JP3010831B2 - Switching power supply - Google Patents

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 of a self-excited type which uses a feedback winding of a transformer to detect a change in output voltage due to a load change and performs constant voltage control.

[0002]

2. Description of the Related Art FIG. 2 shows a conventional example of this type of switching power supply. The switching power supply includes a transformer 2 having a primary winding 2a for input, a secondary winding 2b for output, a base winding 2c for self-excited oscillation, and a feedback winding 2d for output voltage feedback, and 2 includes a switching transistor 4 as a switching element connected in series to the primary winding 2a, and an oscillation control circuit 8 for controlling the switching transistor 4.

The oscillation control circuit 8 is a known circuit, and controls the switching transistor 4 based on the output from the base winding 2c of the transformer 2 to cause self-excited oscillation. Output voltage V from winding 2b
_O constant voltage control is performed. That is, a voltage fluctuation caused by a load fluctuation of the output voltage V _O is detected by the feedback winding 2 d, and the induced voltage V ₁ of the feedback winding 2 d is rectified by the rectification circuit 12 including the diode 14 and the capacitor 16, and then the oscillation control circuit 8, the oscillation control circuit 8 controls the switching of the switching transistor 4 based on the voltage fed back in this way, and controls the output voltage V _{O to} be constant. A voltage dividing circuit 18 for setting the output voltage V _O may be provided between the rectifier circuit 12 and the oscillation control circuit 8 as in this example.

[0004] From the secondary winding 2b of the transformer 2,
In some cases, an AC output is extracted, and in other cases, a DC output is extracted via a rectifier circuit (not shown).

[0005]

In the switching power supply as described above, when the load is, for example, a capacitive load, the magnitude (amplitude) of the output voltage V _O hardly fluctuates due to the fluctuation of the load. in some cases only the frequency varies, in such cases, since the circuit as described above are voltage sense the induced voltage V ₁ of the feedback winding 2d simply rectifying and smoothing, even if the frequency changes the oscillation The feedback voltage to the control circuit 8 hardly changes, so that a change in frequency cannot be linearly fed back to the oscillation control circuit 8. Therefore, there is a problem that the voltage fluctuation rate of the output voltage V _O at the time of load fluctuation is large.

Accordingly, the present invention provides a switching power supply device capable of detecting not only the voltage fluctuation of the output voltage but also the frequency fluctuation, thereby improving the voltage fluctuation rate of the output voltage at the time of load fluctuation. Its primary purpose is to provide.

[0007]

In order to achieve the above object, a switching power supply according to the present invention comprises an integral circuit for integrating an induced voltage of the feedback winding between a feedback winding of the transformer and the rectifier circuit. Circuit,
The voltage from the integration circuit is fed back to the oscillation control circuit via the rectification circuit.

[0008]

According to the above configuration, the magnitude of the voltage output from the integration circuit changes in a relationship opposite to the change when the frequency changes, even if the magnitude of the induced voltage in the feedback winding is constant. Therefore, by feeding back such a voltage to the oscillation control circuit via the rectifier circuit, not only the voltage fluctuation of the output voltage but also the frequency fluctuation can be detected, and the voltage fluctuation rate of the output voltage at the time of load fluctuation is improved. Is done.

[0009]

FIG. 1 is a circuit diagram showing a switching power supply according to an embodiment of the present invention. Parts that are the same as or correspond to those in the conventional example of FIG.

[0010] In this embodiment, the integration circuit for integrating between the feedback winding 2d of the transformer 2 as described above and the rectifier circuit 12, the resistor 22 and the induced voltage V ₁ of the feedback winding 2d consists capacitor 24 20
And the voltage V ₂ from the integration circuit 20 is fed back to the oscillation control circuit 8 via the rectifier circuit 12 as described above.

The magnitude of the voltage V ₂ output from the integrating circuit 20 is V ₁ , the value of the induced voltage of the feedback winding 2 d, the value of the resistor 22, the value of the capacitor 24, and the oscillation. If the frequency is ω, it is expressed by the following equation.

[0012]

V ₂ = V ₁ / (1 + jωCR)

That is, the voltage V output from the integration circuit 20
₂ is equal to the induced voltage V _{1 of the} feedback winding 2d.
Even if the magnitude is constant, if the oscillation frequency changes, the relationship changes inversely to the change. For example, the magnitude of the voltage V ₂ higher the oscillation frequency becomes smaller, the magnitude of the voltage V ₂ the lower the oscillation frequency increases. Of course, if the magnitude of the induced voltage V ₁ of the feedback winding 2d variation,
Voltage V ₂ output from the integrating circuit 20 also varies accordingly.

As an example, the integration circuit 20 as described above
, The output voltage V _O fluctuated as shown in Table 1.

[0015]

[Table 1]

Therefore, for example, the value of the capacitor 24 is set to 0.
When 022 μF is set, the reactance of the capacitor 24 is about 48.2Ω at the time of 100% load (at 150 KHz).
And about 72.3Ω at 0% load (at 100KHz)
And the voltage V ₂ in accordance with the combined impedance of the reactance and the resistance 22 may vary. That is, the integration circuit 2
0 serves to replace frequency fluctuations with impedance changes.

Therefore, such a voltage V ₂ is supplied to the rectifier circuit 1.
By performing the rectification and smoothing in step 2 and feeding back to the oscillation control circuit 8, not only the voltage fluctuation of the output voltage V _O but also the frequency fluctuation can be detected, and the voltage fluctuation rate of the output voltage V _O at the time of load fluctuation is improved. You. An example is shown in Table 2. As can be seen from this, the voltage fluctuation rate of the output voltage V _O is greatly improved from + 26.8% to + 7.3%.

[0018]

[Table 2]

[0019]

As described above, according to the present invention, by providing the above-described integrating circuit, not only the voltage fluctuation of the output voltage but also the frequency fluctuation can be detected with high accuracy. Can be greatly improved.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a switching power supply device according to an embodiment of the present invention.

FIG. 2 is a circuit diagram illustrating an example of a conventional switching power supply device.

[Explanation of symbols]

 2 Transformer 2a Primary winding 2b Secondary winding 2c Base winding 2d Feedback winding 4 Switching transistor (switching element) 8 Oscillation control circuit 12 Rectifier circuit 20 Integrator circuit

Claims (1)

(57) [Claims] A primary winding for input, a secondary winding for output,
A transformer having a base winding for self-excited oscillation and a feedback winding for output voltage feedback, a switching element connected in series to a primary winding of the transformer,
A rectifier circuit for rectifying a voltage from a feedback winding of the transformer, and a switching element controlled based on an output from a base winding of the transformer to cause self-excited oscillation, and based on a voltage from the rectifier circuit. A switching power supply device including an oscillation control circuit that performs constant voltage control of the output voltage, wherein an integration circuit that integrates an induced voltage of the feedback winding is provided between a feedback winding of the transformer and the rectifier circuit. A switching power supply device wherein the voltage from the integration circuit is fed back to the oscillation control circuit via the rectification circuit.