JPH02151266A - Parallel resonance converter - Google Patents

Abstract

PURPOSE:To realize reduction in size of a filter and to reduce its cost by pulse- width controlling a pulse for alternately turning ON/OFF switching means, and largely narrowing the control width of a switching frequency. CONSTITUTION:An amplifier 1 compares an output voltage Vo of secondary side with a reference output voltage Vref, outputs a differential voltage to a VCO circuit 3 to determine the oscillating frequency of the circuit 3 to become the frequency of a pulse to be output from a pulse-width modulator 4. An amplifier 2 compares an output current Io of a secondary side with a reference output current Iref, and outputs its output current to the modulator 4. As a result, the modulator 4 outputs a pulse train having a frequency determined by the circuit 3 and a pulse width responsive to the output current from the amplifier 2. The pulse train is divided in frequency by a frequency devider 5 and output to alternately turn ON/OFF power transistors Q1, Q2 for drivers 6a, 6b.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a parallel resonant converter used as a switching power supply device in various electronic devices.

(Prior Art) A parallel resonant converter including a resonant circuit has been known as one of the switching power supply devices used in various electronic devices. In this parallel resonant converter, two power transistors connected in parallel to the resonant circuit are alternately turned on and off to apply a square wave voltage to both ends of the resonant circuit. A wave voltage is generated, and this voltage is transmitted to the secondary circuit via a transformer, rectified and smoothed, and then supplied to the load.

By the way, in this parallel resonant converter, the output voltage is stabilized by controlling it using an operating frequency higher (or lower) than the resonant frequency of the resonant circuit, that is, the switching frequency of each power transistor.

However, such frequency control needs to be changed in inverse proportion to variations in load power consumption and input voltage, and requires a very wide control range. For this reason, there is a problem in that the filter for smoothing the rectified current in the secondary circuit becomes large and the cost increases.

(Problems to be Solved by the Invention) The present invention is intended to solve the above-mentioned problems.Based on the output of the secondary side circuit, in addition to controlling the switching frequency by the frequency control means, each switching means is alternately controlled. By controlling the pulse width of the on/off pulses, the control width of the switching frequency can be significantly narrowed, thereby realizing a smaller filter and reducing costs. intended to provide.

[Structure of the Invention] (Means for Solving the Problems) In order to achieve this object, the present invention includes a resonant circuit, two switching means each connected in parallel to the resonant circuit, and each of these switching means. In a parallel resonant converter equipped with frequency control means that controls the switching frequency of each switching means so that a constant voltage is obtained on the secondary side of the transformer from the voltage generated in the resonant circuit by alternately turning on and off the secondary The device is equipped with a pulse width control means for controlling the switching frequency by the frequency control means and controlling the pulse width of a pulse that turns each switching means on and off alternately based on the output from the side.

(Function) In the parallel resonant converter of the present invention, the pulse width modulation means controls the switching frequency of each switching means in the frequency control means and alternately turns on each switching means based on the output of the secondary side circuit. Since the pulse width of the OFF pulse is controlled, the control width of the switching frequency can be significantly narrowed, thereby making it possible to downsize the filter and reduce costs.

(Example) Hereinafter, an example of the present invention will be described in detail based on the drawings.

FIG. 1 is a circuit diagram showing the configuration of a parallel resonant converter according to an embodiment of the present invention.

In the same figure, CI and C2 each have a power supply voltage Vg of l
/2 capacitors, L" and C" are inductors and capacitors that form resonant circuits, respectively, Ql and Q
2 is a power transistor connected in parallel to a resonant circuit as a switching means, DISD2 is a rectifier diode that circulates the current immediately before turning on each power transistor Ql and Q2 in its own closed circuit, and C3 and C4 are each a power transistor connected in parallel to a resonant circuit. This is a snubber capacitor that consumes the energy remaining in the resonant circuit when the power transistors Ql and Q2 are turned off. In addition, T is a transformer that transmits the energy on the primary side to the secondary side circuit, D3,
D4 is a rectifier diode that rectifies the current flowing through the secondary coil of the transformer T, and Lo and Co are inductors and capacitors that constitute a choke input filter to smooth the current that has passed through the rectifier diodes D3 and D4. , Ro is the load resistance.

In this embodiment device, each power transistor QI SQ
By controlling the switching frequency of 2 in a range higher than the resonant frequency of the resonant circuit based on the output voltage of the secondary side, the output voltage is stabilized and the power transistors Ql and Q2 are alternately switched. on/
Stabilization control is also performed by controlling the pulse width of the pulse that turns off.

FIG. 2 shows the configuration of this constant voltage control system.

In the figure, 1 is a first amplifier that amplifies and outputs the difference between the output voltage Vo on the secondary side and the reference output voltage V ref', and 2 is the output current 1o on the secondary side and the reference output current 1 ref.
a second amplifier 3 that amplifies and outputs the difference between
0 circuit and 4 are pulse width modulators (PWM) that output pulses with a pulse width corresponding to the output current of the second amplifier 2, and the frequency of the output pulses is determined by the oscillation frequency f'sν of the vCO circuit 3. be done. Further, 5 is a frequency divider that divides the output pulse train of the pulse width modulator 4, and 6 a s 6 b is a gate Gl of the corresponding power transistor Ql and G2 based on the output from the frequency divider 5, respectively.

This is a driver that outputs a drive signal to G2.

Next, the operation of the parallel resonant converter configured as above will be explained.

First, when the power is turned on, each capacitor Cl
Charges corresponding to the case where the power supply voltage Vg is divided into 172 are accumulated in each SC2.

Thereafter, drive signals are input from each driver 6a, 6b to the gates Gl, G2 of the corresponding power transistors Q1%Q2, thereby starting alternate on/off operations in each power transistor Ql, G2. A square wave voltage is applied across the resonant circuit made up of the inductor Lr and the capacitor C.

Then, a phenomenon close to a resonance state appears in the resonant circuit, and
Due to this phenomenon, a voltage close to a sine wave is generated in this resonant circuit.

By the way, in this example device, control is performed using a frequency higher than the resonant frequency of the resonant circuit. Therefore, the current Ic flowing through the resonant circuit has a phase of 9 compared to the voltage Vc.
The sending current is shifted by 0 degrees, and during the period when the diodes DI and D2 are conducting, the power transistor QI SG2
can be turned on. Therefore, deterioration of the power transistors Q1 and G2 can be prevented, and switching loss can be prevented.

Now, when a voltage close to a sine wave is generated in a resonant circuit,
The energy is transmitted to the secondary circuit via the transformer T, thereby generating a current flowing through the secondary circuit. The current generated in this secondary circuit is connected to the rectifier diode D3.
, D4, and the ripple is compressed in a filter consisting of an inductor Lo and a capacitor Co, and then supplied to a load resistor RO.

The above is the basic operation of the parallel resonant converter of this embodiment, and further, in this parallel resonant converter, output voltage stabilization control is performed as follows.

First, in the first amplifier 1, the secondary side output voltage Vo
and the reference output voltage Vrer, and outputs a voltage indicating the difference to the vCO circuit 3. As a result, vCO circuit 3
The oscillation frequency of is determined. This oscillation frequency becomes the frequency of the pulse to be output from the pulse width modulator 4.

On the other hand, in the second amplifier 2, the secondary side output current i
A comparison is made between o and a reference output current 1 rel'. The output current is then output to the pulse width modulator 4.

As a result, the pulse width modulator 4 outputs a pulse train having the frequency determined by the vCO circuit 3 and having a pulse width corresponding to the output current from the second amplifier 2.

After that, the pulse train outputted from the pulse width modulator 4 is frequency-divided by a frequency divider 5, and further, from this frequency divider 5 to each driver 6a, 6b, each power transistor QIS
A pulse train is output to alternately turn on and off Q2.

Thus, according to the parallel resonant converter of this embodiment, the stabilization control of the output voltage is performed by each power transistor QI S
In addition to controlling the switching frequency of G2, we also perform pulse width modulation of pulses that alternately turn on and off each power transistor Ql and G2, which effectively narrows the control range of the switching frequency described above. It becomes possible to convert into Therefore, the inductor Lo and capacitor CO that constitute the filter on the secondary side can be downsized, and costs can be reduced.

Note that the present invention is not limited to the above-mentioned type of parallel resonant converter, but can also be applied to, for example, a full bridge type or a current type converter.

Further, in the above-described embodiment, the operating frequency of the parallel resonant converter is controlled at a higher side than the resonant frequency, but the present invention can be similarly applied to the case where the operating frequency is controlled at a lower side than the resonant frequency. Of course it can be done.

[Effects of the Invention] As explained above, according to the parallel resonant converter of the present invention, in addition to controlling the switching frequency by the frequency control means, each switching means can be turned on and off alternately based on the output of the secondary side circuit. By controlling the pulse width of the pulse, it is possible to significantly narrow the control width of the switching frequency, thereby making it possible to downsize the filter and reduce costs.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram for explaining the configuration of a parallel resonant converter according to an embodiment of the present invention, and FIG. 2 is a block diagram for explaining the configuration of the output stabilization control section in the parallel resonant converter of FIG. 1. It is. L", C"...inductor and capacitor forming a resonant circuit, QI SQ2...power transistor,
T... Transformer transformer, 1... First amplifier, 2...
・Second amplifier, 3...700 circuit, 4...Pulse width modulator. Applicant Toshiba Corporation Representative Patent Attorney Sasa Suyama −

Claims (1)

[Claims] (1) A resonant circuit, two switching means each connected in parallel to this resonant circuit, and by alternately turning on and off each of these switching means, a voltage generated in the resonant circuit is generated on the secondary side of the transformer. In the parallel resonant converter, the frequency control means controls the switching frequency of each of the switching means so as to obtain a constant voltage. A parallel resonant converter characterized by comprising a pulse width control means for controlling the pulse width of a pulse that turns each switching means on and off alternately.