JPH06176946A - Switching power supply - Google Patents

Abstract

(57) [Summary] [Purpose] The purpose is to widen controllable load fluctuations by using inexpensive parts and to secure a high-speed follow-up response to load fluctuations. A forward type switching power supply device uses a choke coil in which an energy storage type choke coil 16 is molded by a ferrite resin 32 formed by kneading ferrite powder and polyamide.

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 device which supplies current by following a load change at high speed.

[0002]

2. Description of the Related Art Generally, a coil that has been mainly used in the past is, for example, a coil wound around a ferrite core of U, E, C, drum type. The characteristics of these coils can be represented by plotting the applied current value to be printed on the coil on the horizontal axis and the inductance of the coil on the vertical axis (see the DC-superimposed characteristic diagram which is the inductance-current characteristic diagram shown in FIG. 2). reference). In the characteristic of the coil shown in FIG. 2, when the value of the flowing current exceeds the guaranteed value of the superimposed DC current, the inductance of the coil is sharply reduced due to the magnetic saturation characteristic of the coil. Therefore, when the load changes in this region, the response of the current flowing through the coil is improved.

[0003]

By the way, as described above, when the load variation demands an increase in the load current, the impedance value in the switching power supply device suddenly decreases, so that the current flowing through the switching element increases. It was sometimes destroyed beyond the safe operating area (ASO) of the device.

Further, the conventional coil has the unsaturated region US shown in FIG. 2, and the inductance does not change even if the current value changes with respect to the load current. Therefore, even if the load current increases, the impedance seen from the switching element is only due to the change in impedance due to the coupling of the insulating transformer. As a result, the response to the load fluctuation deteriorates. In order to improve the deterioration of the response, the switching power supply device should improve the coupling of the isolation transformer as much as possible. Therefore, various proposals have been made for the insulating transformer, such as winding having a sandwich structure of a primary winding and a secondary winding, and winding a copper foil rectangular wire.

As one of concrete proposals for solving these problems, a switching power supply device is disclosed in Japanese Utility Model Laid-Open No. 62-57.
No. 589 is disclosed. This invention uses the magnetic flux of the coil in the saturation region SA of the linear characteristic shown by the broken line in FIG. 2 when supplying the output current of the coil to the load to improve the current response characteristic to the load fluctuation. There is.

However, if a heavy load occurs at a low input voltage in the unsaturated region US shown in FIG. 2, the output voltage cannot be kept constant with respect to load fluctuation.

Therefore, the switching power supply unit needs to increase the feedback gain of the control system used in order to follow the load fluctuation at high speed and supply an output with a stable output. You will have to achieve gain.

However, when the above-mentioned control is performed, this control system malfunctions with respect to disturbance noise and noise generated internally, which causes a problem in the stability of the output voltage. In addition, there is a problem in that a great deal of design man-hours, cost, and extra filter parts are required for countermeasures against abnormal oscillation caused by these causes.

Therefore, the present invention has been made in view of such circumstances, and it is possible to widen the controllable load fluctuation by using inexpensive parts and secure a high-speed follow-up response to the load fluctuation. An object of the present invention is to provide a switching power supply device that can be used.

[0010]

A switching power supply device according to the present invention includes a switching element, an output transformer driven by an output signal of the switching element, a choke coil for storing electromagnetic energy, and an output of the output transformer. In the forward type switching power supply device having a rectifying circuit for rectifying a signal, the choke coil is a choke coil formed by molding a ferrite resin obtained by kneading a soft magnetic powder and a binder. To solve.

[0011]

Since the switching power supply device of the present invention uses the choke coil formed by molding the coil with the ferrite resin obtained by kneading the soft magnetic powder and the binder, the DC superimposed current characteristic of the choke coil is not satisfied. By eliminating the saturation region, the output voltage can be kept constant even at a low input voltage, and the response control to the load fluctuation can be automatically performed.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a switching power supply device according to the present invention will be described below with reference to the drawings.

First, the schematic configuration of the switching power supply device of this embodiment will be described with reference to the block circuit shown in FIG. The switching power supply device includes a filter unit 11 for reducing noise of the input power supply 10,
A rectifying unit 12 for rectifying the output from the filter unit 11,
A converter 13 that converts the output from the rectifier 12, and a controller 1 that controls the change of the input voltage at the input side of the converter 13.
4 and an output rectifier 1 for rectifying the output of the converter 13
5 and choke coil 16 to supply the output to the load 17.

The configuration of each part of the switching power supply device of FIG. 1 will be briefly described. The filter section 11 includes a low-pass filter common mode filter 11a and a normal mode filter 11b.

The rectifying section 12 is composed of a rectifying block 12a composed of a bridge diode, a smoothing capacitor 12b, and a snubber circuit 12c. The output rectifying unit 15 is composed of a diode 15a for rectifying the output and a flywheel diode 15b.

The control section 14 includes a switching transistor TR1, a drive transformer 14b, an auxiliary power supply 14c, an oscillator 14d, an integrator 14e, a comparator 14f, and
It is composed of a pulse width modulation (hereinafter referred to as PWM) unit 14g and a drive transformer driving transistor TR2.

This switching power supply device is connected and operated as described below. Input power 10
Outputs AC to the filter unit 11 via the commercial AC input terminal. The common mode filter 11a of the filter section 11 removes high frequency components of 50 kHz or more and supplies the alternating current to the rectification section 12. The rectifying unit 12 converts alternating current into direct current by the rectifying block 12a, the smoothing capacitor 12b, and the snubber circuit 12c. This DC is the converter 1
3 is supplied to one end side 13a of the primary winding of the conversion transformer 13A.

The other end 13b of the primary winding is connected to the collector of the switching transistor TR1 and
It is connected to the resistor 18 of the snubber circuit 12c and the anode side of the diode 19. In addition, the conversion transformer 13A
One end side 13c of the secondary winding of is connected to the diode 15a of the output rectification unit. The other end 13d of the secondary winding
Is connected to the anode of the flywheel diode 15b.

The base of the switching transistor TR1 is connected to the output winding C side of the drive transformer 14b. On the other hand, the other end D of the output winding is connected to the smoothing capacitor 12b and the rectification block 12a. Also,
A current is supplied to the input winding A side of the drive transformer 14b from the auxiliary power supply 14c when the power is turned on. The input winding B side is a drive transformer driving transistor T
It is connected to the collector side of R2.

The auxiliary power supply 14c supplies a current to the oscillator 14d and the integrator 14e when the power is turned on. The oscillator 14d oscillates a square wave pulse and outputs its output to the integrator 14d.
supply to e. The integrator 14e integrates the supplied pulse to generate a triangular wave or a sawtooth wave, and outputs the triangular wave or sawtooth wave to one end of the PWM unit 14g.

The output rectifier 15 supplies the rectified direct current to the choke coil 16. Here, the choke coil 16 is an energy storage type choke coil. This choke coil will be described in detail later. Direct current through the choke coil 16 is supplied to the load 17 through the smoothing capacitor 20, and the control unit 14
Is supplied to one end of the comparator 14f. A voltage is applied to the other end of the comparator 14f from a DC power supply, for example, as a reference voltage for the comparator 14f. The comparator 14f compares and amplifies the voltage supplied to the load 17 with respect to the reference voltage, and outputs P
Output to the other end of the WM unit 14g.

The PWM section 14g changes the width of the triangular wave or the sawtooth wave in accordance with the comparison output from the comparator 14f, and outputs a pulse width modulation signal having a constant output voltage to the base of the drive transformer driving transistor TR2. We are supplying. The pulse width is changed by changing the inclination of the supplied triangular wave or sawtooth wave. This change in slope determines the on-duty width.

Drive transformer driving transistor TR
2 uses the output from the PWM unit 14g as a control signal for the on / off operation of the transistor, and the drive transformer 1
The current flowing through the input winding (primary side) of 4b is controlled.
When a current flows through the input winding (primary side), the drive transformer 14b causes a current to flow through the output winding (secondary side) of the drive transformer 14b as a control signal for the on / off operation of the switching transistor TR1.

As described above, the collector of the switching transistor TR1 is connected to the other end side 13b of the primary winding of the conversion transformer 13A, and is supplied with the direct current through the snubber circuit 12c of the rectifying unit 12. The flow of the direct current is controlled according to the output supplied from the choke coil 16 to the control unit 14, as is clear from the above-described configuration and operation. A switching power supply device using the energy storage type choke coil 16 is called an Ichikoku forward type switching power supply device.

When the operation of the switching transistor TR1 is on, the conversion transformer 13A transfers electromagnetic energy from the primary winding to the secondary winding. In fact, this electromagnetic energy causes a high-frequency current in the secondary winding to accumulate energy in the choke coil 16 via the output rectifier 15 and at the same time supply energy to the load 17. In addition, the switching transistor T
When the operation of R1 is off, the output current of the switching power supply device is the energy accumulated in the choke coil 16 as a current, and the load 17 and the output rectifier 1
5 through the flywheel diode 15b.

The switching power supply unit is
A soft start circuit that starts while gradually increasing the on-duty width of the pulse width modulation signal may be used. Further, the switching power supply device may limit the maximum duty width of the pulse width modulation signal as a protective measure so as not to be completely turned on, or may be provided with a limiting circuit so as not to exceed the safe operation area of the switching transistor. .

Next, the relationship between the choke coil for controlling the operating characteristics of the switching power supply and the pulse width modulation signal will be described with reference to FIG. In FIG. 2, the horizontal axis represents the applied current value and the vertical axis represents the inductance value, respectively, to represent the linear superposition characteristics of the coil. This straight line superposition characteristic is
In general, it shows a linear characteristic with a downward slope. The characteristics of the conventional choke coil show the characteristics of the saturated region SA and the unsaturated region US. The inclination angle of the straight line described above is determined by the choke coil 16
It is determined by the particle size and magnetic saturation characteristics of the soft magnetic powder used for. When the current increases in the saturation area SA, the choke coil 16 reduces the inductance value and reduces the impedance, so that the current flowing through the switching transistor TR1 can easily flow. For this reason, when the load becomes heavy, the switching power supply device can be a power supply device that has excellent responsiveness and followability for load fluctuations.

However, the conventional choke coil is
Due to having the unsaturated region US indicated by the characteristic of the broken line in FIG. 2, the responsiveness was not good in the region where the load fluctuation was low. The choke coil 16 is desired to be a choke coil that can follow any load change at high speed regardless of the size of the load and that provides stable output. To meet this demand, the choke coil 16 is a choke coil formed by molding a ferrite resin 32 made by kneading a ferrite powder, which is a soft magnetic powder, and a polyamide, which is a binder, into a coil.

This molded choke coil 1
6, a coil formed of, for example, a magnet wire is embedded, and its shape is adjusted by compression or injection molding.

Further, a concrete example of the choke coil 16 will be described with reference to FIGS.
As the soft magnetic powder, for example, Ni diameter ferrite having an average particle diameter of 40 to 100 μm is used. As the binder, for example, a thermoplastic resin such as polyphenylene sulfide (PPS) or polyamide (PA) or a thermosetting resin such as phenol is used.

Examples of various parameters of the choke coil are as follows. Inductance at a frequency of 1 kHz: 47 μH Type of winding: Type 1 PEW Diameter of winding: φ 0.9 mm Number of windings: 32 turns DC resistance of winding: 32 mΩ About ferrite resin Ferrite powder Average particle size: 70 μm Ni-based ferrite Polymer resin: Polyamide Filling density: Weight percentage 90% Insulation resistance of choke coil: Winding-molded portion 1 MΩ or more (DC100V after charging for 1 minute) Outer diameter: φ18.0 mm Height: 20.0 mm Lead terminal Length: 4.0mm

In the choke coil, first, a coil formed by winding a predetermined number of windings 31 under the above conditions is embedded in a ferrite resin 32 (see FIG. 3 (a)). In addition, the choke coil is constructed by inserting a ferrite rod core 33 into the air-core portion of the winding 31 as shown in the sectional view of FIG. Further, as shown in the sectional view of FIG. 3C, the choke coil uses a copper foil 34, a ribbon wire, a rectangular wire or the like instead of the winding wire 31 of FIGS. 3A and 3B. Therefore, a choke coil having a high inductance value may be created.

The choke coil manufactured as described above can always obtain the right-down characteristic without the unsaturated region US as seen in the conventional choke coil as shown by the DC superposition characteristic (solid line) shown in FIG. it can.

Using the choke coil, the switching power supply device uses the choke coil shown in FIG. 4 (a) in which the triangular wave of the output current of the choke coil or the sawtooth wave (solid line) has an inclination angle of ) Larger than the inclination angle of. The choke coil reduces the inductance due to the particle size of the soft magnetic powder and the magnetic saturation characteristics. The reduction in inductance can reduce the impedance of the switching transistor TR1 and facilitate the flow of current.

For this reason, the PWM unit 14g is configured as shown in FIG.
The pulse width of the pulse width modulation signal of the constant voltage (switching voltage) output to the switching transistor TR1 shown in is narrowed. By using this choke coil, the switching power supply device can improve operation response and followability. This switching power supply device is particularly suitable for use in a device such as a television set which causes a load change at high speed by a horizontal synchronizing signal or a computer clock signal.

The switching power supply device can automatically control the load fluctuation by using the choke coil and the direct current superposition characteristic of the choke coil. Therefore, in the switching power supply device, it suffices to dispose the control system on the primary side of the conversion transformer and control the input voltage. Due to this arrangement of the control system, the switching power supply device does not require parts such as an insulation transformer and a photocoupler for insulating the secondary side to the primary side and transmitting the control signal.

By using this choke coil, the switching power supply device can output an output voltage at a low input voltage which is a condition of the maximum pulse width when the conventional choke coil is used, and an input voltage which is lower than that under heavy load. It can be kept constant, and the range of controllable input voltage can be expanded compared to the conventional case.

[0038]

As is apparent from the above description, according to the switching power supply device of the present invention, the choke coil used is a choke formed by molding a ferrite resin obtained by kneading soft magnetic powder and a binder. By using a coil, it is possible to eliminate the unsaturated region of the DC superimposed current characteristics of the choke coil,
Use of a conventional choke coil keeps the output voltage constant even at low input voltage, which was the condition of maximum pulse width, and even lower input voltage than under heavy load, and expands the controllable input voltage range than before. be able to.

Further, since the control for the load fluctuation is automatically performed by the characteristic of this coil, the switching power supply device only needs to control the change of the input voltage by the control system, and the coupling of the insulation transformer is less sparse than before. It allows the use of inexpensive and inexpensive transformers.

Further, by using the above choke coil, it is not necessary to increase the feedback gain of the control circuit in order to supply a stable output, the parts for transmitting the control signal and the like can be reduced, and inexpensive parts are used. However, it is possible to secure a high-speed follow-up response to a load change.

By thus reducing the number of parts and using inexpensive parts, the cost can be greatly reduced.

[Brief description of drawings]

FIG. 1 is a schematic block diagram of an embodiment of a switching power supply device of the present invention.

FIG. 2 is a characteristic diagram showing DC superimposed current characteristics of the choke coil shown in FIG. 1 and a conventional choke coil, respectively.

FIG. 3 is a perspective view showing a part of the choke coil shown in FIG. 1 in order to explain the structural features of the choke coil.

FIG. 4 is a schematic diagram showing waveforms of an output current from a choke coil and a switching voltage for on / off controlling a switching transistor, with respect to a time axis.

[Explanation of symbols]

 10 ... Input power supply 11 ... Filter unit 12 ... Rectification unit 13 ... Conversion unit 14 ... ... Control unit 15 ... Output control unit 16 ... Choke coil 17 ... Load 31 ... Winding 32・ ・ ・ ・ ・ ・ ・ ・ Ferrite resin

Claims (1)

[Claims] 1. A forward type switching power supply having a switching element, an output transformer driven by an output signal of the switching element, a choke coil for accumulating electromagnetic energy, and a rectifying circuit for rectifying an output signal of the output transformer. In the device, the choke coil is a choke coil obtained by molding a coil with a ferrite resin obtained by kneading a soft magnetic powder and a binder.