JP2002218742A - Serially-connected circuit for schottky barrier diode, and the schottky barrier diode thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent generation of forward recovery transient loss by using an SBD, in a circuit of which the voltage is at least 200 V. SOLUTION: A D2 formed, by connecting at least two SBDs in series, is used in place of the conventional diode having a PN junction. This permits forward voltage VF to become a flat waveform without the presence of forward recovery voltage VFR. Thus, transient loss can be prevented from occurring at the time of forward recovery.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a series connection circuit using a Schottky barrier diode (hereinafter abbreviated as SBD) and a structure of an SBD used therefor.

[0002]

2. Description of the Related Art As a rectifier circuit using a general diode having a PN junction, there is a circuit as shown in FIG. In the rectifier circuit shown, the AC power supply E is rectified by a full-wave rectifier bridge circuit B. When the switching element Q is on, a drain current IQ flows through the coil L. Next, when the switching element Q is turned off, a current ID flows through the general-purpose diode D having a PN junction. When the switching element Q is turned on again, the drain current IQ flows,
The current ID becomes zero, and the voltage of the capacitor C is applied to the diode D as a reverse voltage.

FIG. 5 shows operation waveforms in the rectifier circuit. In the figure, the horizontal axis represents time, and the vertical axis represents voltage and current. In the figure, when the switching element Q is turned off at time t0, the current ID increases, and then reaches a steady state. At this time, from time t0 to t1, a steep rising current flows through the diode D1. At a forward voltage t1 of the diode D1, a large forward recovery voltage VFR is generated.
A transient loss occurs due to the product of the VFR and the forward current ID. In particular, when the on / off cycle of the switching element Q is shortened, the transient loss accounts for a large proportion of the total loss of the diode D1, so that the efficiency of this type of circuit is reduced. After the forward recovery voltage VFR is generated, the forward voltage VF becomes a steady state forward voltage VF. On the other hand, the current ID continues to flow while the switching element Q is off.

Next, the behavior of the diode from time t2 to time t4 will be described. When the switching element Q is turned on at the time t2, the current ID decreases, and the carriers remaining in the diode D1 generate a reverse current and a reverse voltage during the reverse recovery time trr as shown in FIG.

Now, the anode electrode side of the diode D1 having a PN junction is set to a negative (-) potential, and the diode D1 is
When the PN junction is reverse-biased so that the cathode electrode side of the P layer becomes a positive (+) potential, an acceptor atom having a negative charge (-qNa) is placed on the P layer side connected to the anode electrode, and the N layer is On the side, a donor atom having a positive charge (+ qNd) forms a biased distribution so as to repel the potential of both electrodes, forming a positive / negative double charge layer. The space charge generates an electric field distribution (E (x)), and furthermore, the electric field distribution (E (x)) generates a potential distribution (−V (x)), and this negative potential distribution (−V (x)). ) Prevents the applied reverse voltage (VR).

Next, when the diode (D1) is biased so as to have a forward voltage, that is, a positive (+) potential on the anode electrode side and a negative (-) potential on the cathode electrode side,
Acceptor atoms having a negative charge on the P layer side are attracted to the positive potential of the anode electrode, and donor atoms having a positive charge on the N layer side are attracted to the negative potential of the cathode electrode, It flows again toward each electrode.

That is, holes which are majority carriers on the P layer side become minority carriers on the N layer side, and N
Hole injection into the layer side is gradually started. N
The same operation is performed for electrons as another carrier from the layer side. However, in the present description, holes are particularly problematic, and therefore, description of electrons is omitted.

By the way, the N layer has a reverse voltage (VR).
Is usually designed to be maintained on the N layer side, so that high resistance (Nd concentration ≒ 1 × 10 ↑ 14 atoms / cm)
↑ 3) and the thickness is, for example, about 500 V / 50 μm, so that it is originally a high-resistance body. However, the holes injected into the N layer side depend on the injection level of the holes, so Body resistivity varies greatly.

That is, if holes are injected into more N layers, conductivity modulation in the N layer becomes stronger, and N
The resistivity of the layer will decrease. However, the time required for the hole injection amount to reach a certain level is not zero. In other words, a certain degree of conductivity modulation occurs to reach a steady state forward voltage drop (VF) depending on the device lifetime (τp) and the current density (J). It has been found that a time of the order of 0.1 μs is required.

From the above results, the above-mentioned forward recovery voltage (VFR) is required in the application of the operation frequency, especially the high-speed operation which affects the high-frequency operation in recent years, until the conductivity modulation is stabilized. Is particularly problematic.

As one measure against the above problem, the ordinary diode D1 can be replaced with an SBD to increase the efficiency. FIG. 3 shows current and voltage waveforms when the above SBD is used. It should be noted in FIG. 3 that the forward recovery voltage (V
FR) does not exist when SBD is used. Therefore, there is almost no transient loss during forward recovery.

That is, even if the on / off cycle of the switching element Q is shortened, the ratio of the entire diode to the loss is small, so that the efficiency of this type of rectifier circuit can be prevented from lowering. Next, the reason why the forward recovery voltage (VFR) is not generated by using the SBD will be considered. The reason is that the SBD does not have minority carriers like a PN junction diode, and because of conduction by majority carriers, there is no high resistance layer as in the PN junction when transitioning from reverse bias to forward bias. Does not occur.

[0013]

As described above, the conventional P
By using an SBD for a rectifier circuit instead of a diode having an N-junction, loss in a high frequency region can be reduced. However, if the circuit voltage is, for example, 200
SBDs cannot be used in rectifier circuits that exceed V. This is because the withstand voltage of SBD is 10
0-150V is the limit and therefore the circuit voltage is 2
If the voltage exceeds 00 V, the SBD cannot be used, and a diode having a PN junction for high-speed switching must be used. For this reason, in this case, a forward recovery voltage VFR still occurs, and as a result, there is a problem to be solved in that the efficiency of the rectifier circuit cannot be reduced.

[0014]

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-described problems. In a connection circuit using a diode, a circuit that reduces the loss even when the voltage applied to the diode is 200 V or more, and S used for the circuit
It is intended to provide a BD.

[0015]

A Schottky barrier diode series connection circuit according to the present invention comprises a Schottky barrier diode having an anode electrode connected to a power supply and a cathode electrode connected to a load. In the circuit, at least two Schottky barrier diodes are connected in series for the purpose of supporting a high-voltage circuit and reducing a forward recovery voltage.

The Schottky barrier diode of the present invention has at least two Schottky barrier diode chips mounted on a conductor plate so as to be electrically connected in series, and has a surface electrode and an external lead-out terminal. Are connected, and the periphery of the conductor plate on which the chip is mounted and a part of the external lead-out terminal are resin-sealed to form a resin mold portion.

[0017]

The series connection circuit of the SBD of the present invention is a conventional PN
Change the SBD to at least 2
By connecting and using these in series, the forward recovery voltage VF
There is no R, and the forward voltage VF has a flat waveform. For this reason, a transient loss during forward recovery does not occur.

In the SBD of the present invention, at least two SBD chips are sealed in one package so as to be electrically connected in series, so that the wiring resistance is relatively small and the usability is good. .

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below.
This will be described with reference to FIG. The series connection circuit of the present invention is characterized in that at least two SBDs are connected in series for the purpose of supporting a high-voltage circuit and reducing the forward recovery voltage VFR. The same components as in FIG. 4 shown as a conventional example are denoted by the same reference numerals, and description thereof will be omitted.

Next, the operation of the series connection circuit and its waveform will be described with reference to FIGS. In FIG. 1, an alternating current of an AC power supply E is rectified into a direct current via a full-wave rectifier circuit B. Next, when the direct current turns on the switching element Q, a drain current IQ flows through the coil L.
Next, when the switching element Q is turned off, a current ID flows through the SBD D2 connected in series, and supplies a current to the load side.

In the above circuit, since the SBD is used as D2, the forward recovery voltage VFR shown in FIG. 5 does not exist. Therefore, the forward voltage VF has a flat voltage waveform as shown in FIG. Therefore, no transient loss occurs during forward recovery. However, the forward voltage VF in the steady state is
Since two SBDs are used, the forward power loss is twice as large as the value when one SBD is used. However, when the ON / OFF cycle of the switching element Q is shortened, that is, when the frequency is increased, the ratio of the transient power loss becomes relatively large. .

On the other hand, as described above, in the current state of the art, S
The withstand voltage of a BD alone is 150 V at the upper limit, and its SBD
Is theoretically limited to 150V. Further, the actual operating circuit voltage is set lower in consideration of safety. Therefore, the circuit voltage is 100 V
In the above description, the SBD cannot be used in practice, and a high-speed diode is used. In the present invention, when a circuit voltage of at least 200 V
Can be used, and the practical effect is great.

Next, the structure of the SBD used in the above circuit will be described with reference to FIG. FIG. 3A is a plan view schematically showing the SBD, and FIG.
It is an equivalent circuit diagram of D. In the figure, SBD chips 2a and 2b are placed on a conductor plate 1 serving as a base, for example, one SB.
The other SBD chip 2b is fixed with solder so that the anode electrode of the D chip 2a is on the upper surface and the cathode electrode is on the upper surface. Next, after connecting the external leads 3a, 3b and the SBD chips 2a, 2b with the bonding wires 4, the portions indicated by the dashed lines in FIG. Finally,
The tie bar portion of the lead frame (not shown) is cut off, and the SBD chips 2a, 2b,
An element of one package in which 2b are connected in series is completed.
In the above embodiment, an example in which two SBD chips are used has been described. However, a package of a series connection circuit including a plurality of SBD chips according to a circuit voltage may be used.

[0024]

As described above, the series connection circuit of the present invention
Instead of the conventional diode having a PN junction, at least two SBDs are connected in series and used.
There is no forward recovery voltage VFR, and the forward voltage VF has a flat waveform. For this reason, a transient loss during forward recovery does not occur. Further, since the SBD of the present invention has at least two SBD chips encapsulated in one package so as to be electrically connected in series, effects such as relatively low wiring resistance and good usability can be obtained. There is.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of an SBD connected in series according to the present invention.

FIG. 2 shows an SBD used for the series circuit, and (a)
Is a schematic diagram showing the structure, and (b) is an equivalent circuit diagram thereof.

FIG. 3 is an operation waveform diagram in the SBD series connection circuit of the present invention.

FIG. 4 is a circuit diagram of a conventional series connection using a diode having a PN junction.

FIG. 5 is an operation waveform diagram in the conventional series connection circuit.

[Explanation of symbols]

 D2 SBD Q Switching element E AC power supply B Full-wave rectification bridge circuit L Coil C Capacitor 1 Conductor plate 2a, 2b SBD chip 3a, 3b External lead-out terminal 4 Bonding wire 5 Resin molded part

Claims (2)

[Claims] An object of the present invention is to provide a connection circuit of a Schottky barrier diode in which an anode electrode of a Schottky barrier diode is connected to a power supply side and a cathode electrode of the diode is connected to a load side, to cope with a high voltage circuit and to reduce a forward recovery voltage. The Schottky barrier diode as at least 2
A series connection circuit of Schottky barrier diodes, which are connected in series. 2. At least two Schottky barrier diode chips are mounted on a conductor plate so as to be electrically connected in series, and a surface electrode of the chip is connected to an external lead terminal, and the chip is mounted. A Schottky barrier diode, characterized in that the periphery of the conductive plate and the external lead-out terminal are resin-sealed to form a resin mold part.