JPH03270675A - Switching regulator - Google Patents

Abstract

PURPOSE:To improve the efficiency for a wide range of DC input voltage by resetting a transformer through the use of resonance thereby absorbing surge voltage. CONSTITUTION:Upon turn ON of FETs 12, 13, an exciting current IL flows to reset a transformer and capacitors C1, C2 are charged. Upon subsequent turn OFF of the FETs 12, 13, the capacitor C1 is discharged through an inductance L1, a diode D1 and the FET 12 whereas the capacitor C2 is discharged through an inductance L2, a diode D4 and the FET 13. At that time, the capacitors C1, C2 are discharged through series resonance of the capacitor CL and the inductance L1 and the series resonance of the capacitor C2 and the inductance L2.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a switching regulator that can obtain a predetermined output voltage even when input voltage changes over a wide range.

In a switching regulator, which controls the on-width of a switching element such as a transistor connected to the primary winding of a transformer so as to achieve a set DC voltage,
It is common to rectify a commercial AC power source to obtain an input DC voltage. In Japan, this commercial AC voltage is 100
V, 200V, but 220V is often used in the United States, and 380V or 415V is used in Europe. Therefore, there is a need for a switching regulator that operates stably even with such various input DC voltages.

[Prior Art] Fig. 6 is a circuit diagram of a main part of a conventional example, showing the case where a series two-stone forward converter is used, 31 is a transformer, 31a is a primary winding with a number of turns N1, and 31b is a primary winding with a number of turns N3. The secondary winding 31c is the auxiliary winding part with the number of turns N2, 32.33
is a field effect transistor as a switching element, 3
4 is a control circuit, 35.36 is a snubber circuit, 37 is a drive transformer, 37a is a primary winding, 37b, 37c are secondary windings, R3-R6 are resistors, D7 to DIO are diodes, C4
~C6 is a capacitor, and L4 is an inductance.

Diode D9. A rectifying and smoothing circuit is configured by DIO, capacitor C4, and inductance L4, and transformer 3
The voltage induced in the secondary winding 31b of No. 1 is rectified and smoothed, and then supplied to a load (not shown). The output voltage of this rectifying and smoothing circuit is compared with a set reference voltage in the control circuit 34, and a drive signal for controlling the pulse width corresponding to the error voltage is applied to the primary winding 37a of the drive transformer 37. The on-width of field effect transistors 32 and 33 whose gates are connected to the secondary windings 37b and 37c of 37 is controlled.

When the field effect transistors 32 and 33 turn on,
Since the DC input voltage Vin is applied to the primary winding 31a of the transformer 31 and a voltage is induced in the secondary winding 31b, this induced voltage is rectified and smoothed by the rectifying and smoothing circuit. Also, when the field effect transistors 32 and 33 are turned off,
The voltage induced in the auxiliary winding portion 31c of the transformer 31 is
Diode D7. It is clamped by the DC input voltage Vin via D8. Also, field effect transistor 32°33
A sharp change (surge voltage) in the voltage Vds between the drain and source when the transistor is turned off is absorbed by the snubber circuit 35.36 consisting of resistors R5, R6 and capacitors C5, C6, and the field effect transistor 32.33 is protected.

FIG. 7 is an explanatory diagram of the operation, and (a) and (b) show the voltage Vt applied to the primary winding 31a of the transformer 31 during the on period Ton and off period Toff of the field effect transistor 32, 33, (C) is a field effect transistor 32
．． 3 shows the drain-source voltage Vds of the field effect transistors 32 and 33 during the on period Ton and the off period Toff of No. 33.

Since the transformer 31 is excited during the on period Ton and reset during the off period Toff,
When the reset voltage is Vr, Ton-Vin=Tof
The relationship f·Vr −(1) is required. Also, if Ton+Toff=T, this period T is constant, so Ton= (Toff f-Vr)/Vin
---(2) becomes.

This reset voltage Vr is applied to the primary winding 31 of the transformer 31.
Vr=(Nl/N2)Vin by the number of turns N1 of a and the number of turns N2 of the auxiliary winding portion 31c. Therefore, (
1) The formula is as follows.

If N1=N2, as shown in FIG. 7(a), T
onwToff, and the on period Ton is the period T.
172 or more is not possible. Therefore, by setting the relationship Nl>N2, the relationship Ton>Toff is obtained as shown in FIG. 7(b), so it is possible to widen the range of change in the DC input voltage Vin.

[Problem that the invention seeks to solve]

In order to obtain a predetermined DC output voltage even for a wide range of DC input voltage Vin, it is necessary to widen the on-period Ton. Therefore, as mentioned above, the auxiliary winding part 3
It is conceivable to make the number of turns N2 of the primary winding 31a smaller than the number of turns Nl of the primary winding 31a and to increase the reset voltage Vr.

However, increasing the reset voltage Vr increases switching loss in switching elements such as field effect transistors 32 and 33, and also increases surge voltage, which has the disadvantage of increasing loss in snubber circuits 35 and 36. be.

An object of the present invention is to enable efficient control even over a wide range of DC input voltages.

[Means for Solving the Problems] The switching regulator of the present invention is capable of resetting a transformer using resonance and absorbing surge voltage, and will be described with reference to FIG. 1.

A switching element 2 such as a transistor that is connected to the primary winding of the transformer 1 and supplies current from a DC power source, and a rectifying and smoothing circuit 3 that is connected to the secondary winding of the transformer 1.
In a switching regulator equipped with a control circuit 4 that detects the output voltage of the rectifying and smoothing circuit 3 and controls the on-width of the switching element 2 to keep the output voltage constant, a capacitor 5 is connected in parallel with the switching element 2. A series resonant circuit consisting of an inductance 6 and a first diode 7 is connected, and a first diode is connected between the capacitor 5 and the DC power supply so that a charging current due to the stored energy of the primary winding of the capacitor 5 and the transformer 1 flows. 2 diodes 8 are connected.

[Effect]

The switching element 2 is turned on by the control circuit 4.

When turned off and turned on, current is supplied from the DC power source to the primary winding of the transformer 1, and the voltage induced in the secondary winding is rectified and smoothed by the rectifier and smoothing circuit 3, resulting in a DC output voltage. . When the switching element 2 is turned off, the capacitor 5 is charged via the diode 8 by the energy stored in the primary winding of the transformer 1. As a result, the transformer 1 is reset, and the surge voltage applied to the switching element 2 is alleviated.

Next, when switching element 2 is turned on, capacitor 5
Due to the resonant circuit formed by the inductance 6 and the inductance 6, the charge of the capacitor 5 is discharged via the switching element 2 and the diode 7.

〔Example〕

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

FIG. 2 is a circuit diagram of main parts of an embodiment of the present invention, in which 11 is a transformer, 12 and 13 are field effect transistors as switching elements, 14 is a control circuit, 15 is a drive transformer, D1 to D6 are diodes, C1 to C3 are capacitors, L1 to L3 are inductances, and R1 and R2 are resistors.

Diode D5. D6, capacitor C3, and inductance L3 constitute a rectifying and smoothing circuit, and capacitor C1
A series resonant circuit is constituted by and inductance L1,
Further, a series resonant circuit is constituted by the capacitor C2 and the inductance L2. Further, the transformer 11 consists of a primary winding and a secondary winding, and has no auxiliary winding section.

A drive signal is applied from the control circuit 14 to the gates of the field effect transistors 12 and 13 via the drive transformer 15,
When the field effect transistors 12 and 13 are turned on, current is supplied to the primary winding of the transformer 11, and a voltage is induced in the secondary winding of the transformer 11, which is rectified and smoothed by the rectifier and smoothing circuit, resulting in a DC output voltage. becomes. This DC output voltage and a set reference voltage are compared in the control circuit 14, and the on-width is controlled in accordance with the error voltage.

FIG. 3 is a circuit diagram for explaining the operation, and the main parts in FIG.
+S is the DC input voltage, VCI+VeZ is the terminal voltage of capacitor CI and C2, ■, is the exciting current of the transformer 11, and ■. The drain is flowing.

When the field effect transistors 12.13 are turned on, the DC input voltage VIN causes the field effect transistors 12.13 to turn on.
The excitation current IL of the transformer flows through the path of the inductance LO and the fi field effect transistor 13. Also, when field effect transistors 12.13 are turned off, diodes D3.
Excitation current IL flows through the path of capacitor C1, inductance LO, capacitor C2, and diode D2 to reset the transformer 11, and capacitors C1 and C
2 is charged.

Next, when field effect transistors 12 and 13 are turned off,
The charge in the capacitor CI is discharged through a path including the inductance Ll, the diode DI, and the field effect transistor 12. Furthermore, the charge in the capacitor C2 is transferred to the inductance L2. Discharge occurs through the path of the diode D2 and the field effect transistor 13.

In this case, the charges in the capacitors C1 and C2 are discharged due to the series resonance between the capacitor C1 and the inductance L1 and the series resonance between the capacitor C2 and the inductance L2.

FIG. 4 is an explanatory diagram of the operation of the embodiment of the present invention, in which (a) is the drain-source voltage vos of the field effect transistor 12, 13, (b) is the excitation current I L , (C) is the capacitor CI, C2 terminal voltage VC1) VC! , (d
) shows the drain current ID of the field effect transistor 12, 13 when the DC input voltage is high.

Also, the curve AI, A2 in (a) is the capacitor C1,
When C2 and inductance Ll, C2 are not provided, curves Bl, B2 are the case when capacitor CI, C2 and inductance Ll, C2 are provided, and curves AI, Bl
When the DC input voltage VIN is high, the curve ILI of A2. B2 and I) curve IL! is the case where the DC input voltage VIN is low.

When the field effect transistors 12 and 13 are turned on at time to, when the DC input voltage VIN is high, the exciting current increases rapidly as shown by the curve ■, and the DC input voltage VI
When N is low, it gradually increases as shown in song 111Lz. Furthermore, when the DC input voltage VIN is high, the on period becomes short; for example, the on period is from tO to t1, and the off period is from C1 to t5. Also, when the DC input voltage VIN is low, the on period becomes long, for example, to-C3 is on period, C3-t
5 is the off period.

When field effect transistors 12, 13 are turned off at time t1 or C3, capacitor C1 is charged via diode D3 and capacitor C2 is charged via diode D4, thereby resetting the transformer 11. Also, the terminal voltage of capacitors C1 and C2 ■. teeth,(
It rises as shown in C). In this case, C1=C2=C
And when L1=L2=L, the terminal voltage is ■. maximum value V
c#ax is vC□x=IL ITr7r-1/2
becomes. Also, this maximum value ■. , the time T1 until reaching X is T.

-(π/2)・J-cho becomes 7-cho. That is, the reset of the transformer 11 is completed when a time period T has elapsed since the field effect transistors 12 and 13 were turned off.

When the field effect transistor 12.13 is turned on next time, the drain current In shown in (d) flows through the field effect transistor 12.13 due to the terminal voltage VC of the capacitors C1 and C2, and the initial peak value 1 p Ha, I P
= V cmmxl"Σ7T"'tft/), the sono period T2 becomes Tz=πft. That is, a resonant current flows through the resonant circuit formed by the capacitor CI and the inductance L1 and the resonant circuit formed by the capacitor C2 and the inductance L2, and the capacitors CI and C2 are discharged. And the next field effect transistor 12.13
The capacitors C1 and C2 are charged with a current due to the energy stored in the primary winding of the transformer 11 when the transformer 11 is turned off.

FIG. 5 is a circuit diagram of a main part of another embodiment of the present invention.
The same reference numerals as in the figure indicate the same parts, and 16 is a mutual inductance corresponding to the inductances Ll and C2. This mutual inductance 16 and the capacitor C1 or C2 constitute a series resonant circuit, and the field effect transistor 12
．． 13 turns on, capacitors C1 and C2 are charged!
When the load is discharged as a resonant current and the field effect transistors 12 and 13 are turned off, a current due to the stored energy in the primary winding of the transformer 11 flows as a charging current to the capacitors C1 and C2, and the transformer 11 is reset. . In this embodiment, by using the mutual inductance A 6, it is possible to reduce the size of the inductances L1 and C2.

〔Effect of the invention〕

As explained above, the present invention connects a series resonant circuit consisting of a capacitor 5, an inductance 6, and a first diode 7 in parallel with a switching element 2 such as a field effect transistor, and connects a transformer l to the capacitor 5. A second diode 8 is connected with a polarity such that a charging current flows due to the energy stored in the primary winding, and when the switching element 2 is turned off, a current flows to charge the capacitor 5 and the transformer 1 is charged. Since the reset is performed and the capacitance of the capacitor 5 can be made relatively large,
Changes in the voltage applied to both ends of the switching element 2 can be made gentler, and the switching element 2 can be protected.

Furthermore, since the charge charged in the capacitor 5 is discharged as a resonant current, even when the on-period Ton is shortened, the capacitor 5 is reliably discharged, and the charging current flows when the switching element 2 is turned off next time. be able to. Furthermore, since there is no need to form an auxiliary winding part for resetting in the transformer 1, the configuration of the transformer 1 can be simplified.

Therefore, even when the DC input voltage VIN is high, the transformer 1 can be reset even if the on-period Ton of the switching element 2 is shortened, and there is an advantage that there is no increase in switching loss. Since the surge voltage is not absorbed by the circuit, there is an advantage that there is no increase in loss even when the DC input voltage v1 is high.

That is, it is possible to obtain a desired DC output voltage for a wide range of DC input voltages VIN, and there is an advantage that efficiency can be improved without increasing the size of the device.

[Brief explanation of drawings]

Fig. 1 is a diagram for explaining the principle of the present invention, Fig. 2 is a main circuit diagram of an embodiment of the invention, Fig. 3 is a circuit diagram for explaining the operation of the embodiment of the invention, and Fig. 4 is a diagram for explaining the operation of the embodiment of the invention. FIG. 5 is a circuit diagram of a main part of another embodiment of the present invention, FIG. 6 is a circuit diagram of a main part of a conventional example, and FIG. 7 is a diagram illustrating an operation of a conventional example. 1 is a transformer, 2 is a switching element, 3 is a rectifier and smoothing circuit, 4 is a control circuit, 5 is a capacitor, 6 is an inductance, 7 and 8 are first . This is the second diode.

Claims (1)

[Claims] A switching element (2) that is connected to the primary winding of a transformer (1) and supplies current from a DC power source, and
A rectifying and smoothing circuit (3) connected to the secondary winding of 1) detects the output voltage of the rectifying and smoothing circuit (3), controls the ON width of the switching element (2), and adjusts the output voltage. In a switching regulator equipped with a control circuit (4) for making constant the switching element (2), a capacitor (5) is connected in parallel with the switching element (2).
), an inductance (6), and a first diode (7) are connected in a series resonant circuit, and the capacitor (
5) A second diode (8) is connected between the capacitor (5) and the DC power source so that a charging current due to the energy stored in the primary winding of the transformer (1) flows through the capacitor (5). switching regulator.