JPH0614545A - Switching regulator - Google Patents

Abstract

(57) [Abstract] [Purpose] To provide a switching regulator that enables stable operation over a wide range of input voltage and output current. A DC voltage is switched by a switching circuit E ₁ , and an input current having a constant pulse width for excitation is generated on the primary winding side of a transformer. The pulse current from the secondary winding of the transformer is rectified and smoothed by the rectifying and smoothing circuit E ₂ . The difference between the output voltage from the rectifying / smoothing circuit E ₂ and the reference voltage is detected and amplified by the target voltage generating circuit E ₃ to generate the target voltage. In the pulse width adjusting circuit E ₄ , the rising point at which the DC voltage of the switching circuit is turned on is the starting point.
The switching circuit is turned on for a time corresponding to the target voltage.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a switching regulator for converting an AC voltage of a commercial power source or the like into a DC voltage. More specifically, a self-excited RCC (linking
The present invention relates to a choke converter) type switching regulator.

[0002]

2. Description of the Related Art Generally, a stable DC power supply is supplied from AC.
The power supply unit for supplying power is roughly divided into linear regulators.
There are a switching regulator and a switching regulator. Switching
The regulator is designed so that the circuit is turned on and off repeatedly.
The input voltage is converted to a constant voltage by the linear
Lighter, smaller and more efficient than gurator. Sanawa
Then, as shown in FIG. 6, the switching transistor Tr₁
Turns on, the primary winding P ₁Current flows through the
Is the primary winding P₁Accumulated in. And the secondary winding S
Energy is released and a current flows. By the secondary winding S
While the energy is being released, the induced back electromotive force
Primary P due to force₁Blocked to prevent current from flowing
Has been. The current flowing in the secondary winding S is
It decreases with the passage of time. And the release of energy
After that, the back electromotive force disappears and the primary side P₁Current to
Flow starts, but primary winding P₁Energy storage by
It grows over time. And the secondary winding S
Output current is rectifying and smoothing circuit E₂And the diode D₁ And
Indexer C₂Secondary side DC voltage V_outIs converted to
Output to terminal B. And let this switch
The closed loop of the negative feedback is used for the composition,
In order to stabilize the output, the secondary smoothing circuit E_FivePassed through
After the DC voltage, the constant voltage diode D₃Through the
Teaching circuit E₆Feedback to. In this circuit
Is the DC voltage V_outWhen the voltage becomes large, the constant voltage diode D
₃Through transistor Tr₂Current flows through the
Switching transistor Tr₁Reduce the base current of
Reduce. That is, the transistor Tr₁ON time is short
Control the collector current.

[0003]

In the above switching regulator, the ON time of the transistor Tr ₁ is minimized when the input voltage is maximum and the output power is minimum. However, in the feedback circuit using the constant voltage diode, the ON time of the storage time of the transistor Tr ₁ remains even if the base current is lowered, and the ON time does not become zero. Therefore, if the input voltage exceeds the limit of the input voltage or output current that minimizes the ON time of the transistor Tr ₁ ,
When the output current drops, there is a problem that normal oscillation cannot be maintained and intermittent oscillation occurs.

Therefore, the present invention has been made by paying attention to the problems existing in such a conventional technique, and its purpose is to enable stable operation over a wide range of input voltage and output current. It is to provide a switching regulator.

[0005]

In order to achieve the above object, according to the present invention, a switching circuit for switching a direct current voltage to generate an input current having a constant pulse width for excitation on the primary winding side of a transformer. , A rectifying and smoothing circuit for rectifying and smoothing the pulse current from the secondary winding of the transformer,
A target voltage generation circuit that detects a difference between the output voltage from the rectifying and smoothing circuit and a reference voltage, amplifies the difference between the voltages, and generates a target voltage, and a rising edge at which the DC voltage of the switching circuit is turned on. The gist of the invention is that a pulse width adjusting circuit for turning on the switching circuit for a time corresponding to the target voltage is provided as a starting point.

[0006]

With the above construction, in the present invention, the rectified and smoothed DC voltage is switched in the switching circuit, and a triangular pulse current is generated on the primary winding side of the transformer. A pulse current is generated on the secondary winding side by this pulse current and is converted into a DC voltage by the rectifying and smoothing circuit. When the DC voltage changes due to the influence of the input voltage or the output current, the target voltage generating circuit compares the reference voltage with the DC voltage, and the difference is amplified and output as the target voltage. The pulse width adjusting circuit turns on the switching circuit for a time corresponding to the target voltage, starting from the rise of turning on the DC voltage of the switching circuit.
Let

[0007]

(First Embodiment) A first embodiment of the present invention will be described below with reference to FIGS.

As shown in FIG. 1, the switching regulator comprises a switching circuit E ₁ , a rectifying / smoothing circuit E ₂ , a target voltage generating circuit E ₃ , a pulse width adjusting circuit E ₄ and a transformer T. The collector side of the switching transistor Tr ₁ of the switching circuit E ₁ is connected to the output side of the primary winding P ₁ of the transformer T. Primary winding P
The input side of ₁ is connected to the input terminal A. A starting resistor R ₁ is connected between the input terminal A and the base of the transistor Tr ₁ . The base of the transistor Tr ₁ is connected to the input side of the feedback winding P ₂ via the resistor R ₂ and the capacitor C ₁ , and is also connected to the collector of the transistor Tr ₂ . The emitters of both transistors Tr ₁ and Tr ₂ are connected to the common terminal COM together with the output side of the feedback winding P ₂ .

The rectifying / smoothing circuit E ₂ comprises a diode D ₁ and a capacitor C ₂ and is connected between both ends of the secondary winding S. The target voltage generation circuit E ₃ has voltage dividing resistors R ₃ and R ₃ .
₄ , a constant voltage diode D ₂ for generating a Zener voltage Vz ₁ which is a reference voltage, and an operational amplifier IC ₁ . The divided voltage of the voltage dividing resistors R ₃ and R ₄ is input to the non-inverting input terminal of the operational amplifier IC ₁ , and the Zener voltage Vz ₁ of the constant voltage diode D ₂ is input to the inverting input terminal.
The output terminal of the target voltage generating circuit E ₃ is connected to the integrating circuit composed of the resistor R ₅ and the capacitor C ₃ of the pulse width adjusting circuit E ₄ . One end of the capacitor C ₃ of the integrating circuit is connected to the collector side of the transistor Tr ₃ whose base is the output side of the secondary winding S and the cathode side of the constant voltage diode D ₃ . On the other hand, the anode side of the constant voltage diode D ₃ is connected to the base of the transistor Tr ₂ .

When the input voltage V _in is applied to the switching circuit E ₁ of the switching regulator configured as described above, the transistor T is driven by the current flowing through the starting resistor R _1.
r ₁ is turned on. Further, the transistor Tr ₁ is forward biased by the voltage generated in the feedback winding P ₂ . Then, the collector current I ₁ increases as shown in FIG. 2A, and after the predetermined time t ₁ and t ₂ set by the pulse width adjusting circuit E ₄ described later, the increase is stopped by turning on the transistor Tr _2. Then, a triangular-wave pulse current is generated. On the other hand, as shown in FIG. 2B, the diode current I ₂ flowing through the diode D _{1 due} to the excitation of the secondary winding S rapidly rises due to induction after the collector current I _{1 is} stopped, and then the secondary winding It gradually decreases according to the time constant of S. In this way, the secondary output is generated as a triangular wave pulse current. At this time, the voltage generated in the feedback winding P ₂ is in the reverse direction, the base-emitter of the transistor Tr ₁ is reverse biased, and the transistor Tr ₁ is turned off while the diode current I ₂ thereof flows.

Rectifying and smoothing circuit E₂At, the secondary output is
Diode D₁ And capacitor C₂DC voltage V_out
Is output to the terminal B. Its DC voltage V_out
Is the target voltage generation circuit E₃Voltage dividing resistor R₃, R_FourBy minutes
Pressurized, constant voltage diode D ₂Zener voltage Vz₁And ratio
Compared. That is, the operational amplifier IC₁By this amount
Pressure voltage and Zener voltage Vz₁The difference between
The target voltage Vt₁As pulse width adjustment circuit E_FourGiven to
Be done.

Next, the operation of the pulse width adjusting circuit E ₄ is shown in FIG.
(C) and will be described in FIG. 3, the diode current I ₂ does not flow, the reverse bias between the base and emitter of the transistor Tr ₁ is released, the transistor Tr ₁ is ON. At the same time, the transistor Tr ₃ is turned off by the induced voltage generated in the secondary winding S, and the capacitor C ₃ starts to be charged. The target voltage Vt ₁ increases according to the time constant formed by the resistor R ₅ and the capacitor C ₃ of the integrating circuit, and when it exceeds the Zener voltage Vz ₂ of the constant voltage diode D ₃ , a current is passed through the base of the transistor Tr _{2 and} the transistor Tr ₂ is generated. ₁ for O
FF.

In this case, if the difference between the divided voltage of the target voltage generating circuit E ₃ and the Zener voltage Vz ₁ is large, the target voltage Vt ₁ becomes large. Then, under the condition of the same time constant, the time t ₁ for reaching the Zener voltage Vz ₂ of the constant voltage diode D ₃ becomes short, and the ON time of the transistor Tr ₁ also becomes short. That is, the pulse current width becomes smaller and the generated secondary side DC voltage V _out becomes smaller.

On the other hand, if the difference between the divided voltage of the target voltage generating circuit E ₃ and the Zener voltage Vz ₁ is small, the target voltage Vt ₂ becomes small. Therefore, the zener voltage V of the constant voltage diode D ₃ is
Time to reach z ₂ t ₂ becomes longer, it becomes longer ON time of the transistor Tr _1. Therefore, the pulse current width increases and the generated secondary side DC voltage V _out also increases.

As described above, since the pulse current width of the transistor Tr ₁ is set to the time corresponding to the difference between the DC voltage V _out and the reference voltage, the intermittent oscillation is prevented and the DC voltage V _out is stably supplied. Like

(Second Embodiment) Next, a second embodiment of the present invention will be described with reference to FIGS. In the following description, the same components as those of the above-described embodiment will be denoted by the same reference numerals in the drawings and will not be described.

As shown in FIG. 4, the switch is the same as in the first embodiment.
The switching regulator is a switching circuit E₁, Rectification flat
Smoothing circuit E₂, Target voltage generation circuit E₃, Pulse width adjustment circuit
E_FourAnd a transformer T. With the first embodiment
The difference is that the switching circuit E₁Then for switching
Transistor Tr₁Pulse width adjustment circuit E directly on the base of _Four
The output of is connected. Also, the target voltage generation circuit E₃To
Voltage dividing resistance R₃, R_FourThe divided voltage is the operational amplifier IC
₁A constant voltage diode D to the inverting input terminal of₂Zener
Voltage Vz₁Are respectively input to the non-inverting input terminals. That
The target voltage generation circuit E₃Is the pulse width adjustment circuit E
_FourComparator IC₂Connected to the non-inverting input of
The inverting input of is the capacitor C of the integrating circuit₃Connected to one end of
Has been. This comparator IC₂The output of
Touching circuit E₁Sent to.

The basic operation of the above construction
Is the same as that of the first embodiment.
The description will be made with reference to FIG. Target voltage generation circuit E₃Order
Flow smoothing circuit E₂DC voltage V_outPartial voltage and reference voltage
Zener voltage Vz₁Difference is the comparator IC₂Non-inverted input
Input to the input terminal and the target voltage Vt₁Becomes This target electric
Pressure Vt₁Is a rectifying and smoothing circuit E₂DC voltage V_outThe lower the
Large output. The voltage Vc of the integrating circuit on the inverting input side
₃Is the diode D ₁Transistor while current is flowing
Ta Tr₃Is turned on, so the value is kept close to zero.
To be done. At this time, the comparator IC₂Output goes high
However, the feedback winding P₂The voltage generated at
And transistor Tr₁Between the base and emitter of
Reverse biased transistor Tr₁Is off
It

When the diode current I ₂ stops flowing, the transistor Tr ₁ is turned on and the transistor Tr ₃ is turned off. This transistor Tr ₃ is O
Integrating circuit FF timing begins to charge, the output of the comparator IC ₂ exceeds the target voltage Vt ₁ is dropped to the low level, to turn OFF the transistor Tr _1. That is,
The transistor Tr ₁ is turned on only during the time when the voltage Vc _{3 of the} integrating circuit reaches the target voltage Vt ₁ .

Therefore, the DC voltage V of the rectifying / smoothing circuit E ₂ is
_{When out} is lower than the predetermined value, the target voltage Vt ₁ is high,
Time t _{4 at which} the voltage Vc _{3 of the} integrating circuit reaches the target voltage Vt ₁
Is long, and the ON time of the transistor Tr ₁ is long. Then, the pulse current width increases and the generated secondary side DC voltage V _out increases. On the contrary, when the DC voltage V _out of the rectifying / smoothing circuit E ₂ is higher than the predetermined value, the target voltage Vt ₂ becomes low and the time t ₃ for the voltage Vc _{3 of the} integrating circuit to reach the target voltage Vt ₂ is short, and the transistor Tr ₁ ON time becomes short.
That is, the pulse current width becomes smaller and the secondary side DC voltage V
_out will be reduced.

As in the first embodiment, the transistor T
Since the pulse current width of r ₁ is set to the time corresponding to the difference between the DC voltage V _out and the reference voltage, intermittent oscillation is prevented and the DC voltage V _out is stably supplied.

The present invention is not limited to the configuration of the above-described embodiment, and may be embodied with any modification, for example, by incorporating a snubber circuit in the primary side, without departing from the spirit of the present invention. It is also possible.

[0023]

As described above, according to the present invention, since the pulse current width of the switching circuit is controlled according to the difference between the DC voltage on the secondary winding side and the reference voltage, intermittent oscillation can be prevented and a wide range can be obtained. This has the effect of operating stably with respect to the input voltage or the output current.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of a switching regulator embodying the present invention.

FIG. 2A is a characteristic diagram showing a collector current of a switching transistor of a switching circuit. (B) It is a characteristic view which shows the diode current of the diode of the rectification smoothing circuit by the side of a secondary winding. (C) A characteristic diagram showing a target voltage in the pulse width adjusting circuit.

FIG. 3 is a characteristic diagram showing a target voltage in a pulse width adjusting circuit.

FIG. 4 is a circuit diagram showing a second embodiment of a switching regulator.

5 is a characteristic diagram showing a voltage of an integrating circuit in the pulse width adjusting circuit of the switching regulator shown in FIG.

FIG. 6 is a circuit diagram showing a conventional example of a switching regulator.

[Explanation of symbols]

 E₁ Switching circuit, E₂ Rectifying and smoothing circuit, E₃ 
Target voltage generation circuit, E _Four Pulse width adjustment circuit, T
Sense.

Claims (1)

[Claims] 1. A switching circuit for switching a DC voltage to generate an input current having a constant pulse width for excitation on the primary winding side of a transformer, and a rectifying and smoothing pulse current from the secondary winding of the transformer. And a target voltage generating circuit that detects a difference between the output voltage from the rectifying and smoothing circuit and a reference voltage, and that amplifies the difference between the voltages to generate a target voltage, and a DC voltage of the switching circuit. A switching regulator comprising: a pulse width adjusting circuit for turning on the switching circuit for a time corresponding to the target voltage, starting from a rising edge of turning on the voltage.