JPH03215167A - Switching power source - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a switching power supply device that supplies DC stabilized voltage from a commercial AC power source to various industrial and consumer electronic devices.

Conventional technology In recent years, switching power supplies have been widely used as DC stabilized power supplies for various industrial and consumer electronic devices due to their highly efficient energy conversion characteristics, but there is a desire for even higher efficiency and smaller size. On the other hand, it is often necessary to set an output hold time to protect the electronic equipment that serves as the load from troubles such as instantaneous power outages of the input power supply.

Conventionally, this type of switching power supply device was as shown in FIG. In FIG. 5, 1-1' is an input terminal which receives a commercial AC voltage. 2 is a full-wave rectifier circuit that rectifies the AC voltage. A capacitor 3 smoothes the rectified voltage and supplies a DC voltage Ei. A switching element 4 converts the DC voltage Ei into an AC voltage by high frequency switching. A transformer 5 has a primary winding 51 and a secondary winding 52. The primary winding 51 receives the high frequency alternating current voltage and emits energy to the secondary winding 52. A diode 8 and a capacitor 9 rectify and smooth the flyback voltage of the high frequency AC voltage generated in the secondary winding 52 to supply a DC output voltage Eo. 10-10'
is an output terminal and supplies the DC output voltage Eo to the load.

Reference numeral 12 denotes a control drive circuit which detects the DC output voltage Eo and outputs a drive pulse with a predetermined on/off ratio to the switching element 4 in order to stabilize it. 13 is a resistor, 14 is a capacitor, and 15 is a diode, and the components 13 to 15 constitute a snubber circuit. FIG. 6 is an operational waveform diagram of each part of the switching power supply shown in FIG. 5, and vl is the primary winding 5.
1, I1 is the current flowing through the primary winding 51, I2 is
represents the current flowing through the secondary winding 52. The operation of the switching power supply shown in FIG. 5 will be explained below with reference to FIG.

The DC voltage Ei is obtained by rectifying and smoothing the commercial AC voltage received at the input terminal 1-1' using a full-wave rectifier circuit 2 and a capacitor 3. When the switching element 4 is on, Ei is applied to the primary winding 51, the primary current II increases linearly, and excitation energy is stored in the transformer 5. When the switching element 4 is off, a flyback voltage is generated in each winding of the transformer 5, and the stored excitation energy is released from the secondary winding 52 as a linearly decreasing secondary current I2. 2
The flyback voltage generated in the secondary winding 52 is EO, and if the turns ratio of the transformer 5 is n, the flyback voltage generated in the primary winding 51 is nEo. If the on period of the switching element 4 is Ton and the off period is Toff, the following equation holds true.

By adjusting the on-off ratio of the switching element 4, the DC output voltage Eo can be stabilized.

On the other hand, a snubber circuit consisting of a resistor 13, a capacitor 14, and a diode 15 plays the role of protecting the switching element 4 by clamping the surge voltage generated due to the leakage inductance of the transformer 5 when the switching element 4 is turned off.

Problems to be Solved by the Invention However, in the above conventional configuration, the setting of the output holding time is largely dependent on the capacitance of the capacitor 3, so the capacitance of the capacitor 3 is determined by the power capacity of the switching power supply and the output holding time. It is determined by time, and even if there is sufficient ripple resistance, it may be necessary to use a large one. In addition, during steady operation, the conduction period of the input current from the commercial AC power supply becomes short, and the input current waveform changes. Since the peak value increases, there is a problem in that the power factor and efficiency decrease.

The present invention solves the above problems, and provides a switching power supply device in which the capacitance of the capacitor used for rectifying and smoothing the input AC voltage is reduced without shortening the output holding time, and the conduction period of the input current is extended. The purpose is to provide.

Means for Solving the Problems In order to solve the problems, the switching power supply device of the present invention includes a rectifier circuit constituted by at least one rectifying element that receives and rectifies an alternating current voltage, and a first rectifier circuit that smoothes after rectifying the alternating current voltage. a capacitor, a first switching means connected in series across the first capacitor, and a transformer.
a secondary winding, a second switching means and a second capacitor connected in series across the primary winding of the transformer;
a rectifying and smoothing circuit that rectifies and smoothes the flypack voltage generated in the secondary winding of the transformer and supplies a DC output voltage to the load; and the first and second switching means for detecting and stabilizing the DC output voltage. It has a configuration consisting of a control circuit that alternately drives the on-off period.

Effect: With this configuration, even if the voltage across the first capacitor, that is, the DC input voltage obtained by rectifying and smoothing the input AC voltage, falls below the stabilization lower limit voltage of the control circuit, the first and second switching means continue to be driven. During this period, the energy stored in the second capacitor is released from the secondary winding via the transformer during the on period of the second switching means, making the output holding time longer than in the conventional configuration. I can do it.

EXAMPLE Hereinafter, an example of the present invention will be described with reference to the drawings.

FIG. 1 is a circuit diagram of a switching power supply device according to an embodiment of the present invention. In FIG. 1, 1-1' is an input terminal which receives a commercial AC voltage. 2 is a full-wave rectifier circuit that rectifies the AC voltage. A first capacitor 3 smoothes the rectified voltage and supplies a DC input voltage Ei. A first switching element 4 converts the DC input voltage Ei into a high frequency AC voltage by high frequency switching. 5 is a transformer having a primary winding 51 and a secondary winding 52
The primary winding 51 receives the high frequency AC voltage and emits energy to the secondary winding 52. 6 is a second switching element, and 7 is a second capacitor. A diode 8 and a capacitor 9 rectify and smooth the flyback voltage of the high frequency AC voltage generated in the secondary winding 52 to supply a DC output voltage Eo. 10-10' is an output terminal that supplies the DC output voltage EO to the load. Reference numeral 11 denotes a control drive circuit which detects the DC output voltage Eo and outputs drive pulses with a predetermined on/off ratio to the first switching element 4 and the second switching element 6 to alternately turn them on and off in order to stabilize it. FIG. 2 is an operational waveform diagram of each part of the switching power supply shown in FIG. 1, where v1 is the voltage across the primary winding 51,
I1 is the current flowing through the primary winding 51, and I2 is the current flowing through the secondary winding 52.
Indicates the current flowing in Below, with reference to Figure 2,
The operation of the switching power supply shown in the figure will be explained.

The input DC voltage Ei is obtained by rectifying and smoothing the commercial AC voltage received at the input terminal 1-1' using the full-wave rectifier circuit 2 and the first capacitor 3. When the first switching element 4 is on, the second switching element 6 is off, and the primary winding 5
Ei is applied to the transformer 5, and the primary current I1 increases linearly to store excitation energy in the transformer 5. When the first switching element 4 is off, the second switching element 6 is on, and the excitation energy stored in the transformer 5 is 1
from the next winding 51 to the second switching element 6
The DC output voltage Eo is released from the secondary winding 52 to the load via the diode 8 and the capacitor 9. At this time, the primary winding ■1
decreases almost linearly with the initial value as the current value immediately before turning off the first switching element 4, and the secondary winding current ■2
gradually begins to flow and increases due to wetting inductance.

If the capacitance of the second capacitor 7 is sufficiently large, its voltage will clamp the flyback voltage of the primary winding 51 to nEo, and the generation of surge voltage will almost disappear. The primary winding current I1 eventually falls below zero and begins to flow in the opposite direction, i.e. the second
flows in the direction of discharge from the capacitor 7 to the primary winding 51. In steady operation, the voltage across the second capacitor 7 is stable, so the average value of its charging and discharging current is zero. When the second switching element 6 turns off,
The winding voltage of transformer 5 is reversed and the secondary winding current is 1. becomes zero, and the first switching element 4 is turned on. If the on period of the first switching element 4 (the off period of the second switching element 6) is Ton, and the off period (the on period of the second switching element 6) is Toff, the following equation holds true.

E i XTon=nEoXTof f In other words, by adjusting the on-off ratio of the first switching element 4 (or the second switching element 6), the DC output voltage Eo can be stabilized.

Now, the manner in which the output holding time of this switching power supply device is longer than the output holding time of a conventional switching power supply will be explained with reference to FIG.

The set value of the DC output voltage is Eo1, the allowable lower limit value is E02, the DC input voltage during steady operation is Eil, and the control circuit 11
Let Ei2 be the stabilization lower limit value of the DC input voltage at which the drive pulse from the control circuit 12 in FIG. 5 showing the conventional example has the maximum on-off ratio, and let Ei3 be the stop voltage of the DC input voltage at which the control circuit 11 stops. . The output holding time is the DC output voltage E after the energy supply from the commercial AC power source is cut off.
This is the time until O falls below the allowable lower limit value Eo2.

In the graph of FIG. 3, it is assumed that the capacitance of the first capacitor 3 in FIG. 1 and the capacitor 3 in FIG. 5 are equal.

After the input is cut off, the DC input voltage decreases from Eil, but the DC output voltage remains at the set value Eo until it reaches the stabilization lower limit value Ei2.
1 is maintained, and there is no difference between this embodiment and the conventional example in this period. When the DC input voltage falls below the stabilization lower limit value Ei2, the drive pulse from the control circuit 11 (control circuit 12 in FIG. 5) is fixed at the maximum on-off ratio, and as the DC input voltage decreases, the DC output voltage decreases to the set value Eol. It decreases from In a conventional switching power supply, the output is supplied only from the energy stored in the capacitor 3, but in the case of the embodiment of the present invention, the energy is also supplied from the second capacitor 7 during the off period of the first switching element 4. Since energy is supplied, the rate at which the DC input voltage and DC output voltage decrease is slower than in the prior art. ■ in Figure 3
2 shows the case of the embodiment of the present invention, and 2 shows the conventional case. This state continues until the DC input voltage falls below the stop voltage Ei3 and the operation is stopped, and during this period the DC output voltage falls below the allowable lower limit value Eo2. As described above, in the embodiment according to the present invention, the output holding time is longer than in the conventional case.

Therefore, in this embodiment, if the same output holding time as in the conventional example is ensured, the capacitance of the first capacitor 3 can be reduced. FIG. 4 is a waveform diagram of the DC input voltage Ei and the input current Ii when the capacitance of the first capacitor 3 is small (■) and large (■). As is clear from FIG. 4, if the capacitance of the first capacitor 3, that is, the capacitor that smoothes the commercial AC power supply after rectifying it, can be made small, the input current 1
The conduction period of i can be widened, the power factor can be improved, and
Efficiency can also be improved by suppressing the peak value of input current ■1.

Effects of the Invention As described above, the present invention provides a rectifier circuit including at least one or more rectifying elements that receives and rectifies an alternating current voltage;
a first capacitor for smoothing after rectification; a first switching means connected in series to both ends of the first capacitor; a primary winding of a transformer; and a first switching means connected in series to both ends of the primary winding of the transformer. a second switching means and a second capacitor, a rectifier and smoothing circuit that rectifies and smoothes the flyback voltage generated in the secondary winding of the transformer and supplies a DC output voltage to the load, and detects the DC output voltage. and a control circuit that alternately drives the first and second switching means in a predetermined on/off period in order to stabilize the output holding time. This makes it possible to reduce the capacitance, extend the conduction period of the input current from the commercial AC power supply, and suppress its peak value, resulting in improved power factor and efficiency. This makes it possible to realize a switching power supply device.

[Brief explanation of drawings]

Fig. 1 is a circuit configuration diagram of a switching power supply device according to an embodiment of the present invention, Fig. 2 is an operation waveform diagram of each part of the embodiment shown in Fig. 1, and Fig. 3 is a state of input/output voltage after input disconnection. FIG. 4 is an input voltage and current waveform diagram, FIG. 5 is a circuit configuration diagram of a conventional switching power supply device, and FIG. 6 is an operational waveform diagram of each part of the conventional example shown in FIG. 1.1'...Input terminal, 2...Full wave rectifier circuit, 3...First capacitor, 4...
...First switching element, 5...Transformer, 6...Second switching element, 7...
...Second capacitor, 8...Diode, 9
...Output capacitor, 10.10'...
・Output terminal.

Claims (1)

[Claims] a rectifier circuit composed of at least one rectifying element that receives and rectifies an alternating current voltage;
a first switching means connected in series to both ends of the first capacitor; a primary winding of a transformer; and a second switching means connected in series to both ends of the primary winding of the transformer. means, a second capacitor, and a rectifying and smoothing circuit that rectifies and smoothes the flyback voltage generated in the secondary winding of the transformer and supplies a DC output voltage to the load;
A switching power supply device comprising a control circuit that detects the DC output voltage and drives the first and second switching means alternately in predetermined on/off periods in order to stabilize the DC output voltage.