JPH0640473Y2 - Switching regulator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Overview] A primary control type switching regulator having a switching element and its control circuit on the primary side of a high frequency transformer, and an object thereof is to improve responsiveness by reducing power loss and shortening startup time. The switching control circuit is provided with a series circuit of a feeding resistor and a capacitor for supplying an operating voltage, and the feeding resistor is connected in parallel with a series circuit of a resistor and a capacitor.

[Industrial application field]

The present invention relates to a primary control type switching regulator having a switching element and its control circuit on the primary side of a high frequency transformer, and more particularly to a starting method thereof.

[Conventional technology]

Conventionally, as the primary control type switching regulator, the circuit type shown in FIG. 3 is known.

In FIG. 3, 1 is an AC power supply, 2 is a rectifying circuit for full-wave rectifying the AC power supply, 3 is a smoothing circuit for smoothing the rectified output from the rectifying circuit 2, and is composed of a reactance L and a capacitor C.

Both ends of the primary winding 4a of the high frequency transformer 4 are connected to the smoothing circuit 3
Is connected via a switching transistor 5 between the DC output terminals. In the secondary winding 4b of the high frequency transformer 4,
A diode 6 for rectifying the voltage induced therein and a capacitor 7 for smoothing the rectified output thereof are connected to each other, so that a DC output is taken out to the output terminals T ₁ , T ₂ .

Reference numeral 8 is a control circuit for switching the switching transistor 5 by pulse width modulation control, and its output terminal 8b is connected to the base of the switching transistor 5. The input terminal 8a of the switching control circuit 8 is connected to the connection point between the power feeding resistor 9 and the voltage fluctuation suppressing capacitor 10 which are connected in parallel between the output terminals of the smoothing circuit 3, and between the input terminal 8a and ground, A Zener diode 11 for keeping the input voltage supplied to the switching control circuit 8 constant through the power feeding resistor 9 is connected in parallel.

In the conventional switching regulator configured as described above, when a power switch (not shown) is turned on,
The alternating current supplied from the alternating current power source 1 is full-wave rectified by the rectifying circuit 2 and further smoothed by the smoothing circuit 3. The smoothed DC output is supplied to the primary winding of the high frequency transformer 4, and is also supplied to the capacitor 10 through the power feeding resistor 9 to charge the capacitor 10. The charging time constant at this time is set by the values of the resistor 9 and the capacitor 10. Resistance 9
The voltage generated at the connection point P between the capacitor 10 and the capacitor 10 is converted to a constant voltage by the Zener diode 11 and applied to the input terminal 8a of the switching control circuit 8, whereby the switching control circuit 8 is activated.

When the switching control circuit 8 is activated, its output terminal 8b
When a pulse signal whose pulse width is modulated is output to the switching transistor 5 and is applied between the base and emitter of the switching transistor 5, the switching transistor 5 is turned on and off, and the primary winding 4a of the high frequency transformer 4 is turned on and off. DC current flows intermittently. Accompanying this, the AC voltage induced in the secondary winding 4b of the high frequency transformer 4 is rectified by the diode 6, smoothed by the capacitor 7, and supplied from the main power terminals T ₁ and T ₂ to an electric device (not shown).

[Problems to be solved by the device]

In the conventional switching regulator as described above, the input voltage V required for the operation of the switching control circuit 8
Is generally about 20V, whereas AC power supply 1
For example, in the case of AC100V, the DC output voltage E at the output end of the smoothing circuit 3 is about 140V. Therefore, the switching control circuit 8
There is a voltage difference of about 120V between the input voltage V and the DC output voltage E, and this voltage difference needs to be stepped down by the power feeding resistor 9.

Therefore, setting the resistance value of the power feeding resistor 9 to a value at which a necessary minimum current flows is an essential requirement for reducing power loss and providing a power supply device with high efficiency.

However, in order to satisfy the above requirements, the power feeding resistor 9
When the resistance value of is increased, the voltage across the capacitor 10 becomes the input voltage V required for the operation of the switching control circuit 8, that is, after the power is turned on until the output voltage appears at the output terminals T ₁ and T _2. There is a problem that it takes time.

Thus, it takes a lot of time from power-on to generation of output voltage, which is problematic in the following points.

In other words, good responsiveness is one condition to aim at a power supply device that is easier to use, but poor responsiveness reduces man-machine interface, and multiple output systems are sequenced in accordance with power-on. If the responsiveness is poor, accurate sequence control will not be possible.

The present invention has been made in view of the above points, and an object of the present invention is to provide a switching regulator capable of reducing power loss and improving responsiveness due to a reduction in startup time.

[Means for Solving the Problems]

The switching regulator according to the present invention has a switching element for chopping DC and its control circuit on the primary side of a high-frequency transformer, and a series circuit of a feeding resistor and a capacitor is connected between the terminals of the DC to connect the resistor / capacitor. In the primary control type switching regulator in which the connection point is connected to the control circuit, a series circuit of a resistor and a capacitor is connected in parallel to the power feeding resistor.

[Action]

When a DC voltage is applied between the series circuit of the power feeding resistor and the capacitor by turning on the power, a large current instantaneously flows through the power feeding capacitor via the parallel circuit of this power feeding resistor and the resistor connected in parallel with this, As a result, the terminal voltage of the power feeding capacitor is rapidly raised to the input voltage level of the switching control circuit.

Therefore, according to the present invention, the switching regulator can be started earlier, the resistance value of the power feeding resistor can be increased, and the power loss can be reduced.

〔Example〕

 Embodiments of the present invention will be described below with reference to the drawings.

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

In the figure, the same parts as those in FIG. 3 are designated by the same reference numerals, and the description of the structure will be omitted. The parts different from those in FIG. 3 will be mainly described.

As is apparent from FIG. 1, in order to shorten the startup time of the switching regulator, a resistor 12 having a resistance value r (sufficiently smaller than the resistance value R of the feeding resistor 9) and a capacitor 13 having a capacitance C ₁ are newly added, A series circuit of the resistor 12 and the capacitor 13 is connected in parallel to the feeding resistor 9.

Next, the operation of this embodiment configured as described above will be described with reference to FIG.

In FIG. 1, when the AC power supply 1 is supplied to the switching regulator by turning on a power switch (not shown), the capacitor 10 is shown in FIG. A current i that gradually decreases exponentially as a characteristic curve I flows, and the terminal voltage V ₁ of the capacitor 10 is changed to the characteristic curve of FIG.
It gradually rises as shown in II. And its voltage V ₁
When the voltage reaches the Zener voltage V of the Zener diode 11 at time t ₁ , thereafter, the specified voltage V is maintained and the switching control circuit 8 is operated. However, it takes too long time t ₁ to activate the switching control circuit 8, that is, to activate the switching regulator.

On the other hand, in this embodiment, the power feeding resistor 9 has a resistor 12
Since the series circuit of the capacitor 13 and the capacitor 13 is connected in parallel, the DC voltage E smoothed by the smoothing circuit 3 when the power is turned on is connected to the power feeding resistor 9 and the series circuit of the resistor 12 and the capacitor 13 connected in parallel to the feeding resistor 9. When applied across the capacitor 10,
A current i ₂ as shown by the characteristic curve III in FIG. 2 which is set by the parallel resistance of the feeding resistor 9 and the resistor 12 instantaneously flows through the capacitor 10. When the capacitor 13 is charged up, the current flowing through the resistor 12 becomes zero. When the current i ₂ flows through the capacitor 10, its terminal voltage V ₂ rises rapidly as shown by the characteristic curve IV in FIG. 2 and maintains a constant voltage after reaching the Zener diode voltage V. Further, the time t ₂ until the terminal voltage V ₂ of the capacitor 10 at this time becomes the operating voltage V of the switching control circuit 8 is shorter than the conventional rising time t ₁ .

Therefore, in this embodiment, the startup time of the switching regulator can be greatly shortened and the responsiveness can be improved.
Further, the resistance value R of the power feeding resistor 9 can be selected to the maximum within a range in which the necessary minimum current to the switching control circuit 8 is maintained, and accordingly, the power loss due to the power feeding resistor 9 is further reduced. A high efficiency switching regulator can be provided.

[Effect of device]

As described above, according to the present invention, the series circuit of the resistor and the capacitor is connected in parallel to the power feeding resistor to the switching control circuit, so that the rise of the input voltage of the switching control circuit is increased. The startup of the switching regulator can be accelerated, a power supply with good response can be obtained, and the power loss of the power supply resistor can be reduced.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of a switching regulator according to the present invention, FIG. 2 is a characteristic diagram for explaining the operation in this embodiment, and FIG. 3 is a circuit diagram of a conventional switching regulator. In the figure, 1 is an AC power supply, 2 is a rectifier circuit, 3 is a smoothing circuit, 4 is a high frequency transformer, 5 is a switching transistor, 6 is a diode, 7, 10 and 13 are capacitors, 8 is a switching control circuit, and 9 is a power supply resistor. , 11 is a Zener diode, and 12 is a resistor.

Claims (1)

[Scope of utility model registration request] 1. A switching element for switching direct current and a control circuit therefor are provided on the primary side of a high frequency transformer, and a series circuit of a power feeding resistor and a capacitor is connected between the terminals of the direct current, and a connection point of the resistor / capacitor. A switching regulator in which the control circuit is connected to the control circuit, wherein a series circuit of a resistor and a capacitor is connected in parallel to the power feeding resistor.