JPH072017B2 - Switching regulator - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a configuration of a self-excited on / off type switching regulator.

[Prior art and its problems]

The switching regulator is roughly divided into a self-excited type and a separately excited type. The separately excited type has a large degree of freedom in design and can meet all specifications, but is expensive. On the other hand, the self-excited type has a limited degree of freedom in design but is suitable for reducing the price. The flyback method is used as the self-excited power conversion method, and the on / off method is hardly used.
This is because it is difficult to balance the current flowing from the choke coil of the rectifying and smoothing circuit to the load when the oscillating transistor is "off" and the excitation energy stored in the choke coil when "on". That is, in a self-excited oscillation circuit such as a blocking oscillation circuit, the oscillation transistor turns “on” when the magnetic flux of the oscillation transformer disappears, but depending on the load, the excitation is performed with the magnetic flux remaining in the choke coil. When such a state is repeated, the magnetic flux of the choke coil is saturated, so it was difficult to prevent damage to the oscillating transistor when the oscillating transistor turned on because of excessive surge current due to its excitation energy. . However, since the flyback type has a large amount of current flowing to the secondary side of the transformer in a short time and the size of the transformer becomes large, the on-on type is preferable.

〔Purpose〕

The present invention uses a blocking oscillator circuit to "turn on" the transistor of the oscillator circuit after the magnetic flux of the choke coil has disappeared and the excitation energy has been completely released.
It is an object of the present invention to provide a self-excited, on-on type switching regulator capable of preventing the damage.

[Technical means for solving problems]

The present invention configures a blocking oscillator circuit using a transformer having a collector winding, a base winding, a secondary winding, and a transistor, and a rectifying diode, a flywheel diode, a choke coil, and a smoothing capacitor are rectified in the secondary winding. In an on / off type switching regulator to which a smoothing circuit is connected, in a closed circuit formed between the base winding and the base / emitter of a transistor, a forward or reverse current in a minute voltage range It is also characterized in that it is connected with a voltage drop circuit for blocking.

〔Example〕

An explanation of the switching regulator of the present invention will be given below with reference to the circuit diagram of FIG. 1 showing an embodiment, the collector voltage V _C of the transistor Q, the magnetic flux Φ _{T of the} transformer T, and the magnetic flux Φ _L of the choke coil L in FIG. This will be performed with reference to FIG.

The blocking oscillator circuit is the collector winding L1, the secondary winding L2,
It is mainly composed of a transformer T having a base winding L3, and a transistor Q connected to the collector winding L1 and connected between the base and the emitter and the base winding L3 to form a closed circuit. The emitter of the transistor Q is connected to one end of the base winding L3, and the base is connected in parallel to the diode D1.
And a resistor R2 in series, and a diode D2 and resistor R3 in series to connect to the other end of the base winding L3. As will be described later, the diode D1, the resistor R2, the diode D2, and the resistor R3 form one voltage drop circuit R in the present invention, and block both forward and reverse currents in a minute voltage range. To do. The base of the transistor Q is connected to the hot side of the input capacitor C1 connected in parallel with the DC source E via the resistor R1 and to the other end of the collector winding L1. The series circuit of diode D1 and resistor R2, along with resistor R1, regulates the input voltage at the base when transistor Q first "turns on". V _IN is the input voltage from the DC source E.

A rectifying diode D3, a choke coil L, a flywheel diode D4, and an output capacitor C2 are connected to the secondary winding L2 of the transformer T.

The voltage V _R across the voltage drop circuit _R is
It is set like an expression.

Forward voltage V ₃ for rectifying diode D3 to conduct, forward voltage for flywheel diode D4 to conduct
V ₄ , the base voltage for turning on the transistor Q
If V _B , the number of turns of the base winding L3 is N ₃ , and the number of turns of the secondary winding L2 is N ₂ , then V _R > {N ₃ (V ₃ −V ₄ ) / N ₂ } −V _B (1) (1) The first term N ₃ (V ₃ −V ₄ ) / N ₂ on the right side of the equation is an induced voltage generated in the base winding L3 when a current flows through the choke coil L and the flywheel diode D4.

The voltage drop circuit R has a function of blocking the current I _R without allowing the current I _R to flow in the minute voltage range as shown in the characteristic diagram of FIG.

Next, the operation of the switching regulator configured as described above will be described with reference to FIG. 2 in which a common time t is plotted on the horizontal axis.

First, due to the small base current flowing through the resistor R1,
Collector current flows. Collector winding for base winding L3
An induced voltage is generated by mutual inductance with L1 and the base potential is forward biased. Therefore, the collector current increases more than before. Increased collector current in base winding
The induced voltage of L3 is increased, the base current is increased, and the collector current is further increased.

Due to such a reproducing action, the transistor Q enters the “on” state at the time t ₁ , and the collector current keeps increasing. Eventually, the base current of the transistor Q is limited by the resistance R, the increase of the collector current stops, and the change of the magnetic flux Φ _T disappears, so that the induced voltage of the base winding L3 starts to decrease. As the base current decreases, so does the collector current, causing transistor Q to "off" rapidly at time t ₂ due to the regenerative action in the opposite direction.

Exciting current flows in the collector winding L1 and the magnetic flux Φ _T is accumulated until just before the time t _{2 when} the transistor Q turns “off”, so that the transistor Q suddenly turns “off” to generate a counter electromotive voltage. Is reverse biased.

The reverse bias state continues until time t ₃ when the magnetic flux Φ _T disappears.

A current for charging the output capacitor C2 flows through the secondary winding L2 through the rectifier diode D3 and the choke coil L when the transistor Q is "on". During this time, the magnetic flux Φ _L is accumulated in the choke coil L as excitation energy.

The time t ₃ after that, output from the choke coil L capacitor C2, a current is sustained by the loop of the flywheel diode D4. The output capacitor C2 continuously supplies a DC output to the load from the output terminals 1A and 1B.

By the way, the blocking oscillator circuit is the magnetic flux Φ _{T of the} transformer _T.
Disappears at time t ₃ , the same state as before time t ₁
Transistor Q attempts to "turn on", but the present invention still remains "off". This is because a current flows through the flywheel diode D4 until the choke coil L completely discharges the excitation energy, the voltage of the first term on the right side of the equation (1) is generated in the base winding L3, and the above voltage is further applied. This is because the descending circuit R exists.

In the voltage of the first term, the forward voltage V ₄ is larger than the forward voltage V ₃ because the currents flowing through the rectifier diode D3 and the flywheel diode D4 are significantly different, and the dot of the base winding L3 is added. The potential is low on the side that did.
Therefore, the starting current flowing from the resistor R1 is the diode D,
It flows with the resistor R2 and the base winding L3, and cannot flow into the base of the transistor Q. There is also an oscillating voltage that occurs when the magnetic flux Φ _T of the transformer T disappears, but this amplitude must also be greater than the forward voltage V ₃ of the rectifier diode D3 because the current of the flywheel diode D4 continues. I can't. Therefore, this oscillating voltage is absorbed by the forward voltage of the diodes D2 and D1, and the base current of the transistor Q is blocked in either direction.

The voltage drop circuit R acts in this way, and the transistor Q
The "off" state of continues. Then, when the excitation energy of the choke coil L is completely released and the voltage of the first term on the right side of the equation (1) generated in the base winding L3 disappears, that is, at the time t ₄ , the voltage V _R of the voltage drop circuit _{R Goes} above the voltage V _B and the transistor Q turns “on”.

The voltage drop circuit R consists of diode D1, diode D
Although it is constituted by 2, the resistor R2 and the resistor R3, the diode D1 and the diode D2 may be connected in parallel in opposite directions, and the resistor R2 and the resistor R3 may be constituted by one resistor. As the rectifier diode D3 and the flywheel diode D4, a PN junction diode and a Schottky barrier diode having different forward voltages may be combined.

〔effect〕

As described above, the switching regulator of the present invention has a small voltage range that is generated before the excitation energy of the choke coil is released in the closed circuit formed between the base winding and the base / emitter of the transistor. A voltage drop circuit that blocks both forward and reverse current is connected with the transformer, and the oscillation transistor turns on after the magnetic flux of the transformer and choke coil that make up the blocking oscillation circuit disappears completely. Is done. Therefore, since the oscillation transistor is not damaged by the surge current, it is possible to realize a self-excited on / off type switching regulator. Since the transformer is smaller than the flyback type, the overall shape is also smaller, and the price can be further reduced.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of a switching regulator of the present invention, FIG. 2 is an operation explanatory diagram, and FIG. 3 is a characteristic diagram of a voltage drop circuit. T: Transformer, L1: Collector winding, L3: Base winding, L2: Secondary winding, Q: Transistor

Claims (1)

[Claims] 1. A blocking oscillation circuit is constructed using a transformer having a collector winding, a base winding, a secondary winding, and a transistor, and a rectifying diode, a flywheel diode, a choke coil, and a smoothing capacitor are provided in the secondary winding. In an on-on type switching regulator in which a rectifying and smoothing circuit is connected, in a closed circuit formed between the base winding and the base-emitter of a transistor,
A switching regulator characterized in that a voltage drop circuit for blocking both forward and reverse currents is connected in a minute voltage range that is generated before the excitation energy of the choke coil is released.