JP2002247844A - Switching power circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To constitute a switching power circuit so that an RCC oscillation circuit and a synchronous rectification circuit are controlled by one and the same microcomputer to link the operations of the two with each other. SOLUTION: The switching power circuit is constituted of an RCC switching regulator circuit that rectifies alternating-current power supply and switches and controls induced voltage produced in primary winding by PWM; and a synchronous rectification circuit that synchronizes and rectifies induced voltage produced in secondary winding which induces voltage produced in the RCC switching regulator circuit through the transformer. The RCC switching regulator circuit and the synchronous rectification circuit PWM-controls the RCC switching regulator circuit and controls synchronization of switching elements in the synchronous rectification circuit by one and the same controlling means.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a switching power supply circuit, and more particularly, to reducing the number of components by controlling an RCC switching regulator circuit and a secondary-side synchronous rectifier circuit by a single microcomputer. It also relates to a switching power supply circuit with improved rectification efficiency.

[0002]

2. Description of the Related Art In a switching power supply circuit according to the prior art, it is well known that an RCC switching regulator circuit and a secondary side synchronous rectification circuit are controlled by separate control circuits.

[0003]

However, if the RCC switching regulator circuit and the synchronous rectifier circuit described in the prior art are controlled by separate control systems, the operation may become unstable with respect to load fluctuations. There's a problem.

Therefore, there is a problem that the RCC switching regulator circuit and the synchronous rectifier circuit constituting the switching power supply circuit must be solved in a circuit configuration that operates stably even when the load fluctuates.

[0005]

In order to solve the above-mentioned problems, a switching power supply circuit according to the present invention has the following configuration.

(1) An RCC switching regulator circuit for rectifying an AC power supply and performing switching control of an induced voltage generated in a primary winding by a PWM method, and a voltage generated by the RCC switching regulator circuit via a transformer. The RCC switching regulator circuit and the synchronous rectifier circuit synchronize and rectify the induced voltage generated in the secondary winding. The RCC switching regulator circuit and the synchronous rectifier circuit control the RCC switching regular circuit by the PWM method using the same control means. A switching power supply circuit wherein synchronous control of a switching element of a synchronous rectifier circuit is performed. (2) The switching power supply circuit according to (1), wherein the control means is generated by a microcomputer. (3) The synchronous rectifier circuit includes a set of a secondary winding, a capacitor connected in parallel to the secondary winding, and a switching element provided between the secondary winding and the capacitor. As a single or a plurality, the switching element performs a voltage level shift of a voltage of the opposite polarity induced by a predetermined secondary winding, and the level-shifted voltage is based on a preset threshold value. (1) The switching power supply circuit according to (1), which is turned on / off by an on / off signal. (4) The switching power supply circuit according to (3), wherein the switching element is an FET.

As described above, by controlling the RCC switching regulator circuit and the synchronous rectification circuit constituting the switching power supply circuit by the microcomputer as one control means, the operation of the RCC switching regulator circuit is completely controlled by the synchronous rectification circuit side. It becomes possible to link to the operation.

[0008]

Next, an embodiment of a switching power supply circuit according to the present invention will be described with reference to the drawings.

The switching power supply circuit according to the present invention, as shown in FIG.
It comprises a C switching regulator circuit and a secondary-side synchronous rectifier circuit.

The RCC switching regulator circuit on the primary side includes a rectifier 1 for rectifying an AC power supply and a transformer TR.
, A primary winding N1 and secondary windings N2, N3,
N4, N5, N6; a starter 2 for supplying a predetermined voltage from the rectifier 1 to the switching element Q1; and a changeover switch 3 for switching between a signal from the starter 2 and a PWM pulse signal controlled by the microcomputer 10. , A switching element Q1 which is an RCC oscillation FET, a switching photocoupler 5 for passing a signal for switching the changeover switch 3, and a PWM photocoupler 4 for passing a PWM signal from the microcomputer 10. .
Of these, the secondary winding N2 is for plus 13 volts, the secondary winding N3 is for plus 6 volts, the secondary winding N4 is for plus 18 volts, the secondary winding N5 is for minus 6 volts,
The secondary winding N6 induces and generates a voltage for the photocoupler.

On the other hand, the synchronous rectifier circuit generates a switching element Q2, which is a synchronous rectifying power FET for generating plus 13 volts, and a signal for synchronizing the microcomputer by level shifting the plus 18 volt power supply voltage. First
, A capacitor C2 for charging / discharging by turning on / off the switching element Q2, a switching element Q3 which is a synchronous rectification power FET for generating plus 6 volts, and a power supply voltage of minus 6 volts. A second level shift 7 for controlling on / off of switching elements Q2 and Q3 by shifting, and a capacitor C3 for charging and discharging by on / off of switching element Q3
Control means for controlling on / off of the switching element Q1 based on the PWN signal of the RCC switching regulator circuit and controlling on / off of the switching elements Q2, Q3 of the synchronous rectification circuit. The microcomputer 10 includes a microcomputer 10 and first and second comparators 8 and 9 which receive signals from the first and second level shifters 6 and 7 and input the signals to the microcomputer 10.

The RCC switching regulator circuit and the synchronous rectifier circuit having such a configuration are connected as follows.

First, in the RCC switching regulator circuit, an AC power supply is connected to the rectifier 1, and the output terminal of the rectifier 1 is connected to one terminal of the primary winding N1 and the starting unit 2. The other terminal of the primary winding N1 is connected to the drain D of the switching element Q1, and the output terminal of the starting unit 2 is connected to one input terminal of the changeover switch 3. The source S side of the switching element Q1 is grounded, and the gate G is connected to the output terminal of the changeover switch 3. A quasi-resonant capacitor C1 is connected to the drain D of the switching element Q1, and the other end is grounded. The other input terminal of the changeover switch 3 is connected to a PWM photocoupler 4 to which a predetermined voltage is supplied from a secondary winding N6. The control terminal of the changeover switch 3 is connected to a switching photocoupler 5, to which a predetermined voltage is supplied from a secondary winding N6.

In the synchronous rectifier circuit, the secondary winding N2
Is connected to the output terminal for plus 13 volts and one end of the capacitor C2, and the other terminal is connected to the drain D of the switching element Q2. Capacitor C2
Is connected to the ground GND. The source S of the switching element Q2 is connected to the ground GND, and the gate G is connected to the SYNC2 terminal of the microcomputer 10. One terminal of the secondary winding N3 is connected to the output terminal for plus 6 volts and one end of the capacitor C3, and the other terminal is connected to the drain D of the switching element Q3. The other terminal of the capacitor C3 is connected to the ground GND. The source S of the switching element Q3 is connected to the ground GND, and the gate G is the SY of the microcomputer 10.
Connected to NC1 terminal. One terminal of the secondary winding N3 is connected to voltage dividing resistors R1 and R2 connected in series,
The other ends of the resistors R1 and R2 are connected to the ground GND, and a terminal from an intermediate position between the resistors R1 and R2 is
0 A / D terminal. One terminal of the secondary winding N4 is connected to a terminal of plus 18 volts via a diode D1, and the other terminal is connected to the ground GND. One terminal of the secondary winding N4 is connected to the first level shift 6, and the output terminal of the first level shift 6 is connected to the first comparator 8. The output terminal of the comparator 8 Is connected to the ZVS terminal of the microcomputer 10. One terminal of the secondary winding N5 is ground G
ND, and the other terminal is connected to a minus 6 volt terminal via a diode D2. The other terminal of the secondary winding N5 is connected to the second level shift 7,
The output terminal of the second level shift 7 is connected to the second comparator 9, and the output terminal of the comparator 9 is connected to the SYNC terminal of the microcomputer 10.

The operation of the RCC oscillation switching regulator circuit and the synchronous rectifier circuit having such a connection state will be described with reference to FIG. 1 and the waveform diagram shown in FIG.

In the RCC switching regulator circuit, a rectangular wave signal from the PWM terminal of
In the case of the embodiment, a rectangular wave signal having a minimum width of 0.9 μsec and a cycle of 10 μsec to 30 μsec is applied to the gate G of the switching element Q1. When a rectangular wave signal is applied to the gate G (position P1), the switching element Q1 turns on, and the drain current Id continues to increase linearly while the drain voltage Vd remains reduced. When the rectangular wave signal applied to the gate G is turned off (position P2), when the drain voltage Vd rises rapidly and reaches a predetermined voltage, the drain voltage Vd gradually attenuates while drawing a parabola.
This change in drain voltage is excited by the secondary winding N4,
That state is input to a first level shift. In the first level shift, the signal on the output side is observed by the comparator 1, and when the signal becomes equal to or higher than a certain threshold Vth1 (position P3), the output becomes HIGH (position P4), and the output becomes higher than the certain threshold Vth1. HI until it goes down (P5 position)
The state of GH is maintained (position P6). At the same time, the signal obtained by the first comparator is input to the microcomputer 10 and fed back to the PWM control to be used as a soft switching timing signal.

Next, the operation of the synchronous rectifier circuit that performs a rectifying operation in synchronization with the operation of the RCC switching regulator circuit will be described.

First, as described with reference to FIG. 1, the switching elements Q2 and Q3 are power FETs for synchronous rectification, and the sources S of the switching elements Q2 and Q3 are connected to the ground GND. , The drain D side is connected to one of the secondary windings N2 and N3, and the other is connected to the capacitors C2 and C3 and the plus 13 volt and 6 volt output terminals. Since the operation is the same for both switching elements Q2 and Q3, switching element Q2 will be described below.

In the synchronous rectification, the switching element Q2 of the operation waveform diagram shown in FIG.
2. Add a rectangular wave signal as indicated by the gate G of Q3.
This square wave signal is generated corresponding to the switching voltage generated by the RCC switching regulator circuit, and will be described in detail below.

First, the secondary winding N2 has a drain voltage Vd of the switching element Q1 of approximately "N1 / N1".
2, a current flows in the order of “source S of switching element Q2, drain D of switching element Q2, secondary winding N2, capacitor C2, source S of switching element Q2”, Capacitor C2
, A smoothed voltage of the secondary winding N2 is generated. this is,
This is the same as when rectification is performed with a normal diode. However, here, if the voltage of the gate G is longer than necessary,
That is, when the voltage of the secondary winding N2 becomes lower than the voltage of the capacitor C2, the capacitor C2 causes a current to flow to the load and the current to the switching element Q2 at the same time, so that the efficiency is deteriorated. This case increases when the control system is different.

That is, when the microcomputer performs the collective control as in the present invention, first, the second level shift 6 changes the level of the drain voltage Vd of the switching element Q1 (the secondary winding N5) completely opposite to the drain voltage Vd. Shift to generate the output shown in the operation waveform diagram. The point a at which the threshold value Vth2 does not become lower than that of the capacitor C2 is compared by the second comparator 8, and when the voltage becomes equal to or lower than the voltage, the rectangular wave signal is turned LOW (off) (position P7). When the output signal of the second comparator becomes LOW, the microcomputer turns the gate signals of the switching elements Q2 and Q3 HIGH (ON) (P
8 position). Next, the microcomputer calculates a synchronous rectification time suitable for the loads of the switching elements Q2 and Q3 from the ON time of the PWM signal for controlling the switching element Q1, and when the time reaches the time, the gate signal of the switching elements Q2 and Q3. To LOW (off).

In this manner, the microcomputer 10 calculates a time width suitable for synchronous rectification from the time width of the gate signal of the switching element Q1 oscillating in the RCC switching regulator circuit, and controls the switching elements Q2 and Q3. You can do it. Here, the switching elements Q2 and Q3 are FETs.
Since the resistance is very small, loss can be reduced as compared with rectification by a diode. In other words, if one microcomputer 10 controls the oscillation of the RCC switching regulator circuit and the synchronous rectification of the synchronous rectifier circuit, it is possible to perform control suited to the mutual situation.

[0023]

As described above, the switching power supply circuit according to the present invention controls the RCC switching regulator circuit and the synchronous rectifier circuit by the same control means, ie, the microcomputer. Oscillation operation in the circuit can be linked to synchronous operation in the secondary-side synchronous rectifier circuit, reducing rectification loss on the secondary side and reducing the number of components for synchronous rectification. There is an effect that can be.

[Brief description of the drawings]

FIG. 1 is a schematic circuit diagram of a switching power supply circuit according to the present invention.

FIG. 2 is an operation waveform diagram showing an operation of the circuit in FIG.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1: Rectifier, 2: Starting part, 3: Switching switch, 4: PW
Photocoupler for M, 5; Photocoupler for switch, 6;
First level shift, 7; second level shift, 8; first comparator, 9; second comparator, 10;

Claims (4)

[Claims] An RC for rectifying an AC power supply and switching-controlling an induced voltage generated in a primary winding by a PWM method.
C switching regulator circuit, and a synchronous rectifier circuit for rectifying the voltage generated by the RCC switching regulator circuit by synchronizing an induced voltage generated in a secondary winding via a transformer. The circuit and the synchronous rectifier circuit are controlled by the same control means and the PWM of the RCC switching regular circuit.
A switching power supply circuit characterized by performing control by a system and synchronous control of a switching element of a synchronous rectification circuit. 2. The switching power supply circuit according to claim 1, wherein said control means is generated by a microcomputer. 3. The synchronous rectifier circuit comprises: a secondary winding; a capacitor connected in parallel to the secondary winding; and a switching element provided between the secondary winding and the capacitor. A single or a plurality is configured as a set, the switching element performs a voltage level shift of a voltage of the opposite polarity induced by a predetermined secondary winding, and sets the level-shifted voltage to a preset threshold. 2. The switching power supply circuit according to claim 1, wherein the switching power supply circuit is turned on / off by a reference on / off signal. 4. The switching power supply circuit according to claim 3, wherein said switching element is an FET.