JPH0515152B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a method for driving a multi-output switching power supply, and in particular, when supplying a plurality of DC voltages to an electronic device, each switching element is driven at a different frequency to realize a small-sized power supply. , relates to a power supply driving method that aims to improve efficiency.

[Prior art]

Conventionally, multi-output power supplies using the switching method have either prepared a single-output switching power supply for each voltage, and combined multiple of these to obtain multiple outputs, or transformed the output of a single switching element using a transformer. multiple output voltages are obtained. In particular, when a high-precision, compact, multi-output switching power supply is required, as shown in Figure 1,
There is a method in which switching elements Q ₁ , Q ₂ , transformers T ₁ , T ₂ rectifying sections, and filter sections are installed independently for the number of outputs, and each switching element Q ₁ , Q ₂ is controlled by a common control circuit 1. It is taken.

In a line operation type (input direct rectification type) switching regulator, the input circuit is connected to the front stage of Figure 1 to absorb the noise superimposed on the input AC voltage, and connect it to a large-capacity electrolytic capacitor C ₁ through a full-wave rectifier. to store energy.

In Fig. 1, the voltage V _io stored in the capacitor C ₁ is converted into a high frequency voltage by switching elements Q ₁ and Q ₂ , and is passed through the high frequency transformers T ₁ and T ₂ to an output circuit (rectifying and smoothing circuit).
and obtain respective output voltages V ₁ and V ₂ . The control circuit 1 generates drive pulses φ ₁ , φ ₂ to the switching elements Q ₁ , Q ₂ using output voltages V ₁ , V _{2 .}
This is to control the pulse width.

In general, there are two switching methods: one is a method that controls the duty cycle by changing the duty cycle with a fixed pulse width (frequency control method), and the other is a method that controls the pulse width by changing the pulse width with a fixed frequency (pulse width control method). However, we will use the latter here.

FIG. 2 is a block diagram of the conventional control circuit shown in FIG.

Conventionally, as shown in Fig. 1, when driving two switching elements Q ₁ and Q ₂ independently, synchronized operation using the same frequency was performed to prevent interference due to each driving frequency. There is.

The control circuit usually includes an error amplifier, an oscillator, a modulation section, a logic gate circuit, and the like. In the pulse width control method, the output voltage V ₁ or V ₂ is input to the error amplifier 4, and the oscillation output of the oscillator 2 is used as a trigger to apply the DC signal from the error amplifier 4 to the comparator 5.
Pulses φ ₁ and φ ₂ of Q ₁ and Q ₂ are modulated.

In FIG. 2, one oscillator 2 is shared, and the pulse from the oscillator 2 is converted into a triangular wave by the waveform shaping circuit 3 and inputted to both comparators 5, and the signal from each error amplifier 4 is input to both comparators 5. The width-converted outputs are extracted by comparing the widths, and the drive pulses φ ₁ and φ ₂ are obtained via the amplifier 6.
In this case, since the drive pulses φ ₁ and φ ₂ are operated synchronously with the same frequency using the oscillator 2, different optimal frequencies cannot be selected depending on each output voltage. The disadvantage of same-frequency, synchronous operation is that due to the frequency limit of high-speed, high-voltage rectifier diodes, it is not possible to take full advantage of the characteristics that allow Schottky barrier diodes to operate at higher speeds.

In particular, in recent years, with the advent of power MOS FETs as high-speed switching elements, 200KHz and 500Hz switching power supplies have been put into practical use, and the problem is the switching speed of the rectifier.

Schottky barrier diodes can be used as rectifier diodes in +5V circuits used in general logic circuits, and their switching frequency is 500KHz.
It can be used up to about 100KHz, but in the case of higher voltage circuits, for example, +12V or higher, the operating limit is about 100KHz due to this rectifier. For this reason, when performing synchronized operation at the same frequency with a multi-output switching power supply, it is necessary to drive at the lowest frequency limited by the slowest element, which is a major constraint on miniaturization and high efficiency of the device. It's summery.

[Purpose of the invention]

The purpose of the present invention is to eliminate such conventional drawbacks by setting the switching frequency for each output voltage to the optimum frequency and performing synchronized operation, thereby creating a multi-output device that can be made smaller and more efficient. An object of the present invention is to provide a switching power supply driving method.

[Summary of the invention]

The multi-output switching power supply driving method of the present invention includes:
In a multi-output switching power supply that independently controls and stabilizes multiple switching elements through pulse width modulation in order to supply multiple different DC voltages, the multiple switching elements are driven at different frequencies. , and is characterized in that the different frequencies are set to an integer ratio.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to FIGS. 1 and 3.

When the present invention is applied to the control circuit 1 shown in FIG. 1, Schottky barrier diodes are used for D ₁ and D ₂ to set the output voltage V ₁ to 5V, while D ₃ ,
A high-speed diode with a PN junction lifetime killer is used for D ₄ , and the output voltage V ₂ is +
Assume that it is set to 24V.

MOS FETs are used for the switching elements Q ₁ and Q ₂ , and driving pulses φ ₁ and φ ₂ are applied to the switching elements Q ₁ and Q ₂ to drive them, respectively.

As shown in FIG. 3, the control circuit for providing these drive pulses φ ₁ and φ ₂ is newly provided with a waveform shaping circuit 3' and a frequency dividing circuit 7 to perform synchronized operation at different frequencies.

In FIG. 3, only one oscillator 2 is installed to generate the fundamental frequency of the multi-output switching power supply, which is shared by both switching elements Q ₁ and Q ₂ . For the frequency generated by oscillator 2,
Waveform shaping circuits 3, 3' generate triangular waves. Here, the pulse φ ₁ that drives the switching element Q ₁ to obtain the first output voltage V ₁ is directly transmitted from the oscillator 2 to the waveform shaping circuit 3, and is processed by the comparator 5 using the triangular wave generated here. generated. On the other hand, the pulse φ ₂ that drives the switching element Q ₂ to obtain the second output voltage V ₂ is obtained by dividing the frequency from the oscillator 2 to a frequency of 1/n by the frequency divider 7, thereby shaping the waveform. generated in circuit 3'.
As a result, the driving pulses φ ₁ and φ ₂ each have an integer ratio of frequencies, allowing synchronous operation at different frequencies. That is, the first output voltage V ₁
The +5V DC voltage using a Schottky barrier diode capable of high-speed switching is 500K.
A second output voltage V ₂ is generated at a switching frequency of Hz, while a second output voltage V 2 is
Since 24V DC voltage is generated at a switching frequency of 100KHz, synchronous operation is possible.

FIG. 5 is a time chart of the pulse width conversion operation of the comparator in FIG. 3.

The triangular wave shown in FIG. 5a from the waveform shaping circuit 3 and the output voltage V ₁ from the error amplifier 4 are compared by a comparator 5, and a modulated output φ ₁ shown in FIG. 5b is obtained by width conversion. Further, the triangular wave shown in FIG. 5c from the waveform shaping circuit 3' and the output voltage V ₂ from the error amplifier 4' are compared by the comparator 5', and the modulated output φ ₂ shown in FIG. 5d is obtained by width conversion. get. In Fig. 5, the frequencies of the modulated outputs φ ₁ and φ ₂ have an integer ratio of 3:2;
If it is set to 1, the embodiment shown in FIG. 3 will be obtained.

FIG. 4 is a block diagram of a control circuit showing another embodiment of the invention.

FIG. 4 shows an embodiment in which an oscillator is separately provided.

That is, a 500KHz oscillator 2 and a 100KHz oscillator 2' generate pulses of each frequency, and input them to the waveform shaping circuits 3 and 3', respectively.
Create a triangular wave as shown in , comparator 5,
5'. Comparators 5 and 5' output modulated outputs φ ₁ and φ ₂ shown in FIGS. 5b and 5d.

In this way, the present invention provides a converter (+5V, etc.) that can use a Schottky barrier diode.
is driven at high frequency, and converters that cannot be used are driven at low frequency, and these can be operated synchronously to eliminate interference between circuits.

〔Effect of the invention〕

As explained above, according to the present invention, in a multi-output switching power supply, by driving each output voltage at an optimal frequency and performing synchronized operation, an optimal power supply that matches the characteristics of the switching element can be realized. It is possible to achieve small size and high efficiency.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of a multi-output switching power supply to which the present invention is applied, Fig. 2 is a block diagram of a conventional control circuit for synchronous operation, and Fig. 3 is a block diagram of a control circuit for different frequency/synchronous operation showing an embodiment of the present invention. Control circuit block diagram,
FIG. 4 is a block diagram of a control circuit showing another embodiment of the present invention, and FIG. 5 is a time chart of the width conversion operation of the comparator in FIGS. 3 and 4. 1... Control circuit, 2, 2'... Oscillator, 3,
3'...Waveform shaping circuit, 4,4'...Error amplifier,
5, 5'... Comparator, 6, 6'... Output amplifier, 7... Frequency dividing circuit.

Claims (1)

[Claims] 1. In a multi-output switching power supply driving method in which a plurality of switching elements are independently controlled and stabilized by pulse width modulation in order to supply a plurality of different DC voltages, the plurality of switching elements are controlled at different frequencies. 1. A method for driving a multi-output switching power supply, characterized in that synchronized operation is performed by driving the power supply at a ratio of integers and setting the respective frequencies to an integer ratio.