JPH03230757A - Self-excited switching regulator - Google Patents

Abstract

PURPOSE:To improve efficiency and control characteristics by providing an element for current control between one end of the driving winding of a transformer and the base of a main transistor, and controlling said element for current control so that the current of said driving winding may be reversely proportional to output voltage. CONSTITUTION:Tr 33 for current control is connected between the base of a main transistor(Tr)4 and the top of a driving winding 11. To the Tr 33 is added a circuit comprising a resistance 34, a diode 35, and a resistance 36 for controlling it. When it becomes light load and output voltage becomes high, the resistance of a phototransistor 23 becomes small, and the base potential of the Tr 15 for bypass control becomes low, and the base current of the Tr 33 falls, and the collector current also falls. For this reason, the current flowing in the resistance 13 becomes small. Reversely, when output voltage falls due to heavy load, the resistance of Tr 23 becomes large, and the potential at the left end of the resistance 34 becomes high, and the collector current of the Tr 33 becomes large.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a self-excited switching regulator such as an RCC system that can improve efficiency.

[Prior Art] As shown in Fig. 2, a conventional RCC type switching regulator has a primary winding 3 of a transformer 2 connected between one end and the other end of a DC power supply 1, and an intermittent It has a main transistor 4 as a switching element for applying a voltage to the main transistor 4. The collector of the main transistor 4 is connected to one end of the DC power supply 1 via the primary winding 3, and the emitter is connected to the other end of the DC power supply 1. The secondary winding 5 of the transformer 2 is connected to an output terminal 9.10 via an output rectifying smoothing port 88 consisting of a diode 6 and a smoothing capacitor 7. Drive winding 11 consisting of the tertiary winding of transformer 2
One end is connected to the base of the main transistor 4 via a diode 12 and a resistor 13, and the other end is connected to the base of the main transistor 4.
is connected to the emitter of Note that a capacitor 14 is connected in parallel to the diode 12. A transistor 15 as a base current bypass control element is connected between the base of the main transistor 4 and the lower end of the drive winding 11. A starting resistor 16 is connected between one end of the $ source 1 and the base of the main transistor 4.

A control power supply winding 17 is provided to configure a constant voltage control circuit for controlling the base current bypass control transistor 15. This control power supply winding 17 is electromagnetically coupled to the transformer 2, and one end thereof is connected to the lower end of the drive winding 11.

The other end (lower end) of the control power supply winding 17 is connected to the base of the base current bypass control transistor 15 via a diode 18 and a resistor 19.20. A smoothing capacitor 21 is connected between the output end of the resistor 19 and the upper end of the control power supply winding 17. A series circuit of a resistor 22, a phototransistor 23, and a capacitor 24 is connected between the base and collector (ground) of the base current bypass control transistor 15. capacitor 24
A diode 26 is connected through a resistor 25 between the lower end of the drive winding 11 and the upper end of the drive winding 11 . A bias resistor 27 is connected between the base of the bypass control transistor 15 and one end of the power supply. A light emitting diode 28 optically coupled here for controlling the phototransistor 23 is connected to an output terminal 9 via a control element 29 and a resistor 30.
．． Connected between 10. Current fltlJll element 2
In order to control the output voltage 9 with the output voltage, voltage dividing resistors 31 and 32 are connected between the output terminals 9 and 10.

U Operation] The operation of this switching regulator will be explained. First, a base current flows through the main transistor 4 via the starting resistor 16, and when this turns on, current flows through the primary winding 3, and a current flows through the drive winding 11 to drive the main transistor 4 by positive feedback. A voltage is generated and the base current of the main transistor 4 is supplied. The current flowing through the collector of the main transistor 4 IC gradually increases, and when this becomes equal to the product of the base current IB and the current amplification factor hFE, the collector current becomes constant, the magnetic flux change of the transformer 2 disappears, and the current of the drive winding 11 increases. There is no power, the base current decreases, and the main transistor turns off abruptly. During the off period, the energy stored in the transformer 2 during the on period is released via the diode 6. When this energy release ends, a ringing voltage is generated in the winding of the transformer 2, the main transistor 4 is turned on again, and oscillation continues.

The main transistor 4 controls the output voltage to be constant.
By bypassing the base current of the main transistor to the control transistor 15, if the amount of bypass is increased and the base current is decreased, the maximum collector current and on-time width of the main transistor become smaller, and the output voltage decreases. Conversely, if the amount of bypass is reduced, the output voltage will increase. The control transistor 15 is controlled by the phototransistor 23
carried out by The resistance value of the phototransistor 23 decreases as the output voltage increases. As a result, the base current of the control transistor 15 flowing through the circuit consisting of the resistor 22, the phototransistor 23, and the capacitor 24 increases, the bypass current (collector current) flowing through the control transistor 15 increases, and the main transistor 4
base current decreases, and the output voltage decreases. Note that the capacitor 24 is charged by the voltage generated in the drive winding 11 while the main transistor 4 is off.

[Problems to be Solved by the Invention] By the way, when the voltage (input voltage) of the power supply 1 fluctuates, the voltage of the drive winding 11 also fluctuates. Further, in the conventional circuit, the base current of the main transistor 4 is kept constant even if the load (not shown) connected to the output terminal 9, 10 changes.

For this reason, the current supplied from the drive winding 11 becomes excessive or insufficient, making it impossible to obtain stable control characteristics, and the current supplied from the drive winding 11 is always constant. This means that unnecessary power loss occurs in the resistor 13 and the bypass transistor 15 due to a current that is more than necessary, which causes a decrease in efficiency.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a self-excited switching regulator that can improve efficiency and control characteristics.

[Means for Solving the Problems] The present invention for achieving the above object includes a primary winding of a transformer connected between one end and the other end of a DC power supply, and a collector connected to the primary winding. a main transistor connected to one end of the DC power supply via the DC power supply and having an emitter connected to the other end of the DC power supply; an output rectifying and smoothing circuit coupled to the primary winding; and an electromagnetic transistor connected to the primary winding. a drive winding coupled with one end coupled to the base of the main transistor and the other end connected to the emitter of the main transistor; and a voltage control element connected between the base and emitter of the transistor. A self-commutated switching regulator comprising: a current control element connected between one end of the drive winding and the base of the main transistor; and a current flowing through the drive winding to the output voltage of the output rectifying and smoothing circuit The present invention relates to a self-excited switching regulator characterized in that a control circuit is provided for controlling the current control element so as to vary in inverse proportion to a voltage corresponding to the current control element.

[Function] In the present invention, when the load becomes light, the current is limited by a current control element such as the transistor 33 in the embodiment. As a result, for example, the transistor 1 of the embodiment
Power loss in the bypass control element etc. consisting of 5 is reduced. Further, stable control characteristics can be obtained by using an optimal drive current.

[Example] Next, referring to FIG. 1, an RCC according to an example of the present invention will be explained.
The switching regulator of this method will be explained. However, parts in FIG. 1 that are common to those in FIG. 2 are designated by the same reference numerals and their explanations will be omitted.

The circuit shown in FIG. 1 includes a circuit consisting of an NPN transistor 33 having a high current amplification factor as a current control element, a resistor 34, a diode 35, and a resistor 36 for controlling the transistor in addition to the circuit shown in FIG. It is formed by adding. The current control transistor 33 is connected in series between the upper end of the drive winding 11 and the base of the main transistor 4. Capacitor 14 is connected in parallel to the series circuit of diode 12 and transistor 33.

A resistor 34 is connected via a diode 35 between the base of the current control transistor 33 and the base of the bypass control transistor 15. Also, capacitor 2
The lower end of 1 is connected to the current control transistor 3 via the resistor 36.
It is connected to the base of 3.

The basic operation of the switching regulator in FIG. 1 is the same as that in FIG. 2. In this embodiment, the phototransistor 23
Constant voltage control is carried out, and current control corresponding to the load is carried out. That is, the current control transistor 33
The base current flows between the capacitor 21, which is almost constantly charged, the resistor 36, the base-emitter of the current control transistor 33, and the base-emitter of the resistor 13 and the main transistor 4.
The current flows through a circuit consisting of the emitter and the emitter-collector of the bypass control transistor 15.

The base potential of the current control transistor 33 is connected to the resistor 36.
and a resistor 34. resistance 34
The left end, that is, the base potential of the bypass control transistor 15 is controlled by the phototransistor 23.

When the load becomes light and the output voltage increases, the resistance of the phototransistor 23 decreases, and the base potential of the bypass control transistor 15 decreases. At the same time, the base potential of the current control transistor 33 decreases, this base current also decreases, and this collector current also decreases.

Therefore, the current flowing through the base current limiting resistor 13 becomes smaller.

Conversely, when the output voltage decreases due to a heavy load, the resistance value of the phototransistor 23 increases, the potential at the left end of the resistor 34 increases, and the voltage of the current control transistor 33 divided by the resistor 34 and 36 increases. The base potential of transistor 33 increases, and the current flowing through this transistor 33 increases.

As is clear from the above, according to the present embodiment, it is possible to supply a drive current that corresponds to load fluctuations, and it is possible to reduce power loss in the resistor 13 and the bypass control transistor 15.

Moreover, an optimal drive current is supplied to the main transistor 4 and the control transistor 15, and stable control characteristics can be obtained.

[Modification] The present invention is not limited to the above-described embodiment, but may be modified.6 For example, the phototransistor 23 may be
A constant voltage control circuit for controlling the transistor 15 and a current control circuit for controlling the transistor 33 may be provided independently, instead of being used for controlling the two control transistors 15 and 33. If insulation on the secondary side is not required, the phototransistor 23 can be replaced with an ordinary transistor.

[Effects of the Invention] As described above, according to the present invention, loss can be reduced and stable control characteristics can be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a circuit diagram showing a switching regulator according to an embodiment of the present invention, and FIG. 2 is a circuit diagram showing a conventional switching regulator. 1...Power supply, 2...Transformer, 3...Primary winding,
4... Main transistor, 5... Secondary winding, 8...
Output rectifying and smoothing circuit, 11... Drive winding, 13... Current limiting resistor, 15... Bypass control transistor, 33... Current 11J11 transistor.

Claims (1)

[Scope of Claims] [1] A primary winding of a transformer connected between one end and the other end of a DC power source, and a collector connected to one end of the DC power source via the primary winding, a main transistor whose emitter is connected to the other end of the DC power supply; an output rectifying and smoothing circuit coupled to the primary winding;
A voltage connected between a drive winding that is electromagnetically coupled to the next winding, one end of which is coupled to the base of the main transistor, and the other end of which is connected to the emitter of the main transistor, and the base and emitter of the transistor. A self-excited switching regulator comprising a control element, a current control element connected between one end of the drive winding and the base of the main transistor, and a current flowing through the drive winding to be used for the output rectification. A self-excited switching regulator comprising: a control circuit that controls the current control element so as to vary in inverse proportion to the output voltage of the smoothing circuit or a voltage corresponding thereto.