JP2002051547A - Flyback converter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a flyback converter that enables the reduction in the size of the parts used therein, the enhancement of the efficiency of circuits, and the reduction of cost of the members thereof. SOLUTION: The flyback converter supplies direct-current voltage through a rectifying and smoothing circuit comprising a first diode 7 and a first smoothing capacitor 8 and connected with a secondary winding P2. The anode of the first diode 7 is connected with the cathode of a second diode 11, and the anode of the second diode is connected with one end of a first resistor 12. A second capacitor 13, a second resistor 14, and a voltage detection circuit 15 that detects the voltage of the second capacitor 13 and outputs signals are parallel connected between the other end of the resistor 12 and the secondary winding P2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flyback converter.

[0002]

2. Description of the Related Art FIG. 2 is a circuit diagram of a conventionally used flyback converter, which detects a load current flowing through a resistor 16 by a current detecting circuit 17 and outputs a signal. To use a large power resistor for
There is a problem that the large power represented by [Equation 1] is consumed, the efficiency of the circuit is reduced, the material cost is increased, and the mounting area is increased.

[0003]

(Equation 1)

[0004]

Because of the above problems, there has been a demand for a flyback converter that consumes less power and can be handled with a small resistor.

[0005]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and when the output load current becomes large,
Utilizing that the ON time of the inverter 5 becomes longer in proportion to the load current and the voltage of the capacitor 13 rises in proportion to the load current, the voltage of the capacitor 13 is detected by the voltage detection circuit 15 and the load current is detected. It is intended to output a value signal. That is, in a flyback converter that supplies a DC voltage via a rectifying / smoothing circuit including a first diode 7 connected to a secondary winding P2 and a first smoothing capacitor 8, an anode of the first diode 7 Connecting the cathode of the second diode 11, connecting one end of the first resistor 12 to the anode of the second diode,
A second capacitor 13, a second resistor 14, and a voltage detection circuit 15 for detecting a voltage of the second capacitor 13 and outputting a signal are provided between the other end of the resistor 12 and the secondary winding P <b> 2. This is a flyback converter characterized by being connected in parallel.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown in FIG. 1, a cathode of a second diode 11 is connected to an anode of a first diode 7 connected to a secondary winding P2, and a first diode is connected to an anode of a second diode. One end of the resistor 12 is connected, and the second capacitor 13 and the second capacitor 13 are connected between the other end of the resistor 12 and the secondary winding P2.
And a voltage detection circuit 15 for detecting the voltage of the second capacitor 13 are connected in parallel. With the above-described configuration, it is possible to realize a flyback converter including a load current detection circuit that consumes less power and is compatible with a small resistor.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to the drawings. FIG. 1 is a basic circuit diagram of a flyback converter according to the present invention. The basic principle of the present invention utilizes the fact that the on-time of the inverter 5 of the flyback converter circuit becomes longer in proportion to the current flowing through the load 10, but when the inverter 5 is on, the secondary winding P2 is connected to the secondary winding P2. When the second capacitor 13 is charged through the connected second diode 11, the voltage of the capacitor 13 also increases in proportion to the current flowing through the load 10, and this voltage is proportional to the ON time of the inverter 5. The voltage can be detected by the voltage detection circuit 15 and a signal can be output. The above relationship is represented by the following [Equation 2].

[0008]

(Equation 2)

FIG. 3 shows the relationship between the current flowing through the load 10 and the voltage of the second capacitor 13 when a flyback converter having an output voltage of 24 V is used. The conditions at that time are as follows: a first resistor: 10 kΩ; Second capacitor: 0.1
μF, second resistance: 33 kΩ. These resistors are
Both are low-power resistors of 1 / 4W or less and are small,
When used in a flyback converter, the power consumed is also a small value as shown in Table 1. Table 1 shows a comparison of the ratings, sizes, and W numbers of resistors used in the load current detection circuits of the embodiment and the conventional flyback converter. As is clear from this, in the embodiment, both the wattage and the size of the resistor can be significantly reduced as compared with the conventional example.

[0010]

[Table 1]

[0011]

As described above, the flyback converter according to the embodiment of the present invention can be handled with a small resistor, can increase the efficiency of the circuit, can greatly reduce the cost of the members, and can mount the components. The area can be reduced.

[Brief description of the drawings]

FIG. 1 is a flyback converter circuit of the present invention.

FIG. 2 is a conventional flyback converter circuit.

FIG. 3 shows a current flowing through a load 10 and a second capacitor 1 when a flyback converter having an output voltage of 24 V is used.
FIG. 6 is a diagram showing a relationship with a voltage of No. 3;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 AC power supply 2 Rectifier diode 3 Smoothing capacitor 4 Converter transformer 5 Inverter 6 Control circuit 7 Diode 8 Capacitor 9 Voltage detection circuit 10 Load 11 Diode 12 Resistance 13 Capacitor 14 Resistance 15 Voltage detection circuit 16 Resistance 17 Current detection circuit

Claims (1)

[Claims] 1. A flyback converter for supplying a DC voltage through a rectifying / smoothing circuit including a first diode connected to a secondary winding and a first smoothing capacitor, wherein a first diode is connected to an anode of the first diode. The second diode has a cathode connected thereto, an anode of a second diode connected to one end of a first resistor, and the other end of the resistor connected to a secondary winding.
A flyback converter in which a second capacitor, a second resistor, and a voltage detection circuit that detects a voltage of the second capacitor and outputs a signal are connected in parallel.