JPH0537311Y2 - - Google Patents

Description

[Detailed description of the invention] [Industrial application field] The present invention introduces the commercial power supply voltage through a noise filter, connects the center potential of the noise filter output to the chassis, and uses this as ground potential to create a built-in measurement circuit. The present invention relates to a device for testing a device under test by connecting a probe between the measurement terminal of the device and the internal circuit of the device under test equipped with an electronic circuit.

[Conventional technology]

The present invention can be applied to, for example, emulators, oscilloscopes, etc. In this specification, an emulator will be used as an example.

FIG. 2 shows an example of the main part configuration of an emulator using a conventional test device. An emulator is a device that tests for bugs in the software installed in devices equipped with computers (hereinafter referred to as CPUs), and tests the quality of the CPU. The emulator removes the target CPU of the device under test from the socket,
Load this into the emulator side. Then, by operating the target CPU loaded on the emulator side with the software of the device under test, and measuring the signals of each part of the target CPU with the emulator, you can search for "insects" in the software and determine whether the target CPU is good or not. is being inspected.

In such emulators, a large voltage difference may occur between the ground potential of the emulator and the ground potential of the device under test, which may destroy electronic elements in the internal circuit of the device under test. There is a problem with it. This will be explained with reference to FIG.

The target CPU (not shown) of the device under test 20
Remove it from the IC socket, and connect the probe 9 from the emulator (hereinafter referred to as test equipment) 30 to pins 11 and 12 of this IC socket (normally, the target CPU has many terminal pins, but only two are shown here). . Removed target CPU
is loaded into an IC socket (not shown) provided on the test device 30 side. Note that each pin of the IC socket of the device under test and each pin of the IC socket of the emulator are connected in parallel by a probe 9.

In the device shown in FIG. 2, the test device 30 receives power from a commercial power source (for example, the pole transformer 1) and obtains a constant voltage from a stabilized power source as shown in FIG. A constant voltage Vc is supplied to the measurement circuits of each part.

Here, since noise is mixed in the commercial power supply, the test device 30 removes this noise using the noise filter 3 and generates a clean voltage waveform at the point P1.
P2 is added to the stabilized power supply shown in Figure 3. As shown in FIG. 2, the noise filter 3 is composed of inductances L1, L2 and capacitors C1, C2 (normally, L1=L2, C1=c2). A connection point A1 between capacitors C1 and C2, which is the center potential of the noise filter 3, is connected to a certain point A2 on the chassis 4 of the test device 30.

To briefly explain FIG. 3, the noise filter 3 in the same figure is shown in FIG. 2, and the output of this noise filter 3 is rectified by a rectifier 4 and applied to a constant voltage circuit 5. The constant voltage circuit 5 converts the introduced voltage into a constant voltage and outputs it. Capacitor C _A has the function of removing ripple included in the output,
This is a large capacity value.

Generally, one terminal of the winding of the pole transformer 1 is grounded, but in Japan's power wiring, it is not known which pole is the ground terminal. Here, assuming that the pole transformer 1 is 100V, the potential of the chassis 4, which is the center potential, is the same value as C1 and C2.
The voltage is divided by 1/2 and has a value of 50V (voltage to ground 7).

Normally, the test device 30 uses a chassis potential as the common potential (ground potential) of the internal circuit, and the ground potential of the circuit (hereinafter referred to as GND potential) is set at a certain point A3 of the chassis 4 as shown in FIG.
connected to.

On the other hand, since the device under test 20 is a device on the user side that uses the test device 30 (various configurations are possible), the chassis 15 of the device under test 20 is
The connection relationship between and the ground potential (GND potential 2),
It is not possible to specify the internal configuration, the ground potential, etc. of the chassis 15. To explain, in some devices under test 20, GND2 and chassis 15 may be directly connected, or may be connected via impedance _Z2 . In some cases, the chassis 15 of the device under test 20 is grounded, and in other cases, the chassis 15 is not grounded and has a certain voltage.

In Figure 2, GND2 is connected via impedance _Z2 .
and chassis 15 are connected, and chassis 15
will be explained assuming that it is grounded. Also, usually
Since a gate element is connected to the target CPU (not shown), the diode D1 in Fig. 2 is connected to the target CPU (not shown).
The gate element 13 composed of the transistor Q1 and the resistor R1 is connected to the socket pin 11.

When the probe 9 of the test device 30 is connected to the IC socket in which the target CPU of the device under test 20 is loaded as shown in FIG. Since GND1 waits for a potential of 50V, the gate element 13 will be damaged.

To explain, the driver 5 of the test device 30
For example, a certain signal is applied to the device under test 20 from the measurement terminal P3, and it can be seen that the measurement terminal P3 and GND1 are normally connected through a certain impedance _Z1 .

This impedance _Z1 is a value explained next. The driver 5 is a third driver built in the test device 30.
It is connected between the stabilized power supply Vc and GND1 as shown in the figure. A large capacity capacitor C _A shown in Figure 3 is connected to the output end of the stabilized power supply.
This is an impedance of several ohms for commercial frequencies.
It is Za. Further, the impedance zb between the power supply line ₁ and the output end of the driver 5 in FIG. 3 is usually about several tens of ohms due to the internal circuit elements of the driver 5. Therefore, the impedance shown in Figure 2
Z ₁ is Z ₁ =za+zb=several 10Ω.

Further, the power supply Vc to which the gate element 13 of the device under test 20 is connected is also connected to GND2 via a stabilized power supply as shown in FIG. Therefore, in the device under test 20 shown in FIG. 2, it can be seen that Vc and GND2 are connected through impedance _Z3 . This impedance Z ₃ can be seen as the capacitor C _A in FIG. 3 and is several ohms.

Now connect the probe 9 to the IC socket pins 11 and 1.
2, socket pin 12 (connection between ground potentials) should always be connected before the signal line (socket pin 11 side), but socket pin 11 of the signal line should be connected first. Sometimes they are connected. Then, during the period when the signal lines are connected and the ground potentials are not yet connected, the following changes occur: earth → ground voltage 7 → point A2 of chassis 4 → impedance Z ₁ → socket pin 11 → transistor Q1 → resistor R1 → impedance Z ₃ → Impedance Z ₂ → point A4 of chassis 15 → ground loop is formed, gate element 1
A high voltage is applied between the base and emitter and between the base and collector of transistor Q1 of No. 3. Normally, the transistors constituting the gate elements are not manufactured to have a high breakdown voltage and are therefore destroyed.

[The problem that the idea aims to solve]

In order to prevent damage to the internal circuits as described above, conventionally, a ground clip is provided with one end connected to GND1 of the test equipment 30. First, this ground clip is connected to GND2 of the device under test 20, and then the test equipment 30 is connected to GND2. The probe 9 was connected after the ground potentials of the tester and the device under test 20 were set to the same potential. In this way, the damage described above can be prevented, but the ground clip once connected may come off just before connecting the probe 9, resulting in damage to the internal circuit of the device under test 20. . Or, you may have accidentally connected the ground clip to the GND of the device under test.
The probe 9 may be connected to a location other than 2, and then the probe 9 may be connected.

An object of the present invention is to solve such problems and provide a test device that does not cause damage to the internal circuit of the device under test.

[Means to solve the problem]

In order to solve the above problems, the present invention introduces the commercial power supply voltage through a noise filter, connects the center potential of the noise filter output to the chassis, uses it as ground potential, and connects it to the measurement terminal of the built-in measurement circuit. In a device that tests the device under test by connecting a probe consisting of multiple lines between the internal circuit of the device under test equipped with an electronic circuit, a relay provided at each measurement terminal and a ground potential of the test device. and the ground potential of the device under test, and a control circuit that turns on all the relays only when this voltage is smaller than the set voltage, one end of which is connected to the ground potential of the test equipment, the other An earth clip 37 whose end can be connected to the ground potential of the device under test by a clip is provided, and the relay is controlled so as not to turn on when the earth clip is removed and the differential voltage is greater than the set voltage.

[Action]

With this invention, even if the ground clip that has been connected becomes disconnected or the ground clip is connected in the wrong position, and the difference voltage between the ground potential of the test equipment and the ground potential of the device under test becomes larger than the set voltage, A control circuit controls the relay to prevent it from turning on.

〔Example〕

Hereinafter, the present invention will be explained in detail using the drawings.

FIG. 1 is a diagram showing an embodiment of a test apparatus and a device under test according to the present invention.

The test apparatus 10 shown in FIG. 1 differs from the test apparatus 30 shown in FIG. 2 in the following points.

Relays K1 and K2 are provided at each measurement terminal P1 and P2.

A control circuit 30 is provided to control on/off of each of the relays.

It is.

Since the other configurations are the same as those in FIG. 2, similar parts are given the same configuration numbers and their explanations will be omitted.

The control circuit 30 introduces a voltage difference between the ground potential GND1 of the test device 10 and the ground potential GND2 of the device under test, and this is set as a set voltage (for example, 7V).
The configuration is not limited to that shown in FIG. 1 as long as it has the function of turning on relays K1 and K2 only when the voltage is smaller. To explain the configuration of FIG. 1, the potentials of GND1 and GND2 are taken out at a position sandwiching relay K2 and applied to the primary winding of transformer 31. The secondary winding of the transformer 31 is rectified by a rectifier 32 and converted into a pulsating DC voltage. The peak value of this pulsating voltage is taken out by a peak detector 33, and the output of this peak detector 33 is applied to a negative input terminal of a comparator 34. The comparator 34 has a set voltage, for example, 7V, applied to its positive input terminal, and compares this 7V with the output level of the peak detector 33. This set voltage of 7V is the relay K2 if it is below this voltage.
This value is based on the assumption that strong sparks will not occur and the relay will not be damaged when the relay is turned on. The output of the comparator 34 is applied to the driver 35, which causes current to flow through the coil 36 and relay K.
1.Turn on K2 at the same time. Of course, GND
If the voltage difference between 1 and GND2 is greater than 7V,
No current flows through the coil 36, and the relays K1 and K2 do not turn on.

In the apparatus shown in FIG. 1 constructed as described above, first, one end is connected to GND1 of the test apparatus 10, and the other end is a clip to connect GND1 and GND2 using the earth clip 37.

Then, since the potentials at both ends of relay K2 become equal, the voltage applied to the primary winding of transformer 31 is
It is 0V. That is, the differential voltage is always 0V, which is smaller than the set voltage (7V). Therefore, the control circuit 3
0 turns on relays K1 and K2, and test device 10 can perform measurement operations.

In this way, once relay K2 is turned on,
GND1 of test equipment 10 and GND of device under test 20
2, the high voltage (for example, 50 V) of the ground voltage 7 is not applied to the internal circuit of the device under test 20. The reason for this will be explained with reference to FIG. FIG. 4 is an equivalent circuit of each impedance Z ₁ , Z ₂ , Z ₃ and gate element 13 shown in FIG. 1. As is clear from the figure, when GND1 and GND2 are connected, each terminal of the gate element 13 (for example, between the base and emitter)
No voltage is applied to.

In other words, once the relay K2 is turned on, there is no risk of damaging the device under test 20 even if the earth clip 37 is subsequently removed.

In addition, without using the ground clip 37, directly turn on relay K2 (relay K1 is off),
It is inconvenient to set GND1 and GND2 to the same potential. The reason for this is that if the ground voltage 7 is, for example, 50V, this voltage will cause a strong spark to fly to the contacts of the relay the moment the relay K2 is turned on, shortening the life of the relay.

[Effects of this invention]

As described above, according to the present invention, relays K1 and K2 are turned on even if the ground clip 37 that has been connected comes off, or if the ground clip 37 is connected to a position other than GND2 by mistake. There's no fear. Therefore, the device under test 20 will not be damaged by mistake.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing an embodiment of the test device and the device under test according to the present invention, Fig. 2 is a diagram showing a conventional example, Fig. 3 is a diagram showing the configuration of a stabilized power supply, and Fig. 4 is a diagram showing the configuration of a stabilized power supply. 1
It is a figure which shows the equivalent circuit of a figure. 3...Noise filter, 10...Test device,
30...Control circuit, 37...Earth clip.

Claims (1)

[Claim for Utility Model Registration] Introducing the commercial power supply voltage through a noise filter, connecting the center potential of the output of the noise filter to the chassis and making it the ground potential, and connecting the measurement terminal of the built-in measurement circuit and the electronic circuit. In a device that tests the device under test by connecting a probe consisting of multiple lines between the internal circuit of the device under test installed, a relay provided at each measurement terminal and a ground potential of the test device and the device under test are connected. A control circuit that introduces a voltage difference between the test equipment's ground potential and turns on all of the relays only when this voltage is smaller than a set voltage; A test device comprising: an earth clip 37 that can be connected to the ground potential of a device under test.