JPH0416638Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a pulse width modulation (PWM) type transistor DC converter, that is, a switching regulator.

[Prior art and its problems] Switching regulators can be broadly classified into self-excited switching regulators and separately excited switching regulators. The former self-excited switching regulator is characterized by a simple circuit configuration, but has a problem in that it is difficult to obtain stable oscillation. On the other hand, the latter separately excited switching regulator generates pulses for pulse width (PWM) control and controls the switching transistors using this.
Although it has the feature that stable switching operation at a predetermined frequency is possible, it has the problem that the circuit configuration becomes complicated.

Therefore, an object of the present invention is to provide a PWM transistor DC converter that is capable of stable operation and has a simple circuit configuration.

[Means for Solving the Problems] The present invention for achieving the above object will be described with reference to the symbols indicating the embodiments.
A switching transistor 4, a primary winding 3 of the transformer, a secondary winding 5 electromagnetically coupled to the primary winding 3, an output rectifying and smoothing circuit 11, and a rectangular wave pulse having a constant pulse width. A rectangular wave pulse generation circuit 31 that generates at a constant cycle, a base current control transistor 20, and the output rectification and smoothing circuit 11
The switching transistor 4 is connected to one side of the DC power supply 1 via the primary winding 3. The output rectifying and smoothing circuit 11 is connected to the secondary winding 5, the square wave pulse generating circuit 31 is connected to the base of the switching transistor 4, and the output rectifying and smoothing circuit 11 is connected to the base of the switching transistor 4. The base current control transistor 20 is connected between the base and emitter of the switching transistor 4 or between the rectangular wave pulse generation circuit 31 and the base of the switching transistor 4 so as to control the base current of the switching transistor 4. The control circuit controls the base current control transistor 20 so that the switching transistor 4 becomes unable to maintain saturation and turns off during the generation period of the square wave pulse. The present invention relates to a transistor DC converter that is characterized by being controlled. Note that the control circuit in the present invention corresponds to the base control circuit of the transistor 20, which is composed of the voltage detection circuit 25 and the error amplification circuit 26 in the embodiment.

[Function] In the present invention, since the switching transistor 4 is connected in series with the primary winding 3, that is, the inductance, the collector current gradually increases during the on period, and when it becomes twice the amplification factor of the base current, saturation is maintained. Can no longer be turned off.
The start of turning on the switching transistor 4 is determined by the rise of a rectangular wave pulse having a constant period. Therefore, the on period of the switching transistor 4 is constant regardless of changes in the output voltage. The base current control transistor 20 functions as a base current bypass element or a base current limiting resistor of the switching transistor 4.

[Embodiment] Next, a switching regulator according to an embodiment of the present invention will be described with reference to FIGS. 1 and 2. In FIG. 1, a series circuit of a primary winding 3 of a transformer 2 and a switching transistor 4 is connected to a DC power supply 1. A secondary winding 5 , a tertiary winding 6 , a quaternary winding 7 , and a fifth winding 8 are electromagnetically coupled to the primary winding 3 of the transformer 2 . The secondary winding 5 is connected to the output terminal 1 via an output rectifying and smoothing circuit 11 consisting of a diode 9 and a capacitor 10.
2 and 13 are provided. In addition, diode 9
is connected to a polarity that turns on at the voltage of the secondary winding 5 when the switching transistor 4 is off.

The tertiary winding 6 functions as an initial base drive winding, and includes a capacitor 14 and resistors 15 and 16.
It is connected to the base of the switching transistor 4 via. Diodes 17 and 18 connected in parallel to resistors 15 and 16 form a reverse bias circuit for switching transistor 4.

A transistor 19 connected between the middle of the resistors 15 and 16 and the lower end of the secondary winding 6 turns on when the switching regulator begins to generate a constant voltage, This is to cut off the supply of base current.

A transistor 20 connected between the base and emitter of the switching transistor 4 constitutes a base current bypass circuit, that is, a base current control circuit.

The quaternary winding 7 functions as a voltage detection winding, and is connected to a rectifying and smoothing circuit including a diode 21, a resistor 21a, and a capacitor 22, and a pair of voltage dividing resistors 23 and 24 to detect the voltage. A detection circuit 25 is configured.

26 is an error amplification circuit, which includes a transistor 27 for error amplification, a Zener diode 28 connected to the emitter for obtaining a reference voltage, and a resistor 29 connected between the emitter and ground;
It consists of a collector current limiting resistor 30. The base of the transistor 27 is connected to the voltage dividing point of the resistors 23 and 24, and the emitter is connected to the Zener diode 2.
The collector is connected to the upper end of the resistor 23 via a resistor 8, and the collector is connected to the base of the base bypass transistor 20 via a resistor 30.

The quintic winding 8 functions as a power supply winding for the pulse generation and drive circuit 31, and is connected to the pulse generation and drive circuit 31 via a rectifying and smoothing circuit including a diode 32 and a capacitor 33. Further, when the voltage of the tertiary winding 8 reaches a level that allows the pulse generation and drive circuit 31 to operate normally, the transistor 19 is turned on to stop the drive by the tertiary winding 6. The cathode of diode 32 is connected to the base of transistor 19 via Zener diode 34.

The pulse generation and drive circuit 31 includes a rectangular wave oscillator 35 whose power source is the quintic winding 8, and a diode 32.
and the base of the switching transistor 4, a driving transistor 36 and a resistor 3 are connected to each other.
7 and a Zener diode 3 connected between the base of the driving transistor 36 and the ground line.
8 and a series circuit of a transistor 40,
The output pulse of the square wave oscillator 35 causes the transistor 4 to
0 is turned on, the driving transistor 3
6 is configured to be turned on.

A resistor 41 connected between one end of the DC power supply 1 and the base of the switching transistor 4 causes a starting current to flow through the switching transistor 4 when the DC power supply 1 is turned on.

(Operation) When the DC power supply 1 constituted by a rectifying and smoothing circuit is connected to a switching regulator, a base current flows through the switching transistor 4, and the switching transistor 4 is turned on. As a result, a voltage is generated in the tertiary winding 6, the base current starts being supplied from there, and the RCC self-excitation operation based on this starts. When the switching transistor 4 is turned on and off by self-oscillation, the diode 9 in the output stage of the secondary winding is turned on during this off period, and the capacitor 10 is charged based on the energy stored in the transformer 2. When a voltage at a level capable of operating the pulse generation and drive circuit 31 is obtained based on self-oscillation, the rectangular wave oscillator 35 generates a rectangular wave pulse as shown in FIG. 2A. In response, drive transistor 3
6 is turned on, and a rectangular wave base current starts to be supplied through this transistor 36. On the other hand, when the output voltage rises, the transistor 19 is turned on and the supply of base current by the tertiary winding 6 is cut off.

When the base current of the switching transistor 4 flows based on the square wave pulse shown in FIG. 2A, the switching transistor 4 is turned on in synchronization with the rise of the square wave pulse, and its collector current
Ic gradually increases as shown in FIG. 2B. The switching transistor 4 can remain on until it is saturated or until the square wave pulse falls; however, in this circuit, the switching transistor 4 is configured to saturate before the square wave pulse falls. There is. Not all of the current supplied from the pulse generation and drive circuit 31 becomes the base current I _B of the switching transistor 4, but the remaining current is bypassed to the transistor 20 and becomes the base current I _B
become. If the base current I _B1 is
As shown in FIG. 2B, when the collector current IC increases to h _FE I _B1 , the switching transistor 4 is turned off. As a result, a voltage in the opposite direction is generated in the tertiary winding 6, and the switching transistor 4 is reverse biased and kept off. Therefore, the on period of the switching transistor 4 becomes narrower than the width of the rectangular wave pulse, as shown in FIG. 2C.

The output voltage is detected by the voltage of the quaternary winding 7 during the off period. If the output voltage becomes higher than a predetermined value, the voltage across the resistor 23 increases, this collector current increases, and the bypass current flowing through the bypass transistor 20 increases.
Conversely, the base current of switching transistor 4 decreases. This base current I _B2 is smaller than I _B1
As shown in FIG. 2B, the saturation state of IC=h _FE I _B2 is reached early after the rise of the rectangular wave pulse, and the on-width of the switching transistor 4 becomes narrow. As a result, the output voltage is reduced and returned to a predetermined value. Note that when the output voltage becomes lower than a predetermined value, the operation is reverse to that when the output voltage becomes higher.

As is clear from the above, this method has the conventional
Although the triangular wave oscillator, comparator, etc. required in the PWM control circuit are not included, the switching transistor 4 can be controlled by PWM.
Therefore, a highly stable oscillation state with a constant period can be obtained. Furthermore, it is no longer necessary to provide an independent stabilizing circuit as a power source for the pulse generation and drive circuit 31, and a constant voltage controlled by a switching regulator can be used as the power source voltage.
The circuit configuration becomes simpler.

[Modifications] The present invention is not limited to the above-described embodiments, but can be modified as follows, for example.

(1) As shown in Figure 3, the secondary winding 5 of the transformer 2
A diode 9 connected to the switching transistor 4 may be connected so as to be turned on during the on period of the switching transistor 4 shown in FIG. 1, thereby forming an on-on type switching regulator.

(2) Instead of voltage detection using the quaternary winding 7 in FIG. 1, a voltage detection circuit 25a may be connected to the output terminal 12 as shown in FIG.

(3) As shown in FIG. 3, it may be connected to the output terminal 12 of the pulse generation and drive circuit 31 and operated by the constant voltage obtained here.

(4) Instead of providing the starting resistor 41, a starting pulse may be supplied.

(5) The base current is controlled by the base of the switching transistor 4 and the pulse generation and drive circuit 31.
A transistor may be connected in series between the two. Furthermore, the value of the base current IB may be changed by controlling the amplitude of the rectangular wave pulse sent out from the pulse generation and drive circuit 31.

[Effects of the Invention] As is clear from the above, according to the present invention, pulse width modulation control can be achieved with a simple circuit configuration.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing a switching regulator according to an embodiment of the present invention, FIG. 2 is a waveform diagram showing the states of each part of FIG. 1, and FIG. 3 is a modified example of a switching regulator. It is a circuit diagram showing a part. DESCRIPTION OF SYMBOLS 1... Power supply, 2... Transformer, 4... Switching transistor, 20... Base current bypass transistor, 25... Voltage detection circuit, 26...
. . . error amplification circuit, 31 . . . pulse generation and drive circuit, 35 . . . square wave oscillator.

Claims (1)

[Scope of claim for utility model registration] DC power supply 1 and switching transistor 4
, a primary winding 3 of the transformer, a secondary winding 5 electromagnetically coupled to the primary winding 3, and an output rectifying and smoothing circuit 11 to generate a rectangular wave pulse having a constant pulse width at a constant cycle. Rectangular wave pulse generation circuit 31
, a base current control transistor 20 , and a control circuit that controls the current of the base current control transistor 20 so as to keep the output voltage of the output rectifying and smoothing circuit 11 constant; is connected between one terminal and the other terminal of the DC power source 1 via the primary winding 3, the output rectifying and smoothing circuit 11 is connected to the secondary winding 5, and the rectangular wave pulse The generation circuit 31 is connected to the base of the switching transistor 4, and the base current control transistor 20 is connected between the base and emitter of the switching transistor 4, or between the base and emitter of the switching transistor 4 so as to control the base current of the switching transistor 4. The control circuit is connected between the rectangular wave pulse generation circuit 31 and the base of the switching transistor 4, and the control circuit controls the switching transistor 4 from being unable to maintain saturation within the generation period of the rectangular wave pulse. The base current control transistor 2 is configured such that the base current control transistor 2
A transistor direct current converter characterized by controlling zero.