JPS581217A - Driving circuit for field effect transistor - Google Patents

Abstract

PURPOSE:To stably operate from DC to high frequencies, by providing the 3rd winding for a driving transformer and compulsively turning off an FET through a deenerigizing current flowed to this winding. CONSTITUTION:The ternary winding III is provided to a driving transformer T1. When a transistor Q1 turns on and a deenergizing current i1 flows to the primary windingI, a capacitor C3 is charged through a diode D6 with the charging current flowing to the winding III. On the other hand, a pulse width control circuit CONT2 applies an output VBE(Q4) between the base and emitter of the Q4 with a pulse width in response to the difference if an output voltage OUT exceeds a reference value. As a result, a transistor T4 turns on to discharge the charge in the capacitor C3. When this discharge current i2 flows, a Q2 is turned on and an energizing current i1 flows to the windingI. When the magnetic flux due to the current i2 is excessive, a voltage induced in the winding III extracts charges from the gate of an FETQ3 allowing to compulsively turn off the Q3.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides an FET for use in switching regulators, etc.
(field effect transistor) drive circuit.

Conventional switches, chinglegs, and regulators are configured as shown in Figure 1, for example, and are connected in series to the primary side of the main transformer TI, and are used to control the on-period of the optical power MO8FgTQ3. By controlling K through 1, the output voltage 0UTt- is kept constant. An input (DC power supply) IN is connected to the primary winding of the main transformer T1, and one end of the clamp winding of the transformer and the input I
A diode) is connected between the other end of N and the other end of N. Furthermore, a diode D4 e Di is connected to the secondary side of the transformer TI.
An average value rectifier circuit REC consisting of an s-inductance L1 and a capacitance C4 is connected. Drive transformer〒1 2nd
Winding 1 is a driving winding of IPETQs and is connected between its gate and source via a resistor R4'1-. Also, FC in series with line capacitance C in the first winding ■! Ipm transistor Qt
# The Q snow collector and air filter are connected. These transistors (b-Q proverbially refer to the oscillation control circuit C0NT
It is driven alternately by t.

The general operation will be explained. The oscillation control circuit C0NT drives the transistor Q1t- with the output pulse, and drives the transistor Q*t with the pulse B having the opposite phase to the nine pulses. Then, during the period when transistor Q1 is on, Q
A current (hereinafter referred to as deenergizing current) flows through the path t - CB - I, and the capacitance C! is charged to the polarity shown. At this time, the second
Since the voltage generated by the winding IK reverse biases the gate and source of iFI'rQs, (b is off. On the other hand, A-I (low) and B=H (high). When the transistor Q1 is turned on (Ql is turned off), the charge in the capacitor CI is discharged from the collector of Q! in the direction toward the edge.At this time, the current flowing through the first winding IK (hereinafter referred to as the energizing current) is A voltage that forward biases Fly Qlt is induced in the secondary winding slave, and the false turns on. When the transistor is on, the primary winding of the input IN terminal 11, Q3
A current flows in the path of terminal S, which induces a voltage in the secondary winding of T, causing current to flow in the path of D4, LhC,
Capacitor Cat - Charge. Note that the mark on the transformer winding indicates the beginning of winding of the coil. When the transistor Qs is off, the voltage induced in the primary winding is the terminal 1) sDl.
, an extension of the primary winding, a current flows in the path of the terminal, clamping the voltage of the crest winding to the voltage IN (IN). At this time, the voltage induced in the inductance L1 is Ll 1C
A current is passed through the path of ae Di and the voltage induced in the inductance is absorbed. The above process is repeated every time the transistor Q3 is turned on and off, thereby performing DC (direct current)-DC conversion.

The voltage value of the DC output OU'r is obtained by rectifying the trough input/output 0 secondary output to an average value using the rectifier circuit REC, and is related to the turns ratio of the transformer T, the primary voltage, and the energization period of the primary winding. Therefore, when the value decreases, the on-time of FieTQs is lengthened, and when the value increases, it can be stabilized by shortening the on-time of FITQs. Therefore, a part (voltage value) of the output OUT is fed back to the oscillation control circuit C0NTIK, which includes an amplifier and a comparator, etc.
(keep the cycle constant).

In this device, insulation between the main power supply system and the control system including transistors is a problem. That is, the drive transformer TI and the main transformer? , 01st and 2nd order are completely insulated, but the DC output OUT voltage tube detection system and oscillation control circuit C0NT are not insulated up to this point, and the auxiliary power supply Q3 control system power supply is also isolated. In the end, it is necessary to take it from the input IN, so IN.

There is a possibility that insulation between OUTs cannot be achieved. In order to insulate this, (1) a commercial isolation transformer and a rectifier should be interposed in part 1, but an auxiliary DC-DC converter including a transformer tt should be interposed in part 1+ to serve as an auxiliary power source, or (2) part Y should be used as an auxiliary power supply. It is necessary to interpose an insulating means that can be operated with a DC circuit, such as a photo-F coupler. However, if the input of the auxiliary power supply is DC, it is not possible to use a commercial isolation transformer in (1), and in that case an auxiliary converter must be used, but this is not a good idea because it requires a large number of parts. do not have.

Although this photocoupler is a useful means, it is expected to cause characteristic fluctuations over the long term, leading to stability problems.

The present invention attempts to solve the above-mentioned nine problems by effectively utilizing a drive transformer.The present invention is characterized by an energizing current flowing in one direction and a deenergizing current flowing in the opposite direction in the first winding of the drive transformer. When the energizing current is applied, the gate charge is accumulated, and when the energizing current is applied, the gate charge is In a drive circuit for a field effect transistor, which turns the transistor on and off by pulling out the transistor, a third winding is provided in the drive transformer,
Then, during the period when the energizing current is flowing through the first winding, the third
The point is that when a forced deactivation current is passed through the winding, the gate charge of the field effect transistor is forcibly drawn out. This will be explained in detail below with reference to illustrated embodiments.

FIG. 2 shows a first embodiment of the invention. In the present invention, the drive transformer T1 is provided with a third winding, and a deenergizing current is passed through the third winding to forcibly turn off FIT (KL1). Then, the above insulation problem can be easily handled.The third volume is connected to the line capacitance C3, to the diode, and to the transistor Q4t'I.
/II! A pulse width control circuit coN'r is connected to the transistor Q4. Further, in this circuit, a capacitor CI is connected in parallel to the pace resistor R of the transistor Q3 for the following reason. That is, the transistor Qs is FE
This T is a voltage control type, and after charging the gate capacitance, the gate voltage can be maintained without flowing current. On the other hand, the resistor - is a high resistance, and the constant pace current of the transistor Ch, so the collector current is small, and only when the transistor is turned on (false is also on at this time), a large pace current is passed through the capacitor C, and the collector current is Therefore, the discharge current iIt of the capacitor CI is made large.

FIG. 3 is an operating waveform chart of each part, and the left side of the center shows a state similar to FIG. 1 in which the transistor Q4 does not operate. In the figure, A and B are the outputs of the oscillation control circuit C0NTH, and are pulses with opposite phases to each other. In this example, it is assumed that the period of this pulse train is constant and the duty is also constant. II (Q) is the pace current of the transistor Qm, vGl (Q is the voltage between its collector and emitter). When it flows in the direction, it becomes a deenergizing current (CI charging current).

Vmg (Qa) is the voltage between the base and emitter of transistor q4, and the current 1. When flowing in the direction shown in the figure, it becomes the aforementioned forced deenergizing current (discharging current of Cs), and when flowing in the opposite direction, it becomes a charging current of C. I@s 1liF
The current between the gate and source of ET Qs, vGl is the gate,
The voltage between the source, ID is the drain current, and vDl is the voltage between the drain and the source.

When not controlled by the transistor Q4, the on-time of the FET Qs within one period T takes a constant value depending on the on-time of the transistor (h).If controlled by a pair of transistors, the on-time To of the FET Qs In other words, when the transistor Qt is turned on and a deactivating current -1 flows through the first winding 2, the charging current -1 flowing through the third winding causes the capacitor C3 to pass through the diode. The pulse width control circuit C0N is charged to the polarity shown.
T* is a pulse width modulation (PWM) circuit that compares the output voltage OUT with a reference value. 2. The voltage is applied between the two terminals. As a result, the transistor T4 turns on and discharges the charge in the capacitor C3. In addition, the pulse width control circuit CON〒Snow is a transformer T
Synchronization is achieved by taking power from the secondary side of the snow, and the tie construction that produces the output Vmg (Q4) is the on period of the transistor Qs (the period when B=H). The discharge current of the capacitor Cs becomes a forced deenergizing current flowing to the third winding. When this current i flows, the transistor Q is on and the energizing current 11 flows through the first winding I. However, if the magnetic flux by LAtl is overcome, the voltage induced by the third volume slave can extract the charge from the gate of FWT Ql, and the ygTQse can be forcibly turned off. In this circuit, as described above, the capacitor C3 is connected in parallel with the pace resistor R1 to make the resistance R larger, so that it can be easily made larger than the steady value of the current 1 and the lamination current 1 m. Note that Fli:TQs is -H
If charge is accumulated in the gate, it will remain on even if no charging current is applied as long as it is not discharged.Therefore, the pace current 11 (Q) is unstable in a steady state, but in reality, the gate charge leaks, so a small pace current is passed through the high resistance RgK to compensate for it.
T, plexus' in the figure is thus shortened to the on-time of nine PE'rQs. The average voltage V of the output OUT is the secondary voltage Vs VC of the main transformer T, and when ignoring the resistance of the transformer winding and the voltage drop of the diode, 'l
.

Therefore, when ToM decreases to T, buy', V. decreases. In the circuit of this example, since the circuit within the dashed line is on the main transformer T, secondary side, the auxiliary power supply for the oscillation control circuit C0NT, side can be directly supplied without going through an auxiliary converter, etc., similar to the photocoupler method. .

This example is characterized in that the charging power source with the capacity C3 is placed on the first winding side of the drive transformer T1.

In contrast, another embodiment of the present invention shown in FIG.
The charging power source for s is the second secondary winding of the main transformer. The winding W is the added second secondary winding, and the capacitor Cs is charged through the resistor R and the diode. DI is a diode interposed in the forward direction in the discharge path of the capacitor Cs, and the operating principle is the same as in FIG. 2. The main parts (changed parts) of the time chart of this circuit corresponding to FIG. 3 are shown in FIG.

In any of the embodiments, if the polarity of the first winding I is reversed, the transistor Q! The current that turns on t and charges the capacitor CIK becomes the energizing current, and t7't) transistor Gh?
The current discharged from the capacitor CI when turned on becomes the deactivating current. Even in this case, the forced energizing current in the third winding must always be applied during the period when the energizing current flows in the first winding, and in order to make this advantageous, the base resistance R on the transistor Ql side is
, connect the capacitors in parallel (Cm is removed). Furthermore, it is clear that a plurality of FETs can be driven at the same time by having a plurality of drive windings. Furthermore, the FIT drive circuit of the present invention includes not only the above-mentioned nine switching legs and rotors, but also
It can also be applied to optical full-bridge circuits, etc. in which four transistors are combined.

As mentioned above, according to the present invention, it is possible to combine an FHT with a single drive transformer having the functions of drive, control, and insulation, so that the input voltage can be high frequency regardless of whether it is direct current or alternating current. It is possible to easily construct a stable switching regulator. In particular, the FIC is voltage driven, unlike the current drive of bipolar transistors, and only the charge/discharge current of the gate capacitance flows, and the driving power is very small. Furthermore, since there is no storage time, switching at a frequency of several hundred KHz or more is possible.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an example of a conventional switching regulator, FIGS. 2 and 3 are circuit diagrams and operation waveform diagrams showing an embodiment of the present invention, and FIGS. 4 and 5 are circuit diagrams showing an example of a conventional switching regulator. FIG. 2 is a circuit diagram and an operation waveform diagram showing an embodiment of the present invention. In the figure, T1 is a drive transformer, 1 to 3 are first to third windings, and T1 is a FET (field effect transistor). Applicant Fujitsu Limited

Claims (1)

[Claims] An energizing current in one direction and a deactivating current in the opposite direction are alternately passed through the first winding of a drive transformer, and the field effect transistor has its gate and source connected to the second winding of the transformer, In a drive circuit for a field effect transistor, which accumulates a gate charge when the core energizing current is applied and draws out the gate charge when the deactivating current is applied to turn the transistor on and off, the drive transformer is provided with a fifth volume. A wire is provided so that when a forced deenergizing current is passed through the third winding while an energizing current is flowing through the first winding, the gate charge of the field effect transistor is forcibly drawn out. A field-effect transistor drive circuit with 1* characteristics.