JP2710509B2 - Smoothing circuit simulation system for evaluating choke coils - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an evaluation of a smoothing choke coil and a core used in a switching power supply, and to an apparatus for evaluating the influence of a core material on the switching power supply.

[0002]

2. Description of the Related Art A smoothing choke coil, which is an application field of the present invention, is one of the main components constituting a smoothing circuit in a switching power supply. The smoothing choke coil is made of a coil made of a soft magnetic material such as soft ferrite or dust core, and is made by winding a conductor around the core.Utilizing the magnetization of the core, an inductance is formed, and the AC component of the switching power supply is removed. I have.

When developing this smoothing choke coil, one of the required performances is that heat generation due to loss is as small as possible under the conditions of use of a switching power supply (switching frequency, duty ratio, drive magnetization range, etc.). I have. For this reason, it is necessary to measure the loss and heat generation under a constant driving condition.

Conventionally, a core loss of a choke coil is evaluated by passing an exciting current of a sine wave having a constant amplitude as shown in FIG. 3 through a coil having a predetermined number of turns of a copper wire covered with an insulator. Induce a specified amount of magnetic flux change inside,
This is done by measuring the loss at this time. Specifically, a current obtained by amplifying a sine wave of a specified frequency by a power amplifier is input to a primary coil of a test coil, and a magnetization amount is measured by a secondary output voltage accompanying the current. Loss evaluation is performed by calculating the area of the hysteresis loop derived from the above measurement. In addition, the same loss evaluation is performed by incorporating a test choke coil into an off-the-shelf switching power supply and observing heat generation of the core when the rated operation is performed.

[0005]

The conventional evaluation method is accurate and useful when evaluating the loss between cores under a sine wave excitation condition.

However, at the time of steady operation by the switching power supply, a current having a waveform in which a DC and a triangular wave are superimposed flows as shown in FIG. At this time, the magnetization state of the core in the choke coil draws a minor loop as shown by the solid line in FIG. This loop appears only in the first quadrant as compared with the hysteresis curve (all loop curves) of the magnetic material shown by the broken line in FIG. This is due to the fact that the DC current is included in the current flowing through the coil. Moreover, the waveform of the current flowing through the coil is a triangular wave, and contains a high-frequency component unlike a sine wave. For the above reasons, it cannot be said that the conventional loss evaluation using a sine wave accurately reproduces the operating conditions of the choke coil, and this is the reason why the heat generation of the smoothing choke coil in the switching power supply cannot always be explained. ing. In addition, as described in the prior art, the heat generation evaluation under actual operating conditions is conventionally performed by replacing the core of a choke coil in a ready-made switching power supply. The switching frequency, duty ratio, output voltage, etc. are fixed, and it is difficult to change the excitation frequency, change the duty ratio, etc.Moreover, since the number of turns of the coil is large, the loss of the core and the loss due to the coil conductor are reduced. There is a problem that they cannot be separated.

The present invention relates to a method of evaluating a choke coil used in a switching power supply, which measures the heat generation and operating characteristics near an actual use condition under arbitrary measurement conditions, thereby providing a more accurate heat generation evaluation than before. It is an object of the present invention to provide an evaluation device that can easily perform the evaluation.

[0008]

A smoothing circuit simulation apparatus for evaluating a choke coil according to the present invention comprises a variable voltage power supply.
And the oscillator controls the frequency and duty ratio.
4-terminal switching circuit and test choke coil
Are connected in series to the variable voltage power supply.
The diode on the input side, the capacitor on the output side,
Π type connected in parallel to the variable voltage power supply
A four-terminal smoothing circuit and a variable load device are sequentially connected in cascade.
And which is characterized in that the thermometer for measuring the heating temperature and the ambient temperature of the test trial choke coil has been attached to the core surface and the vicinity thereof of the test trial choke coil. In the choke coil evaluation smoothing circuit simulation apparatus, the test choke coil is incorporated in a thermostat.

[0009]

The smoothing circuit simulation apparatus for evaluating a choke coil according to the present invention has a circuit configuration as shown in FIG. This circuit forms a smoothing circuit and a simulation circuit of an output circuit in a forward-type switching power supply as shown in the figure. Specifically, a variable voltage power supply a, a switching circuit
b, the smoothing circuit c and the load device d are cascaded as a four-terminal circuit
It consists of a system with a continuous configuration. Among them, the DC power supply 1 is for supplying a current to the test choke coil 12, and the voltage of the power supply is variable so that the excitation conditions (the amount of the DC component, the amplitude of the triangular wave) can be adjusted. . The load device d comprises a variable resistor 2 or an electronic load device and controls the amount of the DC component of the current flowing through the test choke coil 12 so that the resistance value can be variably controlled. An ammeter 3 and a voltmeter 4 are connected to the variable resistor 2 in series and parallel, respectively, for monitoring. This circuit at any frequency and duty ratio Sui <br/> pitch 7 in the switching circuit b is the signal from the oscillator 5 in the switching circuit b
Switching through the driving circuit 6 in the
The generated intermittent voltage waveform is output to the smoothing circuit c. This
This intermittent voltage waveform excites the test choke coil 12 in the smoothing circuit c at a high frequency. The smoothing circuit c includes a test choke coil 12, a capacitor 13, and a diode 14.
Made, the input voltage of intermittent waveform input by the switching circuit b is smoothed, to <br/> output a DC voltage to the load device d.

The test choke coil 12
It is necessary to make the measurement condition of the coil itself constant during evaluation, but has the following relational expression with other constants.

[0011]

(Equation 1) E _out : Smoothing circuit output voltage ΔB: Choke core magnetic flux density variation f: Switching frequency S: Magnetic path cross-sectional area (core) D: Duty ratio n: Number of coil turns

(Equation 2) Generally, the output voltage E _out is determined from the equation because the measurement conditions include a duty ratio, a switching frequency, a core size (cross-sectional area: S), the number of coil turns, and a magnetic flux density change range. Here, unlike the choke coil used in a ready-made switching power supply, the number of coil turns can be set to an extremely small value to suppress heat generation due to copper loss of the coil. Further, the L value is determined from the equation, and the gap in the magnetic path of the core is adjusted according to the L value. In addition, from the L value, according to the set amount of the DC component Φ _dc of the magnetic flux,

(Equation 3) _Is set by adjusting the load circuit.

The present simulation circuit is operated under the above-described condition settings, and measurement is performed after the surface temperature of the core and the ambient temperature have sufficiently reached equilibrium. As shown in FIG. 2, a thermocouple 22 is brazed to the surface of the core 12a of the test choke coil 12. Thermocouple 23 measures the ambient temperature. Thermocouple 2
2 and 23 are connected to the thermometer 21. The value obtained by subtracting the ambient temperature from the core surface temperature is used as an index of substantial heat generation. In addition, in the above-described smoothing circuit simulation apparatus for evaluating a choke coil, only the smoothing circuit portion or the choke coil is incorporated in a thermostat and the ambient temperature is controlled to measure the ambient temperature dependency of heat generation. As a result, heat generation evaluation under conditions close to actual use conditions, which could not be performed by the conventional method, can be easily performed under arbitrary measurement conditions.

[0013]

【Example】

Example 1 In order to obtain the excitation conditions as shown by the BT curve in FIG. 6 in the circuit shown in FIG. 1, the test choke coil and the excitation conditions were set to the following conditions.

(Coil conditions) Core shape: EI30 type Core material: 4 types from A to D Number of coil turns: 5 turns Air gap: about 65 μm (spacer gap 33 μm) (excitation conditions) E _out : 24V I _dc : 4.5 A Switching frequency: 100 kHz Duty ratio: 0.5 Operating under the above conditions, the core surface temperature and the ambient temperature were measured, and the temperature difference was determined (Table 1). As a result, it was found that the material A generated the least heat among the four types of core materials under the present conditions. In addition, when compared with the loss evaluation value obtained by the conventional evaluation method, it is understood that a result having a small loss value obtained by the conventional method does not necessarily result in a small loss obtained by the evaluation using the present apparatus.

[0015]

[Table 1]

[Embodiment 2] In the circuit shown in FIG.
In order to set the excitation conditions as shown in the BT curve, the test choke coil and the excitation conditions were set to the following conditions.

(Coil conditions) Core shape: EI30 type Core material: 4 types from A to D Number of coil turns: 2 turns Air gap: about 20 μm (spacer gap 10 μm) (excitation conditions) E _out : 24 V I _dc : 4 A Switching frequency : 500 kHz Duty ratio: 0.5 Operating under the above conditions, the surface temperature and the ambient temperature of the core were measured, and the difference between the temperatures was obtained (Table 2). As a result, it was found that the material A generated the least heat among the four types of core materials under the present conditions. In addition, when compared with the loss evaluation value obtained by the conventional evaluation method, it is understood that a result having a small loss value obtained by the conventional method does not necessarily result in a small loss obtained by the evaluation using the present apparatus.

[0018]

[Table 2]

[0019]

As described above, by using the apparatus of the present invention, it is possible to obtain the loss information necessary for the development of the core material of the choke coil in a form close to practical use and with a degree of freedom in setting conditions. it can.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an apparatus of the present invention.

FIG. 2 is a drawing showing a temperature measurement state of a test choke coil.

FIG. 3 is a general current waveform diagram at the time of loss measurement according to the related art.

FIG. 4 is a current waveform diagram when the device of the present invention is used.

FIG. 5 shows respective BH loops when using the conventional method and the apparatus of the present invention.

FIG. 6 is a magnetic flux density waveform diagram of a core showing an example.

[Explanation of symbols]

Reference Signs List 1 DC power supply 2 Variable resistor 5 Oscillator 6 Drive circuit 7 Switch 12 Choke coil for test 13 Capacitor 14 Diode 21 Thermometer 22 Thermocouple 23 Thermocouple a Variable voltage power supply b Switching circuit c Smoothing circuit d Load device

Claims (2)

(57) [Claims] A variable frequency power supply and an oscillator
4-terminal switching circuit whose number and duty ratio are controlled
Path and the test choke coil are connected to the variable voltage power supply.
Connected in series and the diode
The capacitor on the output side and the variable voltage power supply
A π-type four-terminal smoothing circuit connected in parallel with each
Load device and are sequentially connected in cascade, and characterized in that the thermometer for measuring the heating temperature and the ambient temperature of the test trial choke coil has been attached to the core surface and the vicinity thereof of the test trial choke coil A smoothing circuit simulation device for evaluating choke coils. 2. The smoothing circuit simulation apparatus for evaluating a choke coil according to claim 1, wherein the test choke coil is incorporated in a thermostat.