JPH0524105Y2 - - Google Patents

Description

[Detailed Description of the Invention] Industrial Application Field The present invention is directed to a protection diode including a first diode and a second diode connected in series with opposite polarities, particularly for a power supply circuit including a resonant circuit that drives a magnetron. Related to protection diodes that can protect this power supply circuit in the event of a short circuit.

BACKGROUND ART In household microwave ovens, a magnetron power supply circuit called a half-wave voltage doubler system is often used. In this power supply circuit, as shown in FIG.
It is publicly known from Publication No. 36534. In the power supply circuit shown in FIG. 2, the primary winding 5 of the magnetic leakage transformer 4 is connected to input terminals 6 and 7 to which commercial AC voltage is applied, and there is no fuse or circuit between the primary winding 5 and the input terminal 6. Overcurrent detection circuit breaker such as kit breaker 8
is connected. Secondary winding 9 of magnetic leakage transformer 4
One end is connected to the magnetron 1 via a capacitor 10.
1 cathode 12. The other end of the secondary winding 9 and the anode 13 of the magnetron 11 are grounded. Note that illustration of the heater power supply circuit used for the magnetron 11 is omitted. The anode of a high voltage rectifier diode 14 is connected between the capacitor 10 and the cathode 12 of the magnetron 11, and the cathode of the rectifier diode 14 is grounded. Connection path 3 consisting of a first diode 1 and a second diode 2
is the capacitor 1 so that the first diode 1 and the rectifier diode 14 have the same polarity when viewed in series.
0 in parallel between the secondary winding 9 and the cathode 12 of the magnetron 11.

In the above configuration, the capacitor 10 and the magnetic leakage transformer 4 constitute a half-wave voltage doubler type resonant circuit. During the half cycle in which an upward voltage is generated in the secondary winding 9, current flows from the secondary winding 9 through the capacitor 10 and the rectifier diode 14, and the capacitor 10 is charged. In the reverse half cycle in which a downward voltage is generated in the secondary winding 9, in addition to the voltage generated in the secondary winding 9 of the magnetic leakage transformer 4, the capacitor 10 charged in the previous half cycle also moves in the same direction. works as a power source. As a result, a high voltage having a peak voltage of about 3.5 kV and having a substantially rectangular wave is applied across the rectifier diode 14 and the magnetron 11 in the commercial cycle. magnetron 11
oscillates and generates microwaves by applying the high voltage during the reverse half cycle.

Next, the protection operation of the power supply circuit shown in FIG. 2 will be explained.

During normal operation, as shown in FIG. 3, a large voltage of about 4 kV is applied to both ends of the capacitor 10 on the positive side, and a small voltage of about 1 kV is applied on the negative side. Note that the positive side and negative side are based on the polarity of the secondary winding 9 side of the capacitor 10. For such a normal applied voltage, the breakdown voltages Vb1 and Vb2 of the first diode 1 and the second diode 2 are set to, for example, first diode 1: Vb1 = 1.75 kV, second diode 2: Vb2 = 9 kV. , the connection path 3 consisting of the first diode 1 and the second diode 2 is in a current blocking state in both directions during normal operation. (However, instantaneous conduction due to surge voltage and conduction at the level of leakage current naturally occur.) Therefore, during normal operation, the connection path 3 does not substantially affect the operation of the power supply circuit.

However, when the magnetron 11 operates abnormally, for example, due to a failure and short circuit, the impedance decreases and the secondary winding 9 of the magnetic leakage transformer 4
winding current increases. In this case, the winding current on the primary winding 5 side of the magnetic leakage transformer 4 is
Since it is sufficient to apply enough power to sustain the resonant operation on the side, the amount of power is reduced compared to normal operation. Therefore, when the connection path 3 is not connected, the overcurrent detection circuit breaker 8 does not provide protection, and the secondary winding 9 of the magnetic leakage transformer 4 generates abnormal heat, leading to a burnout accident. The same applies to the case where the rectifier diode 14 fails and becomes short-circuited.

The connection path 3 is connected to an overcurrent detection circuit breaker 8 during abnormal operation.
is provided to ensure reliable operation and protect the power supply circuit. During the above abnormal operation, if there is no connection path 3, the voltage of the secondary winding 9 of the magnetic leakage transformer 4 is directly applied to both ends of the capacitor 10, and the fourth
As shown in the figure, voltages of approximately 3kV are generated on the positive and negative sides, respectively. Therefore, in the negative half cycle, a reverse voltage of approximately 3V, which greatly exceeds its breakdown voltage Vb1, is applied to the first diode 1, and a large reverse current flows, which causes it to heat up beyond the allowable value and die in a short period of time. Destroy. Since the destroyed first diode 1 becomes short-circuited (including a quasi-short-circuited state), the secondary side of the magnetic leakage transformer 4 becomes short-circuited during the negative half cycle. Therefore, a large current also flows through the primary side of the magnetic leakage transformer 4, and the overcurrent detection circuit breaker 8 operates to protect the power supply circuit.

When configuring the above conventional protection diode,
As shown in FIG. 5, the first diode 1 and the second diode 2 are both chip stacked bodies 16 and 17 in which a plurality of semiconductor chips (silicon chips) 1a and 1b and 2a to 2h are stacked with solder 15.
and are each made as an individual resin-sealed diode. Lead electrodes 18 and 19 are connected to both ends of the chip stack 16 by solder 15. The chip stack 16 is covered with a protective resin 20 and sealed with a sealing resin 21. Similarly,
Lead electrodes 22 and 23 are connected to both ends of the chip stack 17 by solder 15. Chip laminate 1
7 is covered with a protective resin 20 and sealed with a sealing resin 21. The lead electrodes 19 and 22 are connected by soldering or the like, and a protection diode forming the connection path 3 is manufactured.

Problems that the invention aims to solve By the way, with conventional protection diodes, when the rectifier diode 14 or magnetron 11 malfunctions due to a short circuit, the first diode 1 is destroyed and the power supply circuit is cut off by the overcurrent detection circuit breaker 8. However, there is a relatively large variation in the time from the time of the short circuit to the shutdown of the power supply circuit (interruption time). Therefore,
The cut-off time may be prolonged and the protection operation may be incomplete. Therefore, considering this time variation,
Although it is necessary to prevent incomplete protection by providing a margin in the capacity of the magnetic leakage transformer 4, increasing the capacity of the magnetic leakage transformer 4 causes an increase in costs.

Furthermore, when a diode is manufactured from a chip stack obtained by cutting a wafer stack, the breakdown voltage of the semiconductor chips adjacent to the lead electrodes varies more than the breakdown voltage of semiconductor chips not adjacent to the lead electrodes. This is believed to be due to the fact that the etching and cleaning of the semiconductor chip adjacent to the lead electrodes tends to be incomplete during the etching and cleaning process of the chip surface (side surface) during manufacturing. Therefore, the breakdown voltages Vb1 and Vb2 of the first diode 1 and the second diode 2 are also affected by this variation, and the first diode 1 is particularly affected by this variation at a large rate. In this case, no operational problem occurs even if the breakdown voltage Vb2 of the second diode 2 is set sufficiently higher than the applied voltage, so the influence of variations in the breakdown voltage Vb2 can be eliminated. However, the first diode 1
Variations in the breakdown voltage Vb1 of the power supply circuit greatly affect the protection operation of the power supply circuit. That is, when a reverse voltage exceeding Vb1 is applied to the first diode 1 during abnormal operation, the larger Vb1 is, the more difficult it is for thermal breakdown of the first diode 1 to occur, and the cut-off time becomes longer. Therefore, the allowable voltage range of Vb1 must be set within a narrow range with its lower limit relatively close to the maximum value of the applied voltage during normal operation. That is, since a strict breakdown voltage range is set for the first diode 1 whose breakdown voltage has a relatively large variation, the manufacturing yield of the first diode 1 will be low.

Therefore, the purpose of the present invention is to compensate for manufacturing variations in the breakdown voltage of the first diode, and to destroy the first diode quickly and reliably in the event of abnormal operation, thereby reducing the operation of the overcurrent detection circuit breaker. The object of the present invention is to provide a protection diode that can completely protect a power supply circuit.

Means for Solving the Problems The protective diode of the present invention consists of a first diode and a second diode connected in series with opposite polarity, and in a circuit, the protective diode is in a current blocking state in both directions during normal operation. When a connection path is formed and a reverse voltage exceeding the breakdown voltage is applied to the first diode during abnormal operation, an excessive reverse current flows and the first diode is destroyed, causing the connection path to change to at least one-way conduction state. . In this protection diode, the first diode is provided with a first chip stack made of a plurality of semiconductor chips or one semiconductor chip, the second diode is provided with a plurality of second chip stacks made of a plurality of semiconductor chips, and the second diode is provided with a plurality of second chip stacks made of a plurality of semiconductor chips. Both ends of one chip stack are respectively connected to lead electrodes via a second chip stack.

Function During abnormal operation when a voltage exceeding the first diode reverse breakdown voltage Vb1 is applied and an excessive reverse current flows, the amount of heat dissipation of the first diode sandwiched between the two second diodes decreases. The diode reaches a heated state in a short time and is destroyed. Furthermore, since the first chip stack forming the first diode is connected to the lead electrode via the second chip stack forming the second diode, variations in the breakdown voltage of the first chip stack can be reduced. .

Embodiment Hereinafter, an embodiment of the present invention will be described with reference to FIG. In these drawings, the same parts as those shown in FIGS. 2 and 5 are designated by the same reference numerals, and the explanation thereof will be omitted.

In the protective diode of the present invention shown in FIG. 1, the first diode 1 is composed of a single first chip stack 24 consisting of two first semiconductor chips 1a and 1b connected to each other by solder 15. Ru. The second diode 2 also has two second chip stacks 25 each consisting of four second semiconductor chips 2a to 2b and 2e to 2h connected to each other by solder 15 on both sides of the first chip stack 24. It consists of 26 pieces. This protective diode, which consists of a first diode 1 and a second diode 2 connected in series with opposite polarity, is composed of a single chip stack 27 as a whole. The chip stack 27 is manufactured by cutting out the wafer stack. Lead electrodes 28 and 29, which act as main heat radiators, are connected to both ends of the chip stack 27 by solder 15, respectively. The chip stack 27 is covered with a protective resin 20 and sealed with a sealing resin 21.

The protection diode shown in FIG. 1 is used to form the connection path 3 of FIG. in this case,
The breakdown voltage Vb2 of the second diode 2 is larger than the reverse voltage applied to the second diode 2 across the capacitor 10 during normal operation. The breakdown voltage Vb1 of the first diode 1 is the voltage Vb1 of the first diode 1 applied across the capacitor 10 during normal operation.
, and smaller than the breakdown voltage Vb2 of the second diode 2. Breakdown voltage Vb1 and
Specific examples of Vb2 and the voltage applied across the capacitor 10 are the same as the examples given in the "Prior Art" section.

In the structure shown in FIG. 1, the first chip stack 24 constituting the first diode 1 is
Since it is glued to the approximate center of 7, it is in the position where heat dissipation is the worst. Therefore, when used in the power supply circuit of FIG. 2, the reverse breakdown voltage of the first diode 1
During an abnormal operation in which a voltage exceeding Vb1 is applied and an excessive reverse current flows, the first diode 1 tends to reach an overheating state, and breaks down in a shorter time than conventionally, resulting in a short circuit state.

On the other hand, since the first chip stack 24 constituting the first diode 1 is not adjacent to the lead electrodes 28 and 29, the variation in breakdown voltage of the first semiconductor chips 1a, 1b is smaller than in the prior art. Therefore, it becomes possible to set the breakdown voltage Vb1 of the first diode 1 with high precision. Thereby, it is possible to set the breakdown voltage Vb1 low so that the first diode 1 breaks down as quickly as possible without sacrificing manufacturing yield.

Incidentally, when the first diode 1 is overheated, the second semiconductor chips 2a to 2h of the second diode 2 adjacent to the first diode 1 may be thermally destroyed at the same time. By the way, in order to cut off the power supply circuit by operating the overcurrent detection circuit breaker 8, both the first diode 1 and the second diode 2 must be completely thermally destroyed and the connection path 3 must be in a conductive state in both directions. More preferred. Therefore, the second semiconductor chip 2a
The simultaneous thermal destruction of ~2h does not pose any problem in protecting the power supply circuit.

Effects of the invention According to the invention, when an excessive reverse current flows through the first diode, the first diode is overheated and destroyed in a shorter time than conventionally, and the cut-off time is shortened. The problems of breakdown voltage variations and low manufacturing yields of the first diode with the semiconductor chip adjacent to the lead electrode are also improved. Therefore, a protection diode is provided that can more completely protect the power supply circuit. Furthermore, by integrating what was conventionally two diodes into one diode, size reduction, weight reduction, and cost reduction can also be achieved.

[Brief explanation of drawings]

Fig. 1 is a cross-sectional view of a protective diode according to the present invention, Fig. 2 is a circuit diagram of a power supply circuit including a resonant circuit that drives the magnetron, and Fig. 3 is a voltage applied to both ends of the capacitor 10 shown in Fig. 2 during normal operation. FIG. 4 is a graph showing the voltage waveform applied to both ends of the capacitor 10 during abnormal operation, and FIG. 5 is a cross-sectional view of a conventional protection diode. 1... First diode, 1a, 1b... First semiconductor chip, 2... Second diode, 2a to 2h
... Second semiconductor chip, 3 ... Connection path, 4 ... Magnetic leakage transformer, 5 ... Primary winding, 6, 7 ... Input terminal, 8 ... Overcurrent detection circuit breaker, 9 ... Secondary winding wire, 10... capacitor, 11... magnetron, 12... cathode, 13... anode, 14
... Rectifier diode, 15 ... Solder, 24 ... First chip laminate, 25, 26 ... Second chip laminate, 27 ... Chip laminate, 28, 29 ... Lead electrode.

Claims (1)

[Claims for Utility Model Registration] (1) A circuit consisting of a first diode and a second diode connected in series with opposite polarities, forming a protective connection path in which current is blocked in both directions during normal operation. , for protection, in the event of an abnormal operation in which a reverse voltage exceeding a breakdown voltage is applied to the first diode, an excessive reverse current flows, the first diode is destroyed, and the connection path changes to at least one-way conduction state. In the diode, the first diode includes a first chip stack made of a plurality of semiconductor chips or one semiconductor chip, the second diode includes a plurality of second chip stacks made of a plurality of semiconductor chips, and the second diode includes a plurality of second chip stacks made of a plurality of semiconductor chips. 1. A protection diode, wherein both ends of one chip laminate are connected to lead electrodes via the second chip laminate. (2) Each of the opposite ends of the first chip stack is adjacent to two second chip stacks in which a plurality of the semiconductor chips are stacked. diode. (3) The circuit is a resonant circuit in which a capacitor and a rectifier diode are connected in series to the secondary side of a magnetic leakage transformer, and a magnetron is connected in parallel to the rectifier diode, and the first diode is connected to the rectifier. connected in series with the same polarity to the diode and in parallel to the capacitor, the breakdown voltage of the second diode being greater than the reverse voltage to the second diode that is applied across the capacitor during normal operation; The breakdown voltage of the first diode is greater than the reverse voltage applied to the first diode that is applied across the capacitor during normal operation, and smaller than the breakdown voltage of the second diode. ) or (2).