JP2652583B2 - Switching power supply - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a step-up switching power supply, and more particularly, to a switching power supply that can reduce switching loss by utilizing resonance.

[Prior art] A series circuit of a reactor and a switch is connected in parallel to a DC power supply, and a series circuit of a diode and a capacitor is connected in parallel to a switch so that an output voltage is obtained from both ends of the capacitor. The configured step-up switching regulator is already known.

[Problems to be Solved by the Invention] In this type of switching regulator, a capacitor or a stray capacitance may be connected in parallel to the switch in order to gradually change the voltage of the switch when the switch is turned off. However, the energy absorbed by the capacitor or the stray capacitance is released through the switch during the switch ON period, resulting in power loss.

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

Means for Solving the Problems The present invention for achieving the above object includes a DC power supply, a series circuit of a reactor connected between one end and the other end of the DC power supply, and a first switch. A series circuit of a rectifier diode and a first capacitor connected in parallel to the first switch, a first control circuit for turning on / off the first switch, and the reactor A resonance capacitor or a stray capacitance connected to form a resonance circuit, a rectification circuit of a second capacitor and a second switch connected in parallel to the rectification diode, and the first switch includes: Before turning on, the second switch is set so that the voltage of the first switch can gradually fall based on the resonance operation of the reactor and the resonance capacitor or the stray capacitance. And a second control circuit for controlling the switching power supply device.

It is desirable that the second switch be a control switch and a diode connected in anti-parallel.

Further, it is desirable that the second switch is controlled to be turned on and off based on the detection of the voltage of the second capacitor.

Further, by changing the detection level of the voltage of the second capacitor, the on-time width of the control switch included in the second switch can be changed to control the output voltage.

[Operation] According to the present invention, energy is accumulated in the reactor by the charging current flowing through the second capacitor, and a voltage resonance operation between the reactor and the resonance capacitor or the stray capacitance occurs based on the energy, and the resonance capacitor Alternatively, the charge of the floating capacitance is released. Therefore, the electric charge of the resonance capacitor or the stray capacitance is not released during the ON period of the first switch, and the power loss is reduced.

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

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

A series circuit including a rectifier diode 7 and a first capacitor 8 is connected in parallel to the first switch 5. A load 11 is connected between the pair of output terminals 9 and 10 connected to the first capacitor 8.

A first control circuit 12 connected to a control terminal (gate) of the first control switch 5a supplies an on / off control signal to the first control switch 5, and includes an output terminal 9,
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 specifically shows the control circuit 12, which comprises a variable monomultivibrator 15 for generating a pulse in response to a trigger signal given from a switch voltage detection circuit 14, and a drive circuit 16. Variable monomer vibrator 15 is output voltage detection circuit 13
And outputs an output pulse whose pulse width changes in inverse proportion to the output voltage.

A series circuit of a second capacitor 17 and a second switch 18 according to the present invention is connected in parallel with the second diode 7. The second switch 18 comprises a P-channel insulated gate transistor (FET) having a source connected to the substrate, and is equivalent to a second control switch 18a and a second diode 18b connected in anti-parallel to the second control switch 18a. Can be shown. To control the second control switch 18a, a second control circuit 21 including first and second resistors 19 and 20 connected between the pair of output terminals 9 and 10 is provided. The first and second connection midpoints are second control switches
Connected to gate 18a.

[Operation] In the circuit of FIG. 1, a closed circuit including the power supply 1, the reactor 4, and the first control switch 5a is formed while the first control switch 5a is on. Energy is stored in the reactor 4. During the off period of the first control switch 5a, the reactor 4
Is supplied to the first capacitor 8 and the load 11 via the rectifier diode 7. When the ratio (duty) between the ON time width and the OFF time width of the first control switch 5a is changed, the output voltage changes.

 The operation of each section will be described in more detail with reference to FIG.

As shown in FIG. 3 (B), the first control switch 5a at t0.
Is controlled off, the first control switch before t0
Voltage resonance between the inductance of the reactor 4 and the stray capacitance 6 occurs based on the energy stored in the reactor 4 during the ON period of 5a, and the stray capacitance 6 is charged. This voltage, that is, the voltage Vq of the first switch 5 Gradually increase as shown in FIG. 3 (C). This voltage Vq is applied to the first capacitor 8
Is higher than the sum of the voltage V0 of the second capacitor 17, the voltage Vc of the second capacitor 17, and the forward rising voltage Vf of the second diode 18b, the second diode 18b conducts and t1 in FIG. 3 (F).
The current Ic2 flows through the second capacitor 17 as shown in a period from t2 to t2, which is reversely charged (discharged). Second capacitor
When the voltage Vc decreases due to the discharge of 17, the gate potential of the second control switch 18a becomes lower than the source potential, and the second control switch 18a is turned on. When the direction of the charging voltage of the second capacitor 17 is opposite to that in FIG.
The second diode 18b turns off. Almost at the same time, the rectifier diode 7 conducts, and a current Id1 flows as shown in FIG. Since the second diode 18b is biased by the second capacitor 17, it is turned on before the rectifier diode 7.

When the operation of releasing the energy of the reactor 4 is completed and the current of the rectifier diode 7 becomes zero at t3, the first capacitor 8, the second capacitor 17, the second control switch 18a, the reactor 4, and the power source 1 are formed. A closed circuit is formed, and a charging current for the second capacitor 17 (current in the direction opposite to ic2 in FIG. 1) flows as shown at t3 to t4 in FIG. 3 (F). As a result, the voltage Vc of the second capacitor 17 returns to the level at which the second control switch 18a is turned off again, and the second control switch 18a is turned off at time t4.

The resonance operation between the reactor 4 and the floating capacitance 6 occurs based on the energy stored in the reactor 4 during the period from t3 to t4, and the electric charge of the floating capacitance 6 is converted into a closed circuit including the floating capacitance 6, the reactor 4 and the power supply 1. Released, first switch 5
Voltage gradually decreases as shown in the period from t4 to t5 in FIG. 3 (C). The voltage zero of the first switch 5 is detected by the switch voltage detection circuit 14, and a trigger pulse shown in FIG. 3A is generated at t5, and the variable monomultivibrator 15 shown in FIG.
Is triggered, a control pulse having a desired width (t5 to t6) is generated as shown in FIG. 3 (B), and the first control switch 5a is turned on. Since the discharge of the electric charge of the floating capacitance 6 has been completed before the first control switch 5a is turned on, no energy loss occurs in the closed circuit between the first control switch 5a and the floating capacitance 6.

When the first control switch 5a is turned on, energy is again stored in the reactor 4. Thereafter, when the first control switch 5a 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 variable mono-multivibrator 15 changes the pulse width in the period from t5 to t6 in FIG.

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

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

(1) First switch 5 and / or second switch 18
May be constituted by an anti-parallel circuit of a bipolar transistor and a diode. Also, the first and second switches 5,
A control switch may be connected in place of 18, and the control switch may be turned on in accordance with the period during which the diodes 5b and 18b conduct.

(2) An individual capacitor may be connected instead of the stray capacitance 6. Further, instead of connecting a resonance capacitor or a stray capacitance to the first switch 5 in parallel, it may be connected to the reactor 4 in parallel.

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

(4) As shown in FIG. 4, a variable resistor or control element 19a is connected to the second control circuit 21 and is controlled by the output voltage to change the detection level of the voltage of the second capacitor 17 and The output voltage may be controlled by changing the period from t3 to t4 in FIG.

(5) The time point t5 at which the voltage of the first switch 5 becomes zero may not be directly detected but may be detected and predicted from the time points t3 and t4.

[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 both the time of turning off and the time of turning on of the step-up switching power supply device.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a step-up switching power supply according to an embodiment of the present invention, FIG. 2 is a block diagram showing a control circuit in FIG. 1 in detail, and FIG. 3 is a waveform showing states of respective parts in FIG. FIG. 4 is a circuit diagram showing a modification of the second control circuit. 1 ... power supply, 4 ... reactor, 5 ... first switch, 5a ... first control switch, 5b ... first diode, 6 ... floating capacitance, 7 ... rectifier diode, 8 ... 1st capacitor, 9,10 ... output terminal, 12 ... control circuit,
17 ... second capacitor, 18 ... second switch, 18a
... Second control switch, 18b... Second diode.

Claims (4)

(57) [Claims] A dc power supply; a series circuit of a reactor connected between one end and the other end of the dc power supply; and a rectifier connected in parallel to the first switch. A series circuit of a diode and a first capacitor; a first control circuit for controlling on / off of the first switch; a resonance capacitor connected to form a resonance circuit with the reactor or a floating capacitor; A capacitor; a series circuit of a second capacitor and a second switch connected in parallel to the rectifier diode; and a voltage of the first switch before the first switch is turned on. A second control circuit that controls the second switch so that the reactor can gradually fall based on a resonance operation between the reactor and the resonance capacitor or the stray capacitance. Switching power supply device. 2. The control apparatus according to claim 2, wherein said second switch is 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 antiparallel. 3. The switching power supply according to claim 2, wherein the second control circuit is a circuit that controls on / off of the control switch included in the second switch based on a voltage of the second capacitor. apparatus. 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.