JP3388707B2 - Self-excited step-down DC-DC converter - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for simplifying the circuit configuration of a self-oscillation type step-down DC-DC converter.

[0002]

2. Description of the Related Art A self-excited DC-DC converter has a simple circuit structure and a small number of circuit elements to be used.
It is used in power supplies with small output capacity and relatively low price. As an example of such a DC-DC converter,
The present inventor has proposed in Japanese Patent Application No. 5-83849 a self-oscillation type step-down DC-DC converter having a circuit configuration as shown in FIG. In FIG. 4, 1 and 2 are DC
-Shows the input and output terminals on the high potential side of the DC converter. Although the input and output terminals on the low potential side are not shown,
It shall be connected to earth. The circuit shown in FIG. 4 has the following configuration.

A switching transistor Q3 and a choke coil L3 are connected in series between the input terminal 1 and the output terminal 2, and a diode D2 and a smoothing capacitor C6 are connected to both ends of the choke coil L3, respectively. These switching transistor Q3, choke coil L3,
The diode D2 and the smoothing capacitor C6 form a step-down chopper circuit type DC-DC converter. A resistor R5 is connected between the base of the switching transistor Q3 and ground, and the main current path of the driving transistor Q4 is connected between the base and emitter of the switching transistor Q3. The base of the driving transistor Q4 is connected to the switching transistor Q3 via the resistor R6.
Of the switching transistor Q3 via the feedback circuit 3. This feedback circuit 3 is formed by a series circuit of a resistor R7 and a capacitor C7.

A series circuit of a resistor R10 and a resistor R11 is connected between the output terminal 2 and the ground, and the resistor R10 and the resistor R11 are connected.
The connection point of 11 is connected to the base of the transistor Q5. The collector of the transistor Q5 is connected to the base of the driving transistor Q4 via the resistor R9, and the emitter is connected to the ground via the constant voltage diode DZ3.
A resistor R is placed between the emitter of the transistor Q5 and the output terminal 2.
8 are connected to the resistors R8, R9, R10, R11,
The control circuit 4 is formed by the transistor Q5 and the constant voltage diode DZ3. The operation of the circuit of FIG. 4 configured as described above has been described in detail in Japanese Patent Application No. 5-83849, and therefore the description thereof is omitted here.

[0005]

The DC-DC converter having the circuit configuration shown in FIG. 4 is capable of self-excited oscillation by providing the driving transistor Q4 and the feedback circuit 3. Therefore, according to the DC-DC converter having the circuit configuration of FIG. 4, it is possible to use a single-winding coil component without a feedback winding for the choke coil L3, and it is possible to reduce the size and cost of the power supply device. Had the advantage.
However, the market constantly demands further miniaturization and cost reduction of existing power supply devices. Therefore, it is an object of the present invention to obtain a self-excited step-down DC-DC converter that can form a more compact and inexpensive power supply device.

[0006]

Means for Solving the Problems Self-excited step-down type D of the present invention
The C-DC converter has a first winding whose one end is connected to the input terminal, a switching element connected between the other end of the first winding and the output terminal, and a first winding. Magnetically coupled feedback winding, a first capacitor connected between one end of the feedback winding and the control terminal of the switching element, one end connected to one end of the feedback winding, and the other end switched. A resistance element connected to the control terminal of the element and a reference voltage source for supplying a reference voltage signal to the control terminal of the switching element are provided. Alternatively, a reference voltage source for generating a reference voltage signal and one end of the main current path are connected to the control terminal of the switching element together with the above-mentioned first winding, switching element, feedback winding, first capacitor and resistance element. And a control transistor that changes the amount of current flowing according to the voltage difference between the signal corresponding to the output voltage and the reference voltage signal.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION First, a first winding and a switching element are connected in series between an input terminal and an output terminal. First
A feedback winding that is magnetically coupled to the winding is provided, and one end of the feedback winding is connected to the control terminal of the switching element via the first capacitor. One end of the feedback winding is further connected to one end of the resistance element, and the other end of the resistance element is connected to the control terminal of the switching element. A reference voltage source is connected between the control terminal of the switching element and the reference potential point. Basically, a filter capacitor is connected between the input terminal and the reference potential point, and a smoothing capacitor is connected between the output terminal and the reference potential point.

In the first embodiment of the present invention, in the above basic structure, a constant voltage diode is used as a reference voltage source, and one end of the constant voltage diode is connected to a control terminal of a switching element via a backflow prevention element. . The other end of the resistance element is connected to the control terminal of the switching element via the backflow prevention element. In the second embodiment of the present invention, a control transistor is further provided in addition to the above basic configuration, and the reference voltage source is connected to the control terminal of the switching element via the main current path of the control transistor.
A plurality of resistors are connected in series between the output terminal and the reference potential point, and the control terminal of the control transistor is connected to the connection point between the predetermined resistors.

In the third embodiment of the present invention, in addition to the above basic structure, a second winding magnetically coupled to the first winding is provided, and one end of the second winding is rectified. It connects to an output terminal through an element, and the other end of the second winding is connected to a reference potential point. In the fourth embodiment of the present invention, in addition to the basic configuration described above, a third winding constituted by a component independent of the first winding is provided, and one end of the third winding is It is connected to the output terminal via a rectifying element, and the other end of the third winding is connected to the reference potential point. Then, a third capacitor is connected between one end of the third winding and one end of the first winding on the switching element side.

[0010]

FIG. 1 shows a circuit of a self-excited step-down DC-DC converter according to a first embodiment of the present invention, which is capable of forming a small-sized and inexpensive power supply device. The circuit shown in FIG. 1 has the following circuit configuration. Input terminal 1 to transformer T 1
The secondary winding N1 is connected to one end, and the primary winding N1 is connected to the output terminal 2 via the main current path of the switching transistor Q1. A filter capacitor C1 is connected between the input terminal 1 and ground, and a smoothing capacitor C2 is connected between the output terminal 2 and ground. One end of the feedback winding N3 of the transformer T is connected to the base of the switching transistor Q1 via the capacitor C3, and the feedback winding N3 is connected.
The other end of is connected to the input terminal 1.

One end of the feedback winding N3 is further connected to one end of the resistor R1 , and the other end of the resistor R1 is connected to the base of the switching transistor Q1 via the diode D2. The base of the switching transistor Q1 is further connected to the cathode of the constant voltage diode DZ1 via the diode D2, and the anode of the constant voltage diode DZ1 is connected to the ground. One end of the secondary winding N2 of the transformer T is connected to the output terminal 2 via the diode D1, and the secondary winding N2 is connected.
Connect the other end of the to ground. A capacitor C4 is connected between one end of the secondary winding N2 on the diode D1 side and the other end of the primary winding N1 on the switching transistor Q1 side.

The operation of the circuit of FIG. 1 having the above-described circuit configuration is as follows. First, when a voltage is externally supplied to the input terminal 1, the feedback winding N is fed from the input terminal 1.
A current (base current) flows into the base of the switching transistor Q1 through the capacitor 3 and the capacitor C3. The switching transistor Q1 forward biased by the base current makes the main current path between its collector and emitter conductive. Then, a current (collector current) begins to flow in the main current path of the primary winding N1 and the switching transistor Q1. At this time, since the current flows through the primary winding N1,
A voltage having a high potential on the capacitor C3 side appears in the feedback winding N3.

The voltage appearing in the feedback winding N3 serves to supply more base current to the switching transistor Q1, and as a result, the switching transistor Q1.
1 shifts to the ON state. At this time, the smoothing capacitor C2 is charged by the current passing through the main current path of the primary winding N1 and the switching transistor Q1, and at the same time energy is accumulated in the transformer T. While the switching transistor Q1 is in the ON state, the base current is continuously supplied to the switching transistor Q1 by the input voltage and the voltage generated in the feedback winding N3. Here, the base current of the switching transistor Q1 is a combined current of the current flowing through the capacitor C3 and the current flowing through the resistor R1 and the diode D2.

The collector current passing through the main current path of the switching transistor Q1 in the ON state is the primary winding N
The inductance appearing at 1 increases linearly with time. After a certain time passes, when the collector current increasing with this time reaches a collector saturation current value determined by the magnitude of the base current at that time, the collector current stops increasing further. At the moment when there is no incremental change in the collector current of the switching transistor Q1, the voltage generated in the feedback winding N3 until then disappears, and the base current of the switching transistor Q1 decreases.

Then, the collector current of the switching transistor Q1 decreases and a flyback voltage appears in each winding of the transformer T. The flyback voltage generated in the feedback winding N3 supplies a reverse bias voltage to the base of the switching transistor Q1 together with a voltage between the terminals of the capacitor C3 having a high potential on the feedback winding N3 side to rapidly turn off the switching transistor Q1. . While the flyback voltage appears in each winding of the transformer T, a reverse bias voltage due to the flyback voltage generated in the feedback winding N3 and the terminal voltage of the capacitor C3 is applied to the base of the switching transistor Q1. As a result, the switching transistor Q1 maintains the off state.

During this time, the flyback voltage generated in the secondary winding N2 of the transformer T causes a current to flow from the secondary winding N2 into the smoothing capacitor C2 through the diode D1 and the smoothing capacitor C2 is charged. On the other hand, the capacitor C3 is discharged, and the inter-terminal voltage that brings the feedback winding N3 side to a high potential is lowered. After a certain period of time, the energy emission and the capacitor C due to the flyback voltage generation of the transformer T
When the voltage drop across the terminals of 3 progresses, the current passing through the feedback winding N3 and the capacitor C3 from the input terminal 1 toward the base of the switching transistor Q1 due to the input voltage, the feedback winding N3, the resistor R1, and the diode D2. Occurs and the base current begins to flow into the switching transistor Q1 again.

Then, the main current path of the switching transistor Q1 becomes conductive, and a current starts to flow in the main current path of the primary winding N1 and the switching transistor Q1. Primary winding N
When a current flows through 1, a voltage having a high potential on the capacitor C3 side appears in the feedback winding N3. The voltage appearing in the feedback winding N3 acts to supply more base current to the switching transistor Q1, and as a result, the switching transistor Q1 shifts to the ON state. Thereafter, the above-described operation is repeated to activate the circuit shown in FIG. 1 and increase the voltage across the smoothing capacitor C2.

Next, the voltage across the smoothing capacitor C2 is a constant voltage diode DZ1 which functions as a reference voltage source.
1 rises to a value approximately equal to the Zener voltage of, the circuit shown in FIG. 1 enters a steady operation state, and the operation part when the switching transistor Q1 turns on and off changes as follows. Switching transistor Q
While 1 is in the ON state, the smoothing capacitor C2 is charged by the current passing through the main current path of the primary winding N1 and the switching transistor Q1. When the voltage between the terminals of the smoothing capacitor C2 becomes substantially equal to the Zener voltage of the constant voltage diode DZ1 due to this charging, the current flowing through the resistor R1 that has been flowing into the base of the switching transistor Q1 via the diode D2 until then becomes constant. The current flows into the voltage diode DZ1.

At this time, the base current of the switching transistor Q1 decreases, the collector current of the switching transistor Q1 decreases accordingly, and a flyback voltage appears in each winding of the transformer T. The flyback voltage generated in the feedback winding N3 supplies a reverse bias voltage to the base of the switching transistor Q1 together with the voltage across the terminals of the capacitor C3 to turn off the switching transistor Q1. While the flyback voltage appears in each winding of the transformer T, a voltage in the reverse bias direction is applied to the base of the switching transistor Q1 by the flyback voltage generated in the feedback winding N3 and the terminal voltage of the capacitor C3. It As a result, the switching transistor Q
1 remains off. During this period, the smoothing capacitor C2 is supplied with flyback energy from the secondary winding N2, while supplying energy from the output terminal 2 to an external load, and eventually lowers the terminal voltage.

After the elapse of a certain time, when the energy emission of the transformer T, the voltage drop across the capacitor C3, and the voltage drop across the smoothing capacitor C2 proceed,
Due to the input voltage, a current passing through the feedback winding N3 and the capacitor C3, a current passing through the feedback winding N3, the resistor R1 and the diode D1 is generated from the input terminal 1 toward the base of the switching transistor Q1. The base current begins to flow in again. Then, the main current path between the collector and the emitter of the switching transistor Q1 becomes conductive, and the current starts to flow in the primary winding N1 and the main current path of the switching transistor Q1. When a current flows through the primary winding N1, a voltage having a high potential on the capacitor C3 side appears in the feedback winding N3. The voltage appearing in the feedback winding N3 acts to supply more base current to the switching transistor Q1, and as a result,
The switching transistor Q1 shifts to the ON state.

The smoothing capacitor C2 is charged by the current passing through the main current path of the primary winding N1 and the switching transistor Q1 until the voltage across its terminals becomes substantially equal to the Zener voltage of the constant voltage diode DZ1. The voltage between the terminals of the smoothing capacitor C2 is a constant voltage diode DZ.
When the value becomes substantially equal to the Zener voltage of 1, the current flowing through the resistor R1 that has flowed through the diode D2 into the base of the switching transistor Q1 until then flows into the constant voltage diode DZ1. After that, the above operation is repeated, and the circuit shown in FIG. 1 performs self-oscillation and stabilization of the output voltage. Thus, FIG.
The circuit shown in (1) has a smaller number of elements required to form the circuit than the conventional circuit shown in FIG. 4, and it is possible to form a small and inexpensive self-excited step-down DC-DC converter. There is.

Although not described, the capacitor C4 in FIG. 1 supplies a part of energy due to the flyback voltage generated in the primary winding N1 to the smoothing capacitor C2 via itself and the diode D1. . This fulfills the function of improving the efficiency of the circuit, but it is omitted depending on the specifications of the circuit. In addition, the diode D2 in FIG.
When turning on the switching transistor Q1,
Switching transistor Q1 via capacitor C3
It is possible to prevent a part of the current to be supplied to the base of the device from leaking to the constant voltage diode DZ1 side. As a result, the current for applying the forward bias at turn-on is supplied to the base of the switching transistor Q1 without waste,
Performs the function of improving the efficiency of the circuit.

FIG. 2 shows a circuit of a self-excited step-down DC-DC converter according to a second embodiment of the present invention. The circuit shown in FIG. 2 is different from the circuit shown in FIG. 1 in the following circuit parts. That is, a first choke coil L1 having a main winding N4 and a feedback winding N5 is provided in place of the transformer T, and the main winding N4 is connected between the input terminal 1 and the collector of the switching transistor Q1. N5 is connected between the input terminal 1 and the capacitor C3. And
The second choke coil L1 is composed of a component independent of the second choke coil L1.
The circuit configuration is such that the choke coil L2 is connected between the ground to which the secondary winding N2 is connected and the anode of the diode D1. The circuit parts other than the above-described parts have the same configuration in FIG. 1 and FIG.

In the circuit of FIG. 2 having such a configuration, the operation for charging the smoothing capacitor C2 is as follows. First, when the switching transistor Q1 is turned off, a flyback voltage is generated in each of the windings N4 and N5 of the first choke coil L1. Then, the flyback voltage generated in the main winding N4 causes the smoothing capacitor C2 to pass from the main winding N4 through the capacitor C4 and the diode D1.
An electric current flows into. At this time, the capacitor C4 is connected to the main winding N
It is charged in such a manner that one end on the 4 side has a high potential. After that, when the switching transistor Q1 is turned on, a current passing through the main winding N4 and the switching transistor Q1 is generated, and this current causes the smoothing capacitor C2.
Is charged.

Here, when the switching transistor Q1 is turned on, the capacitor C4 is discharged, and a current flows from the second choke coil L2 to the capacitor C4. At this time, since current flows through the second choke coil L2, energy is accumulated in the second choke coil L2. The energy stored at this time produces a current flowing from the second choke coil L2 to the smoothing capacitor C2 via the diode D1 when the switching transistor Q1 is turned off. As described above, the circuit shown in FIG. 2 has the independent first and second choke coils L1 and
Although L2 is used, the action and timing of charging the smoothing capacitor C2 are substantially the same as those of the transformer T of FIG. The operation of the circuit shown in FIG. 2 for self-oscillation and stabilization of the output voltage is the same as that of the circuit shown in FIG.

FIG. 3 shows a circuit of a self-excited step-down DC-DC converter according to a third embodiment of the present invention. The circuit shown in FIG. 3 differs from the circuit shown in FIG. 1 in the following circuit parts. That is, the other end of the resistor R1 is directly connected to the base of the switching transistor Q1, and the main current path of the control transistor Q2 and the constant voltage diode DZ2 as the reference voltage source are connected between the base of the switching transistor Q1 and the ground. Connect in series. Input terminal 1
And a resistor R4 is connected between the constant voltage diode DZ2 and the connection point of the control transistor Q2. Further, the resistors R2 and R3 are connected in series between the output terminal 2 and the ground, and the connection point of the resistors R2 and R3 is connected to the control transistor Q2.
The circuit configuration is connected to the base of.

The circuit parts other than the parts described above have the same structure in FIGS. 1 and 2. In the circuit of FIG. 3 having such a configuration, a voltage signal corresponding to the output voltage is obtained at the connection point of the resistors R2 and R3. The control transistor Q2 receiving the voltage signal becomes conductive when the voltage value of the voltage signal becomes higher than the Zener voltage of the constant voltage diode DZ2, and the current flows through the main current path. Then, at this time, switching transistor Q
The base current of 1 decreases, and the switching transistor Q
Trigger to turn off 1. The operation of the circuit shown in FIG. 3 for self-oscillation and stabilization of the output voltage is substantially the same as that of the circuit shown in FIG.

The circuit of FIG. 3 has a large number of elements as compared with the circuit of FIG. 1, but has the following advantages. That is, the voltage condition when the switching transistor Q1 is turned off is the constant voltage diode DZ2.
It can be changed by adjusting the Zener voltage of or the ratio of the resistance values of the resistors R2 and R3. Therefore, in the circuit shown in FIG. 3, the value of the output voltage can be easily changed by adjusting the resistance value of at least one of the resistors R2 and R3. Further, the output voltage of the control transistor Q2 can be stabilized with higher accuracy than the circuit of FIG.

[0029]

According to the self-excited step-down DC-DC converter of the present invention, the first winding and the switching element are connected in series between the input terminal and the output terminal, and the self-excitation is applied to the control terminal of the switching element. It is characterized by a configuration for inputting a reference voltage signal together with a feedback signal for oscillation. According to the present invention having such a configuration, it is possible to obtain a self-excited step-down DC-DC converter that requires only a small number of elements to form a circuit, and can form a small-sized and inexpensive power supply device.

[Brief description of drawings]

FIG. 1 is a self-excited step-down type D according to a first embodiment of the present invention.
The circuit diagram of a C-DC converter.

FIG. 2 is a self-excited step-down type D according to a second embodiment of the present invention.
The circuit diagram of a C-DC converter.

FIG. 3 is a self-excited step-down type D according to a third embodiment of the present invention.
The circuit diagram of a C-DC converter.

FIG. 4 is a circuit diagram of an example of a conventional self-excited step-down DC-DC converter.

[Explanation of symbols]

1: Input terminal 2: Output terminal C3: Capacitor (first capacitor) C4: Capacitor (second capacitor) D1: Diode (rectifier element) D
Z1, DZ2: Constant voltage diode (reference voltage source)
L1: first choke coil L2: second choke coil (second winding) N1: primary winding (first winding) N2: secondary winding (second winding) N3,
N5: Feedback winding (third winding) N4: Main winding (first winding) T: Transformer Q1: Switching transistor (switching element) Q2: Control transistor R1: Resistor (resistive element)

Claims (4)

(57) [Claims] And 1. A first winding having one end connected to the input terminal, a switching element connected between the other end and the output terminal of the first winding, the first winding Magnetically coupled , one end of which is the input terminal
A feedback winding connected to the feedback winding, a first capacitor connected between the other end of the feedback winding and the control terminal of the switching element, one end connected to the other end of the feedback winding, and the other Diode at the end
Through characterized by comprising a resistor connected to the control terminal of the switching element, and a reference voltage source for supplying a <br/> reference voltage signal through the diode to the control terminal of the switching element A self-excited step-down DC-DC converter. 2. A first winding whose one end is connected to an input terminal.
When, A switch connected between the other end of the first winding and the output terminal.
A switching element, The first windingWhenMagnetically coupled, One end of which is the input terminal
Connected toFeedback winding, Of the feedback windingThe other endAnd the control terminal of the switching element
A first capacitor connected in between, One end of the feedback windingThe other endConnected to the other end of the switch
A resistance element connected to the control terminal of the switching element, A reference voltage source for generating a reference voltage signal, Main current pathButControl terminal of the switching elementAnd reference voltage source
Connected between,Supplied to its control terminalOutput voltage
And a signal equivalent toSupplied to one end of its main current pathThe basis
Control that changes the amount of current flow according to the voltage difference of the quasi-voltage signal.
A transistor,A second one end of which is connected to the output terminal through a rectifying element
Winding of The other end of the first winding and the rectifying element side of the second winding
A second capacitor connected between one end and Self-excited step-down DC-DC converter characterized by comprising
Inverter. 3.One end to the output terminal via a rectifying element
A second winding connected, The other end of the first winding and the rectifying element side of the second winding
A second capacitor connected between one end and 2. The self-excited body according to claim 1, further comprising:
Type step-down DC-DC converter. 4. The primary winding is a transformer primary winding.
Yes, the second winding is the secondary winding of the transformer
The self-excited step-down DC-D according to claim 3, characterized in that
C converter.