KR20100010324A - A protection circuit for a normally-on (depletion mode) jfet and the power apparatus - Google Patents

Abstract

PURPOSE: A circuit for protecting a depletion JEFT(Junction Field Effect Transistor) and a power supply unit using the same are provided to generate a negative voltage for switching operation of JFET by including a regulator. CONSTITUTION: A filter(310) remove a noise element of an input AC power(300). A bridge diode(320) rectifies an AC signal to a DC voltage. Two DC link capacitors(330,340) are charged with the DC voltage. A regulator protects the JFET from a rush current. The regulator generates the negative voltage for driving the JFET. A gate control signal generator generates a control signal for switching the JFET.

Description

Depletion type junction field effect transistor protection circuit and power supply using the same {A protection circuit for a normally-on (depletion mode) JFET and the power apparatus}

The present invention relates to a protection circuit for protecting the depletion-type JFET from the destruction by overcurrent when the power is applied, and a power supply device using the same.

 Unlike the gates that control the opening and closing of IGBTs or MOSFETs, which are used in general switching devices, in an oxide structure, JFETs have a p-n junction structure, which provides high reliability and low input capacitance.

Therefore, silicon carbide (SiC), which has recently been spotlighted as a material for next-generation power devices, has a favorable condition for growing an oxide film like silicon, but there is still a problem in the quality and reliability of the oxide film. Therefore, a junction field effect transistor (JFET) that opens and closes an element is expected to be commercialized first.

However, depletion-type JFETs generally have a channel through which current can flow before gate power is applied, and when a power supply is made using a JFET, excessive current flows through the JFET at the same time and destroys the device. have.

Because of this depletion JFET normally-on characteristic, it is rarely used in most power supplies, which are mainly controlled by a single supply. In recent years, as the power supply device is becoming more dense and smaller, the operating frequency of the power supply device is increasing and the switching loss and the conduction loss of the switch element are also increasing. These losses are mainly due to the input and output capacitance and turn-on resistance of the switching devices. Silicon carbide JFETs are being installed in power supplies due to their low input / output capacitance and turn-on resistance.

In order to protect the device and the power supply from the normally-on characteristic of the JFET, the conventional technology is to arrange the JFET having the normally-on characteristic and the MOSFET having the normally-off characteristic as shown in FIG. Cascoded to have

As shown in FIG. 1, when a zero voltage is applied to the gate 130, the MOSFET 110 is turned off. If there is a leakage current passing through the drain 120 and the source 140, most of the voltage between the drain and the source is applied to the JFET 100 having a large breakdown voltage, and some voltage is applied to both the drain and the source of the MOSFET. Therefore, a negative voltage is applied between the gate and the source of the JFET so that the entire cascade is turned off.

On the other hand, if a voltage higher than the threshold voltage is applied to the gate of the MOSFET, a channel is formed between the MOSFET source and drain, so that the resistance decreases drastically, and thus the voltage of the gate and source of the JFET rapidly increases to approach zero voltage.

In this way the entire cascade is turned on. The conventional method using the cascode has a short circuit configuration, but the input stage is a MOSFET, which increases the input capacitance, and in particular, the advantage of using a silicon carbide JFET cannot be used properly.

Another conventional technique is to use quasi-normally-off JFETs, as shown in FIG. The quasi-normally-off JFET 240 has a low breakdown voltage because the channel is not completely closed when the gate voltage is zero.

Therefore, the voltage applied at power-on can be prevented sufficiently, but it cannot prevent the dynamic voltage generated when the power supply starts to operate. 2 is designed to block the voltage at the initial power-up and to charge the capacitor 210 with the negative voltage in the secondary winding of the transformer 220 by the switching signal generated by the gate control signal. However, this uses a quasi-normally-off JFET, which results in a large turn-on resistance, which increases the conduction loss of the switching device.

An object of the present invention is to provide a protection circuit that protects a depletion type JFET from overcurrent at power-on and provides a negative voltage sufficient to operate the JFET as a switch.

In order to achieve the above object, the present invention, the two DC link capacitors for charging the rectified DC voltage; Regulators that form a common power supply circuit across the upper DC link capacitors, and across the lower DC link capacitors protect the normally-on JFET from inrush current generated during initial power-up and provide sufficient voltage to turn off the JFET. A depletion junction type field effect transistor protection circuit comprising: a flyback, a feedforward, a half-bridge, a full-bridge to which the protection circuit is applied; bridge) type power supply is the technical subject.

The present invention also provides a filter for removing noise components of an input AC power supply; A bridge diode for converting an AC signal from which a noise component is removed to a DC component; Two DC link capacitors for charging the converted direct current; A regulator which protects the JFET from inrush current generated when the power is applied and generates a negative voltage necessary for driving the JFET; A gate control signal generator for generating a control signal for switching the JFET; A transformer for adding negative voltage and zero voltage to the JFET gate by adding an output voltage of the regulator and a voltage generated from the gate control signal; A depletion type JFET characterized in that a channel is formed and a current flows even when a gate voltage is not applied; A transformer for producing a desired output voltage through the secondary winding; And a depletion type junction field effect transistor protection circuit comprising: a secondary power supply which transfers a negative voltage generated from the auxiliary winding of the transformer to a capacitor when the steady state is reached and turns off the operation of the regulator. Flyback, feedforward, half-bridge, and full-bridge type power supplies to which this protection circuit is applied are technical points.

에서 결정되는 전압에 이르렀을 때 충전전류를 끊어주는 스위치소자(380); 캐패시터(370)에 충전되는 전류의 크기를 제한하며 전원 투입시 JFET의 통전시간(τ)을

에 결정되게 만드는 저항으로 구성된 것이 바람직하다.Here, the regulator includes a zener diode for providing a reference voltage; A resistor protecting the zener diode; A capacitor for charging a negative voltage; The voltage of the capacitor (V _C3 )

Switch element 380 to cut off the charging current when the voltage determined in the; Limits the amount of current charged in the capacitor 370 and the energization time (τ) of the JFET when the power is turned on.

It is desirable to consist of a resistor that makes it crystallized.

 As described above, when the switching mode power supply using the JFET switching device is configured, the circuit configuration is simple, and thus, the destruction of the device can be prevented from the inrush current generated during initial startup at low cost and the JFET is switched by the PWM IC. There is an effect that can provide a negative voltage sufficient to operate.

Most switching power supplies include a filter 310 for removing noise components of the input AC power source 300, a bridge diode 320 for converting an AC signal from which noise components are removed to a DC component, and two for charging the converted DC. DC link capacitors 330 and 340 are included.

3 is an example of applying a depletion type JFET protection circuit according to the present invention to a flyback type switching power supply. As shown, according to a preferred embodiment of the present invention, the filter 310 to remove the noise component of the input AC power source 300, and the bridge diode 320 to convert the AC signal from which the noise component is removed to the DC component conversion Two DC link capacitors 330 and 340 to charge the direct current, a regulator 400 to protect the JFET from inrush current generated when the power is applied and to generate the negative voltage required to drive the JFET, and to switch the JFET. A gate control signal generator 410 for generating a control signal, a transformer 420 for applying a negative voltage and a zero voltage to the JFET gate by adding an output voltage of the regulator and a voltage generated from the gate control signal, Depletion type JFET 450, characterized in that a channel is formed even when not applied, the current transformer to create the desired output voltage through the secondary winding Murray 440 and is largely configured to operate the regulator to deliver a negative voltage generated in the capacitor 370 from auxiliary winding 460 of the transformer 440 when it reaches a steady state with the auxiliary power source for turning off.

In the present invention, a JFET having a normally-on feature at initial power-up may be placed on a DC link to produce sufficient negative voltage within a time that does not destroy the device (ie, allows the device to operate within a safe operating area). Capacitors were connected in series.

That is, the lower DC link capacitor 330 is set to zero voltage so that the lower DC link capacitor 340 naturally takes a negative voltage. In the upper DC link capacitor C1 and the lower DC link capacitor C2, a voltage inversely proportional to the capacity ratio is applied to each capacitor due to the series connection, and the sum V _{DC ( link )} is expressed by Equation 1 as follows. It is approximately 1.414 times the AC value of the input power supply (V _AC ).

(Formula 1)

If possible, the capacitance value is determined so that the voltage across the capacitor C2 is small. In general, since the voltage applied across the capacitor C2 is large and varies each time the input AC voltage is changed, the regulator 400 is configured to make the voltage applied to the capacitor 370 constant. At this time, the voltage applied to the capacitor 370 is determined by the following equation 2 by the zener diode 350 and the transistor 380.

(Formula 2)

Where V _ZD1 is the breakdown voltage of the zener diode and V _{BE ( ON )} is the turn-on voltage of the transistor 380. V _C3 must be determined to have a negative voltage sufficient to turn off the JFET. The resistor 360 is a resistor for protecting the zener diode 350 and the resistor 390 is a resistor for limiting the maximum value of the current charged in the capacitor 370. However, since the voltage is charged to the capacitor 370 through the resistor 390 when the power is turned on, the time constant τ is calculated from Equation 3 so that the depletion type JFET can be turned off quickly enough so that the JFET is not destroyed due to the inrush current. Decide

(Formula 3)

4 shows a protection circuit determined by the above-described equation. As described above, the voltage is distributed by C1 and C2, and the negative voltage for turning off the JFET is formed by a regulator composed of C2 and C3, D1, D2, S1, R1, and R2.

5 shows output waveforms detected at each part. The voltage waveform 510 shows the result of the input DC voltage V1 divided by the capacitors C1 and C2. The simulation assumes that the AC input voltage increases linearly from 0V to 350V for 16ms to see the transient overcurrent of a normally-on device caused by insufficient regulator voltage at zero voltage input. Voltage waveform 500 shows the voltage charged to C3 by the regulator. Due to the short time constant of R2 x C3, the voltage applied across the capacitor C2 is charged to the capacitor C3 at about the same time. The voltage of capacitor (C2), which is enough to turn off the nomally-on JFET, is -25V, but it should be made almost 2ms, but as the voltage of capacitor (C2) is close to -25V, the channel of JFET is closed. 530 hardly flows at 1 ms.

On the other hand, the power consumed through the JFET is closely related to the destruction of the device and is shown in 520 of FIG. The peak power is 5.5W and the width is 1ms, so the device operates in the SOA region and is not destroyed. Once 2ms is reached, the device is in a switchable state, that is, fully openable and open, so that it can start switching by receiving a signal from the gate control signal generator. When switching starts and becomes a normal state, the voltage is charged to C3 through the auxiliary winding 460 so that the negative voltage required to turn off the JFET is no longer generated by the regulator 400.

1 shows a cascoded circuit arrangement configured with a device having a normally-off characteristic to have a normally-off characteristic according to the prior art.

Figure 2 shows a power supply configured via a JFET with Quasi-normally-off characteristics.

3 shows an embodiment of a power supply comprising a regulator for protecting a JFET with normally-off characteristics in accordance with the present invention.

4 is a circuit diagram for simulating the characteristics of the regulator according to the present invention.

5 shows output waveforms of a regulator and a JFET according to the present invention.

<Description of Major Symbols Used in Drawings>

100, 240, 430: JFETs with normally-on features

110: MOSFET with normally-off characteristic

120: drain 130: gate 140: source

200, 410: Gate signal generator for switching JFET

210: capacitor for charging negative voltage

220, 420: Transformers that add voltage so that zero and negative voltages can be applied to the gate of a JFET.

Claims (5)

Two DC link capacitors 330 and 340 for charging the rectified DC voltage; A general power supply circuit is formed at both ends of the upper DC link capacitor 330, and both ends of the lower DC link capacitor 340 are protected from inrush current generated during initial power-up and the JFET is turned off. A depletion type junction field effect transistor protection circuit comprising: a regulator (400) for supplying a sufficient voltage.  The method of claim 1, wherein the regulator A zener diode 350 providing a reference voltage; A resistor 360 protecting the zener diode; A capacitor 370 to charge a negative voltage; The voltage of the capacitor (V _C3 )

Switch element 380 to cut off the charging current when the voltage determined in the; Limits the amount of current charged in the capacitor 370 and the energization time (τ) of the JFET when the power is turned on.

A depletion junction type field effect transistor protection circuit, characterized in that consisting of a resistor (390) to be determined to. A filter 310 for removing noise components of the input AC power supply 300; A bridge diode 320 for converting an AC signal from which a noise component is removed into a DC component; Two DC link capacitors 330 and 340 for charging the converted direct current; A regulator 400 that protects the JFET from inrush current generated when power is applied and generates a negative voltage necessary for driving the JFET; A gate control signal generator 410 for generating a control signal for switching the JFET; A transformer 420 for adding negative voltage and zero voltage to the JFET gate by adding an output voltage of the regulator and a voltage generated from the gate control signal; A depletion type JFET 450 characterized in that a channel is formed and a current flows even when no gate voltage is applied; A transformer 440 for generating a desired output voltage through the secondary winding; When a steady state is reached the auxiliary voltage for transferring the negative voltage generated from the auxiliary winding 460 of the transformer 440 to the capacitor 370 to turn off the operation of the regulator; PIP-type field effect transistor protection circuit. The method of claim 3, wherein the regulator A zener diode 350 providing a reference voltage; A resistor 360 protecting the zener diode; A capacitor 370 to charge a negative voltage; The voltage of the capacitor (V _C3 )

Switch element 380 to cut off the charging current when the voltage determined in the; Limits the amount of current charged in the capacitor 370 and changes the energization time (τ) of the JFET when the power is turned on.

A depletion junction type field effect transistor protection circuit, characterized in that consisting of a resistor (390) to be determined to. Any one of a flyback, feedforward, half-bridge and full-bridge type, characterized in that the protection circuit of any one of claims 1 to 4 is applied Power supply.

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