JPS58136137A - Control circuit for field effect transistor - Google Patents

Abstract

PURPOSE:To drive stably an FET in high speed, by providing a switch element short-circuiting a control electrode and a main electrode when the FET is turned off. CONSTITUTION:When a control signal is applied to a terminal VB, a transistor TR6 is conductive, a current charging a capacitance Ciss between the gate and source in an MOSFET1 from the positive polarity (marked.) flows and the FET1 is quickly conductive. When the control signal is interrupted and the TR6 is set off, the electric energy stored in a pulse transformer 2 is consumed in a circuit consisting of a resistor 41 and a diode 5. Since the exciting current appearing at a winding 203 conducts a switching element 14, the stored charges in the capacitor Ciss flow in a resistor 13 and are consumed quickly. Since the capacitor Ciss is not discharged by the exciting current, the charges are discharged at a constant time at all times with the resistor 13 and the turn-off characteristics are made stable. Since the exciting current is designed very small, the control circuit is designed in small size and small power.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a control circuit for field effect transistor t-temperature agitation.

It has been proposed to use a field effect transistor (hereinafter referred to as FET) as a t-switch element. In that case,
Typically, a source electrode and a drain electrode are used as a pair of terminals of a switch, and conduction between the pair of terminals is controlled by a control signal applied between the gate and source electrodes. in this case.

The purpose is to electrically isolate the field effect transistor gate circuit and side signal source! 1. A method is known in which a transformer is interposed between the two. Regarding an example of such a circuit, the fourteenth
This will be explained in .

In the 11th E, N channel Enhancement Men) MO8O8
An object to be controlled (not shown) is connected to the drain electrode (D) and source electrode (S) of an external effect transistor (hereinafter simply MOSFET) 1, and a pulse is connected between the gate electrode (G) and the source electrode. A winding 202 on the secondary side of the transformer 2 is connected. Primary winding 20 of pulse transformer 2
1, a gate power supply 3, a current control resistor 4, and an emitter electrode and a collector electrode of a transistor 6 are connected in series. In addition, a diode 5 and a resistor 41 are connected to the secondary winding @202 to circulate the exciting current R of the pulse transformer.
series circuit is connected. The base electrode of the transistor becomes the input terminal VB of the control voltage.

This circuit turns on the transistor 6 by applying a control signal from the terminal VsK control signal generation circuit (FIG. 11, not shown), and during that period, the voltage tIL from the gate power supply 3 is applied to the primary side of the pulse transformer. energizes the secondary MOSFET IK of the pulse transformer.
A corresponding gate voltage is applied to keep it in the on state. Note that the number of turns, inductance, etc. on the primary and secondary sides of the pulse transformer 2 are determined by M Kaida to which the above-mentioned control signal is applied.

It is designed to operate at a voltage of 1c on the secondary side.

The present inventors have found that the above-mentioned circuit has the following input points. That is, if the MOSFET is made to perform fast switching in the above circuit, +40S? E
Due to the capacitance ML (gate input capacitance, hereinafter referred to as C18) between the gate and source electrodes in 1', the desired switching operation cannot be performed.

This point will be explained with reference to FIG. 2, which shows the operating waveforms of the trough in the circuit of FIG. 8.41.

When the control signal v1 shown by the K east line in FIG. 2(a) is input to the terminal v3 in FIG. 1, a current 18. , is the flow.

Then C1118 was photoelectrically charged, and M(J8F'E
T Vion attack. , Fig. 2, c) shows the voltage Va between the gate and source electrodes of M(JSFE'l'' at this time).
g k and (ct) respectively indicate the voltage Van k between the drain and source electrodes.

Next, when %VB becomes O and the transistor 6 is turned off, the energy stored in the pulse transformer 2 is released as an excitation current through the diode 5 and the resistor 41, and the secondary @7 turns [202 to 15. , and is emitted as a current 1get+ of reverse 4i property. This Ig*l( causes CIam to discharge, which causes the MOSFET to
turns off. Here, the period during which the control signal v1 is applied, ie.

Operation 1 when the ON period of MOSFET changes is shown in 2nd example.
This will be explained using figures.

The excitation current flowing through the pulse transformer 2 increases as the -next-side energization period becomes longer, so the current released to the outside from the pulse transformer when the transistor 6 turns off also increases as the -next-side energization period increases. Become.

During the primary side power loss period shown by the solid line in Figure VII2 (a), 1
Assume that a current of 1off4 is discharged from the pulse transformer, and at this time the turn-off time Vi of the MO8FET is -t, rt-1 as shown in FIG. 2(d). Next, if the negative side energization period becomes longer as shown by the broken line, the magnitude of the current emitted from the pulse transformer changes as shown in 4ig*tt-2. If the value of dVow/d is almost constant, even if spike noise occurs,
Although it is relatively easy to take countermeasures against this in terms of circuits, it also has the drawback that if the dVos/dll directivity fluctuates and the noise level also fluctuates, the countermeasures against these are sloppy and difficult to take in practice. .

This results in the disadvantage that noise leaks into the controlled circuit (for example, a computer's memory power supply).

In addition, even when the energization period of the control signal Vm is the smallest, C1
Since it is necessary to supply Igslf that can sufficiently generate g-, the core of pulse transformer 2 is designed with a large excitation inductance (for example, an air cap core).
. However, according to this, as the energization period of VII becomes longer, *'I''1*fl also increases, and the reverse photoelectric voltage of Ct** increases, which may damage the Mo5FET, which limits the practical control range. There were some drawbacks.

Next, another conventional method will be explained using FIG. 3.

In the diagram @3, a capacitor 1ot- is connected between the gate and source electrodes of the MQSFET 1 and the winding MA202, and the Mo8FET 11 is turned on and off by its charging and discharging charges.

The diode 7 is in the forward direction [ii, . The transistor 8 is provided to flow a reverse polarity current 11sff. 9 is a base resistance.

This circuit is suitable for the purpose of keeping AtO8I"ET1 conductive for a long time, but it is suitable for high-speed driving of VC1 as a switching element for a switching regulator.
Mo8FET'! il- cannot be applied to circuits that utilize it effectively.

This is because the photodischarge time constant of capacitor C is large and +
In order to increase Ig*a and Igeff 1,
It is rejected because it has many disadvantages, such as the large size of the pulse transformer 2, the large fx diode, and the large capacity of the gate power supply 3.

, 1. Furthermore, first), the conventional circuit shown in FIG. 3 has the following drawbacks, making it difficult to put it into practical use.

That is, in many cases, the winding of the main transformer is connected in series between the drain and source electrodes of the 81108B'ET 1, and power conversion is performed by switching WJJ (not shown). . , control signal V
When l is turned off, the gate and source electrodes are reverse biased, so Mo8FE'l' 1 is turned off. At this time, Vov+ is increased to the flyback voltage of the input voltage transformer by d Vos / d t, which is determined by the characteristics of Mo5s'ET.

- C1 through C1, abbreviated as C6@I)
2 and capacitor 10'i (for charging h 840
S F ET 1 is pulled back to ON IIK again. Here T is the change darkness of Vns.

If the drain mA flows under such a voltage state, the Mo8)i'ET will cause thermal runaway, so this drawback must be completely corrected for practical purposes.

The object of the present invention is to provide a control circuit (2) which eliminates the above-mentioned drawbacks of the conventional circuit and can drive -□ FET'It at high speed and stably.

A feature of the present invention is that in the control circuit of the FET, which applies a control @IM signal to the gate terminal of the FET to conduct its conduction t11KII141, it is provided with a means for quickly discharging the accumulated charge between the electrodes through the resistor at the time of turn-off. Tokoro KT
oru.

Examples of the present invention will be described below. Figure 4 shows the main components of the accumulated charge discharging means according to the present invention.
In the figure, 1 is a field effect transistor, 12 is a current control resistor, 13 is a resistor, and 14 is a switch element, which can be used for conductors such as bipolar transistors, field effect transistors, and photocube transistors.

The control signal is applied to the input terminals 11a and llb, and the positive signal C1 flows through the current control resistor 12' to the gate electrode Kfi, making the JSFET lt- conductive.

Next, the current of the negative signal is passed through the control circuit 15 by forming a current path through the control circuit 15 so that the switch element 14 becomes conductive, and the accumulated charge between the gate and source electrodes is quickly removed. can be discharged. The negative signal requires only a small amount of current to make the switch element 14 conductive.

Even if CI-VCtl is exceeded, problems such as excessive reverse charging as described in the conventional example will not occur. therefore.

Mo8FET 1 turn-off time, ctl@
Since the discharge time can be set to a constant time determined by the time constant of the resistor 13 and the time constant of the resistor 13, the turn-off characteristics become stable.

Next, more specific examples will be described.

In FIG. 5, in the embodiment using the pulse transformer 2, a diion 15 is connected to the opposite polarity of the winding 202 to block the excitation current. A separate winding 20 is used for the accumulated charge discharge medium wave.
3 through the current control resistor 121 and diode 151.

This is done by flowing it through the control electrode of the switch element 14.

That is, when the terminal VmKlltl (Ml signal is applied).

A current to charge CI-f flows from the positive electrode @ (・mark), and Mo
8FET 1 becomes conductive immediately. Next, when the control signal is interrupted and the transistor 6 is turned off, the electrical energy stored in the pulse transformer 2 flows into the circuit 1 of the resistor 41 and the guide 5 connected to the negative side and is consumed. At this time, the excitation type I5t appearing in the separate winding 203
flows in one reverse polarity direction and makes the switch element 14 conductive, so the accumulated charge of iC1m5 flows through the resistor 13 and is quickly consumed.

Excitation type #l should appear in the secondary winding 202, but is blocked by the diode 15 and does not flow.

Therefore, unlike the conventional system, the excitation current does not cause discharge of C15s, so the resistor 13 is used.

It is always discharged over a certain period of time.

Another embodiment of the present invention will be described with reference to FIG. This example is in separate volume 4! This is a simplified control circuit by omitting I. That is, the switching element 14 is passed through the excitation current get flow control resistor 121 which is blocked by the diode 15.
It is made to flow into the electrode. In this case, the excitation type f
Although i flows between the gate and source in the direction of discharging the CI, the purpose is to flow a small current t- enough to make the switch resistor 14i conductive. Therefore, the discharge time of the accumulated charge is determined as in the above embodiment. can be kept constant in almost the same way.

Therefore, in the above two embodiments, the excitation at flow? Since it can be designed to be extremely small, there is no need to use a gap core like in the past, and the power required for the control circuit is also small, so the control circuit is small.

Designing for low power makes it possible to achieve iiJ performance.

The method described above uses a transformer with windings and an excitation type a to apply positive and negative control signals, but FIG. An example of the method will be described.

In FIG. 7, 16 is a disk-type piezoelectric element with electrode films on both sides, 168 is a vibration element, and 16b is a power receiving element. They are fixed to each other with one edge 17.

When a control signal is applied to Vm and the transistor becomes conductive, the voltage of the gate power supply 3 is applied between the electrodes 16a.

This voltage tv is illustrated in FIG.

Vibrating confectionery 168 causes magnetostriction due to V, and this mechanical force is transmitted to power receiving element 16b, and a voltage V- appears between the poles of 16b with a rising characteristic based on the natural vibration frequency of the element. At this time, since the input impedance of ~108 FETl is extremely high, if the internal loss of element 16b and the surface leakage current flt1 are ignored, V
Although b is retained.

In reality, electrical energy is consumed by the element itself.

C15m is charged with a decreasing voltage as shown by the concentrated line.

Next, when the control signal is interrupted, the magnetostriction of 16a is released, and as a result, the mechanical force received by power receiving element 16b is reversed, and at time Lfl, a current is supplied in the direction in which -Vb conducts to switch element 14.

In the piezoelectric element, two pairs of oriented m-poles were provided on one plate-like element. It is possible to use a so-called piezoelectric transformer.

The method using such a piezoelectric element has many advantages such as a simple structure and elimination of the influence of electromagnetic induction interference. - The invention will be further explained with practical circuit application examples. Figure 9 shows a well-known inverter circuit, where El is the input power supply.

T is the main transformer, 18 is the output terminal, MO8Fl series
It is shown as a push-pull type using 1a+ and 1bt.

When this circuit is driven by a conventional control circuit, as shown in FIG. 10, the time when MOSFET 1a turns off! @ff-a and opponent @lb turn 1) Lf
It is known that a drain current flows through fj. This is dV/dt at Lff-a B T, ft-b
Therefore, this is due to the charging of ctAI through the output capacitance C, , t between the electrodes, and in the present invention, this charging 'vt'wLf
Since the current can be made to flow through the resistor 13gl1l, these drawbacks can be eliminated. - That is, by maintaining the conduction period of the switch element 14 for the entire period from the time when the control signal of Vm is interrupted until the period of time T14, it is possible to prevent the charge from flowing into Ctms. A specific example of this is the excitation inductance of the pulse transformer 2 and tit of the resistor 41 - optimum Ki! By doing this, the reset time of the transformer can be determined.

As described above, according to the present invention, it is possible to obtain a control circuit that can drive MOSFET k at high speed and stably by providing the accumulated charge discharging means.

[Brief explanation of the drawing]

Figure 1 is a conventional control circuit diagram, Figure 2 is a diagram explaining the characteristics at PET turn-off, and Figure 3 is a diagram of another conventional IK.
1m circuit diagram, FIG. 4 is a circuit diagram explaining the present invention in detail,
5, 6, and 7 are circuit diagrams showing implementation f1 of the present invention, FIG. 8 is a diagram explaining the piezoelectric element OIEgL signal, and FIG. 9 is an example circuit in which the present invention is applied to an inverter. 10A and 10B show operation waveform diagrams during driving. 1-...MOSFET, 11 a, l l b
- Teruko Jinriki. 1% Rumor Sa・shi゛1'bii・ノにL2Figure 2Figure 31Figure 4: '5: ! 5 Figure 8 Figure 8 8 Figure 8 Graph 8 Procedural Amendment Document Patent Office Quantitative Officer Kazuo Chikusugi Case Display 1982 Patent Application No. 17560 Title of the Invention Person who corrects control circuits of field effect transistors Relationship between Patent Applicant: 5-1 Marunouchi-chome, Chiyoda-ku, Tokyo Name: 19 Hitachi Co., Ltd. Representative: 3 1) Osamu Katsu Shigeyo Location: Marunouchi-chome, Chiyoda-ku, Tokyo 5 No. 1) Subject of the amendment Contents of amendment in the Scope of Claims and Detailed Description of the Invention column of the &A specification As shown in the attached sheet 1, 5 units of patent claims are amended as follows. rl, II control reefing pair of main electric currents and field effect transistors t4 through IIKII! In the circuit, when the field effect transistor is turned off, the control II
IPH Goen-Ayu is a field effect transistor that is equipped with a switch element that short-circuits L& and one main voltage threshold. 2. Claim 11! ] *The control circuit for a field effect transistor according to item 1, wherein a transformer is provided between the control electrode and one of the raw electric wires, and a control signal is applied to the control electrode H through the transformer. 3. In Section 1 of the Permission Request, a piezoelectric element is provided between the control electrode and one of the main electric connectors, and a control signal is given to the control electrode through this piezoelectric element. Control circuit for field effect transistors. 4. Percentage of Claims In the first product, the second product, or the third item, a field effect patent is provided in which a resistor is inserted in series with the 11Ill period switch confectionery.(1) A control circuit M for a transistor. 5. %ff Constraint 0 Yoke In any one of the first term to the fourth product, the switch element is made conductive by the f91J control signal set to the electric field infant transistor rise 4) & electric field set to t buttock value. Control circuit for infant transistor. 6. In the second product of the fF constraint, a tertiary housing 4I is provided in the transformer, and a field effect transistor whose t# value is such that the switch element 'ftm is activated by the output of this tertiary bonding. control circuit. ” 2. Specification S9 * Line 3 “Through resistance”? Correct to [via switch cable]. More than 169-

Claims (1)

[Claims] 1. In a circuit for conducting conduction (111) control of a field effect transistor having a control electrode and a pair of main electrodes, the control electrode and one of the main electrodes are short-circuited during a non-conduction period of the field effect transistor. A control K1 circuit for a field effect transistor, characterized in that it is equipped with means for discharging charges accumulated between electrodes. 2. In claim 1, a transformer is provided between the control electrode and one main electrode, and a control signal is applied to the control electrode through the transformer. circuit. 3. Permissible field effect transistor according to claim 1, characterized in that a piezoelectric element is provided between the control electrode and one O main electrode, and a control signal is applied to the first control electrode via this piezoelectric element. 44 control circuits! Scope of claims I1
In item 1, @ 2, or 3, the IITffi interelectrode accumulated charge discharging means consists of a series connection of a resistor and a switch element. & Claims! l! 4. The control circuit for a field-effect transistor according to item 4, wherein the switch element is made conductive by a control signal that makes the field-effect transistor non-conductive. 6. A field effect transistor characterized in that, in the second term of the range of %t'Fiifl, the transformer is provided with a tertiary winding of 4 m, and the inter-electrode accumulated charge discharging means is operated by the output of the tertiary winding. The system of control (wealth).