JPH0244260A - Current transformer - Google Patents

Abstract

PURPOSE:To achieve cost reduction and miniaturization by providing a plurality of through-holes in a magnetic body to wind secondary winding around one of the through-holes and directly inserting a diode in the other one to omit primary winding. CONSTITUTION:Through-holes 12, 13 having different sizes are provided to an almost columnar magnetic body and an insulated coated conductor is wound around the larger through-hole 12 to form secondary winding 14. The anode terminal 15 of a rectifying diode 16 is inserted in the smaller through-hole 13. The inserted terminal 15 is also used as primary winding and it is unnecessary to specially provide the primary winding. By eliminating the primary winding as mentioned above, voltage drop is reduced and, therefore, a power supply circuit is made stable. Since the diode 16 is directly inserted in the through-hole 13, beads choke function is obtained and the number of the parts of a circuit can be reduced. As a result, the whole of the circuit can be miniaturized and cost can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a current transformer for current detection used in a switching power supply, which has a function of detecting a secondary current and operating an overcurrent protection function.

2. Description of the Related Art Conventionally, this type of current transformer has a structure as shown in FIGS. 4 to 7. A conventional current transformer will be explained below with reference to the drawings. FIG. 7 shows a circuit example of a switching power supply using the same current transformer. The current transformer was constructed by winding a primary winding 3 and a secondary winding 4 around a bobbin 2, and incorporating a magnetic material 1 into the bobbin 2, as shown in FIG. Such a current transformer is a transformer 10 as shown in FIG.
The output current of the secondary winding is detected by the current transformer, the output current value is converted to voltage by the resistor 9, and the primary side control circuit 7
In addition, when an overcurrent flows through the secondary winding, the switching transistor 8 is controlled and the output current of the secondary winding is stabilized. The bead choke was constructed by incorporating a bead core 5 into a rectifier diode 6 as shown in FIG. As shown in Figure 7, such a bead choke is used in the circuit configuration of a switching power supply to improve the recovery characteristics by removing spike current by inserting the bead choke in series with the rectifier diode 6. Was.

Problems to be Solved by the Invention In such a conventional configuration, the primary winding 3 of the current transformer is used to detect the output current of the secondary winding of the transformer 10.
Therefore, when the output current of the secondary winding is large, a stable output cannot be obtained due to a voltage drop in the primary winding 3 of the current transformer. Furthermore, in order to improve the recovery characteristics of the rectifier diode 6, the bead choke is also configured separately from the current transformer, which not only increases costs but also complicates mounting on a printed circuit board, making it difficult to miniaturize the switching power supply. The problem was that there was no.

The present invention solves these problems, and aims to reduce the cost of current transformers and bead chokes, and downsize switching power supplies.

Means for Solving the Problem In order to solve this problem, the present invention has a structure in which a magnetic body having two or more through holes around which a secondary winding is wound is inserted directly into the terminal of a rectifier diode. It is something.

By inserting the magnetic body with the working through hole directly into the rectifier diode, the primary winding can be omitted and the voltage drop across the primary winding can be ignored. Furthermore, since it can have a bead choke function, parts such as a bobbin and bead choke and the number of work steps can be reduced.

Embodiments Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings, FIGS. 1 to 3. Figure 1 shows a current transformer according to the present invention, in which a large-shaped through-hole 12 of a magnetic body 11 having circular through-holes 12 and 13 of different shapes formed from the upper surface to the lower surface is connected to a conductive wire with an insulating coating. It is constructed by winding the next winding 14.

In FIG. 2, the portion mounted on the rectifier diode 16 will be explained. The anode side terminal 15 of the rectifier diode 16 is inserted into the small through hole 13 of the magnetic body 11 around which the secondary winding 14 is wound.

A current transformer having such a configuration is used as a switching power supply with an overcurrent protection function on the secondary side, as shown in FIG. In FIG. 3, 17 is an input terminal, and this input terminal 17 is connected to the primary winding 20 of the converter transformer via a rectifier diode 181 and a smoothing capacitor 19, and is also connected to one end of the feedback winding 21. The other end of feedback winding #1I21 is grounded via diode 22. The other end of the primary winding 2o is connected to the collector of the switching transistor 23. The emitter of this switching transistor 23 is grounded, and the base is connected to the primary side control circuit 24. Further, one end of the drive winding 25 is connected to the primary side control circuit 24 via a diode 26. The other end of the drive winding 26 is grounded.

Further, the secondary winding 27 of the converter transformer includes a rectifier diode 16a, a smooth diode 28. Smoothing capacitor 29
Output terminals 30, 30' are connected via. Further, the rectifier diode 18a connects the primary winding 1 of the current transformer via the rectifier diode 16 as a rectifier diode.
5.

Further, the secondary winding 14 of the current transformer is connected to the primary side control circuit 24 via a resistor 31.

With such a configuration, the rectifier diode 16
By suppressing the spike current, the recovery characteristics of the rectifier diode 16 are improved, there is no need to provide a bead choke, and the circuit configuration can be simplified.

Effects of the Invention As described above, according to the present invention, by eliminating the primary winding, there is no voltage drop, so the power supply circuit can be stabilized, and since it is inserted directly into the rectifier diode, a bead choke function can be achieved. Therefore, it is possible to construct a circuit with a small number of parts, and the cost of the entire circuit constituting the power supply can be reduced.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing one embodiment of the current transformer of the present invention, FIG. 2 is a perspective view of a state in which rectifier diodes are mounted, and FIG.
The figure is a circuit diagram of a switching power supply using the same current transformer, Figure 4 is a perspective view of a conventional current transformer, Figures 5 and 6 are a perspective view and mounting diagram of a conventional bead choke, and Figure 7 is the same. FIG. 2 is a circuit diagram of a switching power supply using a current transformer and a bead pattern. 11...Magnetic material, 12.13...Through hole, 14...Secondary winding, 15...Terminal,
16... Rectifier diode.

Claims (1)

[Claims] A magnetic body is approximately cylindrical in shape and has two or more through holes penetrating at least the upper and lower surfaces, and a secondary winding as a primary feedback coil is wound around one of the through holes using an insulated conductor. A current transformer is made by attaching one terminal of the secondary rectifier diode to the other through hole when mounted on a printed circuit board.