JP2721928B2 - Switching power supply - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a resonance-type switching power supply device configured to reduce switching loss by using resonance.

2. Description of the Related Art There is known a forward (on-on) type resonance type switching regulator configured to reduce a switching loss of a switching element by using a resonance phenomenon between an inductance of a transformer winding and a resonance capacitor.
It is also known that in a reverse type (on / off type) switching regulator, a capacitor is connected in parallel with a switch, and the voltage at the time of turn-off is absorbed by the capacitor to reduce switching loss.

[Problems to be Solved by the Invention] However, in a system in which a capacitor is connected in parallel with a switch in a reverse-type switching regulator, electric charges charged in the capacitor are discharged through the switch during the ON period of the switch, resulting in power loss. Becomes

SUMMARY OF THE INVENTION It is an object of the present invention to provide a reverse switching power supply having a small switching loss at both the time of turn-off and the time of turn-on.

Means for Solving the Problems According to the present invention for achieving the above object, there is provided a DC power supply, a transformer connected between one end and the other end of the DC power supply, and a transformer connected in series to the transformer. A first switch connected to one of the pair of output terminals of the transformer in a direction in which the first switch is turned on by a voltage generated between the pair of output terminals of the transformer when the first switch is off. Rectifier diode, a first capacitor connected between an output terminal of the rectifier diode and the other of the pair of output terminals of the transformer, and a transformer connected to the transformer so as to resonate with an inductance of the transformer. The second capacitor connected in parallel with the rectifier diode, and the second capacitor connected in parallel to the rectifier diode.
A second switch connected in series to the first capacitor, a first control circuit for controlling the first switch, and a voltage of the first switch before the first switch is turned on. A second switch for controlling the second switch so as to be able to gradually decrease by resonance between a transformer inductance and the resonance capacitor or stray capacitance.
And a switching power supply device comprising:

Preferably, the second switch comprises a combination of a control switch and a diode.

It is desirable that the voltage of the second capacitor be detected to control the second switch.

Further, the output voltage can be controlled by changing the level of the reference voltage to be compared with the second capacitor.

According to the present invention, the second capacitor is charged by the voltage of the first capacitor near the end of the off period of the first switch. At this time, energy is stored in the transformer in a direction that helps resonance between the resonance capacitor or the stray capacitance and the inductance of the transformer. Thereby, the charge of the resonance capacitor or the stray capacitance is released by resonance. Therefore, when the first switch is turned on, substantially no voltage loss due to the resonance capacitor or the stray capacitance occurs.

First Embodiment Next, a resonance-type switching regulator according to a first embodiment of the present invention will be described with reference to FIGS.

In FIG. 1 showing a switching regulator, a primary winding 3 of a transformer 2 is connected between one end and the other end (ground) of a DC power supply 1 composed of a rectifying and smoothing circuit connected to an AC power supply (not shown). A series circuit with the first switch 4 is connected. The first switch 4 comprises an insulated gate field effect transistor (FET) having a source connected to a substrate. Since this FET has a built-in diode, it can be equivalently represented by an anti-parallel circuit of the controllable first control switch 5 and first diode 6. Of course, the first control switch 5 and the first diode 6
May be used as individual elements.

The transformer 2 has a secondary winding 7 and a tertiary winding 8 electromagnetically coupled to the primary winding 3. One output terminal (upper end) of the secondary winding 7 is directly connected to one end of the load 9, and the other output terminal (lower end) is connected to the other end (lower end) of the load 9 via the rectifier diode 10. I have. In the secondary winding 7, a downward voltage is generated during the ON period of the first control switch 5, and an upward voltage is generated during the OFF period. Therefore, the rectifier diode
Reference numeral 10 denotes a direction in which the first control switch 5 is turned on during the off period. The first capacitor 11 is a rectifier diode
It is connected in parallel to the secondary winding 7 via 10, and smoothes the voltage of the secondary winding 7 and supplies it to the load 9.

A resonance capacitor 12 associated with the inductance of the transformer 2 so as to resonate is connected in parallel to the first switch 4. This resonance capacitor 12 can also be obtained with a stray capacitance.

The first control circuit 13 is a circuit for controlling the turning on and off of the first control switch 5. The first control circuit 13 detects a time point t5 in FIG. 2, that is, a time point at which the voltage of the first control switch 5 becomes zero. It comprises a detection circuit 51 and a variable pulse generation circuit 52 triggered by this detection signal. The variable pulse generation circuit 52 is formed of, for example, a variable monomultivibrator, and the width of the output pulse is controlled by the output of the output voltage detection circuit 15. The output line of the variable pulse generation circuit 52 is connected to the gate of the control switch 5. The output voltage detection circuit 15 is connected to both ends of the load 9.

In FIG. 1, a series circuit of a second capacitor 23 and a second switch 24 according to the present invention is connected in parallel with the rectifier diode 10. The second switch 24 comprises an N-channel insulated gate transistor (FET) having a source connected to the substrate, and a second control switch 25 and a second diode 26 connected in anti-parallel thereto.
And can be equivalently represented by

A second control circuit 27 for controlling the second control switch 25 includes a resistor 28, a Zener diode 29, and a comparator 30. Reference voltage from zener diode 29 (reference voltage)
, A Zener diode 29 is connected in parallel with the first capacitor 11 via a resistor 28. Comparator 30
One input terminal is connected to the cathode of a Zener diode 29, and the other input terminal is connected to the left end of the second capacitor 23, that is, the source of the second control switch 25.

[Operation] In the circuit of FIG. 1, when the first control switch 5 is on, a closed circuit including the power supply 1, the primary winding 3, and the first control switch 5 is formed, and the primary winding is turned on. Energy is stored in line 3. During this ON period, a voltage is generated in the secondary winding 7 in a direction to reverse bias the rectifier diode 10. When the first control switch 5 is turned on at time t0 in FIG.
When the off control is performed by the transformer 13, the LC resonance circuit of the inductance of the transformer 2 and the resonance capacitor 12 enters a voltage resonance state based on the energy stored in the transformer 2, and the resonance capacitor 12 is connected to the resonance capacitor 12 as shown in FIG. The current Ic1 flows as shown in FIG.
q gradually increases as shown in the section from t0 to t1 in FIG. 2 (A). Thereby, the overlap between the voltage Vq of the first switch 4 in FIG. 2A and the current Iq of the first switch 4 in FIG. 2B is reduced, and when the first control switch 5 is turned off. Switching loss (power loss) is reduced.

During the off period of the first switch 4, an upward voltage is generated in the secondary winding 7. However, the rectifier diode 10 does not turn on immediately, but first the second diode 26 turns on. After the switch and the second capacitor 23 are precharged to the polarity shown in FIG. 1 or charged through the second control switch 25, the voltage of the secondary winding 7 is applied to the rectifier diode 10. While a voltage V2-V0, which is the difference between V2 and the voltage V0 of the first capacitor 11, is applied, the second diode 26
When Vc is the voltage of the second capacitor 23, V2 +
Since the voltage of Vc−V0 is applied, the second diode 26 is turned on before the rectifier diode 10. As a result, a current Ic2 shown in FIG. 2 (F) flows through a closed circuit including the secondary winding 7, the first capacitor 11, and the second diode 26, and the second capacitor 23 is charged in the opposite direction. Discharge occurs and this voltage gradually decreases. At this time, the first capacitor 11 is of course charged.

When the voltage of the Zener diode 29 becomes lower than the voltage due to the discharge of the second capacitor 23, the output of the comparator 30 is changed to a high level, and the ON control signal is applied to the second control switch 25. Although generated slightly after the ON control signal 1, the first control switch 25 is not immediately turned ON because the first control switch 25 is in a reverse bias state with the voltage V2 of the secondary winding 7. When the discharge of the second capacitor 23 is completed at time t2,
The forward bias state of the rectifier diode 10 and the second diode 26 becomes the same, and the rectifier diode 10 turns on.
When the direction of the charging voltage of the second capacitor 23 is reversed, the second diode 26 is turned off, and during the period from t2 to t3, the secondary winding 7 and the first capacitor 11, and the load 9 and the rectifying diode
A closed circuit is formed with the rectifier diode 10, and a current Id flows through the rectifier diode 10 as shown in FIG. At time t3 near the end of the release of the stored energy of the transformer 2, the voltage of the secondary winding 7
When V2 becomes equal to the voltage V0 of the first capacitor 11 and then the secondary winding voltage V2 becomes lower than the capacitor voltage V0, the first capacitor 11, the secondary winding 7 and the second control switch 25 The second control switch 25 is in a forward-biased state by a closed circuit composed of the second capacitor 23 and the second capacitor 23, and the charging current flows through the second capacitor 23 as shown in the period from t3 to t4 in FIG. Thus, the second capacitor 23 is charged to the polarity shown in FIG. 1, and the voltage Vc gradually increases.
At the same time, the voltage Vd of the rectifier diode 10 gradually increases as shown in FIG. When the voltage Vc of the second capacitor 23 becomes higher than the voltage of the Zener diode 29 at time t4, the output of the comparator 30 is inverted, and the second control switch 25 is turned off.

When the current Ic2 flows during the period from t3 to t4, energy is accumulated in the transformer 2 so as to generate an upward voltage in the primary winding 3, and the inductance and the inductance of the transformer 2 resonate during the period from t4 to t5 based on the energy. Voltage resonance of the capacitor 12 occurs. As a result, the charge of the resonance capacitor 12 is released, and the voltage Vq of the first switch 4 becomes substantially zero at time t5.

This time point t5 is determined based on the detection of the voltage between both terminals of the first switch 4 in the voltage detection circuit 51, and in response to this, an ON control pulse (not shown) is generated from the variable pulse generation circuit 52, The first control switch 5 turns on.

When the first control switch 5 is turned on at t5 in FIG.
As shown in FIG. 2 (B), after a current in the opposite direction due to resonance slightly flows through the first diode 6, a gradually increasing current Iq flows through the first control switch 5. The ON period t5 to t6 of the first control switch 5 is controlled by the output detection voltage.

As is apparent from the above, according to this embodiment, the switching loss can be reduced both when the first control switch 5 is turned off and when it is turned on.

Second Embodiment Next, a switching regulator according to a second embodiment shown in FIG. 3 will be described. However, in FIG. 3 and FIGS. 4 to 6, which will be described later, the substantially same parts as those in FIG. 1 are denoted by the same reference numerals, and description thereof will be omitted.

3 is different from FIG. 1 in that the voltage control is not performed by the first control circuit 13 and the reference voltage source of the second control circuit 27 is changed.
That is to do in 29a. The reference voltage source 29a is a variable voltage source and generates reference voltages having different levels in response to the output of the voltage detection circuit 15. Thereby, the period from t3 to t4 in FIG. 2 changes, and the output voltage can be controlled.

Third Embodiment In the switching regulator of the third embodiment shown in FIG. 4, the load of the first capacitor 11 is the first control circuit 13. That is, first and second secondary windings 7 and 7a are provided, and a second capacitor related to the present invention is connected in parallel with the rectifier diode 10 at the output stage of the first secondary winding 7.
A series circuit of 23 and a second switch 24 is connected, and a first capacitor 11 as a power supply is connected to a first control circuit 13. In this example, the second control switch 25 of the second switch 24 is replaced with a bipolar transistor. Further, a resistor 31 for initially charging the capacitor 11 is connected between the power supply 1 and the capacitor 11. The load 9 is connected to the second secondary winding 7a via a rectifier diode 10a and a capacitor 11a.

The second capacitor 23 and the second switch 24 in FIG. 4 operate in the same manner as in FIG. 1, and when the first switch 4 is turned off, voltage resonance occurs, and the switching loss is reduced.

[Modifications] The present invention is not limited to the above-described embodiment, and for example, the following modifications are possible.

(1) As shown in FIG. 5, a resonance capacitor 12 is connected in parallel to the primary winding 3, and a tertiary winding 40 is provided as shown in FIG. It is possible to connect a resonance capacitor in parallel with the secondary winding 7.

(2) Diodes 6 of the first and second switches 4, 24,
Instead of 26, a control switch may be connected, and this control switch may be turned on so as to correspond to the period during which the diodes 6, 26 conduct.

(3) An inductance element (reactor) may be connected to the primary winding 3, the secondary winding 7, or the tertiary winding 40 of the transformer 2 in order to easily cause LC resonance.

(4) The transformer 2 can have a single-turn transformer configuration.

[Effects of the Invention] As described above, according to the invention of each claim, it is possible to reduce the switching loss by causing a resonance operation at the time of turning off and turning on the reverse type switching power supply device.

[Brief description of the drawings]

1 is a circuit diagram showing a switching regulator according to a first embodiment of the present invention, FIG. 2 is a waveform diagram showing the state of each part in FIG. 1, and FIGS. 3 and 4 are second and third embodiments of the present invention. FIG. 5 is a circuit diagram showing a third embodiment, and FIGS. 5 and 6 are circuit diagrams respectively showing a switching regulator according to a modification. DESCRIPTION OF SYMBOLS 1 ... Power supply, 2 ... Transformer, 3 ... Primary winding, 4 ... First switch, 5 ... Control switch, 6 ... Diode, 7 ... Secondary winding, 9 ... Load, 10 ... Rectifier diode, 11 ... 1 capacitor, 12 ... resonance capacitor, 13 ... first control circuit,
23 ... second capacitor, 24 ... second switch.

Claims (4)

(57) [Claims] 1. A DC power supply, a transformer connected between one end and the other end of the DC power supply, a first switch connected in series to the transformer, and an off state of the first switch. A rectifier diode connected to one of the pair of output terminals of the transformer having a direction of being turned on by a voltage generated between the pair of output terminals of the transformer during a period, and an output terminal of the rectifier diode and A first capacitor connected between the other of the pair of output terminals of the transformer, a resonance capacitor or stray capacitance associated with the transformer so as to resonate with the inductance of the transformer, and in parallel with the rectifier diode A second capacitor connected in series to the second capacitor, a second switch connected in series to the second capacitor, and a first control for controlling the first switch. The first switch so that the voltage of the first switch can be gradually reduced by resonance between the inductance of the transformer and the resonance capacitor or stray capacitance before the first switch is turned on. And a second control circuit for controlling the second switch. 2. The control device according to claim 1, wherein the second switch includes a control switch;
2. The switching power supply device according to claim 1, further comprising a diode built in or externally connected to the control switch and connected in anti-parallel to the control switch. 3. The second control circuit detects a voltage of the second capacitor, and turns on the control switch included in the second switch only during a period when the voltage is equal to or less than a predetermined value. 3. The switching power supply according to claim 2, wherein 4. The second control circuit includes: a reference voltage generation circuit; a reference voltage obtained from the reference voltage generation circuit;
And the control switch included in the second switch is turned on by the comparison output.
3. The switching power supply device according to claim 2, comprising: a comparator that controls off, and a circuit that controls the reference voltage to control an output voltage.