JPS589514Y2 - switching regulator - Google Patents

Description

[Detailed description of the invention] The present invention relates to an improvement of a switching regulator equipped with a smoothing circuit with a flywheel diode and a surge absorption circuit, and is capable of minimizing the reverse current flowing through the rectifier diode when the switching transistor is turned off. The present invention relates to a switching regulator having means for reducing the size.

First, let's look at an example of a conventional switching regulator.
This is shown in the figure and will be described below.

The switching transistor Q□ repeats on and off operations based on the control signal f inputted from the outside, and intermittents the current flowing through the primary winding of the electric quadrant T, and outputs an alternating current to the secondary winding of the electric quadrant T. By rectifying and smoothing the AC output, the DC power of the DC power source Ei is supplied to the load RL connected to the output terminal f as a desired output power.

Both ends of the primary winding L1 of the output transformer T are connected in parallel with a parallel circuit of a capacitor C1 and a resistor R8, and a surge absorption circuit consisting of a diode D1.

In addition, a smoothing circuit consisting of a choke coil CH and a capacitor C2 is connected in parallel to the front stage of the output terminal, and a flywheel diode DF that takes out the electromagnetic energy stored in the choke coil CHI when the switching transistor Q1 is turned off smooths the smoothing circuit. In the circuit 1 configured as described above, where both ends of the circuit are connected, when the switching transistor Q1 is on, 2 of the voltage transformer T is connected.
The AC output obtained from the next winding passes through the rectifier diode D2 and the choke coil CH to cause current to flow through the smoothing capacitor C2 and the load RL, and the choke coil CH) stores electromagnetic energy.

Next, when the switching transistor Q1 turns off, the electromagnetic energy stored during the ON period of the switching transistor Q1 is transferred to the choke coil CH, the smoothing capacitor C2, the load RL, and the flywheel diode DF.
Flow through a closed circuit consisting of

At this time, the primary and secondary windings L□, L2 of the electric quadrant T
The coupling coefficient between
Since the transformer is not an ideal transformer, the magnetic flux generated in the core used in the quadrature transformer Tt is completely equal to the current flowing through the primary winding L1f of the transformer T and the current flowing through its secondary winding L2. cannot be canceled out.

Therefore, when the switching transistor Q1 is on, electromagnetic energy is stored in the capacitor T, and when the switching transistor Q1 is off, the electromagnetic energy is stored at both ends of the primary winding of the capacitor T (in the opposite direction). An induced voltage is generated and the surge absorption circuit operates.

2. Since an induced voltage in the opposite direction is generated at both ends of the secondary winding of the electric cadence T due to the electromagnetic energy, the anode side of the rectifier diode D2 has a negative potential with respect to the cathode side, and the rectifier diode D21 Since the accumulated carriers remain, a small reverse current (2) flows through the flywheel diode DF.

Furthermore, a reverse current ■ flowing backward through the rectifier diode D2,
vanishes with steep d i / d t, so
The output current i2 of the rectifier diode D2 has a current waveform as shown in FIG. 2Q.

In other words, in the circuit shown in Figure 1, the power loss in the rectifier diode D2i increases, and it not only makes the circuit operation of the switching regulator unstable, but also generates high frequency noise of tens of MHz to hundreds of h. This has the disadvantage that it also has a negative effect on external devices.

SUMMARY OF THE INVENTION The present invention aims to eliminate the above-mentioned drawbacks, and aims to provide a means for minimizing the reverse current flowing through a rectifier diode connected to the secondary winding of a capacitor.

That is, the present invention includes a series circuit of a DC power supply, a primary winding of a voltage transformer, and a switching transistor;
A switching regulator is equipped with a surge absorption circuit connected in parallel to the secondary winding, a rectifying diode for the output obtained from the secondary winding of the voltage transformer, and a smoothing circuit with a flywheel diode connected in parallel to the load. Here, a part of the surge absorption circuit is a switching regulator connected to a series circuit of a secondary winding of a capacitor and a rectifier diode via a coupling transformer.

Next, an embodiment of the present invention is shown in FIG. 3, and the features of the present invention will be described in detail below.

To is a coupling transformer that plays an important role in the switching regulator according to the present invention, and other circuit components are given the same symbols as the circuit components in FIG.

This coupling transformer T. is the switching transistor Q
This is to suppress the reverse current (2) of the rectifier diode D2 that flows during the first turn-off to one point smaller than the conventional one.

That is, in the present invention, since the switching transistor Q1 is turned off while the electromagnetic energy of the electric quadramp TIC is stored, a surge current flows through the surge absorption circuit due to the electromagnetic energy, and the switching transistor Q1 is turned off. Rectifier diode D according to
This was done by focusing on the fact that when 2 is also turned off, the anode side of the rectifier diode D2 has a negative potential compared to the cathode side, so that a phenomenon in which a reverse current flows through the rectifier diode D2+ occurs at the same time. It is.

To explain this point in detail, when the switching transistor Q1 is turned off, the surge current caused by the electromagnetic energy stored in the capacitor Tf tries to flow in the forward direction through the diode D1 of the surge absorption circuit. , coupled transformer T.

In the winding L3, there is one coil that generates an induced voltage that causes the forward direction to flow through the rectifier diode D2.
The current flowing from one of the stored carriers is the coupling transformer T.

An induced voltage that flows in the opposite direction to the surge current is generated in the winding L4.

Therefore, the present invention uses a coupling transformer T.

By optimally selecting the turns ratio of the windings L3 and L4, the surge current and the current due to the accumulated carriers of the rectifier diode D2 are electromagnetically coupled in the coupling transformer Tc, and the current generated in the windings L3 and L4t is The induced voltages caused by the electromotive force are mutually canceled out.

As a result, the output current i2 of the rectifier diode D2 has a current waveform as shown in FIG.

In other words, the present invention can suppress the reverse current flowing through the rectifier diode D2t to an extremely low level, thereby eliminating the power loss that occurs in the conventional rectifier diode D2, and also reducing the circuit operation of the switching regulator. Not only does this stabilize the noise level, but also eliminates the generation of high-frequency noise, which eliminates any negative effects on external devices.

In addition, since a part of the electromagnetic energy stored in the electric quadrature T is used to eliminate the accumulated carriers in the rectifier diode D2, it is possible to reduce the surge current that flows when the switching transistor Q1 is turned off. Due to this, the power loss in the surge absorption circuit f can also be reduced.

As above, the present invention has been explained based on the embodiment shown in FIG. 3, with reference to a separately excited oscillation type switching regulator. However, the present invention is not limited to the above-mentioned embodiment, and can also be applied to, for example, a self-excited oscillation type switching regulator. This is a very effective means for practical application.

In the embodiment shown in FIG. 3, part of the surge absorption circuit is a coupling transformer T.

An example has been described in which the secondary winding L2 of the quadratic transformer T and one node of the flywheel diode DF are connected through the coupling transformer T.

For example, between the secondary winding L2 of the electric cadence T and the 7 node of the rectifier diode D2, between the cathode of the rectifier diode D2 and the cathode of the flywheel diode DF, etc., between the secondary winding L2 of the electric cadence T and the rectifier. Diode D2
The same effect as described above can be expected no matter where the series circuit is inserted.

[Brief explanation of drawings]

Fig. 1: A circuit diagram showing an example of a conventional switching regulator, Fig. 2: A waveform diagram of the current flowing through the rectifier diode D2 shown in Fig. 1, Fig. 3:・
・Circuit diagram showing one embodiment of the switching regulator according to the present invention, FIG. 4...FIG. 3Q: Current waveform diagram flowing through rectifier diode D2 shown in FIG. ...Electronic cadence, Q
l...Switching transistor, D2...
... Rectifier diode, DF ... Flywheel diode, CH ... Choke coil, C
2...Smoothing capacitor, RL...Load, To...Coupling transformer, surge absorption circuit (C
t... Capacitor, R1... Resistor, D
l...diode)

Claims (1)

[Scope of utility model registration request] A DC power supply, a series circuit of the primary winding of the electric quadramp and a switching transistor, a surge absorption circuit in which the three primary windings are connected in parallel, and a rectifier that rectifies the output obtained from the secondary winding of the electric quadrangle. In a switching regulator equipped with a diode and a smoothing circuit with a flywheel diode connected in parallel to the load, part of the surge absorption circuit is connected to a series circuit of the secondary winding of the capacitor and the rectifier diode via a coupling transformer. A switching regulator characterized by one connection.