JPS62290356A - Switching power source - Google Patents

Abstract

PURPOSE:To realize high efficiency, by a method wherein a circuit detecting valley portion time of oscillation voltage and a pulse generator are added, and a switching element is turned on at the valley portion of the oscillation voltage. CONSTITUTION:In a switching power source, input side of a transformer 2 and a switching element 3 are connected to both ends of an input power source 1, and a capacitor 4 is connected in parallel to the element 3. A rectifier circuit 5, a load 6, and a transformer reset discrimination circuit 7 are connected to output side of the transformer 2. The reset discrimination circuit 7 is connected through a delay circuit 8 and a pulse generator 9 to the switching element 3. In order to detect valley portion of oscillation voltage, since discrimination is performed by variation amount of current (voltage) within the circuit, this is detected and ON-command is transmitted from the pulse generator 9 to the switching element 3. As a result, the switching element 3 can be turned on at the valley portion of the oscillation voltage.

Description

Detailed Description of the Invention 3. Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a switching power supply, and particularly to a single-wheel switching power supply suitable for loads requiring large amounts of power such as microwave ovens.

[Conventional technology]

A common method for operating resonant converters is to turn on the switching element at the point where the switching element voltage is at its minimum. However, these methods generate a resonant voltage by installing a new resonant circuit on the input side of the transformer or by utilizing the operation on the output side of the transformer. It is not known that a resonant voltage can be generated only by an absorbing capacitor.

Regarding this type of device, for example, Japanese Patent Application Laid-Open No. 58-36
It is disclosed in Japanese Patent Application Laid-open No. 178 and Japanese Patent Application Laid-open No. 58-69427.

[Problem that the invention seeks to solve]

Conventional resonant converters have a narrow operating range and cannot be used, for example, when the input power source has an unsmoothed voltage waveform.On the other hand, as switching power supplies for loads that require high power such as microwave ovens, they are is large, so attempting to smooth the input voltage would require a large capacitor, making it impractical.

The purpose of the present invention is to obtain f! ! The purpose of the present invention is to provide a high-efficiency power source with a wide operating range and a switching power source that requires large amounts of power, such as a microwave oven.

Means for solving the problem of c-conversion point] Among the above objectives, obtaining a wide operating range can be satisfied by adopting the conventionally existing flyback and forward converters instead of the so-called resonant converter system. Ru.

When operating a high-power load such as a microwave oven using the flyback and forward converters, the surge voltage of the switching element becomes excessive, so a capacitor with a large capacity for absorbing the surge voltage is inevitably required. Ru.

Since the resonance time constant between the capacitor capacitance and the transformer excitation inductance becomes large, a large oscillating voltage is generated after the transformer is reset. Note that conventional flyback and forward converters are used for small power applications, and therefore the capacitors that absorb surge voltages have a small capacity, and the large oscillating voltages mentioned above do not occur.

The other of the above objectives, high efficiency, can be achieved by adding a circuit that detects the time of the trough of the oscillating voltage and a pulse generation circuit that controls on/off.

[Effect]

The valley of the oscillating voltage can be detected based on the amount of change in current or voltage inside the circuit of the switching power supply of the present invention. When the oscillating voltage reaches the valley, a signal is generated and sent to the next stage pulse generation circuit. The pulse generating circuit receives this signal and sends an on command to the switching element. By such an operation, the switching element can be turned on at the valley portion of the oscillating voltage.

〔Example〕

An embodiment of the present invention will be described below with reference to FIGS. 1 and 2, taking a flyback converter as an example.

In the switching power supply shown in FIG. 1, an input side of a transformer 2 and a switching element 3 are connected in series to both ends of an input power supply 1, and a capacitor 4 is connected to the switching element 3 in parallel. Note that this capacitor 4 may be configured with a so-called snubber circuit in which a resistor and a diode are added.
A rectifier circuit 5 is provided on the output side of the transformer 2. Load 6. A transformer reset determination circuit 7 is connected. Although the rectifier circuit 5 shown here is of a flyback type, the connection of the rectifier elements is of course not limited to this, and may be of other types.

Further, the connection position of the transformer reset determination circuit is not limited to the location shown in the figure, but may be any location where the excitation current of the transformer can be detected. From the reset determination circuit 7, a delay circuit 8.
It is connected to the switching element 3 via a pulse generating circuit 9.

The switching FF power supply having such a configuration operates as follows. First, when the switching element 3 is turned on, the switching element voltage E is changed from to to tl in FIG. 2(a).
s becomes approximately Ov, and the input voltage E is applied to the excitation inductance of the transformer 2. The current flowing through this excitation inductance is: ■=Ed・(tt-to)/L...(
1) (where L is the value of excitation inductance), and when the zero-order switching element 3, which increases linearly as shown in Fig. 2(b), turns off at time t1, the switching element voltage becomes a surge. After generating the voltage, the voltage is maintained almost constant until the transformer 2 is reset, and during this time, I=Eouc・(tz tz)/a−L −(2
) However, Eout is the applied voltage a of the load 6, and the exciting current flows due to the relationship between the turns ratio of the input side to the output side of the transformer, and as shown in Fig. 2 (b), when the time reaches tz, the exciting current becomes It becomes 0. This point is called transformer reset. When the transformer 2 is reset, the switching element voltage, which was held above the input voltage E-, starts to drop towards the input voltage E, since the transformer loses energy. Here, if the proposed switching power supply is of low power, the switching element voltage Es after tz will follow the trajectory drawn by the dotted line as shown in FIG. 2(a). This is generally known. However, in the case of a high-power device such as a microwave oven, the excitation inductance of the transformer 2 and the value of the capacitor 4 inevitably generate an oscillating voltage as shown after t2 in FIG. 2(a). Note that this vibration period τ is τ=2π, π− (3) where C is expressed as the capacitance value of the capacitor 4. If the control of the present invention is not carried out here, it is not known at which part of the vibration waveform the vibration will turn on, so it may turn on near the peak value of the waveform, resulting in a large turn-on loss.The present invention solves the above problem. The specific control method will be described below. When the excitation current of the transformer shown in FIG. 1 becomes O, the reset determination circuit 7 generates a signal. This signal is delayed by the delay circuit 8 by half the time of equation (3), and a command to turn on is sent to the pulse generation circuit 9. Then, a signal is sent from the pulse generation circuit 9 to the switching element 3, and the turn-on operation can be performed at the valley part of the switching element voltage by an operation such as 0 or more that turns on at ta in FIG. Turn-on loss of the switching element can be reduced.

The control method is not limited to the above, but may be the one shown in FIG.
This time sequence is shown in FIG.

The source of the switching 1 in FIG. 3 is that the on-timing detection part 7 is changed to 10 compared to the one in FIG.
A voltage comparator 10 between the input power source E- and the switching element voltage Es is used. The operation is based on the switching element voltage E
1 if s is higher than the input voltage E-. If it is low, a 0 signal is output. This operating waveform is shown in FIG. 4(b). The delay circuit 8 delays this signal by τ/4 as shown in FIG. Pulse generation circuit 9
Then, the negative edge signal of this signal is determined to be on, and an on signal is sent to the switching element 3. The polarities shown in FIGS. 4(b) and 4(c) above may be reversed, and in this case, the pulse generating circuit 9 is caused to judge that the positive edge signal is on.

Further, as a third control method, the following can also be realized.Equation (1) and Equation (2) both represent the peak value of the excitation current and are the same value. Therefore Ei(tt-to) Eout・(tz tt)
・=(4) L a-L Abbreviated as Eout Here, (12-1,) is the reset time of the transformer, (t
s-to) is the on-time of the switching element.

In equation (5), if the output voltage Eout is constant and Ei
・(tt-to)=constant ・When the switching power supply of the present invention is operated under the conditions of (6),
The reset time (lz-tt) is constant. Furthermore, since the resonance period τ of the oscillating voltage of the switching element can be determined in advance from the circuit constants, the off-time Toxt of the switching element may be oui, where T on is a constant time determined by the equation of the on-time of the switching element. This embodiment is shown in FIG. 5, and the time sequence is shown in FIG.

In the switching power supply shown in FIG. 5, the off-time setting circuit 11
As shown in FIG. 6(b), a certain period of time is given, and when the time reaches ta, an on command is given to the pulse generation circuit 9 to turn on the switching element.

Above, we have described a control method that turns on the switching element at the first (ta) trough of the voltage, but as an application example, the second (ta), third (tII) l...
We propose to perform power control by turning on at the valley of .... In other words, in the switching power supply shown in FIG. 1, the delay circuit 8 is configured as shown in FIG.
/2τ, 5/2τ.

For a delay circuit set as 7/2τ..., an appropriate delay amount to obtain the necessary power is digitally selected. Regarding the switching power supply shown in FIG. 3, in the power determination circuit 12 shown in FIG.
The power is controlled by digitally specifying the count number.

In the switching power supply shown in Fig. 5, the off time is 9
With the settings as shown in the figure, the appropriate off time to obtain the necessary power is digitally selected. Also,
Regarding the switching power supply shown in FIG. 3, it is also possible to digitally select the on-time and control the power.

In other words, when equation (7) is solved for the on-time Ton, a
'E-', therefore, the on-time Ton should be selected according to the power from those set as shown in Fig. 10.

As a further application of the above application example, there is also a method of setting which valley to use according to the change in the input voltage E4. That is, in FIG. 11, when the input voltage E is 0 to Es, it is turned on at the first valley, and E
1 to E2 are turned on at the second valley.

It is also possible to control the power by operating as follows.

At this time, E i HE x + E a, etc. may be varied to obtain the required amount of power, and as shown in Figure 11, if this control method is used, it can be used as peak power protection. You can also do it.

Furthermore, when compared with any resonant converter, as the input voltage Ei increases in a resonant converter, the switching frequency must generally be increased; however, in the switching power supply of the present invention, the on-timing is set to the second level. , the frequency can be lowered and used by moving to the third valley. This is effective in reducing switching loss of the switching element.

Although the above details are limited to flyback converters,
As can be seen from formulas (1) to (8), the present invention is independent of the output side of the transformer, and in the case of a one-way switching power supply, the forward converter's half-wave rectification and after-wave rectification are Of course, a voltage doubler type can also be used. Examples of these are shown in Figures 12 to 15. Figure 12 shows half-wave rectification, Figure 13 shows full-wave rectification, Figure 14 shows voltage doubler half-wave rectification, and Figure 15 shows voltage doubler full-wave rectification. Each rectification method is shown below.

As described above, the switching power supply of the present invention can minimize switching loss by simply adding the above-mentioned auxiliary circuit, and is extremely advantageous in practice.

〔Effect of the invention〕

According to the present invention, since the turn-on loss of the switching element can be reduced, not only the efficiency of the power supply circuit can be improved, but also the following effects are expected.

(1) The switching elements used can be configured with smaller allowable loss values than conventional ones. This allows cost reduction, size and weight reduction.

(2) Since the switching frequency can be further increased, the transformer can be made smaller, lighter, and lower in cost.

[Brief explanation of drawings]

Figure 1 is a wiring diagram of one embodiment of the present invention, Figure 2 is the waveform of Figure 1, (a) is a voltage waveform diagram of the switching element, (b)
is a diagram of the excitation current waveform of the transformer, FIG. 3 is a wiring diagram of another embodiment of the present invention, FIG. 4 is the waveform of FIG. 3, (a) is a voltage waveform diagram of the switching element, and (b) is a diagram of the voltage waveform of the switching element. (a) is a waveform diagram of the voltage comparator; (c) is a waveform diagram of the delay circuit; FIG. 5 is a wiring diagram of yet another embodiment of the present invention; FIG. 6 is the waveform of FIG.
is a voltage waveform diagram of the switching element, (b) is a waveform diagram of the off-time setting circuit, FIG. 7 is a block diagram of the application example of FIG. 1, FIG. 8 is a block diagram of the application example of FIG. 3, and FIG. The figure is number 5
Figure 10 is a block diagram of the application example (Part 1) in Figure 5, Figure 11 is an explanatory diagram of the power control of the present invention, Figures 12 to 15 are , is a circuit diagram to which the present invention is applicable.

Claims (1)

[Claims] 1. In a single-stone switching power supply comprising an input power supply, a switching element connected in series to the input side of a transformer at both ends of this power supply, and a capacitor for absorbing surge voltage connected in parallel with the switching element, A switching power supply characterized in that when the switching element is in an off period, a resonant voltage is generated only by the excitation inductance of the transformer and the capacitor, and the switching element is turned on at the valley of the voltage applied to the capacitor.