JPS633550B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a switching control type power supply device,
In particular, the object is to prevent the output voltage of one of the two output windings provided in the converter transformer from fluctuating due to the voltage fluctuation of the other.

A switching control type power supply device has been widely used in recent television receivers and the like, and FIG. 1 shows a schematic configuration of such a power supply device. That is, in the same figure, IP is the input terminal to which the commercial AC power supply is connected,
D ₁ and C ₁ are rectifying and smoothing diodes and capacitors, CT is a converter transformer with input winding N ₁ , output windings N ₂ a, N ₂ b, and detection winding N ₃ , TR is a switching transistor, OC is a pulse oscillation circuit, PW is a pulse width control circuit, DR is a drive circuit, DT is an error voltage detection circuit, and OPa and OPb are output terminals.

Such a power supply, as is already well known, has a detection winding.
By controlling the duty cycle of the switching transistor TR according to fluctuations in the DC voltage obtained from _N3 , constant DC output voltages are obtained at the output terminals OPa and OPb, respectively. Since two output windings N ₂ a and N ₂ b are provided, the following problem occurs. Therefore, first, this will be explained and the problems to be solved by the present invention will be presented.

In Fig. 1, if the output voltage Vb obtained from the output terminal OPb changes depending on the load condition of this terminal, this will cause the output voltage Va of the other output terminal OPa and the detection winding N ₃ to change. The DC voltage Vc at point P obtained from the change also changes. Therefore, the output winding N ₂ a and the detection winding N ₃ are fully coupled (coupling degree M ₁ = 1), and the coupling degree M between the output winding N ₂ b and the detection winding N ₃ is ₂ and output winding N ₂ a, N ₂ b coupling degree M ₃
If they are equal to each other (M ₂ = M ₃ ), the output terminal
Since the amount of variation in the voltage Va of OPa is equal to the amount of correction, this output voltage Va is held substantially constant with respect to load variation at the other output terminal N ₂ b.
Of course, the voltage Va is sufficiently stabilized even against load fluctuations at its own output terminal N ₂ a.

However, there is leakage inductance between each of the windings of the converter transformer CT, and its value varies depending on the winding position and winding order of each winding. The bonding relationship becomes even more complicated, so
It is very difficult to set the coupling degrees M ₁ , M ₂ , and M ₃ as described above. Therefore, when the load condition of one output terminal OPb fluctuates greatly, in order to obtain a stable voltage Va from the other output terminal OPa,
It would have been almost impossible to do so using only the basic configuration shown in FIG.

Therefore, in the above case, in order to always obtain a constant output voltage Va from the output terminal OPa, a constant voltage control circuit or the like that separately stabilizes this voltage Va is required.
However, this method could not be considered a good idea since the circuit configuration would become complicated and the cost would increase significantly.

Although not described in detail above, as an example of using the power supply device shown in Fig. 1 under the conditions described above, for example, the voltage Va from the output terminal OPa can be applied to the horizontal deflection/high voltage generation circuit of a television receiver. As a power source,
Further, it is conceivable that the voltage Vb from the other output terminal OPb is used as a power source for the audio output circuit of the receiver, particularly a class B push-pull type audio output circuit. That is, in the audio output circuit, a current of a magnitude corresponding to the audio signal flows, so the load state seen from the output terminal OPb changes from no load to full load.
There is no particular problem even if the voltage Vb changes accordingly. On the other hand, in the horizontal deflection and high voltage generation circuit, a picture tube beam current of a magnitude corresponding to the video signal flows, so the load condition seen from the output terminal OPa also changes. If the output voltage Va is not maintained at a substantially constant constant value, image width changes and image curvature will occur.

Therefore, the present invention has been made with attention to this point, and the details of the present invention are shown in Figs. 2 and 3 below.
Description will be given based on the embodiment shown in the figures.

In the embodiment shown in FIG. 2, the same components as those in FIG. 1 are given the same reference numbers and their explanations are omitted, but the features are as follows. In other words, a relatively small core CR is used separately from the converter transformer CT.
is prepared, two inductors L ₁ and L ₂ are provided by windings wound around this core, one inductor L 1 is connected in series with the output winding N 2 b, and the other inductor L ₁ is connected in series with the output winding N ₂ b. ₂ is connected in series with the output winding N ₂ a together with a resistor R having a minute resistance value. At this time, the windings constituting the inductors L ₁ and L ₂ are wound with opposite polarities as shown in the figure, and
On the other hand, L ₁ is configured to have an inductance comparable to or less than that of the output winding N ₂ b, and on the other hand, L ₂ is configured to have an inductance sufficiently small to about 1/10 of L ₁ .

Now, in this embodiment, it is assumed that the voltage Vb at the output terminal OPb has now decreased due to the above-mentioned reason. Then, when the switching transistor TR is off, the current flowing into the smoothing capacitor _C3 via the inductor _L1 , the output winding _N2b , and the rectifying diode _D3 increases. Therefore, due to the increase in the magnetic flux of opposite polarity in the output winding N ₂ b due to this current, the magnetic flux generated by the input winding N ₁ and passing through the output winding N ₂ b decreases. As a result, the magnetic flux of the other output winding N ₂ a magnetically coupled to both windings N ₁ and N ₂ b also decreases, so the voltage Va at the output terminal OPa also tends to decrease.

However, when the current I ₁ flowing through the inductor L ₁ increases, this current causes the other inductor to
The voltage induced in _L2 also increases, and the voltage Vr across the resistor R increases. Therefore, the voltage applied to the rectifier diode D ₂ , which corresponds to the sum of this voltage Vr and the induced voltage of the output winding N ₂ a, increases, the current I ₂ flowing into the smoothing capacitor C ₂ increases, and the output terminal
It acts to prevent the voltage Va of OPa from decreasing.
Also, if the voltage Vb of the output terminal OPb increases,
The completely opposite operation acts to prevent the other output voltage Va from increasing. Therefore, the output voltage
Coupled with the correction operation of the control unit CC due to the fluctuations in Vb, the output voltage Va is maintained at a substantially accurate constant value regardless of the fluctuations in Vb.

The resistor R adjusts the voltage correction amount Vr, and also has the function of rapidly dissipating the energy stored in the inductors L ₁ and L ₂ when the switching transistor TR is turned on. It is also possible to appropriately design and delete L ₁ and L ₂ .

Furthermore, in the previous embodiment, each of the inductors L ₁ and L ₂ was constructed with a coil wound around the same core CR, but by configuring the converter transformer CT as shown in FIG. It is also possible to simplify. That is, the converter transformer shown in Fig. 3 uses an EI type core, and the input winding N ₁ and the output winding N ₂ a are connected to the central magnetic leg of this core.
and a detection winding N ₃ are wound respectively, and the other output winding N ₂ b and a winding for the inductor L ₂ are wound around the magnetic leg at the end. In this way, there is a lot of leakage magnetic flux in the magnetic legs at the ends, so the leakage inductance of the output winding N ₂ b increases, so this leakage inductance is used as the inductor L ₁ in Figure 2. .

The present invention can be applied not only to the separately excited type shown in FIG. 2, but also to a self-excited type in which blocking oscillation is performed using a converter transformer.

Since the switching control type power supply device of the present invention is configured as described above, one of the output voltages obtained from each of the two output windings provided in the converter transformer can be sufficiently stabilized regardless of voltage fluctuations in the other. Moreover, it can be realized at low cost with a very simple configuration, and is therefore suitable for cases where the respective output voltages are supplied to load circuits having different properties.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the general configuration of a switching control type power supply device, FIG. 2 is a diagram showing one embodiment of the power supply device of the present invention, and FIG. 3 is a diagram for explaining another embodiment of the present invention. It is a diagram. CT...Converter transformer, _N1 ...Input winding,
N ₂ a, N ₂ b...output winding, _N3 ...detection winding, TR...switching transistor, _L1 ...first inductor, _L2 ...second inductor.

Claims (1)

[Claims] 1. An input winding connected to a switching element, 2.
In the power supply device, the converter transformer has two output windings and a detection winding, and the switching element is controlled according to the voltage obtained from the detection winding. The degree of coupling of the other output winding to each of these three windings is set to be smaller than the degree of coupling between the respective windings of the winding and the detection winding, and A first inductor having an inductance equal to or lower than that of the winding is provided in series, and a second inductor is magnetically coupled to the first inductor and exhibits an inductance sufficiently smaller than that of the inductor. The first inductor is connected in series to the one output winding so that the direction of the magnetic flux generated is opposite to the magnetic flux of the first inductor, and the one output winding is A switching control type power supply device that prevents fluctuations in the output voltage obtained from the 2. The input winding, the one output winding, and the detection winding are wound around the same magnetic leg of the converter transformer, and the other output winding and the second inductor are wound around the other magnetic leg of the transformer. 2. The switching control type power supply device according to claim 1, wherein the first inductor is formed by the leakage inductance of the other output winding by winding the coil.