JP2652584B2 - Switching power supply - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a switching power supply device generally called a step-down switching regulator.

[Prior Art] A conventional step-down switching regulator includes a switch connected in series to a line, and a smoothing circuit provided at an output stage of the switch and including a smoothing reactor, a smoothing capacitor, and a flywheel diode. It is configured.

[Problem to be Solved by the Invention] By the way, when the switch is turned off from on, a high voltage (surge voltage) is generated in the reactor, and this voltage is applied to the switch. In order to absorb this surge voltage and moderate the rise of the voltage of the switch at the time of turning off, it is conceivable to connect a capacitor in parallel to the switch or provide a stray capacitance. However, the charge of this capacitor or stray capacitance is lost because it is discharged therethrough when the switch is turned on.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a switching power supply device that can reduce the switching loss both when the switch is turned on and when the switch is turned off.

Means for Solving the Problems To achieve the above object, the present invention provides a DC power supply, a first switch connected in series between the DC power supply and an output terminal, and the first switch. A smoothing circuit including a reactor, a first capacitor, and a flywheel diode provided at a subsequent stage, a resonance capacitor or stray capacitance connected to form a voltage resonance circuit with the reactor, and a flywheel diode. , A series circuit of a second capacitor and a second switch connected in parallel with each other, a first control circuit for controlling on / off of the first switch, and switching of the first switch to on The first switch so that the voltage of the first switch can gradually fall based on the resonance operation between the reactor and the resonance capacitor or the stray capacitance. And a second control circuit for controlling the second switch.

According to a fifth aspect of the present invention, there is provided a switching power supply device in which a winding for energy release is electromagnetically coupled to a reactor and this winding is connected in parallel to a first capacitor via a flywheel diode. Thus, a series circuit of the second capacitor and the second switch can be connected in parallel.

It is desirable that the second switch is composed of a combination of a control switch and a diode.

It is desirable that the second switch be controlled by detecting the voltage of the second capacitor.

Further, as described in claims 4 and 6, the output voltage can be controlled by changing the detection level of the voltage of the second capacitor.

[Operation] 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 accumulated in the reactor in a direction that helps the resonance between the resonance capacitor or the stray capacitance and the inductance of the reactor. Thereby, the charge of the resonance capacitor or the stray capacitance is released by resonance. Therefore, when the first switch is turned on, power loss due to the resonance capacitor or the stray capacitance does not occur.

First Embodiment Next, a step-down switching power supply according to a first embodiment of the present invention will be described with reference to FIGS.

A series circuit of a first switch 4, a reactor 5, and a first capacitor 6 is connected between the first and second power supply terminals 2, 3 to which the DC power supply 1 is connected. The first switch 4 comprises a channel insulated gate field effect transistor having a source connected to the substrate,
This can be equivalently represented by the first control switch 4a and the first diode 4b connected in anti-parallel to the first control switch 4a. This first
The switch 4 has a stray capacitance 7 indicated by a dotted line between the drain and the source.

The flywheel diode 8 is connected in parallel to a series circuit including the reactor 5 and the first capacitor 8. Flywheel diode 8 is reactor 5
And the first capacitor 6 to form an output smoothing circuit.
A pair of output terminals 9 and 10 connected to the first capacitor 6
A load 11 is connected between them.

The first control circuit 12 connected to the control terminal (gate) of the first control switch 4a supplies an on / off control signal to the first control switch 4a.
A desired control pulse is output based on the voltage detected by the voltage detection circuit 13 connected to 10 and the voltage detected by the voltage detection circuit 14 across the first switch 5. FIG. 2 shows the first
The variable mono multivibrator 15 that generates a pulse in response to a trigger signal given from a switch voltage detection circuit 14 and a drive circuit 16
Consisting of The variable mono multivibrator 15 is controlled by the output voltage detection circuit 13 and sends out an output pulse whose pulse width changes in inverse proportion to the output voltage.

In FIG. 1, a series circuit of a second capacitor 17 and a second switch 18 according to the present invention is connected in parallel with the flywheel diode 8. The second switch 18 is a second control switch 18 comprising an N-type transistor.
a and an anti-parallel circuit of the second diode 18b. The second switch 18 can be replaced with an insulated gate transistor (FET) having a source connected to the substrate.

A second control circuit 19 for controlling the second control switch 18a includes a resistor 20, a Zener diode 21, and a comparator 22. In order to obtain a reference voltage (reference voltage) from the Zener diode 21, the Zener diode 21 is connected in parallel to the first capacitor 6 via a resistor 20. One input terminal of the comparator 22 is connected to the cathode of the Zener diode 21, and the other input terminal is connected to the upper end of the second capacitor 17, ie, the anode of the second diode 18b.

[Operation] In the circuit of FIG. 1, a closed circuit including the power supply 1, the first control switch 4a, the reactor 5, and the first capacitor 6 is formed while the first control switch 4a is on. You. As a result, a current Iq shown in FIG. 3 (G) flows through the reactor 5. The first control switch 4a is
When the control circuit 12 turns off the power at time t0, a current flows through the first capacitor 6 and the load 11 based on the energy stored in the reactor 5. At the time of turn-off, first, the surge voltage generated in the reactor 5 is absorbed by the stray capacitance 7, and the voltage Vq of the first switch 4 gradually increases as shown in the period t0 to t1 in FIG. Thereby, the switching loss of the first switch 4 is reduced.

When a voltage equal to or higher than the forward rising voltage is applied to the second diode 18b at the time t1, this is turned on, and the second diode 18b is turned on.
The current shown in the period of t1 to t2 in FIG.
Ic2 flows, and the second capacitor 17 is reversely discharged (discharged). When this voltage decreases due to the discharge of the second capacitor 17, the potential of the inverting input terminal of the comparator 22 becomes lower than the potential of the non-inverting input terminal, and the output of the comparator 22 becomes a high level voltage. The control switch 18a is turned on.
When the polarity of the charging voltage of the second capacitor 17 is opposite to that in FIG. 1, the second diode 18b is turned off. Almost simultaneously with this, the flywheel diode 8 is turned on, and a current Id1 shown in FIG. The second diode 18b is turned on before the flywheel diode 8 because it is biased by the second capacitor 17.

When the operation of releasing the energy of the reactor 5 ends and the current of the flywheel diode 8 becomes zero at t3, the first
Capacitor 8, reactor 5 and second control switch 18
a and a second capacitor 17 form a closed circuit,
As shown at t3 to t4 in FIG.
Charging current flows. As a result, the second capacitor 17
The voltage Vc returns to a level that causes the output of the comparator 22 to go low again, and the second control switch 18a at time t4 is turned off.

A resonance operation between the reactor 5 and the floating capacitor 7 occurs based on the energy stored in the reactor 5 during the period from t3 to t4, and the electric charge of the floating capacitor 7 is changed to the floating capacitor 7, the power supply 1, the first capacitor 6, the reactor 5, This voltage and the voltage Vq of the first switch 4 gradually decrease as shown in the period t4 to t5 in FIG. 3 (C). Thereby, the switching loss at the time of turn-on is reduced.

The voltage zero of the first switch 7 is a switch voltage detection circuit.
14, the trigger pulse shown in FIG. 3A is generated at t5, the variable monomultivibrator 15 shown in FIG. 2 is triggered, and the control pulse having the desired width (t5 to t6) is generated as shown in FIG. )
And the first control switch 4a is turned on. Before the first control switch 4a is turned on, the stray capacitance 7
Has been released, the first control switch
No energy loss occurs in the closed circuit composed of 4a and the stray capacitance 7. When the first control switch 4a is turned on, current flows again through the reactor 5. Thereafter, when the first control switch 4a is turned off at time t6, the same operation as in the period from t0 to t6 is repeatedly performed.

When controlling the output voltage, the width of the pulse in the period from t5 to t6 in FIG.

As is apparent from the above description, according to this embodiment, the switching loss can be reduced both when the first control switch 4a is turned on and when it is turned off.

Second Embodiment Next, a switching power supply according to a second embodiment shown in FIG. 4 will be described. However, in FIG. 4 and FIG. 5, which will be described later, portions common to FIG. 1 are denoted by the same reference numerals, and description thereof is omitted.

In the circuit of FIG. 4, the reactor 5 is connected between the power supply 1 and the first switch 4. The energy emitting winding 5a is electromagnetically coupled to the reactor 5. The energy emitting winding 5a is connected in parallel to the first capacitor 6 via a flywheel diode 8. A series circuit of a second switch 18 and a second capacitor 17 is connected in parallel with the flywheel diode 8 as in FIG.

A second control circuit 19 for turning on / off the second control switch 18a is configured by a voltage dividing circuit of two resistors 20 and 21. In this circuit, energy stored in the reactor 5 during the ON period of the first switch 4 is released via the winding 5a during the OFF period of the first switch 4. The operation waveforms of the respective parts in FIG. 4 are substantially the same as those in FIG. 3, so that substantially the same operation and effect as in the first embodiment can be obtained.

Third Embodiment In the switching power supply according to the third embodiment shown in FIG. 5, a variable reference voltage source 21a is provided instead of the Zener diode 21 shown in FIG.
Is controlled by the output. As a result, in FIG.
It is possible to control the output voltage by changing the off period by controlling the period from t3 to t4.

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

(1) The first switch 4 may be configured by an anti-parallel circuit of a bipolar transistor and a diode. Also, the second
The switch 18 may be an insulated gate FET with a built-in diode as in the case of the first switch 4. A control switch is connected in place of the diodes 4b and 18b of the first and second switches 4 and 18, and this control switch is connected to the diodes 4b and 4b.
On-control may be performed so as to correspond to a period during which the 18b is conducting.

(2) The stray capacitance 7 can be replaced with an individual capacitor.

(3) The time point t5 at which the voltage of the first switch 4 becomes zero may not be directly detected, but may be detected from the time points t3, t4 and the like.

(4) The second control switch 18a may be configured to be turned on only during the period from t3 to t4.

(5) The second control circuit 19 in FIG. 4 can be configured similarly to FIG. 1 or FIG. Further, the second control circuit 19 in FIG. 1 can have the same configuration as that in FIG.

(6) In FIG. 1, the reactor 5 may be moved to the position of the flywheel diode 8, and the flywheel diode 8 and the second switch 18 and the second capacitor 17 parallel thereto may be moved to the position of the reactor 5. . That is,
The present invention can be applied to a circuit called a polarity reversal type DC-DC converter. Further, the first switch 4 can be connected between the power supply terminal 3 and the output terminal 10.

[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 both at the time of turning off and at the time of turning on the first switch.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a switching power supply unit according to a first embodiment of the present invention, FIG. 2 is a block diagram showing a first control circuit, and FIG. , FIG. 4 is a circuit diagram showing the switching power supply device of the second embodiment, FIG. 5 is a circuit diagram showing the switching power supply device of the third embodiment, 1... Power supply, 4. 1 switch, 5 ... reactor, 6 ... first capacitor, 7 ... floating capacitance, 8 ...
Flywheel diode, 9,10 …… Output terminal, 12 ……
1st control circuit, 17 ... second capacitor, 18 ... second
Switch.

Claims (8)

(57) [Claims] A first DC power supply connected in series between the DC power supply and an output terminal;
A smoothing circuit including a reactor, a first capacitor, and a flywheel diode provided at a stage subsequent to the first switch; and a resonance capacitor connected to form a voltage resonance circuit with the reactor. Or a stray capacitance; a series circuit of a second capacitor and a second switch connected in parallel to the flywheel diode; a first control circuit for controlling on / off of the first switch; Before the first switch is turned on, the second switch is set so that the voltage of the first switch can gradually fall based on the resonance operation between the reactor and the resonance capacitor or the stray capacitance. And a second control circuit for controlling the 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 more than a predetermined value. 4. The switching power supply according to claim 3, wherein 4. An on-time width of said control switch included in said second switch by changing a detection level of said second capacitor.
A switching power supply as described. 5. A DC power supply, a series circuit including a reactor connected between one end and the other end of the DC power supply, a first switch, and a first capacitor; An energy emitting winding connected in parallel to the first capacitor; a flywheel diode connected in series to the energy emitting winding; and a resonance connected to form a voltage resonance circuit with the reactor. Capacitor or stray capacitance, a series circuit of a second capacitor and a second switch connected in parallel to the flywheel diode, and a first control circuit for controlling on / off of the first switch And before the first switch is turned on, the voltage of the first switch causes a resonance between the reactor and the resonance capacitor or the stray capacitance. And a second control circuit for controlling the second switch so that the second switch can gradually fall based on the operation. 6. The first and second switches each comprise a one-way control switch, and a diode built-in or externally connected to the control switch and connected in anti-parallel to the control switch. The switching power supply according to claim 5, characterized in that: 7. 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 more than a predetermined value. 7. The switching power supply device according to claim 6, wherein 8. A switching power supply according to claim 7, wherein a detection level of said second capacitor is changed to change an on-time width of said control switch included in said second switch. apparatus.