JP7052409B2 - Pulse current application circuit and its control method - Google Patents

Description

The present invention relates to a pulse current application circuit for applying a short pulse of a large current to a device under test (hereinafter referred to as DUT: Device Under Test) and a control method thereof.

The characteristics of a semiconductor element may deteriorate due to the application of a surge current for a short period of time, and in order to confirm its reliability, a circuit that applies a large current pulse current is required. In addition, the existence of crystal defects that grow by repeatedly applying a pulse current to the semiconductor device is confirmed by applying a large current pulse current in a time much shorter than the time when the crystal defects grow. May be applied to the screening of semiconductor devices. In this case as well, a pulse current application circuit that applies a large current pulse current is required. The pulse current applied by such a pulse current application circuit is shorter than the switchable pulse width of several microseconds (μs) of the IGBT (Insulated Gate Bipolar Transistor), for example, about 200 nanoseconds (ns). Is desired. Further, the current value of the pulse current is required to be as large as several tens of amperes (A), for example.

The pulse current application circuit that applies this large current pulse current to the semiconductor element is controlled so as to be connected in series with the DUT between the power supply and ground and to be turned on (conducting) or turn off (cutting off). Semiconductor switching devices are known (see, for example, Patent Document 1). In the pulse current application circuit described in Patent Document 1, a bipolar transistor is used as a switch. On the other hand, MOSFETs (Metal-Oxide-Semiconductor Field-Effect Transistors, hereinafter referred to as MOS transistors) are used in recent pulse current application circuits that require high-speed switching speeds.

FIG. 8 is a circuit diagram illustrating a conventional pulse current application circuit using a MOS transistor, and FIG. 9 is a load curve illustrating the operation of the conventional pulse current application circuit. In FIG. 9, the horizontal axis represents the power supply voltage, and the vertical axis represents the current flowing through the DUT and the resistor.

As shown in FIG. 8, the conventional pulse current application circuit includes a MOS transistor 101, and the gate terminal of the MOS transistor 101 is connected to the gate drive circuit 102. The source terminal of the MOS transistor 101 is connected to the ground, and the drain terminal of the MOS transistor 101 is connected to the cathode terminal of the diode 103 as a DUT. The anode terminal of the diode 103 is connected to one terminal of the current limiting resistor 104, and the other terminal of the current limiting resistor 104 is connected to the power supply Vdc.

The MOS transistor 101 is turned on or off by the gate drive signal G supplied from the gate drive circuit 102. When the MOS transistor 101 is turned off, no current Idt flows through the diode 103. On the other hand, when the MOS transistor 101 is turned on, a current Idut determined by the voltage of the power supply Vdc and the resistance value of the current limiting resistor 104 flows through the diode 103. For the sake of simplicity, the characteristics of the diode 103 are ignored.

The MOS transistor 101 has output characteristics as shown by reference numeral 101a in FIG. 9, for example, when it is in a low temperature state of about 25 ° C. At this time, assuming that the voltage of the power supply Vdc is Vdc1 and the current-voltage characteristic of the current limiting resistor 104 is the reference numeral 104a, the current at which the intersection of the output characteristic 101a of the MOS transistor 101 and the current-voltage characteristic 104a of the current limiting resistor 104 flows through the diode 103. Ia (= Idut).

Since the loss of the MOS transistor 101 is the product of the on-resistance of the MOS transistor 101 and the square of the current, when a large current pulse current is passed through the diode 103, the temperature of the MOS transistor 101 rises. Generally, when the temperature of the MOS transistor 101 rises, the mobility of electrons decreases, so that the on-resistance becomes high and it becomes difficult for current to flow. For example, the output characteristics when the MOS transistor 101 is in a high temperature state of about 150 ° C. It becomes as shown by reference numeral 101b. That is, the MOS transistor 101 has a characteristic that a large current Ia flows at the initial stage of application of the pulse current, but the current changes depending on the temperature that the temperature of the MOS transistor 101 rises to the current Ib1 when the temperature of the MOS transistor 101 rises. Have. In this case, since the current applied to the diode 103 changes greatly depending on the temperature of the MOS transistor 101, the MOS transistor 101 cannot stably apply the current to the diode 103.

On the other hand, when the voltage of the power supply Vdc is raised to Vdc2 and the resistance value of the current limiting resistance 104 is increased, the intersection of the output characteristic 101a of the MOS transistor 101 and the current-voltage characteristic 104b of the current limiting resistance 104 is defined as the current Ia. It is possible. In this case, the intersection of the output characteristic 101b of the MOS transistor 101 in the high temperature state and the current-voltage characteristic 104b of the current limiting resistor 104 is the current Ib2. As a result, the current difference in which the current changes depending on the temperature of the MOS transistor 101 becomes ΔI1 in the case of the current-voltage characteristic 104a when the resistance value of the current limiting resistance 104 is small. On the other hand, when the resistance value of the current limiting resistance 104 is increased to obtain the current-voltage characteristic 104b, the current difference in which the current changes depending on the temperature of the MOS transistor 101 becomes ΔI2 (<ΔI1), which is dependent on the temperature characteristic. It can be seen that is getting smaller.

In the pulse current application circuit shown in FIG. 8, a diode 103 as a DUT is arranged between the drain terminal of the MOS transistor 101 and the current limiting resistor 104, but the source terminal of the MOS transistor 101 and the ground are arranged. It may be placed in between. In this case, by setting the reference potential of the gate drive circuit 102 to the source terminal of the MOS transistor 101, the operation and temperature dependence are basically the same as when the diode 103 is arranged on the drain terminal side of the MOS transistor 101. be.

Japanese Unexamined Patent Publication No. 5-95148

However, if the resistance value of the current limiting resistance is increased and the voltage of the power supply is increased in order to reduce the current difference that changes depending on the temperature of the MOS transistor, the voltage applied to the current limiting resistance increases and the current The loss due to the limiting resistance is greatly increased. As a result, there is a problem that the total loss of the pulse current application circuit increases.

The present invention has been made in view of these points, and is a pulse current application circuit that outputs a large current pulse with a pulse width of several hundred ns or less by high-speed switching, in which the fluctuation of the pulse current value due to the temperature characteristics of the switching element is small. And its control method.

In the present invention, a pulse current application circuit is provided in order to solve the above problems. This pulse current application circuit includes a first switching element, an inductive load connected in series with the first switching element and connected between a power supply and a reference potential, and a first switching element and an inductive load. No current flows when the second switching element connected in series with the current application target between the connection point and the reference potential and the second switching element connected in parallel with the inductive load are in a conductive state. , A commutation circuit through which a current flows when the first switching element and the second switching element are in a cutoff state.
The commutation circuit has a reverse series connected diode and a Zener diode, and the sum of the built-in voltage of the diode in which the second switching element is forward biased in the conduction state and the breakdown voltage of the Zener diode in which the second switching element is reverse biased. , The voltage drop of the second switching element and the current application target when a predetermined current is passed through the second switching element and the current application target is made larger than the voltage drop, and the first switching element is made conductive to perform the first switching. The energy supplied from the power supply is stored in the inductive load connected in series with the element, the second switching element is made conductive, and the inductive load is applied to the current applied target connected in series with the second switching element. The current supplied to the current is applied to the reverse bias state, the first switching element is cut off, the current of the inductive load is transferred to the current application target, and the current of the inductive load is transferred to the current application target for a predetermined period. After flowing, the second switching element is put into a cutoff state.

Further, the present invention provides a control method for a pulse current application circuit. According to the control method of this pulse current application circuit, the first switching element, the inductive load connected in series with the first switching element and connected between the power supply and the reference potential, and the first switching. The second switching element connected in series with the current application target between the connection point of the element and the inductive load and the reference potential, and the second switching element connected in parallel with the inductive load are in a conductive state. A pulse current application circuit comprising: when no current flows, and when the first switching element and the second switching element are cut off, a current flows, and a commutation circuit including a reverse series connected diode and a Zener diode. Then, the total value of the built-in voltage of the diode in which the second switching element is forward-biased in the conduction state and the breakdown voltage of the Zener diode in which the second switching element is reverse-biased is passed through the second switching element and the current application target. It was made larger than the voltage drop of the second switching element and the current application target when the current was applied, and the first switching element was made conductive and supplied from the power supply to the inductive load connected in series with the first switching element. The first switching is performed by accumulating energy, making the second switching element conductive, and applying the current supplied to the inductive load to the current application target connected in series with the second switching element in the reverse bias state. The element is cut off, the current of the inductive load is transferred to the current application target, the current of the inductive load is transferred to the current application target for a predetermined period, and then the second switching element is cut off.

In the pulse current application circuit and its control method having the above configuration, sufficient energy is accumulated in advance for the pulse current applied to the current application target by sequentially cutting off the first switching element and the second switching element. Since it is generated from an inductive load, it can output a large current pulse with a narrow pulse width.

Further, since the current applied to the current application target is supplied from the inductive load and the current rising rate di / dt is determined by the voltage applied to the inductive load, the power supply voltage Vdc is set from the on voltage of the first switching element. By setting a sufficiently high voltage and precisely controlling the on period of the first switching element, the influence of the temperature characteristics of the first switching element can be reduced, and the fluctuation of the pulse current value due to the temperature characteristics is small. There are advantages.

It is a circuit diagram which illustrates the pulse current application circuit which concerns on 1st Embodiment. It is a timing diagram explaining the operation of the pulse current application circuit which concerns on 1st Embodiment. It is a circuit diagram which illustrates the pulse current application circuit which concerns on 2nd Embodiment. It is a timing diagram explaining the operation of the pulse current application circuit which concerns on 2nd Embodiment. It is a circuit diagram which illustrates the pulse current application circuit which concerns on 3rd Embodiment. It is a timing diagram explaining the operation of the pulse current application circuit which concerns on 3rd Embodiment. It is a circuit diagram which illustrates the pulse current application circuit which concerns on 4th Embodiment. It is a circuit diagram which illustrates the conventional pulse current application circuit by a MOS transistor. It is a load curve explaining the operation of the conventional pulse current application circuit.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. It should be noted that each embodiment can be implemented by partially combining a plurality of embodiments within a consistent range.

FIG. 1 is a circuit diagram illustrating the pulse current application circuit according to the first embodiment, and FIG. 2 is a timing diagram illustrating the operation of the pulse current application circuit according to the first embodiment.
As shown in FIG. 1, the pulse current application circuit according to the first embodiment includes a MOS transistor (first switching element) 11, and the drain terminal of the MOS transistor 11 is a positive electrode terminal of the power supply 10. It is connected. The negative electrode terminal of the power supply 10 is connected to a reference potential (GND). The source terminal of the MOS transistor 11 is connected to one terminal of the inductor (inductive load) 12, and the other terminal of the inductor 12 is connected to the reference potential (GND).

The source terminal of the MOS transistor 11 is also connected to the source terminal of the MOS transistor (second switching element) 13, and the drain terminal of the MOS transistor 13 is connected to one terminal of the DUT (current application target) 14. There is. The other terminal of the DUT 14 is connected to the reference potential (GND). The DUT 14 can be, for example, a PiN diode using a SiC (Silicon Carbide) material, a body diode of a MOS transistor, or the like. Therefore, the cathode terminal of the diode of the DUT 14 is connected to the drain terminal of the MOS transistor 13, and the anode terminal of the diode of the DUT 14 is connected to the reference potential (GND). Here, the series circuit of the MOS transistor 13 and the DUT 14 constitutes a first commutation circuit connected in parallel to the inductor 12 to commutate the current flowing through the inductor 12 and apply a pulse current to the DUT 14.

The source terminal of the MOS transistor 11 is further connected to the cathode terminal of the diode 15, and the anode terminal of the diode 15 is connected to the anode terminal of the Zener diode 16. The cathode terminal of the Zener diode 16 is connected to a reference potential (GND). In this way, the diode 15 and the Zener diode 16 connected in anti-series are connected in parallel with the inductor 12, and the second current flowing through the inductor 12 and the first commutation circuit is commutated and consumed. It constitutes a commutation circuit. Here, the condition that the sum of the built-in voltage of the diode 15 and the breakdown voltage of the Zener diode 16 is larger than the voltage drop that occurs in the first commutation circuit when the current is flowing in the first commutation circuit is satisfied. I am doing it. That is, when a forward current is flowing in the first commutation circuit, the forward current is prevented from flowing in the second commutation circuit. In this embodiment, the diode 15 and the Zener diode 16 are each composed of one diode, but each of them may be composed of two or more elements in order to satisfy the above conditions.

Gate drive circuits 17 and 18, respectively, are connected to the gate terminals of the MOS transistors 11 and 13, and gate voltages G1 and G2 are supplied, respectively. Since the gate voltages G1 and G2 use the source terminals of the MOS transistors 11 and 13 as reference potentials, an isolated circuit such as a digital isolator is used for signal transmission from the host device to the gate drive circuits 17 and 18. ing.

Here, as the MOS transistors 11 and 13, for example, a power switching element having a withstand voltage of 1200 volts (V) and a pulse drain current of 100 A is used. As the inductor 12 for storing energy for applying a pulse current to the DUT 14, for example, a coil of several microhenries (μH) to several tens of μH, preferably 5 to 30 μH is used. The voltage V (DC) of the power supply 10 is set from several tens of volts to several hundreds of volts. Further, the Zener diode 16 of the second commutation circuit uses a power Zener diode having a large power consumption.

Next, the operation of the pulse current application circuit having the above configuration will be described with reference to FIG. First, as shown in FIG. 1, the DUT 14 is connected between the MOS transistor 13 and the reference potential (GND) so as to form the first commutation circuit.

When the gate drive circuit 17 applies a gate voltage G1 which becomes a high (H) level at time t1 to the gate terminal of the MOS transistor 11, the MOS transistor 11 turns on and the current I (L) starts to flow in the inductor 12. At the same time, the same current I (MOS1) flows through the MOS transistor 11. At this time, the current I (L) flowing through the inductor 12 increases, but its slope is
di / dt = {V (DC) -Von (MOS1)} / L ... (1)
Will be. In the equation (1), V (DC) is the voltage of the power supply 10, Von (MOS1) is the drain-source voltage when the MOS transistor 11 is turned on, and L is the inductance of the inductor 12.

At this time, in the first commutation circuit, the DUT 14 is reverse-biased, so no current flows, and in the second commutation circuit, the diode 15 is reverse-biased, so no current flows. If the withstand voltage of the DUT 14 is less than the voltage V (DC) of the power supply 10 and there is no current blocking capability in this state, a diode with a withstand voltage higher than the power supply voltage is connected in series with the DUT 14 together with the DUT 14. Need to connect to.

Next, at time t2 during the ON period of the MOS transistor 11, the gate drive circuit 18 applies the gate voltage G2 to the gate terminal of the MOS transistor 13. As a result, the MOS transistor 13 turns on, but since only the reverse bias voltage is applied to the DUT 14, there is no particular change.

Next, when the MOS transistor 11 is turned off at time t3, the current supplied to the inductor 12 is cut off, so that the current I (L) of the inductor 12 becomes the maximum current Imax at that time. After that, the current I (L) flowing through the inductor 12 tends to flow in the same direction. At this time, since the MOS transistor 13 has already been turned on, the current I (L) of the inductor 12 is commutated to the first commutation circuit composed of the DUT 14 and the MOS transistor 13, and the current is transferred to the DUT 14. I (DUT) flows. The change in the current I (L) at this time is
-Di / dt = {Von (MOS2) + Vf (DUT)} / L ... (2)
Will be. In the equation (2), Von (MOS2) is the drain-source voltage when the MOS transistor 13 is turned on, and Vf (DUT) is the forward voltage of the DUT 14. At this time, the voltage drop in the first commutation circuit is lower than the total voltage of the breakdown voltage of the Zener diode 16 and the built-in voltage of the diode 15, so that the voltage drop does not flow to the second commutation circuit.

Next, when the MOS transistor 13 turns off at time t4, the current I (DUT) of the DUT 14 is cut off at that time. As a result, a short pulse having a pulse width of time (t4-t3) flows through the DUT 14.

Since the current flow of the first commutation circuit is cut off at the time t4 when the MOS transistor 13 is turned off, the current I (L) of the inductor 12 uses the energy stored in order to maintain the flow as the second current. Aim at the commutation circuit. At time t4, the current I (ZD) of the Zener diode 16 shows the maximum value, but then decreases. The change in the current I (L) of the Zener diode 16 at this time is
-Di / dt = {V (ZD) + Vf (D2)} / L ... (3)
Will be. In this equation (3), V (ZD) is the breakdown voltage + operating voltage of the Zener diode 16, and Vf (D2) is the forward voltage of the diode 15. As a result, all of the energy stored in the inductor 12 is consumed in the Zener diode 16 and the diode 15 of the second commutation circuit.

In order to apply the pulse current to the DUT 14 again, the above sequence may be repeated after the current flowing through the Zener diode 16 and the diode 15 (second commutation circuit) becomes 0, that is, in the so-called discontinuous mode. Therefore, in this pulse current application circuit, the timing at which the MOS transistor 13 is turned on is set to the period during which the MOS transistor 11 is turned on, but it may be after the timing when the current flowing through the second commutation circuit becomes 0. Just do it. As can be seen from Eq. (3), it goes without saying that it is effective to increase the voltage V (ZD) applied to the Zener diode 16 in order to shorten the time when the current becomes 0 and increase the repetition frequency. stomach.

As described above, the MOS transistor 11 stores energy in the inductor 12, the MOS transistor 13 applies a short pulse current from the inductor 12 to the DUT 14, and the remaining energy of the inductor 12 is consumed by the Zener diode 16.

Further, this pulse current application circuit does not generate the pulse current applied to the DUT 14 by high-speed switching of one switching element, but generates the pulse current at the timing of turning off the two switching elements. Therefore, it is possible to reduce the pulse width of the generated pulse current, and in the first embodiment, it is possible to generate a rectangular wave having a pulse width of 200 ns.

FIG. 3 is a circuit diagram illustrating the pulse current application circuit according to the second embodiment, and FIG. 4 is a timing diagram illustrating the operation of the pulse current application circuit according to the second embodiment. In the circuit diagram of FIG. 3, the same or equal components as the components of the circuit shown in FIG. 1 are designated by the same reference numerals.

As shown in FIG. 3, the pulse current application circuit according to the second embodiment includes a MOS transistor 11, and the drain terminal of the MOS transistor 11 is connected to the positive electrode terminal of the power supply 10. The negative electrode terminal of the power supply 10 is connected to a reference potential (GND). The source terminal of the MOS transistor 11 is connected to one terminal of the inductor 12, and the other terminal of the inductor 12 is a drain terminal of the MOS transistor (third switching element) 19 and an anode terminal of the diode (regenerative diode) 20. It is connected to the. The source terminal of the MOS transistor 19 is connected to a reference potential (GND), and the gate drive circuit 21 is connected to the gate terminal of the MOS transistor 19. The cathode terminal of the diode 20 is connected to the positive electrode terminal of the power supply 10 and constitutes a third commutation circuit. The diode 20 has a withstand voltage higher than the voltage of the power supply 10.

The source terminal of the MOS transistor 11 is also connected to the source terminal of the MOS transistor 13. The drain terminal of the MOS transistor 13 is connected to the cathode terminal of the DUT 14, and the anode terminal of the DUT 14 is connected to the reference potential (GND). The MOS transistor 13 and the DUT 14 form a first commutation circuit.

The source terminal of the MOS transistor 11 is further connected to a reference potential (GND) via a circuit in which n diodes 15a, 15b, ... 15n are connected in series. That is, the source terminal of the MOS transistor 11 is connected to the cathode terminal of the diode 15a, and the anode terminal of the diode 15n is connected to the reference potential (GND). The diodes 15a, 15b, ... 15n prevent current from flowing when the MOS transistor 13 is turned on, similarly to the second commutation circuit of the pulse current application circuit according to the first embodiment. Has the function of

Next, the operation of the pulse current application circuit having the above configuration will be described with reference to FIG. First, as shown in FIG. 3, the DUT 14 is connected between the MOS transistor 13 and the reference potential (GND).

When the gate drive circuit 21 applies a gate voltage G3, which becomes a high (H) level at time t11, to the gate terminal of the MOS transistor 19, the MOS transistor 19 turns on. As a result, the other terminal of the inductor 12 is connected to the reference potential (GND), and the series connection circuit of the MOS transistor 11 and the inductor 12 is connected between the positive electrode terminal of the power supply 10 and the reference potential (GND). become.

Next, when the gate drive circuit 17 applies a gate voltage G1 that becomes a high (H) level at time t12 to the gate terminal of the MOS transistor 11, the MOS transistor 11 turns on and a current I () is applied to the MOS transistor 11 and the inductor 12. L) begins to flow,
di / dt = {V (DC) -Von (MOS1) -Von (MOS3)} / L
... (4)
It will increase as you go. Here, Von (MOS3) is the drain-source voltage when the MOS transistor 19 is turned on.

Next, at time t13 during the ON period of the MOS transistor 11, the gate drive circuit 18 applies the gate voltage G2 to the gate terminal of the MOS transistor 13. As a result, the MOS transistor 13 turns on, but since a reverse bias voltage is applied to the DUT 14, no current flows through the DUT 14.

Next, when the MOS transistor 11 turns off at time t14, the current supplied to the inductor 12 is cut off. The inductor 12 directs the energy stored in order to maintain the current flow toward the first commutation circuit, and the current I (DUT) flows through the DUT 14. This current I (DUT) reaches the maximum current Imax at the timing of the time t14 when the current starts to flow in the DUT 14, and then gradually decreases.

Next, when the MOS transistor 13 turns off at time t15, the current I (DUT) of the DUT 14 is cut off at that time. As a result, a short pulse having a pulse width of time (t15-t14) flows through the DUT 14.

When the MOS transistor 13 is turned off, the current flowing through the first commutation circuit now flows through the second commutation circuit, and the current I (D1) is applied to the diodes 15a, 15b, ... 15n. ) Flows. At time t16 immediately after the MOS transistor 13 is turned off, the MOS transistor 19 is turned off. As a result, the closed-loop circuit including the inductor 12, the MOS transistor 19, the diodes 15a, 15b, ... 15n is cut off, so that the current of the inductor 12 is regenerated to the power supply 10 via the diode 20 and the current I ( D2) flows. After the MOS transistor 13 is turned off, almost all the energy remaining in the inductor 12 is consumed by the second commutation circuit if the MOS transistor 19 is not turned off, and the current I (D1) is shown by the broken line. It will decrease over a long period of time. Therefore, by shortening the period from the time t15 when the MOS transistor 13 is turned off to the time t16 when the MOS transistor 19 is turned off as short as possible, the consumption in the second commutation circuit is reduced, and the energy is regenerated to the power supply 10 by that amount. Energy can be increased. Since the power supply 10 has a configuration in which most of the energy that does not contribute to the application of the pulse current is regenerated in the pulse current application circuit, a power supply having a small capacity is sufficient.

In the first embodiment, it was necessary to increase the value of the voltage drop in the second commutation circuit in order to accelerate the decay of the current of the inductor 12, but in the second embodiment, the inductor Since the attenuation of the current of 12 is almost determined by the power supply voltage, it is not necessary to increase the value of the voltage drop in the second commutation circuit. Rather, the total value of the built-in voltages of the diodes 15a, 15b, ... 15n is less than the total value of the forward voltage Vf of the DUT 14 at a predetermined current and the drain-source voltage Von when the MOS transistor 13 is turned on. Not increasing it is effective in reducing the loss in the diodes 15a, 15b, ... 15n.

FIG. 5 is a circuit diagram illustrating the pulse current application circuit according to the third embodiment, and FIG. 6 is a timing diagram illustrating the operation of the pulse current application circuit according to the third embodiment. In the circuit diagram of FIG. 5, the same or equal components as the components of the circuit shown in FIG. 1 are designated by the same reference numerals.

As shown in FIG. 5, the pulse current application circuit according to the third embodiment includes a MOS transistor 11, and the drain terminal of the MOS transistor 11 is connected to the positive electrode terminal of the power supply 10. The negative electrode terminal of the power supply 10 is connected to a reference potential (GND). The source terminal of the MOS transistor 11 is connected to one terminal of the inductor 12, and the other terminal of the inductor 12 is connected to the drain terminal of the MOS transistor 19 and the anode terminal of the diode 20. The source terminal of the MOS transistor 19 is connected to a reference potential (GND), and the gate drive circuit 21 is connected to the gate terminal of the MOS transistor 19. The cathode terminal of the diode 20 is connected to the positive electrode terminal of the power supply 10. The diode 20 has a withstand voltage higher than the voltage of the power supply 10.

The source terminal of the MOS transistor 11 is also connected to the source terminal of the MOS transistor 13. The drain terminal of the MOS transistor 13 is connected to the cathode terminal of the DUT 14, and the anode terminal of the DUT 14 is connected to the reference potential (GND). The MOS transistor 13 and the DUT 14 form a first commutation circuit.

The source terminal of the MOS transistor 11 is further connected to the source terminal of the MOS transistor (fourth switching element) 22, and the drain terminal of the MOS transistor 22 is connected to the cathode terminal of the diode 23. The anode terminal of the diode 23 is connected to a reference potential (GND). A gate drive circuit 24 is connected to the gate terminal of the MOS transistor 22. The MOS transistor 22 and the diode 23 form a second commutation circuit.

Next, the operation of the pulse current application circuit having the above configuration will be described with reference to FIG. First, as shown in FIG. 5, the DUT 14 is connected between the MOS transistor 13 and the reference potential (GND).

First, when the current I (L) of the inductor 12 becomes 0 in the previous pulse application and then the gate drive circuit 21 applies a high (H) level gate voltage G3 to the gate terminal of the MOS transistor 19, the MOS transistor 19 turns on. As a result, the other terminal of the inductor 12 is connected to the reference potential (GND).

Here, when the gate voltage G1 at which the gate drive circuit 17 becomes a high (H) level at time t21 is applied to the gate terminal of the MOS transistor 11, the MOS transistor 11 turns on. At this time, since the diode 23 of the second commutation circuit is in a reverse bias state, currents I (MOS1) and I (L) flow from the power supply 10 to the inductor 12 via the MOS transistor 11. The change in the current I (L) flowing through the inductor 12 increases according to the above equation (4).

Next, at time t22 during the ON period of the MOS transistor 11, the gate drive circuit 18 applies a high (H) level gate voltage G2 to the gate terminal of the MOS transistor 13. As a result, the MOS transistor 13 turns on, but since a reverse bias voltage is applied to the DUT 14, no current flows through the DUT 14.

Next, when the MOS transistor 11 is turned off at time t23, the current I (MOS1) supplied to the inductor 12 is cut off. The inductor 12 commutates the energy stored in an attempt to maintain the current flow to the first commutation circuit. As a result, the current I (DUT) flows through the DUT 14. This current I (DUT) becomes the maximum current Imax at the timing of the time t23 when the current starts to flow in the DUT 14. After that, the current I (DUT) is
-Di / dt = {Von (MOS2) + Von (MOS3) + Vf (DUT)} / L
... (5)
It gradually decreases as it increases.

Next, at time t24, the MOS transistor 22 receives a high (H) level gate voltage G4 from the gate drive circuit 24 and turns on. This constitutes a second commutation circuit . At this time, if the total voltage of the drain-source voltage Von when the MOS transistor 22 is turned on and the forward voltage of the diode 23 is lower than the voltage drop in the first commutation circuit, the first Current flows through both the commutation circuit and the second commutation circuit.

Next, when the MOS transistor 13 is turned off at time t25, the current I (DUT) flowing through the first commutation circuit is completely transferred to the second commutation circuit having the MOS transistor 22 and the diode 23. It is swept and the current I (D3) flows. As a result, a short pulse having a pulse width of time (t25-t23) flows through the DUT 14.

Next, when the MOS transistor 19 is turned off at time t26, the path to the reference potential of the second commutation circuit is cut off, and the current flowing through the inductor 12 is transferred to the third commutation circuit by the diode 20. It is flowed and becomes a current I (D2) and is regenerated to the power supply 10.

In this pulse current application circuit, the total value of the forward voltage drop of the diode 23 in the second commutation circuit and the drain-source voltage Von when the MOS transistor 22 is turned on is small, so that the second commutation The loss in the circuit can be reduced. Further, since the electric power after the pulse current is applied can be regenerated to the power source 10 and the energy remaining in the inductor 12 can be attenuated at an early stage, the frequency in the discontinuous mode repeatedly applied to the DUT 14 can be increased.

FIG. 7 is a circuit diagram illustrating the pulse current application circuit according to the fourth embodiment. In the circuit diagram of FIG. 7, the same or equal components as the components of the circuit shown in FIG. 5 are designated by the same reference numerals.

In the pulse current application circuit according to the fourth embodiment, n diodes 15a, 15b, ... 15n are connected in series to the second commutation circuit of the pulse current application circuit according to the third embodiment. The circuit that was used is added. The total value of the forward voltages of the diodes 15a, 15b, ... 15n is larger than the total value of the on voltage of the MOS transistor 13 and the forward voltage of the DUT 14.

The pulse current application circuit according to the fourth embodiment turns on the MOS transistor 22 at the same time as the turn-off of the MOS transistor 13 as in the pulse current application circuit according to the third embodiment. Here, the turn-off timing of the MOS transistor 13 and the turn-on timing of the MOS transistor 22 do not match, and the turn-on timing of the MOS transistor 22 may be delayed. At this time, since the current I (L) of the inductor 12 cannot be smoothly commutated from the first commutation circuit to the second commutation circuit, a voltage exceeding the breakdown voltage is applied to the MOS transistor 13. There is a possibility that the MOS transistor 13 will be destroyed.

However, when the turn-on timing of the MOS transistor 22 is delayed from the turn-off timing of the MOS transistor 13, the current I (L) of the inductor 12 flows through the series circuit of the diodes 15a, 15b, ... 15n. As a result, the MOS transistor 13 of the first commutation circuit is not subject to an abnormally high voltage, so there is no risk of damage.

10 Power supply 11 MOS transistor (first switching element)
12 Inductor 13 MOS transistor (second switching element)
14 DUT (current application target)
15, 15a, 15b, ... 15n diode 16 Zener diode 17,18 Gate drive circuit 19 MOS transistor (third switching element)
20 diode (regenerative diode)
21 Gate drive circuit 22 MOS transistor (fourth switching element)
23 Diode 24 Gate drive circuit

Claims (8)

The first switching element and
An inductive load connected in series with the first switching element and connected between the power supply and the reference potential,
A second switching element connected in series with the current application target between the connection point of the first switching element and the inductive load and the reference potential, and the like.
A commutation circuit connected in parallel to the inductive load, in which no current flows when the second switching element is in a conductive state, and current flows when the first switching element and the second switching element are in a cutoff state. When,
Equipped with
The commutation circuit has a diode and a Zener diode connected in reverse series, and the built-in voltage of the diode in which the second switching element is forward biased in the conduction state and the breakdown voltage of the Zener diode in which the second switching element is reverse biased. The total value of is made larger than the voltage drop of the second switching element and the current application target when a predetermined current is passed through the second switching element and the current application target.
The energy supplied from the power supply is stored in the inductive load connected in series with the first switching element by making the first switching element conductive.
The current supplied to the inductive load is applied to the current application target connected in series with the second switching element in the reverse bias state by making the second switching element conductive.
The current of the inductive load is transferred to the current application target with the first switching element cut off.
After the current of the inductive load is commutated to the current application target for a predetermined period, the second switching element is brought into a cutoff state.
Pulse current application circuit. The first switching element and
An inductive load connected in series with the first switching element and connected between the power supply and the reference potential,
A second switching element connected in series with the current application target between the connection point of the first switching element and the inductive load and the reference potential, and the like.
A commutation circuit connected in parallel to the inductive load, in which no current flows when the second switching element is in a conductive state, and current flows when the first switching element and the second switching element are in a cutoff state. When,
Equipped with
The commutation circuit has a plurality of series connection diodes, and when a predetermined current is passed through the second switching element and the current application target, the total value of the built-in voltages of the series connection diodes is applied to the second switching element. It is made larger than the voltage drop of the switching element and the current application target .
The energy supplied from the power supply is stored in the inductive load connected in series with the first switching element by making the first switching element conductive.
The current supplied to the inductive load is applied to the current application target connected in series with the second switching element in the reverse bias state by making the second switching element conductive.
The current of the inductive load is transferred to the current application target with the first switching element cut off.
After the current of the inductive load is commutated to the current application target for a predetermined period, the second switching element is brought into a cutoff state.
Pulse current application circuit. A third switching element connected between the inductive load and the reference potential, and a regenerative diode connected between the connection point between the inductive load and the third switching element and the power supply. 2. The pulse current application circuit according to claim 2 . The first switching element and
An inductive load connected in series with the first switching element and connected between the power supply and the reference potential,
A second switching element connected in series with the current application target between the connection point of the first switching element and the inductive load and the reference potential, and the like.
A commutation circuit connected in parallel to the inductive load, in which no current flows when the second switching element is in a conductive state, and current flows when the first switching element and the second switching element are in a cutoff state. When,
Equipped with
A third switching element connected between the inductive load and the reference potential, and a regenerative diode connected between the connection point between the inductive load and the third switching element and the power supply. Further, the commutation circuit includes a fourth switching element that conducts when the second switching element becomes non-conducting, and a diode in which the fourth switching element is forward-biased in the conducting state. Have and
The energy supplied from the power supply is stored in the inductive load connected in series with the first switching element by making the first switching element conductive.
The current supplied to the inductive load is applied to the current application target connected in series with the second switching element in the reverse bias state by making the second switching element conductive.
The current of the inductive load is transferred to the current application target with the first switching element cut off.
After the current of the inductive load is commutated to the current application target for a predetermined period, the second switching element is brought into a cutoff state.
Pulse current application circuit. The commutation circuit has a plurality of series connection diodes, and when a predetermined current is passed through the second switching element and the current application target, the total value of the built-in voltages of the series connection diodes is applied to the second switching element. The pulse current application circuit according to claim 4 , wherein the voltage drop is larger than that of the switching element and the voltage drop of the current application target. A first switching element, an inductive load connected in series with the first switching element and connected between a power source and a reference potential, and a connection point between the first switching element and the inductive load. When the second switching element connected in series with the current application target between the reference potential and the second switching element connected in parallel with the inductive load and the second switching element is in a conductive state, no current flows. A pulse current application circuit comprising: a commutation circuit including a diode and a Zener diode connected in anti-series series in which a current flows when the first switching element and the second switching element are in a cutoff state.
The total value of the built-in voltage of the diode in which the second switching element is forward-biased in the conduction state and the breakdown voltage of the Zener diode in which the second switching element is reverse-biased is determined for the second switching element and the current application target. Make it larger than the voltage drop of the second switching element and the current application target when a current is applied.
The energy supplied from the power supply is stored in the inductive load connected in series with the first switching element by making the first switching element conductive.
The current supplied to the inductive load is applied to the current application target connected in series with the second switching element in the reverse bias state by making the second switching element conductive.
The current of the inductive load is transferred to the current application target with the first switching element cut off.
After the current of the inductive load is commutated to the current application target for a predetermined period, the second switching element is brought into a cutoff state.
Control method of pulse current application circuit. The control method for a pulse current application circuit according to claim 6 , wherein the current to be applied to the current is commutated to the commutation circuit after the second switching element is cut off. Before accumulating energy in the inductive load, the third switching element connected between the inductive load and the reference potential is brought into a conductive state.
The seventh aspect of claim 7 , wherein after the current to be applied to the current is commutated to the commutation circuit, the third switching element is turned off and the current commutated to the commutation circuit is regenerated to the power supply. How to control the pulse current application circuit.

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