JPH076710Y2 - Self-excited DC-DC converter - Google Patents

Description

[Detailed Description of the Invention] [Industrial field of application] The present invention relates to a self-excited DC-DC converter capable of obtaining a stable DC output against voltage fluctuations.

[Conventional technology]

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

In the figure, 1 is an input terminal to which a DC voltage source V ₀ is connected,
2 denotes an output terminal to obtain a DC voltage whose polarity is reversed for a predetermined value, 5 ₁ control circuit, the blocking oscillator 6, 7 is a rectifying and smoothing circuit.

The capacitor C ₁ is connected between the input terminal 1 and the ground, and the resistor R ₁ and the emitter of the main switching transistor Q ₁ are connected to the connection point between the input terminal 1 and the capacitor C ₁ .
The other end of the resistor R ₁ is connected to the base of the control transistor Q ₂ and the cathode of the Zener diode ZD. A resistor R ₀ is connected between the base of the transistor Q ₁ and the collector of the transistor Q ₂ . The control circuit 5 ₁ is composed of a transistor Q ₂ and resistors R ₁ and R ₀ . The primary coil L ₁ of the transformer 3 is connected between the collector of the transistor Q ₁ and the ground, its base is connected to one end of the secondary coil L ₂ of the transformer 3 via the capacitor C ₂ , and the other end is a transistor. It is connected to the emitter of Q ₁ (input terminal 1) to form a blocking oscillator circuit 6. The collector of the transistor Q ₁ is connected to the cathode of the diode D ₁ and the anode thereof is connected to the smoothing capacitor C ₃ to form the rectifying / smoothing circuit 7. Zener diode ZD
The resistance R ₁ and the transistor of the cathode control circuit 5 ₁
It is connected to the connection point with the base of Q ₂ , and the anode is connected to the rectifying and smoothing circuit 7. Reference numeral 8 is a load circuit.

The operation of the self-excited DC-DC converter shown in FIG. 4 will be described.

When a DC voltage V ₀ is applied to input terminal 1, the transistor
Flows into a base current I _B to Q _2, resistors R ₀ to the collector current of the transistor Q ₂ flows from the base of the transistor Q ₁ through the transistors Q _1, Q ₂ are turned on. The collector current of the transistor Q ₁ is the primary coil of the transformer 3.
It flows into L _1, two on the primary coil L _2, induced current to charge the capacitor C ₂ flows. The charging of the capacitor C _2, the base potential of the transistor Q ₁ is increased, the transistor Q ₁ is being cut off. When the transistor Q ₁ is cut off, a counter electromotive force is generated in the secondary coil L ₂ to charge the capacitor C ₂ in the opposite direction. The charging current transistor Q ₁ again since the positive bias the base of transistor Q ₁ is turned to ON state. The same operation is repeated, and the oscillation output is obtained from the collector of the transistor Q ₁ . This oscillated output is rectified by the diode D ₁ , smoothed by the capacitor C ₃ , and a DC voltage of a predetermined value with the polarity inverted is obtained from the output terminal 2.

Further, the Zener diode ZD is connected in order to stabilize the output voltage against the load current during operation and the fluctuation of the DC voltage V ₀ on the input side. As a zener current I _z , a relatively large current needs to flow through the load circuit 8 through the zener diode ZD.

[Problems to be solved by the present invention]

The self-excited DC-DC converter of FIG. 4, in order to stabilize the output voltage, the control circuit 5 ₁ and the Zener diode ZD between the rectifying and smoothing circuit 7 is connected, at the time of startup, the Zener diode ZD Zener current I _z flowing through the load circuit 8 via
Flows as the base current of the control transistor Q ₂ . The base current of the transistor Q ₂ is, Zener current I _z base current I _B of the transistor Q ₂ value current so that the flow of the are summed (I _B + I _z) to. Therefore, the collector current of the transistor Q _2, in order to draw the base of the main switching transistor Q _1, a large current easily flows as the collector current of the transistor Q _1, the drawback of a risk of damage to the transistor Q ₁ is increased Have. From this point of view, if the Zener current is set to a small value, the output voltage cannot be sufficiently stabilized.

The present invention has been made to solve the above problems, and its main purpose is to provide an improved self-excited DC-DC that can obtain a stable DC output with respect to load fluctuations.
A converter is provided.

Another object of the present invention is a self-excited DC-DC that can obtain a stable DC output against load fluctuations and does not damage the main switching transistor at startup.
A converter is provided.

[Means for solving the problem]

The self-excited DC-DC converter of the present invention comprises a switching transistor, a blocking oscillator composed of a transformer composed of primary and secondary coils, and a capacitor, and a control circuit including a control transistor for controlling the switching transistor. In a self-excited DC-DC converter comprising a rectifying / smoothing circuit that makes the oscillation output from the blocking oscillator a DC output, for stabilizing the output connected between the control circuit and the rectifying / smoothing circuit. A zener diode is provided, and a zener current is supplied only to the zener diode and a first current source that supplies a zener current to the zener diode via a backflow prevention element while supplying a base current to the control transistor to the control circuit. And a second current source that operates.

[Action]

The self-excited DC-DC converter of the present invention divides the Zener current supplied to the Zener diode connected to stabilize the output voltage against the load fluctuation and the base current supplied to the control transistor. It is possible to supply a zener current having a relatively large value without damaging the main switching transistor by supplying the zener currents via different current sources.

〔Example〕

A self-excited DC-DC converter according to the present invention will be described based on the embodiment shown in FIG.

The embodiment shown in FIG. 1 has the same circuit as that of the conventional example shown in FIG. 4, the same parts are designated by the same reference numerals, and the only part different from the conventional example is the control circuit.

In FIG. 1, the blocking oscillator circuit 6 and the rectifying / smoothing circuit 7 are the same as those in the conventional example shown in FIG. 4, and therefore their explanations are omitted.

The control circuit 5 is composed of a control transistor Q ₂ and current sources 4 ₁ and 4 ₂ diode D ₂ . The base of the input terminal 1 and the control transistor Q _2, the control transistor base current I primarily supplies current sources 4 _{1 B} Q ₂ 'are connected. The connection point between the base and the current source 4 ₁ of the control transistor Q _2,
The anode of a reverse current prevention element diode D ₂ is connected, between the input terminal 1 and its cathode, the Zener diode ZD only current source for supplying a Zener current I _z 4 ₂ are connected. The Zener diode ZD has its cathode connected to the connection point between the current source 4 ₂ and the cathode of the diode D ₂ , and its anode connected to the connection point between the anode of the diode D ₁ of the rectifying and smoothing circuit 7 and the capacitor C _3. ing.

Next, the operation of the self-excited DC-DC converter of the present invention will be described with reference to FIG.

When the DC voltage V ₀ is applied to the input terminal 1, the current I ₁ mainly flows into the base of the transistor Q ₂ via the current source 4 ₁ .
A part of the current I ₁ is supplied to the Zener diode ZD via the diode D ₂ according to the voltage fluctuation of the load circuit 8. On the other hand, the current I ₂ supplied from the current source 4 ₂ is not flow into the base of the control transistor Q ₂ by the diode D ₂ of the backflow prevention device, the output flows to a load circuit 8 via the Zener diode ZD Stabilize. Current I ₁ supplied from the current source 4 ₁ in this manner, is mainly supplied as a base current I _B of the control transistor Q _2, the current I ₂ is supplied only to the Zener diode ZD.

The mutual relationships among these currents I ₁ and I ₂ , the base current I _B , and the zener current I _z can be expressed as in the following equation.

I _z = I ₂ + I ₁ −I _B (1) Further, the relation between the current values of the currents I ₁ and I ₂ flowing from the current sources 4 ₁ and 4 _{2 is} expressed as I ₁ << I ₂ . If set, the relationship between the current source 4 _1, 4 base current to the diode D ₂ of the backflow prevention device between ₂ are connected I _B and Zener current I _z is Taken together (1), I _B << I _z . Since a larger current than the base current I _B can be supplied as the Zener current I _z , the output voltage can be further stabilized.

Furthermore, in the self-excited DC-DC converter of FIG. 1, the DC power source V ₀ is applied to the input terminal 1 and the current source 4 _{2 is} applied even before the output voltage rises or after the output voltage rises. The current I ₂ supplied from is not supplied to the base of the control transistor Q ₂ , and a large current does not flow to the base of the main switching transistor Q ₁ .

2 and 3 are circuit diagrams showing other embodiments of the self-excited DC-DC converter according to the present invention.

In the embodiment of FIG. 2, the current sources 4 ₁ , 4 ₂ of the control circuit 5 are connected to the input terminal 1 to which the DC voltage source V ₀ is applied, and the resistors R ₁ , R ₂ are connected.
It is configured by ₂ and is adapted to be supplied with currents I ₁ and I ₂ determined by the DC voltage V ₀ and the resistance values of the resistors R ₁ and R ₂ . In this embodiment, the relationship between the resistance values of the resistors R ₁ and R ₂ is R
By setting the of ₁ >> R ₂ relationship, easily currents I _1, I ₂ relationship may be I ₁ «I _2.

In the embodiment of Figure 3, the current source 4 _1, 4 ₂ of the control circuit 5 is constituted by a current mirror type current source. The current source 4 ₁ consists of a transistor Q ₃ biased by a diode D ₃ and a resistor R ₃ connected to its emitter.
The other end of the resistor R ₃ is connected to the input terminal 1 and
The collector of Q ₃ is connected to the base of the controlling transistor Q ₂ and the anode of the diode D ₂ . Further, the current source 4 ₂ is constituted by a resistor R _4, which are connected to the transistor Q ₄ which is biased by the diode D ₃ to the emitter, the other end of the resistor R ₄ is connected to the input terminal 1, the transistor Q The collector of ₄ is connected to the cathode of diode D _{2 and} the cathode of zener diode ZD.

For this embodiment, the resistance value of the resistor R _3, R ₄ by setting the relationship of R ₃ >> R _4, to the base current I ₁ and the Zener current I ₂ in relation I ₁ «I ₂ You can

〔effect〕

In the self-excited DC-DC converter of the present invention, the Zener current supplied to the Zener diode connected for stabilizing the output voltage and the base current supplied to the control transistor of the blocking oscillator are different from each other. The zener current is supplied from a current source, and therefore, a zener current having a relatively large value can be supplied to the zener diode, so that a more stable output voltage can be obtained and the zener current is a control transistor. It is equipped with a diode that prevents the zener current from flowing to the base of the control transistor during start-up, so it is a very effective self-excited DC-type that does not damage the main switching transistor. A DC converter can be provided.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of a self-excited DC-DC converter according to the present invention, and FIGS. 2 and 3 show other self-excited DC-DC converters according to the present invention. FIG. 4 is a circuit diagram showing an essential part of the embodiment, and FIG. 4 is a circuit diagram showing an example of a conventional self-excited DC-DC converter. 1: Input terminal, 2: Output terminal, 3: Transformer, 4 ₁ , 4 ₂ : Current source, 5:
Control circuit, 6: blocking oscillator, 7: rectifying and smoothing circuit, Q ₁ :
Main switching transistors, Q _2: control transistor, D _1, D _2: diodes, C _1, C _2: Capacitor, ZD: Zener diode, R ₀ to R _4: the resistance, V _0: DC voltage source

Claims (4)

[Scope of utility model registration request] 1. A blocking oscillator composed of a switching transistor, a transformer composed of primary and secondary coils, and a capacitor, a control circuit including a control transistor for controlling the switching transistor, and an oscillation output from the blocking oscillator. In a self-excited DC-DC converter including a rectifying / smoothing circuit that outputs a DC output, a Zener diode connected between the control circuit and the rectifying / smoothing circuit is provided, and a base current is supplied to the control transistor. And a first current source for supplying a zener current to the zener diode via the backflow prevention element, and a second current source for supplying a zener current to the load circuit via the zener diode. Self-excited DC-DC converter. 2. A blocking oscillator comprising a switching transistor, a transformer having primary and secondary coils, and a capacitor, a control circuit including a control transistor for controlling the switching transistor, and an oscillation output from the blocking oscillator. In a self-excited DC-DC converter including a rectifying / smoothing circuit that outputs DC as a DC output, the first current source is connected to the base of the control transistor, and the anode of the diode is connected to the base of the control transistor. A self-excited DC-DC converter, wherein a second current source is connected to the cathode, and a Zener diode is connected between the cathode of the diode and the rectifying / smoothing circuit. 3. The first and second current sources are respectively composed of first and second resistors connected to a DC voltage source, and the resistance value of the second resistor is set smaller than that of the first resistor. The self-excited DC-DC converter according to claim 1 or 2, wherein the utility model is registered. 4. The self-excited DC-DC converter according to claim 1 or 2, wherein the first and second current sources are current mirror type current source circuits.