JP3493270B2 - Measurement circuit for diode reverse recovery time - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a measuring circuit for measuring a reverse recovery time of a diode.

[0002]

2. Description of the Related Art FIGS. 1 and 2 show an example of a reverse recovery time measuring circuit which has been conventionally used. FIG. 1 shows a measuring circuit by the IF and IR methods, and FIG. 3 shows a measuring circuit by the di / dt method.

In the measuring circuit using the IF and IR methods shown in FIG. 1, a rectangular wave of 1 kHz, for example, is applied to a diode D1 to be measured through a resistor R1. (2) As a result, the current waveform of the diode D1 becomes a waveform as shown in FIG. IF (forward current), IR (reverse current)
Is set to the specified value in advance, and the resistance R
Since there is a current limiting period of IR by 1, the reverse recovery time (trr) is measured from this.

In the measuring circuit according to the di / dt method shown in FIG. 3, a switch S1 is closed from one power source voltage V1 to cause a current to flow forward through a resistor R2 to a diode D1 to be measured. Next, while the switch S1 is kept closed, the switch S2 is closed by the other power source voltage V2 higher than V1 to measure the measured diode.
A current flows in the opposite direction to D2. Inductance L1
Is a constant that determines the current reduction rate.

Therefore, in the measuring circuit by the di / dt method of FIG. 3, a current waveform as shown in FIG. 4 is generated. Here, the reverse recovery time trr is measured under the condition of the designated value of IF and the current decrease rate during the current commutation period.

[0006]

The above-mentioned IF, IR method, d
In any measurement method of the i / dt method, when measuring in a production line, the diode to be measured is pinched and measured using a contactor, etc., so that the wiring becomes long and the current decrease rate is not constant. , A problem occurs in the reproducibility of measured values. Further, the wiring inductance up to the contact becomes a size that cannot be ignored, so that di / dt cannot be increased, and there is a problem that a high speed diode with a reverse recovery time trr ≦ 50 ns cannot be measured. .

Further, FIG. 5 shows current waveforms in the case of a good diode and a defective diode by the IF and IR methods.
The reverse recovery time trr is generally defined as the time when the IR has recovered to 10%, but in FIG. 5A (good product), B
(3) There is a problem that the waveform cannot be discriminated in the case of (defective product).

Therefore, according to the present invention, the diode to be measured is pinched by a contactor or the like in the production line, and the reciprocating wiring is 60 cm.
Even if there is a degree, it is a good or bad dio-
It is an object of the present invention to provide a reverse recovery time measuring circuit capable of discriminating a reverse recovery waveform of a drive signal with good reproducibility.

[0009]

SUMMARY OF THE INVENTION The present invention is directed to a measured diode.
The voltage of a sine wave oscillator having a frequency equal to or higher than the reciprocal of the reverse recovery time of the diode is applied to the diode to be measured through impedance, and a current is applied to the diode to be measured in the forward direction to charge the capacitor. , When a reverse current flows through the diode to be measured, a charge proportional to the storage time is discharged to the capacitor, and the capacitor terminal voltage is measured. If the reverse recovery time is short, the capacitor terminal voltage is high and the reverse recovery is performed. A diode reverse recovery time measurement circuit characterized by measuring the reverse recovery time of a diode by utilizing the fact that the capacitor terminal voltage becomes low when the time is long.

[0010]

Further, the reverse recovery time of the diode to be measured can be measured by the conversion table of the terminal voltage of the capacitor and the reverse recovery time.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 6 shows an embodiment of the present invention.
2 is a sine wave oscillator, R1 and R3 are forward and reverse current limiting resistors of the diode, C1 is a capacitor for measuring the rectified voltage of the diode D1 to be measured, and R4 is a resistor for determining the charging / discharging time constant of the capacitor C1. , R5 is the internal impedance of the measuring device (DC voltmeter), and D1 is the diode to be measured.

A sine wave voltage is applied by the sine wave oscillator G2 in order to reduce the dependency of the inductance. (4) When the measured diode D1 is in the forward direction, G2 → R1 → D1 →
A current flows through the path R3 → G2, and the terminal voltage of the resistor R3 charges the capacitor C1 through the resistor R4.

When the diode D1 to be measured is in the reverse direction, the charge accumulated in the capacitor C1 by the accumulated charge of the diode D1 is C1 → R4 → D1 → R1 → G2.
→ It is discharged through C1. This discharge load is
It is in proportion to the accumulated charge of D1.

Therefore, the diode with the larger accumulated charge is
The terminal voltage of the capacitor C1 becomes smaller. FIG. 7 shows this characteristic. That is, FIG. 7 is a characteristic diagram showing the difference in the terminal voltage of the capacitor C1 due to the difference in the reverse recovery waveform.

In FIG. 7, the frequency of the sine wave oscillator G2 is a frequency that cannot be ignored with respect to the reverse recovery time of the diode D1 to be measured. Generally, it is selected to be 5 to 10 MHZ having a frequency almost equal to the reverse recovery time. In this frequency range, the diode with a large accumulated charge has a large discharge load, so the terminal voltage of the capacitor C1 becomes small, and the diode shown in FIG.
It becomes the characteristic of B. On the other hand, since the diode with a small accumulated charge has a small discharge load, the terminal voltage of the capacitor C1 becomes large and the characteristic of A is obtained.

In the waveform of FIG. 5, a diode having a small accumulated charge amount exhibits a recovery characteristic like A, and a diode having a large accumulated charge amount exhibits a recovery characteristic like B. . However, in both cases of A and B, the recovery-time tr is the time when the recovery current is recovered to 0,1IR.
Since it is defined as r, in the conventional measurement method, the reverse recovery time is measured at the same value, and the difference between superiority and inferiority does not appear. (5)

However, in the case of classifying diodes according to diode selection, the characteristic A having a small accumulated charge amount is the A class, and the characteristic B having a large accumulated charge amount is the B class. Is preferred.

Therefore, in the present invention, in the measuring circuit of FIG. 6, the frequency of the sine wave oscillator G2 is set to a measurable frequency band of about 5 to 10 MHZ, and the terminal voltage of the capacitor C1 is measured by digibol or the like.

As a result, the characteristics A and B shown in FIG. 7 can be selected. On the other hand, if the relationship between the reverse recovery time trr and the terminal voltages of the characteristics A and B is prepared in the table in advance, the reverse recovery time can be read from the terminal voltage of the capacitor C1.

Now, the effect of the wiring of the measuring circuit was examined by actual measurement. The difference between when the anode wiring and cathode wiring of the diode to be measured approached and when they largely separated was as follows. As the measurement conditions, the frequency of the sine wave oscillator is 5 MHZ, the wiring length between the measuring terminals is 60 cm, and the reverse recovery time trr of the diode to be measured trr = 155 ns, the terminal voltage of the capacitor C1 is 594 when the wiring is separated.
It was found that the reproducibility of the measured values was extremely good, which is 597 mv when the wiring approaches.

[0022]

According to the present invention, when the diode reverse recovery time is measured on the production line, it is not affected by the measurement wiring, and therefore the measurement can be performed with extremely good reproducibility. Further, since the influence of the wiring inductance is small, it is possible to measure a high speed diode. Further, it is possible to classify the diodes (6) by the difference in the reverse recovery current waveform, which does not appear as the difference in the reverse recovery time, and it is possible to finely select the diodes.

[Brief description of drawings]

FIG. 1 is a circuit for measuring the reverse recovery time of a diode by the IF and IR methods.

FIG. 2 is a current waveform of a diode according to the IF and IR methods.

FIG. 3 is a circuit for measuring a reverse recovery time of a diode by a di / dt method.

FIG. 4 is a current waveform of a diode by the di / dt method.

FIG. 5 shows a current waveform due to a difference in accumulated charge of a diode.

FIG. 6 shows an embodiment of a reverse recovery time measuring circuit for a diode according to the present invention.

FIG. 7: Difference in terminal voltage of the capacitor C1 due to difference in reverse recovery time of diode.

[Explanation of symbols]

G1 pulse generator G2 sine wave generator R1 rectifier forward current, reverse current limiting resistor R2 rectifier forward current limiting resistor R3 rectifier forward current, reverse current limiting resistor R4 Capacitor C1 charging / discharging time constant resistance Equivalent input impedance of measuring instrument for measuring R5 C1 terminal voltage D1 Measured diode C1 Measured diode rectified voltage measuring capacitor

Continuation of front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) G01R 31/26 G01R 31/28-31/3193 H01L 21/66

Claims (2)

(57) [Claims] 1. A reciprocal of a reverse recovery time of a diode to be measured or less.
The voltage of the sine wave oscillator with the above frequency is
Is applied to the measured diode via the
Current in the forward direction to charge the capacitor,
When a reverse current flows through the constant diode, the capacitor
Discharges a charge proportional to the storage time to the capacitor
If the reverse recovery time is short after measuring the terminal voltage, the capacitor
If the terminal voltage is high and the reverse recovery time is long, the capacitor end
Using the lower child voltage, the reverse direction of the diode
At the time of diode reverse recovery characterized by measuring recovery time
Measuring circuit between. 2. A circuit for measuring a reverse recovery time of a diode according to claim 1, wherein the reverse recovery time is measured by a conversion table of the terminal voltage of the capacitor and the reverse recovery time.