JPH02182020A - Switching driving circuit - Google Patents

Abstract

PURPOSE:To reduce the driving power of a switching element by forming a series resonance circuit comprising a parasitic capacitor such as a gate-source capacitor of a main switching element, a capacitor and a resonance inductor when the switching element is turned on. CONSTITUTION:With a transistor(TR) 11 turned off, a gate signal S3 is fed to a TR 18 and a series resonance circuit comprising a capacitor 13, a gate- source capacitor Cgs of the TR 11, a resonance inductance 16 and a diode 17 is formed via the TR 18 and a half wave of the resonance current flows through the diode 17. Then the charge charged in the gate-source capacitor Cgs of the TR 11 is transferred to the capacitor 13, the gate-source voltage Vgs of the TR 11 is made zero, which is turned off. Thus, the charge stored in the capacitor 13 is utilized to drive turn on/off of the TR 11.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a switching drive circuit that drives switching elements in switching power supplies and the like.

A switching power supply device uses MOS in the primary winding of the transformer.
A switching element such as an FET is connected, and the ON period of the switching element is controlled so that the DC output voltage of the output of a rectifying and smoothing circuit connected to the secondary winding of the transformer becomes a set value.

In order to reduce the size of such switching power supply devices, a configuration that performs high frequency switching operation of several hundred kilohertz or more is adopted, and accordingly, high-speed operation switching elements are used, and this switching There is a demand for improved efficiency in driving devices.

[Conventional technology]

For example, as shown in FIG. 4, a conventional switching drive circuit includes a switching element 23 for turning on a field effect transistor 21 as a main switching element.
and a switching element 24 for turning off, and when the switching element 23 is turned on and the switching element 24 is turned off, the field effect transistor 2 is connected to the DC power supply 22.
A voltage is applied between the gate and source of 1, and the gate and source of
A current 1 gl for charging the source-to-source capacitance lcgs flows through the switching element 23, and the field effect transistor 21 is turned on.

Also, the switching element 23 is turned off, and the switching element 24 is turned off.
When turned on, the gate of the field effect transistor 21
The sources are short-circuited via the switching element 24, and a current of 1 g2 is generated by the charge of the gate-source capacitance Cgs.
flows through the switching element 24, and the field effect transistor 21 is turned off.

When the field effect transistor 21 is turned on in this way,
In the switching power supply device, current flows from the DC power supply 27 to the primary winding of the transformer 25.
The voltage induced in the secondary winding is rectified and smoothed by the rectifying and smoothing circuit 26 to become a DC output voltage. The switching elements 23 and 24 are controlled by a control circuit (not shown) to turn on and off the field effect transistor 21 so that the DC output voltage becomes a set value.

FIG. 5 is an explanatory diagram of the operation, (al is the on (ON) and off (OFF) operation of the switching element 23, (b) is the on (ON) and off (OFF) operation of the switching element 24, and tc+ is the switching A current 1 g 1 , (
d) is the current 1g2 flowing from the gate of the field effect transistor 21 via the switching element 24, and (e) is the drain-source voltage Vds of the field effect transistor 21.
An example of drain current 1d is shown.

Gate-source capacitance i1c of field effect transistor 21
gs is approximately several 1,000 pF, and when the switching element 24 is turned off and the switching element 23 is turned on, the gate-source capacitance Cgs from the DC power supply 22 is
A current of 1 gl shown in fc) flows to charge the field effect transistor 21, and the field effect transistor 21 is turned on. Thereby, t
Drain current 1d flows as shown at e+, and transformer 2
The current Id can be supplied to the primary winding of 5.

Also, the switching element 23 is turned off, and the switching element 24 is turned off.
When turned on, the charge stored in the gate-source capacitance Cgs of the field effect transistor 21 is discharged, and (d
A current Ig2 shown in l flows, and the field effect transistor 21
is off. Therefore, the drain-source voltage Vds of the field effect transistor 21 has a value corresponding to the voltage of the DC power supply 27, as shown in (a).

[Problem to be solved by the invention]

As mentioned above, in the conventional switching drive circuit, when the gate-source capacitance Cgs of the field effect transistor 21 is the voltage of the DC power supply 22 as Vg, Eg=(1/2)Cg s −Vg ” --
(Eleven energy is accumulated. This accumulated energy is
It is released by turning on the switching element 24. Therefore, each time the field effect transistor 21 is turned on, it is necessary to supply the energy shown in equation (11) from the DC power supply, and as the switching frequency becomes higher, the driving power of the field effect transistor 21 increases.

The present invention aims to reduce the driving power of switching elements such as field effect transistors as described above.

[Means to solve the problem]

The switching drive circuit of the present invention reduces drive power by using resonance current, and will be explained with reference to FIG. 1.

A first switching element 4 that is periodically turned on to charge the capacitor 3 from the DC power supply 2, and a main switching element such as a field effect transistor that is turned on during the off period of the first switching element 4. The terminal voltage of the capacitor 3 is applied to the gate of the second switching element 5 to turn on the main switching element 1, and the second switching element 5 is turned on during the off period of the first and second switching elements 4 and 5. Therefore, the parasitic capacitance such as the gate-source capacitance of the main switching element 1 and the resonant inductance 6
and a third switching element 8 that is controlled so that a half-wave resonant current flows through the diode 7 in a series resonant circuit with the capacitor 3 and the charged charge of the parasitic capacitance is released to the capacitor 3. It is something.

[Effect]

Gate-source capacitance Cg of main switching element 1
When the third switching element 8 is turned on, a series resonant circuit is formed by the parasitic capacitance such as s, the capacitor 3, and the resonant inductance 6, and a half wave of the resonant current flows through the diode 7. . FIG. 2 is an explanatory diagram of the operation, (11 is the second switching element 5, (2
) is the third switching element 8, and (3) is the on (ON) and off (OFF) of the first switching element 4, respectively.
The operation is shown, and (4) shows the current 11 supplied from the DC type R2 when the first switching element 4 is turned on. In addition, (5) is the gate-source voltage V g due to the gate-source capacitance fJCgs of the main switching element 1.
3, +61 is the terminal voltage V c of capacitor 3, (
7) shows an example of the current 12 flowing through the diode 7, (81 shows an example of the current I3 flowing through the gate of the main switching element 1.

When the second switching element 5 is turned on, a current flows from the capacitor 3 to charge the gate-source capacitance Cgs of the main switching element 1 as shown in (8), and the terminal voltage Vc of the capacitor 3 becomes (6). decrease as shown. Furthermore, the gate-source voltage Vgs increases as shown in (5). Then, the main switching element 1 is turned on.

Next, when the second switching element 5 is turned off and the third switching element 8 is turned on, a series resonant circuit is formed as described above, and a half wave of the resonant current shown in (7) flows through the diode 7. I2 flows, and the main switching element l
The charged charge of the gate-source capacitance Cgs completely flows into the capacitor 3, and the gate-source voltage Vgs becomes O
As a result, the main switching element 1 is turned off, and the terminal voltage Vc of the capacitor 3 rises due to the flowing current I2. That is, the electric charge charged in the parasitic capacitance to turn on the main switching element 1 is fed back to the capacitor 3, and at the time of the next turn-on control, the charge charged in the parasitic capacitance is fed back to the capacitor 3.
Ideally, if the capacitor 3 is initially charged, the DC power supply 2 can be omitted.

However, since there is a small amount of circuit loss in each part, in order to compensate for this loss, the first switching element 4 is turned on from the DC power supply 2, and the current I shown in (4) is passed through the capacitor 3 to charge it. It turns out. In this case, the terminal voltage of the capacitor 3 charged by the half wave of the resonant current is Vc
1. Current from DC power supply 2. When the terminal voltage of the capacitor 3 charged by
12). and (Vc 2” −Vc l”
)<VH2, so as is clear from the comparison with equation (1), the energy Ec of the motor becomes small, and the driving power can be reduced.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the drawings.

11 is a field effect transistor (MOSFET) as a main switching element, 12 is a DC power supply, 13 is a capacitor, 14 is a field effect transistor as a first switching element, 15 is a field effect transistor as a second switching element, 16 17 is a diode, 18 is a field effect transistor as a third switching element, and 19 is a control circuit.

Hereinafter, for the sake of simplicity, each field effect transistor serving as a switching element will be abbreviated as a transistor.

A control signal for controlling on/off of the transistor 11 is applied to the control circuit 19, and a gate signal 31. for controlling the transistors 14, 15, 18 as the first to third switching elements is applied. S2. S3 is output. This gate signal s1 is shown in (3) in FIG. 2, and the gate signal S2 is shown in (1) in FIG.
), the gate signal s3 corresponds to (2) in FIG. Therefore, the control circuit 19 can be realized by a relatively simple logic circuit or the like.

When the ON signal of the transistor 11 is applied to the control circuit 19, the gate signal S2 is applied to the transistor 15, a voltage is applied from the capacitor 13 to the gate of the transistor 11 via the transistor 15, and the gate-source capacitance Cgs increases. Charged, the transistor 11 is turned on.

To turn off the transistor 11, a gate signal S3 is applied to the transistor 18, and the transistor 18 is turned off.
is on, transistor 15 is off, and capacitor 13 and transistor 11 are connected via transistor 18.
A series resonant circuit is formed including the gate-source ICgs, a resonant inductance 16, and a diode 17, and the diode 17 causes a half wave of the resonant current to flow.

As a result, the charge in the gate-source ICgs of the transistor 11 is transferred to the capacitor 13, the gate-source voltage Vgs of the transistor 11 becomes 0, and the transistor 11 is turned off.

Therefore, the charge charged in the gate-source capacitance Cgs of the transistor 11 from the capacitor 13 via the transistor 15 is returned to the capacitor 13 via the transistor 18 by a half wave of the resonant current, reducing losses in each part. If the capacitor 13 is initially charged, the charge of the capacitor 13 can be used to turn on and off the transistor 11.

However, in reality, losses occur due to the resistance of each part, so during the off period of transistors 15 and 18, gate signal S1 is applied to transistor 14 to turn it on, and the loss is replenished from DC power supply 12 to capacitor 13. Charge like this. That is, as shown in (3) in FIG.
As shown in (4), a current of 1. It is intended to supply In that case, DC power supply 1
When charging of the capacitor 13 is completed, the transistor 14 can be turned off. That is,
It is also possible to shorten the ON period (3) in FIG.

As mentioned above, the current ■1 supplied from the DC power source to the capacitor is small compared to the current I3 for driving the transistor 11, which reduces driving power and improves efficiency compared to the conventional example. can be improved.

The present invention is not limited only to the above-described embodiments, but it is also possible to configure the first to third switching elements using bipolar transistors, etc., or use other voltage-driven semiconductors as the main switching element. It is also possible to use elements.

Moreover, it can be used not only for driving the main switching element of a switching power supply device but also for driving various switching elements.

〔Effect of the invention〕

As explained above, the present invention turns on the third switching element 8 during the period when the first and second switching elements 4 and 5 are off, and changes the gate-source capacitance ICgs, etc. of the main switching element 1. Parasitic capacitance and capacitor 3
A series resonant circuit including a resonant inductance 6 and a diode 7 is formed, and in order to turn on the main switching element 1, the charge charged in the parasitic capacitance is transferred to the capacitor 3 by a half wave of the resonant current. Then, when the main switching element 1 is turned on, the charge of the capacitor 3 is added to the gate of the main switching element 1 via the first switching element 4 to supplement the drive energy, and the main switching element 1 is then turned on. The energy supplied from the capacitor 3 to turn on the switching element 1 is accumulated in the parasitic capacitance of the main switching element 1, but when the main switching element 1 is turned off, it is fed back to the capacitor 3 and used for the next main switching. Since it is used when turning on the element 1, the power supplied from the direct type tA2 to the capacitor 3 is small.

That is, the driving power of the main switching element I is reduced,
There is an advantage that efficiency can be improved.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram of the principle of the present invention, Fig. 2 is an explanatory diagram of the operation of the present invention, Fig. 3 is a circuit diagram of an embodiment of the invention, Fig. 4 is a drive circuit of a conventional example, and Fig. 5 is a conventional example. FIG. 6 is an explanatory diagram of an example operation. 1 is a main switching element, 2 is a DC power supply, 3 is a capacitor, 4, 5.8 is a first . Second. The third switching element 6, a resonant inductance 7, is a diode. Patent Applicant: Fujitsu Denso Co., Ltd. Representative Patent Attorney Akio Aitani Representative Patent Attorney Hiroshi Watanabe - Circuit diagram of an embodiment of the present invention Third factor Diagram explaining the principle of the present invention Figure 1 Diagram explaining the operation of the present invention Figure 2. Conventional example drive circuit Figure 4. Conventional example operation diagram Figure 5.

Claims (1)

[Claims] In the switching drive circuit that drives the main switching element (1), the circuit is periodically turned on to supply electricity from the DC power supply (2) to the capacitor (
3); a first switching element (4) for charging the capacitor (3); and a terminal voltage of the capacitor (3) that is turned on during the off period of the first switching element (4) and is applied to the gate of the main switching element (1). a second switching element (5) for turning on the main switching element (1) by applying
4, 5) is turned on during the off period, and the parasitic capacitance of the main switching element (1) and the resonant inductance (
6) and the capacitor (3), a half-wave resonant current flows through the diode (7) from the parasitic capacitance of the main switching element (1) to the capacitor (3).
A third switching element (8
) A switching drive circuit characterized by comprising: