circuit 7 by the resistor R2 via the differential amplifier circuit 9 having a voltage follower circuit configuration. The voltage is fed back, thereby correcting the voltage drop of the driving power source due to the cable 6F connecting the test head 2 and the main body device 3 or the like. Further, in the test power supply device 5, the output signal of the differential amplifier circuit 9 is subjected to analog-digital conversion processing and output to a central processing unit (not shown), whereby the central processing unit obtains a voltage measurement result of the driving power supply. It has been made possible.

In the test power supply device 5, a reference voltage I _ref is generated by a digital-analog conversion circuit (not shown), and this reference voltage I _ref is supplied to the current detection circuit 8. Further, the current value of the driving power source output from the differential amplifier circuit 7 is detected by the current detection circuit 8, and the difference is made via the input resistor R1 so that this current value becomes a current value corresponding to the reference voltage I _ref. The current flowing into the dynamic amplification circuit 7 is absorbed by the current detection circuit 8. Thereby, in the test power supply device 5, when the current value of the drive power supply is going to exceed the current value corresponding to the reference voltage _Iref , the output voltage of the differential amplifier circuit 7 is lowered, and this current value is Control is performed so as not to exceed the current value specified by the reference voltage I _ref . As a result, the test power supply 5 outputs the driving power supply by constant voltage control and constant current control according to the settings of the reference voltages V _ref and I _ref , and further drives by the setting of the reference voltage I _ref. A current control mechanism for preventing an overcurrent of the power supply is configured.

  Further, in the test power supply device 5, the current value of the drive power supply detected by the current detection circuit 8 in this way is subjected to analog-digital conversion processing and output to a central processing unit (not shown). The current value measurement result of the drive power supply can be acquired.

  In the test power supply device 5, a protection circuit 10 is connected between the input side of the differential amplifier circuit 9 and the output side of the current detection circuit 8. Here, the protection circuit 10 is generally formed by connecting a series connection circuit of a plurality of diodes in parallel so as to have opposite polarities. Further, a high resistance is added to the parallel circuit of the plurality of diodes. Consists of circuits connected in parallel. In the test power supply device 5, the protection circuit 10 forms a feedback circuit for the drive power supply in the test power supply device 5, and thus, for example, defects in the relays Ss <b> 1 to Ssn and Sf <b> 1 to Sfn in the test head 2 Even when the feedback loop of the differential amplifier circuit 9 is opened due to the occurrence of an abnormality in the path from the output side of the detection circuit 8 to the relays Ss1 to Ssn, Sf1 to Sfn, an abnormal condition is detected from the differential amplifier circuit 7. A high voltage is output or an abnormal high voltage is applied to the differential amplifier circuit 9 to prevent the differential amplifier circuit 9 from being damaged.

  With such a configuration, the test apparatus 1 measures the voltage-current characteristic for measuring the current flowing through the test object 4 when a constant voltage is applied to the test object 4 or when the constant current is applied to the test object 4. A current-voltage characteristic for measuring a voltage drop generated in the test object 4 is measured so that the quality of the test object 4 can be inspected.

  In the inspection of a device using such a test apparatus, depending on the device, when a high voltage is applied, the test object 4 is damaged due to insufficient breakdown voltage due to a manufacturing defect, and the terminal to which the voltage is applied and the ground May become short-circuited between. In this case, although it is instantaneous, a very large short-circuit current may flow to the test object 4 from the test power supply device 5 via a relay or a prober in the test head.

  In the test power supply device 5, such an excessive current is prevented by the current limit circuit by the current detection circuit 8, but there is a slight amount until the current limit circuit 8 functions normally. Since it takes time, when the short-circuit current rises sharply, the voltage applied immediately before the occurrence of the short-circuit is divided by the impedance of the short-circuit until the current limiting circuit 8 functions normally. Excessive current will flow.

  In general, there is a stray capacitance of a size that cannot be ignored on the output side of the test power supply device 5. Furthermore, since the test power supply device 5 and the test head 2 are connected by a cable of several meters, a considerably large stray capacitance also exists between them. These stray capacitances are in a state of being charged by the voltage of the driving power supply applied at that time immediately before the occurrence of a short circuit, and a considerable amount of electric charge is accumulated. In the test apparatus 1, when a short-circuit accident occurs, the charge charged in the stray capacitance is instantaneously discharged through the short-circuit, and even if there is no delay time in the operation of the current control mechanism by the current detection circuit 8, it is excessive. Current will flow.

  In addition to the case of such a device failure, for example, a relay in a state where a drive power supply is applied is switched due to a mistake in a test program for executing a series of test processes, a malfunction of a control system, etc. Similarly, when a voltage driving power source is connected to a low impedance load connected to a low potential, an excessive current flows.

  Although the test power supply device 5 has a structure capable of withstanding such a temporary excessive current, a relay, a prober, or the like cannot withstand such a temporary excessive current. In such a case, damage such as welding or fusing of the contacts or melting of the tip of the prober is caused. As a result, the test apparatus 1 becomes unusable and the inspection process is stopped.

  For this reason, in Japanese Patent Application Laid-Open No. 2004-77166, current limiting circuits 12 and 13 are provided on the test head 2 side, and at least until the current control mechanism of the test power supply device functions, the current limiting circuits 12 and 13 are short-circuited. There has been proposed a method for effectively avoiding damage to each part even when the test object 4 is short-circuited by limiting an excessive current at the time.

  Here, the current limiting circuits 12 and 13 disclosed in Japanese Patent Application Laid-Open No. 2004-77166 include a series circuit including an enhancement type MOSFET 21 and a resistor 22 which is an impedance element connected to the source of the MOSFET 21, as shown in FIG. Are respectively provided in the drive power supply path and the feedback path, and the gate of the MOSFET 21 is forward-biased by the floating power supply 24 via the resistor 23.

  As a result, in the current limiting circuits 12 and 13, when the test apparatus operates normally and the flowing current is small, the MOSFET 21 operates in the resistance region, and the resistance value between the source and drain of the MOSFET 21 is called a so-called on-resistance. Thus, in a normal operation state, the voltage drop due to the current limiting circuits 12 and 13 can be held at a sufficiently small value, and the driving power source 5 by the test power source device 5 can be maintained. It is designed not to affect the supply.

  On the other hand, when the current flowing due to the short circuit or the like of the test object increases, the voltage drop due to the resistor 22 increases correspondingly, thereby reducing the bias voltage between the gate and the source. Switch the operation area to. By switching the operation region to the saturation region due to this increase in current, the MOSFET 21 limits the flowing current to a constant current value, thereby effectively avoiding damage of each part due to excessive current.

  However, in the configuration disclosed in Japanese Patent Laid-Open No. 2004-77166, the limit value of the flowing current is determined by the DC characteristics of the MOSFET 21. On the other hand, in the MOSFET 21, the direct current characteristic (gate voltage versus drain current characteristic) varies depending on the element, and changes greatly depending on the temperature. As a result, the current limit value varies in various ways, and there is a problem that the current limit value cannot be set with high accuracy.

In addition, after starting the current limitation, there is a wide range of currents until the finally flowing current is limited to a constant value, which makes it difficult to limit the current with high accuracy.
JP 2004-77166 A

  The present invention has been made in consideration of the above points, and an object of the present invention is to propose a current limiting circuit and a test apparatus capable of current limiting with higher accuracy than in the past.

  In order to solve such a problem, in the invention of claim 1, it is applied to a current limiting circuit, a series circuit of a MOSFET and a current detection circuit provided in a flow path of a load current, and a bias for holding the MOSFET in an on state. A floating power supply circuit that supplies a voltage to the gate of the MOSFET, and a bipolar transistor that switches to an ON state due to an increase in the terminal voltage of the current detection circuit and lowers the bias voltage.

  According to a second aspect of the present invention, in the configuration of the first aspect, the current detection circuit is a resistor.

  According to a third aspect of the present invention, in the configuration of the first aspect, the current detection circuit is a series circuit of a resistor and an inductance.

  According to a fourth aspect of the present invention, there is provided a test power supply device that outputs a drive power supply to be applied to the test target by constant current control or constant voltage control, and is connected to the test power supply device by a cable and connected to the test target at least. Applying to a test apparatus having a test head for applying the drive power, the test power supply apparatus feeds back the drive power applied to the test object to correct the drive power, Alternatively, a current control mechanism is provided that can measure the voltage of the driving power source applied to the test target by feeding back the driving power source applied to the test target and limits the current value of the driving power source. The test head has a first current limiting circuit for limiting a flowing current in the path of the driving power supply, and the feedback path is connected to the test target side of the first current limiting circuit. And a second current limiting circuit for limiting a flowing current in the feedback path, and the first and second current limiting circuits flow currents in the driving power supply path and the feedback path. A series circuit of a MOSFET and a current detection circuit, a floating power supply circuit that supplies a bias voltage for holding the MOSFET in an ON state to the gate of the MOSFET, and an ON state that is switched on by an increase in the terminal voltage of the current detection circuit And a bipolar transistor for lowering the bias voltage.

  According to a fifth aspect of the present invention, in the configuration of the fourth aspect, the current detection circuit is a resistor.

  According to a sixth aspect of the present invention, in the configuration of the fourth aspect, the current detection circuit is a series circuit of a resistor and an inductance.

  According to the configuration of claim 1, when applied to a current limiting circuit, a series circuit of a MOSFET and a current detection circuit provided in a flow path for a load current, and a bias voltage for holding the MOSFET in an ON state are applied to the gate of the MOSFET. If a floating power supply circuit to be supplied and a bipolar transistor that switches to an on state due to an increase in the terminal voltage of the current detection circuit and lowers the bias voltage, a current detection circuit that switches the bipolar transistor to an on state The current flowing by the terminal voltage can be limited, and thus the limit value can be set with high accuracy. In addition, after starting the current limitation, the range of the current until the finally flowing current is limited to a constant value can be narrowed, and thereby the current can be limited with high accuracy.

  Further, according to the configuration of claim 2, if the current detection circuit is a resistor in the configuration of claim 1, the current can be limited with high accuracy by a simple configuration.

  According to the configuration of claim 3, in the configuration of claim 1, if the current detection circuit is a series circuit of a resistor and an inductance, the pulsed current change due to the stray capacitance is suppressed, and high accuracy is achieved. The current can be limited.

  According to the configuration of claim 4, a test power supply device that outputs a drive power supply to be applied to the test target by constant current control or constant voltage control, and the test power supply device connected to the test target by a cable and at least the test target is connected to the test target. Applied to a test apparatus having a test head for applying a drive power supply, wherein the test power supply apparatus feeds back the drive power supply applied to the test object to correct the drive power supply, or A current control mechanism that limits the current value of the driving power supply by allowing the voltage of the driving power supply applied to the testing object to be measured by feeding back the driving power supply applied to the testing object; The test head has a first current limiting circuit for limiting a flowing current in the path of the driving power supply, and the feedback path is connected to the test target side of the first current limiting circuit. And a second current limiting circuit for limiting a flowing current in the feedback path, wherein the first and second current limiting circuits are MOSFETs through which currents in the driving power supply path and the feedback path flow. And a series circuit of the current detection circuit, a floating power supply circuit that supplies a bias voltage for holding the MOSFET in an on state to the gate of the MOSFET, and an increase in the terminal voltage of the current detection circuit is switched to an on state, If the bipolar transistor that lowers the bias voltage is included, the current that flows can be limited by the terminal voltage of the current detection circuit that switches the bipolar transistor to the on state, whereby the limit value can be set with high accuracy. it can. In addition, after starting the current limitation, the range of the current until the finally flowing current is limited to a constant value can be narrowed, and thereby the current can be limited with high accuracy.

  Further, according to the configuration of claim 5, in the configuration of claim 4, if the current detection circuit is a resistor, the current can be limited with high accuracy with a simple configuration.

  According to the configuration of claim 6, in the configuration of claim 4, if the current detection circuit is a series circuit of a resistor and an inductance, the pulsed current change due to the stray capacitance is suppressed, and high accuracy is achieved. The current can be limited.

  According to the present invention, the current can be limited with higher accuracy than in the past.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings as appropriate.

(1) Configuration of Embodiment FIG. 1 is a connection diagram showing a current limiting circuit according to Embodiment 1 of the present invention. The test apparatus according to this embodiment is configured in the same manner as the test apparatus described above with reference to FIG. 6 except that the current limit circuit 31 is applied instead of the current limit circuits 12 and 13.

  Here, in the current limiting circuit 31, a series circuit is formed by the enhancement type MOSFET 41 and the current detection circuit 42 connected to the source of the MOSFET 41 so that a current flows from the enhancement type MOSFET 41 to the current detection resistor 42. A series circuit is arranged in the current path to be controlled. In this embodiment, a current detection resistor 42 that is an impedance element is applied to the current detection circuit 42.

  In this current limiting circuit 31, one end of the floating power supply 45 is connected to the gate of the MOSFET 41 via a series circuit of resistors 43 and 44, and the other end of the floating power supply 45 is connected to the output side end of the current detection resistor 42. As a result, the gate voltage of the MOSFET 41 is sufficiently biased in the forward direction, and the MOSFET 41 is kept on in a normal state.

  In the current limiting circuit 31, the connection point of resistors 43 and 44 for supplying a bias voltage to the gate of the MOSFET 41 and the current detection resistor 42 side of the floating power supply 45 are connected to the collector and emitter of the bipolar transistor 46, respectively. A base resistor 47 of the transistor 46 is connected to a connection point between the source of the enhancement type MOSFET 41 and the current detection resistor 42. As a result, when the current flowing through the series circuit of the enhancement type MOSFET 41 and the current detection resistor 42 is small, the current limiting circuit 31 sets the bipolar transistor 46 to the off state, and the bias voltage from the floating power supply 45 is sufficiently increased. In contrast, when the current flowing through the series circuit reaches a predetermined limit current, the bipolar transistor 46 is switched to the ON state, and the bias voltage of the MOSFET 41 by the floating power supply 45 is lowered. .

  FIG. 2 is a connection diagram showing an example of the floating power supply 45 applied to such a current limiting circuit 31. The floating power supply 45 is configured to receive light emitted from the light emitting diode 56 by photodiodes 57A to 57n connected in series, and the output voltage of the series circuit by the photodiodes 57A to 57n is stabilized by a constant voltage diode (not shown). To use as a power source. Such a floating power source including the light emitting diode 56 and the photodiodes 57A to 57n has a feature that the coupling capacity between the primary and secondary is extremely small as compared with a floating power source such as a DC-DC converter. As a result, according to the power supply limiting circuit 31, the charge due to the primary-secondary coupling capacitance is not superimposed on the short-circuit current. Further, the gate voltage of the MOSFET 41 is prevented from changing, and the current limiting process by the current limiting circuit 31 can be executed reliably.

(2) Operation of Example In the above configuration, in the test apparatus according to this example, a current limiting circuit 31 is provided instead of the current limiting circuits 12 and 13 in the conventional test apparatus 1. In the current limiting circuit 31, a series circuit of a MOSFET 41 and a current detection resistor 42 is provided in the current path. In the normal state, the gate voltage is biased by the floating power supply 45 and the MOSFET 41 is held in an on state. As a result, in the current limiting circuit 31, the current related to the test object 4 flows through the drain and source of the MOSFET 41 and the current detection resistor 42.

  Here, for example, when driving power is supplied from the test power supply device 5, the test power source 4 is connected to the test terminal of the test target 4 that is short-circuited or short-circuited by switching the relay. Is supplied, the current flowing through the current limiting circuit 31 increases. In this case, in the current limiting circuit 31, the increased current flows through the current detection resistor 42 connected in series to the MOSFET 41, whereby the potential difference between both ends of the current detection resistor 42 becomes large, and the operation of the transistor 46 is switched to the ON state. . The transistor 46 is turned on to lower the bias voltage of the MOSFET 41 by the floating power supply 45, thereby preventing the drain current of the MOSFET 41 from increasing. As a result, the current limiting circuit 31 limits the load current to a constant current value, thereby preventing the probe from being damaged by a large current.

  When the current is limited in this way, the voltage at both ends of the current detection resistor 42 rises from the threshold voltage between the base and emitter of the bipolar transistor 46 to limit the current in the current limiting circuit 31. By starting the operation by switching the operation of the transistor 46 to the ON state, the current limit value can be set with high accuracy by setting the resistance value of the current detection resistor 42. In addition, the current range from the start of current limiting to the time when the finally flowing current is limited to a constant value can be reduced, and the current can be limited with higher accuracy than in the past.

(3) Effects of the embodiment According to the above configuration, the load current is caused to flow through the series circuit of the MOSFET and the current detection resistor, and the bipolar transistor is increased by increasing the terminal voltage of the current detection resistor due to the increase in the load current. By turning on and lowering the bias voltage for holding the MOSFET in the on state, the current can be limited with higher accuracy than in the past.

  FIG. 3 is a connection diagram illustrating a current limiting circuit applied to the test apparatus according to the second embodiment of the present invention. This current limiting circuit 51 uses the current limiting circuit 31 described above with reference to FIG. In FIG. 3, corresponding to the respective configurations described above with reference to FIG. 1, the configurations related to the polarities are indicated by subscripts A and B, respectively.

  That is, in the current limiting circuit 51, a load current is supplied to the series circuit of the MOSFET 41A, the current detection resistors 42A and 42B, and the MOSFET 41B, and bias power is supplied to the gates of the MOSFETs 41A and 41B. Configured to fall.

  According to the configuration shown in FIG. 3, the same effect as that of the first embodiment can be obtained regardless of whether the polarity of the driving power supply applied to the test object is positive or negative.

  FIG. 4 is a connection diagram illustrating a current limiting circuit applied to the test apparatus according to the second embodiment of the present invention. The current limiting circuit 61 is configured in the same way as the current limiting circuit 31 described above with reference to FIG. 1 except that the current detection circuit is different.

  In this current limiting circuit 61, the current detection circuit is formed by a series circuit of a resistor 62 and an inductance 63, and a damping resistor 64 is connected in parallel to the inductance 63.

  Here, the MOSFET 41 has a stray capacitance between the drain and source, between the drain and gate, and between the gate and source. As a result, when an abnormality occurs in the load, an excessive current flows in a pulse shape due to the charge / discharge current of such stray capacitance. However, if the current detection circuit is constituted by a series circuit of a resistor 62 and an inductance 63 as in this embodiment, a sudden current change due to this stray capacitance can be suppressed.

  The damping resistor 64 connected in parallel to the inductance 63 suppresses transient current vibration when the stray capacitance of the inductance 63 is large, and may be omitted if such vibration does not cause a problem in practice. . In place of the damping resistor, a diode or a series circuit of a diode and a resistor may be provided.

  FIG. 5 is a connection diagram illustrating a current limiting circuit applied to a test apparatus according to Embodiment 4 of the present invention. This current limiting circuit 71 uses the current limiting circuit 61 described above with reference to FIG. Note that, in FIG. 5, corresponding to each configuration described above with reference to FIG.

  That is, in this current limiting circuit 61, a load current is passed through the series circuit of the MOSFET 41A, the inductance 63A, the current detection resistors 62A and 62B, the inductance 63B, and the MOSFET 41B, and the bias power is supplied to the gates of these MOSFETs 41A and 41B, Each bias power supply is configured to fall.

  According to the configuration shown in FIG. 5, the same effect as in the third embodiment can be obtained regardless of whether the polarity of the driving power supply applied to the test object is positive or negative.

  In the above-described embodiment, the case where the current limiting circuit is provided on the test power supply device side of the test head has been described. However, the present invention is not limited to this, and the test head is provided on the test target side of each relay. It may be.

  Further, in the above-described embodiment, the case where damage to each part due to a short-circuit accident to be tested is prevented is described on the assumption that a driving power supply having a relatively high voltage is supplied. The present invention can also be widely applied to supply of driving power by voltage.

  The present invention relates to a current limiting circuit and a test apparatus, and can be applied to a test apparatus for a semiconductor element that operates at a high voltage, such as a PDP panel drive IC.

It is a connection diagram which shows the current limiting circuit applied to the test apparatus which concerns on Example 1 of this invention. It is a connection diagram which shows the power supply of the current limiting circuit of FIG. It is a connection diagram which shows the current limiting circuit applied to the test apparatus which concerns on Example 2 of this invention. It is a connection diagram which shows the current limiting circuit applied to the test apparatus which concerns on Example 3 of this invention. It is a connection diagram which shows the current limiting circuit applied to the test apparatus which concerns on Example 4 of this invention. It is a block diagram which shows the conventional test apparatus. It is a connection diagram which shows the current limiting circuit applied to the test apparatus of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Test apparatus, 2 ... Test head, 3 ... Main body apparatus, 4 ... Test object, 5 ... Test power supply device, Ss1-Ssn, Sf1-Sfn ... Relay, 12, 13, 31, 51 , 61, 71 ... current limiting circuit, 21, 41, 41A, 41B ... MOSFET, 22, 23, 42, 42A, 42B, 43, 43A, 43B, 44, 44A, 44B, 47, 47A, 47B ... Resistor, 24, 45 ... Floating power supply, 46, 46A, 46B ... Bipolar transistor

Claims (6)

A series circuit of a MOSFET and a current detection circuit provided in the flow path of the load current;
A floating power supply circuit for supplying a bias voltage for holding the MOSFET in an ON state to a gate of the MOSFET;
A current limiting circuit comprising: a bipolar transistor that switches to an ON state by a rise in a terminal voltage of the current detection circuit and lowers the bias voltage. The current limiting circuit according to claim 1, wherein the current detection circuit is a resistor. The current limiting circuit according to claim 1, wherein the current detection circuit is a series circuit of a resistor and an inductance. A test power supply device that outputs a drive power supply to be applied to a test object by constant current control or constant voltage control; and
In a test apparatus having a test head connected to the test power supply apparatus by a cable and applying at least the driving power supply to the test object,
The test power supply is
Feedback the driving power applied to the test object to correct the driving power;
Alternatively, it is possible to measure the voltage of the driving power source applied to the test target by feeding back the driving power source applied to the test target,
A current control mechanism for limiting a current value of the driving power supply;
The test head is
A first current limiting circuit for limiting a flowing current in the path of the driving power supply;
The feedback path is connected to the test object side of the first current limiting circuit;
A second current limiting circuit for limiting a flowing current in the feedback path;
The first and second current limiting circuits are:
A series circuit of a MOSFET and a current detection circuit through which a current of the driving power supply path and the feedback path flows; and
A floating power supply circuit for supplying a bias voltage for holding the MOSFET in an ON state to a gate of the MOSFET;
And a bipolar transistor that switches to an on-state due to an increase in a terminal voltage of the current detection circuit and lowers the bias voltage. The test apparatus according to claim 4, wherein the current detection circuit is a resistor. The test apparatus according to claim 4, wherein the current detection circuit is a series circuit of a resistor and an inductance.

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