JPH01157268A - Switching power source device - Google Patents

Abstract

PURPOSE:To improve reliability and miniaturize the title device, by a method wherein a load is conducted only when an output current is lower than a prede termined value to restrain intermittent oscillation. CONSTITUTION:A switching power source device induces a voltage in the secon dary winding of a transformer 5 by applying a DC voltage 4 on the primary winding of the transformer 5 by switching and generates the output of DC voltage through a choke input type rectifying and smoothing circuit. On the other hand, the switching power source device connects the primary winding of a current transformer 14 and applies a voltage, generated in the secondary winding of the same, on the base terminal 20 of a transistor(Tr) 20 through a rectifying and smoothing circuit consisting of a diode 16 and the like. When a load is light, the base potential of the Tr 20 is reduced and the Tr 20 is brought into ON condition, whereby current is conducted through a bleeder resistor 10, however, said current is interrupted when the load is heavy. Accord ing to this method, the load 11 is conducted only when the output current is lower than a predetermined value whereby intermittent oscillation may be restrained.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a switching power supply device used as a power source for various electronic devices.

2. Description of the Related Art Conventional technologies include 1, for example, as shown in the circuit diagram of FIG. 4, switching transistors 2 and 3 are alternately turned on and off to supply power to the output;
The output voltage is collected and returned to the primary side, and the on-time of each switching transistor 2 and switching transistor 3 is varied to maintain a constant output voltage.A resistor is connected to the output terminal of the push-pull converter to maintain the output voltage intermittently. A method of suppressing oscillation is used.

The operation of the circuit shown in FIG. 4 will be explained below. When the switching transistors 2 and 3 are alternately turned on and off by the output of the drive circuit 1, a voltage proportional to the winding ratio of the transformer 6 appears on the secondary side of the transformer 6 due to the power supply voltage 4. This is rectified by a diode 6 or a diode γ, smoothed by a choke coil 8 and a capacitor, and a DC voltage is supplied to the output. Further, the output voltage is detected, and the error is increased. It is compared with the reference voltage 12 by the stone tool 13, increased, and then fed back to the drive circuit 1.

This feedback signal controls the on-periods of switching transistors 2 and 3 to keep the output voltage constant. The load 11 connected to the output end is:=
-, the power supplied to the output becomes zero, and intermittent oscillation occurs in the output in order to bring the on-periods of the switching transistors 2 and 3 closer to zero.

Therefore, intermittent oscillation of the circuit is suppressed by connecting a bleeder resistor 10 in parallel to the load 11.

Problems to be Solved by the Invention In the conventional circuit as described above, the circuit loss is extremely high because current is constantly flowing through the bleeder resistor 1o.
The drawback was that the size was suppressed, the size increased, and the price increased.

In addition, in order to reduce the circuit loss, the bleeder resistor 1
There was a problem in that the resistance value of 0 became large and intermittent oscillation could not be sufficiently suppressed.

The present invention has been made in view of these points, and an object of the present invention is to provide a switching power supply device that is highly efficient, highly stable, compact, and inexpensive.

Problem f. Means for Solving In order to solve the above problems, the present invention is designed to induce a voltage in the secondary winding of the transformer by switching the DC power supply and applying it to the primary winding of the transformer. The secondary of the current transformer has a primary winding connected in series between the secondary winding of the transformer and the choke input rectifier and smoothing circuit. A resistor is connected to both ends of the winding, and a current proportional to the current flowing through the primary winding of the current transformer is passed through the resistor to the secondary winding to generate a voltage proportional to the current flowing through the secondary winding. By rectifying and smoothing the voltage, a DC voltage proportional to the current flowing in the primary winding of the I-lance is obtained, and the voltage is compared with a reference voltage to determine whether the voltage is below a predetermined value. In this case, a series connection circuit of a switching element and a load is connected to the output of the choke input type rectifying and smoothing circuit, and the switching element is energized.

Effect: With the circuit configuration described above, the load is energized only when the output current is below a predetermined value, thereby suppressing intermittent oscillation. In addition, the efficiency at full output is improved because the current is applied only under light loads, and the overall heat generation is reduced due to low loss, which improves the reliability of the switching power supply and allows it to be made smaller and cheaper. becomes.

Embodiment FIG. 1 shows an embodiment of the switching power supply device of the present invention. This circuit has a switching power supply that switches a DC voltage and applies it to the primary winding of the transformer to induce a voltage in the secondary winding of the transformer, and generates a DC voltage at the output through a choke input type rectifier and smoothing circuit. are doing.

In Fig. 1 h, 1 is a circuit, 2 and 3 are switching transistors, 4 is a power supply voltage, 5 is a transformer, and 6.71
d diode, 8 is choke coil, 9 is capacitor, 1o is bleeder resistor, 11 is load, 1
2 is a reference voltage, 13 is an error amplifier, 14 is a current transformer, 15.18, 19.21 are resistors, 16 is a diode, 17 is a capacitor, 20 is a PNP) transistor, and the secondary winding of the transformer 5. A current transformer 14 has a primary winding connected in series with a diode 7 of a choke input type rectifying and smoothing circuit, and a resistor 16 is connected to both ends of the secondary winding.
Connect. A current shown in FIG. 3 M flows through the primary winding of the current transformer 140, and a current proportional to the above current flows through the secondary winding of the current transformer 14.
A voltage shown in FIG. 3B is generated across the resistor 16. This voltage is connected to diode 16 and capacitor 17.
The waveform shown in FIG. 3G is obtained through a rectifying and smoothing circuit consisting of a resistor 18. It is adjusted to a predetermined voltage via a resistor 19 and applied to the base terminal of the PNP transistor 2o.

The emitter terminal of the PNP transistor 2o is connected to the output positive potential side of the switching power supply, and the collector terminal of the PNP transistor 20 is connected to the zero potential side of the output via the bleeder resistor 1o.

The operation shown in FIG. 1 will be explained below. When the output is under light load,
PNP) The base potential of the transistor 20 decreases, and the PNP
) The voltage between the base and emitter of the transistor 2o increases, and when this voltage reaches the operating voltage, the PNP) transistor 20 is turned on, and current flows through the bleeder resistor 1Q. Also.

When the output becomes a heavy load, the base potential of the PNP transistor 20 increases, the voltage between the base and emitter of the PNP transistor 20 decreases, and the PNP transistor 20
is turned off, and the current flowing through the bleeder resistor 1o is cut off.

Another embodiment is shown in FIG. In FIG. 2, current transformer 14. Resistance 16. Diode 16°, capacitor 7, resistor 18. Connection of resistor 19.

The configuration and operation are the same as those in FIG. 1, so they are omitted.

The voltage divided by resistor 18 and resistor 19 is NPN
In addition to the transistor 220 base terminal.

The collector terminal of the NPN transistor 22 is connected to the positive potential side of the output of the switching power supply via the resistor 21, and the base terminal of the NPH transistor 23 is connected to the connection point between the resistor 21 and the collector terminal of the NPN transistor 22. The emitter terminals of the NPN transistor 22 and NPN transistor 23 are connected to the zero potential side of the output of the switching power supply, and the collector terminal of the NPN transistor 23 is
It is connected to the positive potential side of the output via a bleeder resistor 1o.

The operation shown in FIG. 3 will be explained below. When the output is under light load,
NPN ) The base potential of transistor 22 decreases, and NPN
N) The transistor 22 is turned off, and the base potential of the NPN) transistor 23 rises, and the NPN) transistor 2
3 is turned on and current flows through the bleeder resistor 1o. Also, when the output becomes heavy load, NPN) transistor 2
When the base potential of the NPN transistor 23 rises and reaches the operating voltage, the NPN transistor 22 is turned off, and the base potential of the NPN transistor 23 is set to zero potential.
) Turn off the transistor 23 and set the bleeder resistance to 1o.
interrupts the current flowing to the

Effects of the Invention As described above, according to the present invention, the load is energized only when the output current is below a predetermined value, so that intermittent oscillation can be suppressed.In addition, since the load is energized only when the load is light, the full output can be suppressed. The switching efficiency is improved, the overall heat generation is reduced due to the low loss, the efficiency of the switching power supply is improved, the size is reduced, and the cost is reduced, making it extremely useful.

[Brief explanation of the drawing]

1 and 2 are circuit diagrams of a switching device according to an embodiment of the present invention, FIG. 3 is a current or voltage waveform diagram of the same essential parts, and FIG. 4 is a conventional circuit diagram. DESCRIPTION OF SYMBOLS 1...Drive circuit, 2...Switching transistor, 3...Switching transistor, 4...Power supply voltage, 5...Transformer, 6 ······diode. 7...Diode S8...Choke coil, 9...Capacitor S10...Bleeder resistance, 11...Load, 12...・
・Reference voltage, 13...Error amplifier. 14... Current transformer, 15...
Resistor, 16...Diode, 17...
Capacitor, 18... Resistor s19...
Resistor, 20...PNP) Resistor, 21.
...Resistor, 22...NPN) transistor, 23...NPN) transistor. Name of agent: Patent attorney Toshio Nakao and 1 other person1-
Swing circuit 2, 3--Switching transistor 4-Power supply voltage 5-)-Lance≦, 7.16--Diode 10--Bleeder Iha II--Load No. 2--Base voltage 13-Reading difference Intensifier j4-・Current transformer JE, I8.19.21-Ichilow 滇昶-PNP transistor Ml Figure Wc2 Figure 3

Claims (1)

[Claims] By switching the DC power supply, a voltage is induced in the primary winding of the transformer as well as the secondary winding of the transformer, and a DC voltage is generated at the output through the choke input type rectifying and smoothing circuit, and the voltage is induced in the secondary winding of the transformer. A resistor is connected to both ends of the secondary winding of a current transformer in which the primary winding is connected in series with the diode of the choke input type rectifier and smoothing circuit, and the current flows through the resistor to the primary winding of the current transformer. A current proportional to the current is passed through the secondary winding to
Generating a voltage proportional to the current flowing through the secondary winding, rectifying and smoothing the voltage to obtain a DC voltage proportional to the current flowing through the primary winding of the current transformer, and comparing and determining the voltage with a reference voltage; A switching power supply device configured to connect a series connection circuit of a switching element and a load to the output of the choke input type rectifying and smoothing circuit, and to energize the switching element only when the value is below a predetermined value.