JPH11285251A - Method for compensating leakage inductance of transformer of switching power supply and power supply circuit implementing the method - Google Patents

Abstract

(57) [Summary] A switching power supply using a primary winding voltage control method is affected by the degree of coupling of a transformer and has a large variation in output voltage. In order to increase the accuracy of a switching power supply using this method, the cost of selecting the characteristics of the transformer increases, so realizing a high-precision power supply was not practically feasible because its characteristics were lost. . SOLUTION: In a switching power supply of a primary winding voltage control method, a junction capacitance value of a rectifier diode connected to a primary side output voltage detection winding is determined by a leakage inductance of a transformer of the switching power supply. To realize a compensation circuit for a switching power supply transformer leakage inductance which is selected to a value at which a resonance component is generated and compensates for the variation of the secondary output voltage to compensate for the switching power supply transformer leakage inductance. 2 without additional parts
This is to improve the variation of the secondary output voltage.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for compensating a transformer leakage inductance of a switching power supply and a power supply circuit implementing the method. A method of compensating for a transformer leakage inductance of a switching power supply according to the present invention and a power supply circuit implementing the method are designed to improve a variation of a secondary output voltage due to a leakage inductance of a transformer in a primary winding voltage control method of a switching power supply. It was done.

[0002]

2. Description of the Related Art FIG. 6 shows the configuration of a conventional primary winding voltage control type switching power supply circuit conventionally used. In FIG. 6, E is a DC power supply, and T is a transformer. The transformer T includes a primary winding L1, a secondary winding L2,
It has a winding L3 for detecting a secondary output voltage. Reference numeral 11 denotes a drive circuit, and 12 denotes an output voltage detection control circuit. 13
Is a switching transistor. Dz is a Zener diode that generates a reference voltage. D1 and D2 are diodes, and C is a capacitor. FL is a filter constituted by a condenser C21. OUT is an output terminal of the power supply.

A DC power supply E is connected to a series circuit of a primary winding L1 of a transformer T and a switching transistor 13. Winding L3 for detecting primary output voltage of transformer T
Is connected to a drive circuit 11 and to an output voltage detection control circuit 12 via a diode D1 and a capacitor C. The switching transistor 13 is driven by a drive circuit 11, and the drive circuit 11 is controlled by an output voltage detection control circuit 12. Transformer T 2
The next winding L2 includes a diode D2 and a filter FL.
OUT terminal is connected to the output terminal through the terminal. In the switching power supply circuit of the primary voltage control system having such a configuration,
When the output of the DC power supply E is interrupted by the switching transistor 13 and the interrupted current flows through the primary winding L1 of the transformer T, an output corresponding to the interrupted current of the primary winding L1 is generated in the secondary winding L2. . The output of the secondary winding L2 is rectified by the diode D2, smoothed by the filter FL, converted into a DC voltage, and sent to the output terminal OUT.

A drive circuit 11 drives a switching transistor 13 for interrupting the output of a DC power supply E. The drive circuit 11 includes an output voltage detection control circuit 12
Is controlled by The output voltage detection control circuit 12 rectifies the output voltage of the winding L3 for detecting the primary side output voltage of the transformer T with a diode D1, smoothes the output voltage with a capacitor C, and a reference zener diode Dz.
The drive circuit 11 is controlled so as to drive the switching transistor 13 so that the terminal voltage of the capacitor C becomes constant. Thus, 1
The voltage of the output terminal OUT is controlled by controlling the voltage of the capacitor C to which a current obtained by rectifying the output of the winding L3 for detecting the secondary side output voltage to be applied to a constant value. The value is controlled to a constant value corresponding to the reference voltage.

[0005] A switching power supply using such a primary winding voltage control system has a primary side and a secondary side which are different from a secondary side control system in which an output value of an output terminal OUT is directly controlled. Since there is no need for a feed hack circuit using a photocoupler or the like to be connected, the circuit configuration is simple and the circuit can be manufactured at low cost. However, a diode used for rectifying the output voltage of a conventional switching power supply is generally selected to have a high switching speed and a small junction capacitance in order to reduce the switching loss and the like of the diode. In. Therefore, the variation of non-control output is
Since the dispersion was large due to the influence of the degree of transformer coupling as compared with the control output, it was difficult to cancel the dispersion of the coupling between the transformer windings.

[0006]

Therefore, in a switching power supply using a primary winding voltage control method,
When trying to improve the variation accuracy of the output voltage on the secondary side of the output terminal OUT, the variation in the characteristics of the transformer of the switching power supply affects. It was necessary to do. Under the circumstances described above, if an attempt is made to improve the accuracy of a switching power supply using the conventional primary winding voltage control method, the cost of selecting the characteristics of the transformer increases, so that a high-precision power supply is required. Realization was not a practical solution because of the loss of its features. SUMMARY OF THE INVENTION An object of the present invention is to realize a high-precision power supply without increasing the manufacturing cost by utilizing the characteristics of a switching power supply using a primary winding voltage control method.

[0007]

According to the present invention, in a switching power supply of a primary winding voltage control system, a value of a junction capacitance of a rectifier diode connected to a winding for detecting a primary output voltage is determined by a transformer of the switching power supply. Compensation for the leakage inductance of the switching power supply transformer, which is selected so as to compensate for the variation of the secondary output voltage by selecting a value at which a resonance component is generated by the leakage inductance of the switching power supply. By realizing a method and a power supply circuit implementing the method, the variation of the secondary side output voltage is improved without adding any components.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION

FIG. 1 is a diagram for explaining a leakage inductance compensation method of a transformer of a switching power supply according to the present invention. FIG. 1 shows relevant parts of an output voltage detection control circuit of the switching power supply circuit of the primary winding voltage control system shown in FIG. 1, the same parts as those in FIG. 2 are denoted by the same reference numerals, and description thereof will be omitted.
Lo in FIG. 1 is a leakage inductance. The leakage inductance Lo indicates the leakage inductance between the primary winding L1 of the transformer T and the primary output voltage detecting winding L3. Primary winding L1 of transformer T
Although leakage inductance exists between the secondary winding L2 and the secondary winding L2, the tendency of coupling between the sense windings of the transformer is similar.

The leakage inductance Lo is considered as a series connection component in an equivalent circuit. The value of the leakage inductance Lo changes due to variations in the coupling of the windings of the transformer. Winding L for primary side output voltage detection
The output of No. 3 is rectified by a diode Dl, charged in a capacitor Cl, smoothed, and converted into a DC voltage.
The output voltage detection control circuit controls the intermittent frequency of the switching transistor 13 so that the voltage of the capacitor Cl becomes a constant value, so that the secondary side output voltage is operated to be kept at a constant value. I have.

In this case, the leakage inductance Lo of the winding for detecting the primary side output voltage varies within a certain range depending on the transformer used due to variations in the coupling of the windings of the transformer T. If the value of the junction capacitance of the diode Dl is selected within a certain range with respect to the value of the change in the leakage inductance Lo, the secondary side output voltage decreases because the coupling of the transformer T is poor and the leakage inductance is large. Even in such a case, since the leakage inductance Lo of the winding for detecting the primary side output voltage is large, the resonance impedance with the junction capacitance of the diode Dl becomes large, and the value of the charging voltage of the capacitor C1 becomes the value of the leakage inductance Lo. It becomes smaller accordingly.

However, the voltage detecting capacitor C1
Of the switching transistor 13 is controlled so as to increase the power applied to the primary winding L1 of the transformer T so that the voltage of the transformer T becomes constant by the output voltage detection control circuit. As a result, the secondary output voltage of the secondary winding L2, which is the output, tends to increase. As a result, in the case of a transformer with poor coupling, the characteristics of canceling the decrease in the output voltage on the secondary side are canceled out. On the contrary, when the coupling of the transformer is good and the leakage inductance Lo is small, the characteristics are reversed. For this reason, the variation range of the secondary output voltage is reduced, and the secondary output voltage accuracy of the transformer T is improved.

FIGS. 2 and 3 show data obtained by measuring the relationship between the leakage inductance of the winding of the transformer T and the output of the voltage detection winding L3. FIG. 2 shows a diode having a small junction capacitance and a high speed (DINL20U trr = 3).
5 to 50 nS) are shown, and FIG.
Is a slow-speed diode (D
(IN20R trr = 10 to 16 μS) is shown. In FIGS. 2 and 3, 463, 467, 459, to 83, and 90 in the left column indicate the diodes used, respectively. Cp-s indicates the value of the junction capacitance of each diode, 80 mA and 180 mA, respectively.
The graph shows the measured values of the input current, output voltage, efficiency, and primary power at a power of mA. The right column shows leakage inductance data of each coil of the transformer T used in combination with the used diodes 463, 467, 459, to 83, 90. The upper and lower columns show the measured diode groups, respectively.

In the case of a diode having a small junction capacitance and a high speed as shown in FIG. 2, for example, the data in the lower column is the coil of the short pin 5-6 of the measurement pin 1-3 of the transformer T (the primary coil of the transformer T). If the leakage inductance between the winding L1 and the winding L3 for detecting the primary side output voltage varies in the range of 1249 μH to 1407 μH, the output voltage is 80 mA.
It shows that the output voltage fluctuates in the range of 6.660 V to 6.75 V at the time, and the output voltage fluctuates in the range of 5.640 V to 5.890 V at the time of 180 mA. On the other hand, in the case of a diode having a large junction capacitance and a low speed in FIG. 3, for example, the data in the lower column indicates the coil (transformer T) of the short pin 5-6 of the measurement pin 1-3 of the transformer T. Of 1
When the leakage inductance of the leakage inductance between the secondary winding L1 and the primary side output voltage detection winding L3 varies in the range of 1249 μH to 1407 μH, the output voltage is 80 mA and the output inductance is all 7. 4V
This indicates that the output voltage falls within the range of 6.8 V to 6.9 V when the output voltage is 180 mA.

As is clear from the data of FIGS. 2 and 3,
This indicates that when the coupling of the transformer is poor and Lo is large, the output value of the voltage detection winding L3 also increases.
The reason for this is that a resonance component is generated by the leakage inductance Lo and the junction capacitance of the diode D1 that rectifies the output of the voltage detection winding L3. Poor transformer coupling L
When o is large, the resonance impedance increases, and C
It is considered that the charging voltage of No. 1 is caused by a decrease. FIGS. 4 and 5 are diagrams showing the relationship between the waveform when the switch of the switching transistor of the switching power supply circuit of the primary winding voltage control system is opened and closed, and the current of the diode Dl. 4 and 5, Vds indicates a voltage between the drain and source of the switching transistor, Ik indicates a current flowing through the diode, and a current flowing between the drain and source of the Id switching transistor.

FIG. 4 shows a diode having a small junction capacitance and a high speed (DINL20U trr = 35 to 50 n).
5A and 5B show waveforms in the case where S) is used. FIG. 5 shows a low-speed diode (DIN20R t
rr = 10 to 16 μS).
In the case of the diode having a small junction capacitance and a high speed in FIG. 4, the resonance current Ik flowing through the diode D1 is
Only the forward charging current for opening and closing the switch of the switching transistor flows only momentarily. On the other hand, FIG. 5 shows a case where a diode having a large junction capacitance and a low speed is used.
In addition to the forward current for opening and closing the switch of the switching transistor, the resonant current Ik flowing through the switch 1 flows in the reverse direction as well as in the forward direction. Is shown.

As described above, the leakage inductance Lo changes due to the variation in the coupling between the windings of the transformer.
If the junction capacitance of the diode Dl is selected within a certain range with respect to this Lo, the leakage inductance Lo is large even when the transformer coupling is poor and the secondary output voltage is low. The impedance increases, and the charging voltage of the capacitor C1 decreases.
For this reason, if the value of the junction capacitance of the rectifier diode connected to the primary output voltage detection winding is appropriately selected, a resonance component is generated according to the leakage inductance of the transformer, and the smoothed capacitor after rectification is generated. Can be changed. By utilizing this effect, as a result, the dispersion of the secondary output voltage can be improved without adding any components. In the above description, the switching power supply of the primary output voltage control method has been described.
With the secondary side output voltage control method, the variation of the primary side output voltage can be similarly reduced.

[0017]

As is apparent from the above description, the method for compensating the leakage inductance of the transformer of the switching power supply of the present invention and the power supply circuit implementing the method are the same as those in the primary winding voltage control type switching power supply. The value of the junction capacitance of the rectifier diode connected to the side output voltage detection winding is selected as a value at which a resonance component is generated by the leakage inductance of the transformer of the switching power supply.
By compensating for the variation of the secondary output voltage, it is possible to realize a power supply circuit in which the variation range of the secondary output voltage is narrowed and the leakage inductance of the transformer of the switching power supply is improved with improved accuracy. . For this reason, according to the present invention, it is possible to improve the characteristics of the variation in the secondary output voltage without adding new components and without increasing the number of components or the cost. Conventionally, the STBY power supply for TV has been required to have a low cost due to the limitation of input power (1 W or less).
Although the following control method is adopted, it is advantageous to keep the output voltage constant in order to keep the power consumption constant. For this reason,
When the present invention is applied to the STBY power supply for TV, it is particularly effective for the voltage accuracy of the STBY power supply and the energy saving effect during STBY.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining a leakage inductance compensation method for a transformer of a switching power supply according to the present invention.

FIG. 2 shows data obtained by measuring the relationship between the leakage inductance of the winding of the transformer T and the output of the voltage detection winding L3 when a high-speed diode (DINL20Utr = 35-50 nS) having a small junction capacitance is used.

FIG. 3 is a graph showing data obtained by measuring the relationship between the leakage inductance of the winding of the transformer T and the output of the voltage detection winding L3 when a diode with a large junction capacitance and a low speed (DIN20R trr = 10-16 μS) is used. 2 and FIG.

FIG. 4 is a diagram showing a relationship between a waveform at the time of opening / closing of a switch of a switching transistor and a current of a diode D1 when a high-speed diode (DINL20Utr = 35-50 nS) having a small junction capacitance is used.

FIG. 5 is a diagram showing a relationship between a waveform when a switch of a switching transistor is opened and closed and a current of a diode Dl when a slow-speed diode (DIN20R trr = 10-16 μS) having a large junction capacitance is used.

FIG. 6 shows a configuration of a conventional primary winding voltage control type switching power supply circuit which has been conventionally used.

[Explanation of symbols]

E: DC power supply, T: transformer, primary winding of transformer T L1: primary winding of transformer T,
L2: secondary winding of transformer T; L3: winding for detecting primary side output voltage of transformer T;
..Drive circuit, 12 ... output voltage detection control circuit, 13 ... switching transistor,
Dz: Zener diode for generating a reference voltage, Lo: Leakage inductance, D
1, D2: diode, C1: capacitor, FL: filter circuit, OUT
... Power supply output terminal, Vds ... Drain-source voltage of switching transistor, I
k: current flowing through the diode, Id: current flowing between the drain and source of the switching transistor

Claims (3)

[Claims] In a switching power supply of a primary winding voltage control system, a resonance component is determined by a value of a junction capacitance of a rectifier diode connected to a primary side output voltage detection winding and a leakage inductance of a transformer of the switching power supply. A method of compensating for leakage inductance of a transformer of a switching power supply, which is selected to a value to be generated and compensates for variation in a secondary output voltage. 2. A switching power supply of a primary winding voltage control system, wherein a value of a junction capacitance of a diode for rectifying an output of a winding for detecting a primary side output voltage is determined by a coupling of a winding of a transformer. A primary winding voltage control type switching power supply characterized in that a resonance impedance is generated by a leakage inductance and a junction capacitance of a diode by selecting an inductance within a certain range. 3. A switching power supply of a primary winding voltage control system, wherein a value of a junction capacitance of a diode for rectifying an output of a winding for detecting a primary side output voltage is determined by a coupling of a winding of a transformer. With respect to the inductance, the reverse recovery time (trr) is set to a value within the range of the level of microseconds (μS), so that a resonance impedance is generated by the leakage inductance and the junction capacitance of the diode. Primary winding voltage control type switching power supply.