JPH0121699B2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention provides a DC stabilized power supply device that can obtain a constant stabilized output voltage in response to input voltage switching or wide range input voltage fluctuations. This relates to switching power supplies.

[Technology background]

Commercial AC power supply voltage is AC100V or AC200V in Japan, and AC100V or AC200V in foreign countries.
The AC200V system is used, and although the voltages vary widely, the operating voltage of electronic equipment is determined to be DC voltage, such as DC5V or DC12V, and such DC operating voltage can be stably converted into commercial AC. Pulse width control type switching power supplies have conventionally been used as DC stabilized power supplies for obtaining power from a power source.

Furthermore, there is an increasing demand for switching power supplies that can handle multiple commercial AC power supply voltages or wide range input voltage fluctuations.

Here, we will explain how to respond to multiple commercial AC power supply voltages or wide range input voltage fluctuations using the conventional pulse width control method that stably controls the output voltage in response to output load fluctuations and input fluctuations. think about.

The relationship between the output voltage Eo and the input voltage Ei in the pulse width control method of the switching power supply is as follows: the turn ratio between the primary winding and the secondary winding of the transformer is N, the operating period of the switching transistor is T, and the switching transistor is If the conduction width is ton, then Eo=ton・Ei/T・N.

If the output voltage Eo is constant, the relationship between the duty ratio ton/T of the control pulse and the input voltage Ei becomes a hyperbola as shown in FIG.

For example, if the switching frequency of the switching power supply is 20KHz, the input voltage will be
At AC100V, ton is about 7μs, and the input voltage is
At 200 VAC, it is less than 3.5 μs, which approaches the storage time of the switching transistor, resulting in unstable operation and increased loss. (If the pulse width becomes less than the accumulation time, control becomes impossible.) In addition, the gain of the error amplifier in the pulse width control circuit needs to be increased as the fluctuation width of the input voltage increases, resulting in instability such as oscillation. cause a cause.

In general, in a switching power supply, the components used can be made smaller by increasing the switching operating frequency, and thereby the power supply device can also be made smaller, but for the reasons mentioned above, increasing the frequency becomes a very difficult problem.

It is extremely difficult to respond to multiple commercial AC power supply voltages or wide range input voltage fluctuations using conventional pulse width control methods, so it is generally possible to respond by switching the input voltage. It is being done.

[Prior art and its problems]

The configuration of conventional input voltage switching type switching power supplies is, for example, the input voltage is 100V AC and 200V AC.
In order to support this, it is common to use a common inverter INV as shown in Figure 2, and switch the rectifier circuit to a voltage doubler rectifier circuit when the voltage is AC100V, and to a bridge rectifier circuit when the voltage is AC200V. There is.

However, this configuration requires expensive parts such as high-power switch elements as a switching circuit on the input side, and also requires switching operations, which poses cost and operational problems.Furthermore, the input is a DC voltage. There is a problem that in some cases it cannot be dealt with.

[Purpose of the invention]

The present invention aims to provide a switching power supply for solving the above problems.

[Structure of the invention]

The above purpose is to control the relationship between the output voltage and the output reference voltage in a switching power supply that uses a pulse width control circuit to turn on and off a switching element connected to the primary side of a transformer according to the output voltage on the secondary side of the transformer. a first pulse width control circuit that controls the pulse width according to the error voltage; and a constant frequency lower than the frequency of the first pulse width control circuit according to the error voltage between the input voltage of the transformer and the input reference voltage. a second pulse width control circuit that controls a pulse width; and a logic circuit that performs a logical operation on an output pulse of the second pulse width control circuit and an output pulse of the first pulse width control circuit; This is achieved by a switching power supply characterized in that the switching element is driven and controlled by the output pulse of the circuit.

[Embodiments of the invention]

Hereinafter, the present invention will be explained based on examples.

FIG. 3 is a circuit diagram of an embodiment of the present invention, in which Ei is an AC input voltage, REC1 and REC2 are rectifier circuits, T1 is a main transformer, T2 is a drive transformer,
Q is a switching transistor, PWM1 is the first pulse width control circuit, PWM2 is the second pulse width control circuit, AND is the logic circuit, DRV is the drive circuit, L is the inductance, C1 and C2 are the capacitors, and Eo is the DC output. Voltage and R indicate the load, respectively.

FIG. 4 is a waveform diagram of control pulses in the circuit of this embodiment.

The AC input voltage Ei is rectified by a rectifier circuit REC1, smoothed by a capacitor C1, and converted into a DC voltage, which is switched on and off by a switching transistor Q and supplied to the main transformer T1 as a rectangular wave AC.

The rectangular wave AC voltage converted to the secondary winding of the main transformer T1 is rectified by a rectifier circuit REC2, smoothed by an inductance L and a capacitor C2, and output as a DC output voltage Eo.
Supplied to load R.

This DC output voltage Eo is input to the first pulse width control circuit PWM1 as an output detection voltage,
Here, the output voltage is compared with a reference voltage for setting the output voltage, and a control pulse whose pulse width is controlled is generated using the error voltage, and this operation is similar to the conventional one.

The output pulse B of the first pulse width control circuit PWM1 at this time is a rectangular wave as shown in FIG. 4a, and the pulse width is controlled by the error between the output voltage and the reference voltage.

On the other hand, the primary side DC voltage obtained by rectifying and smoothing the AC input voltage Ei is input to the second pulse width control circuit PWM2 as a detected value of the input voltage, and is compared with the reference voltage of the input voltage. A second pulse width control circuit as a pulse A with an inversely proportional on width.
Output from PWM2.

This pulse A is applied to the first pulse width control circuit.
It is a frequency lower than the frequency of PWM1, and is an arbitrary constant frequency according to the switching voltage value or fluctuation range of the input voltage.
Figure c shows the case of AC200V, and the duty ratio decreases as the input voltage increases.

Next, the output pulse B of the first pulse width control circuit PWM1 and the output pulse A of the second pulse width control circuit PWM2 are input to the logic circuit AND,
A logical AND operation is performed, and this output pulse is used by the drive circuit.
It is amplified and matched via DRV and drive transformer T2, and controls switching transistor Q on and off.

At this time, when the input voltage is AC100V, the output pulse of the logic circuit AND is as shown in Figure 4 d as the logical product of Figure 4 b and a, and the input voltage is
In the case of AC200V, the logical product of FIG. 4 c and a is as shown in FIG. 4 e.

Such output pulses increase or decrease the number of pulses of the first pulse width control circuit PWM1 depending on the level of the input voltage during a frequency period determined by the second pulse width control circuit PWM2, By increasing the number of pulses when the input voltage is low and decreasing the number of pulses when the input voltage is high, the switching transistor Q is driven and controlled, and the power energy supplied to the secondary winding of the main transformer T1 is kept constant. This is to stabilize the output voltage.

In the case of this embodiment, the second pulse width control circuit
The operating frequency of PWM2 is controlled by the first pulse width control circuit.
Although it is selected to be about 1/5 to 1/10 times the operating frequency of the PWM 1, it can be set arbitrarily depending on the switching voltage value of the input voltage or the fluctuation width of the input voltage.

Furthermore, in this example, the DC input voltage on the primary side is directly input to the second pulse width control circuit, but if insulation between the primary side and the secondary side (output side) is required, , the DC input voltage can also be input to the second pulse width control circuit via an insulating element such as a photo coupler.

Furthermore, although this embodiment has been described with reference to an AC input power source, it goes without saying that it can also be applied to a DC input power source such as a battery that has large voltage fluctuations.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to realize a switching power supply that does not require input voltage switching, can respond to a wide range of input voltage fluctuations, and can also be applied to DC input voltage, and is also advantageous in terms of cost and reliability. It is extremely useful.

Also, when the input voltage is high, switching
By reducing the number of times the transistor is switched, loss in the switching transistor is reduced, efficiency is improved, and the switching operation frequency can be increased.

Furthermore, since fluctuations in the input voltage can be controlled by both the first and second pulse width control circuits, the gain of the error amplifier in the pulse width control circuit can be reduced, allowing extremely stable operation.

[Brief explanation of drawings]

Figure 1 shows the input voltage Ei in the pulse width control method.
Fig. 2 is a diagram showing the circuit configuration of a conventional input voltage switching type switching power supply, and Fig. 3 is a diagram showing a switching power supply as an embodiment of the present invention. FIG. 4 is a diagram showing the waveform of the control pulse of the circuit of this embodiment. In the figure, T1 is the main transformer, Q is the switching
Transistor, PWM1 is the first pulse width control circuit, PWM2 is the second pulse width control circuit, AND
is a logic circuit, and DRV is a drive circuit.

Claims (1)

[Claims] 1. In a switching power supply that uses a pulse width control circuit to turn on and off a switching element connected to the primary side of a transformer according to the output voltage on the secondary side of the transformer, an error voltage between the output voltage and the output reference voltage is used. a first pulse width control circuit that controls the pulse width according to the error voltage between the input voltage of the transformer and the input reference voltage at a constant frequency lower than the frequency of the first pulse width control circuit; a second pulse width control circuit that performs a logical operation on an output pulse of the second pulse width control circuit and an output pulse of the first pulse width control circuit; A switching power supply characterized in that the switching element is driven and controlled by pulses.