JPS5848125A - Switching regulator - Google Patents

Abstract

PURPOSE:To obtain a sufficiently stable DC output over a wide input range by using a coverter transformer having two primary windings, and swithching those primary windings which are driven in accordance with a low and a high input. CONSTITUTION:A changeover switch circuit 8 connects the base of a transistor (TR) 4b to the output side of a driving circuit 5 normally, and performs a stabilizing function when high inputs are supplied to input terminals 1a and 1b. On the other hand, when the voltage supplied between the input terminals 1a and 1b becomes a low input, a low input detecting circuit 9 operates and the changeover switch circuit 8 performs switching operation to supply a driving signal from the driving circuit 5 to the base of TR4a. At this time, the TR4b requires high dielectric strength, but a TR4a with low dielectric strength is usable, and such a TR has a large DC amplification factor generally and operates with a relatively small base current.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a switching regulator whose purpose is to obtain a stabilized DC output voltage over a wide range of AC or DC input voltages.

Generally, portable type audio equipment and video equipment can use a commercial AC power supply, an AC-DC conversion adapter, a car battery, or a dry battery as a power source. The allowable input range for AC power supplies, adapters, etc. is I.
20% oov, or 200% by switch
About V±20%, by low frequency transformer, rectifier/smoothing circuit, etc.

Although the required DC voltage is obtained, the DC output voltage fluctuates because it does not have a stabilizing function. Similarly, in the case of DC input, the DC output voltage fluctuates in response to DC input fluctuations. Therefore, the circuit design inside the device should be adjusted to compensate for the variation.
must be designed with sufficient thermal margin in mind, especially for the power part.
It had the disadvantage of requiring a large heat sink or the like.

In addition, active elements, passive elements, etc. used in the circuit must be able to withstand the maximum value of the DC output voltage, which tends to increase the size of the circuit. However, the size of the equipment itself is becoming smaller and lighter in order to conserve resources and energy, and in order to eliminate the drawbacks mentioned above, stabilized direct current The emergence of a small, lightweight, stabilized power supply device that provides an output voltage has been awaited.

The present invention provides for a wide range of AC or DC inputs.
The present invention provides a switching regulator that can obtain a stabilized DC voltage.

Generally, the flyback method is suitable as a switching regulator that can control a wide range of inputs. Its basic configuration is shown in Figure 1.

In the same figure, 1a and 1b are DC 1oV-saoV2a
, 2b is an output terminal to which a stabilized DC output voltage is applied, 3 is a converter transformer, 4 is a switching transistor whose collector-emitter path is connected in series with the primary winding 3a of the converter transformer 30, 6 numeral 6 is a driving circuit for applying a driving pulse to the base of the transistor 4, and 6 is a rectifying and smoothing circuit for rectifying and smoothing the AC output voltage obtained from the secondary winding 3b of the converter transformer 3. Now, in FIG. 1, the maximum value of the impulse ratio of transistor 4 is 0.8. The converter transformer 30 has a winding ratio of n, a DC input voltage applied between input terminals 1a and 1b of 1ov, and an output terminal 2a.

When the DC output voltage obtained between input terminals 1a and 1b is 15V, 0.8 10 15-□ ・□ 1-0.8 n Therefore, n-2,67 At this time, the DC input voltage between input terminals 1a and 1b is 38
If the impact ratio at 0v is Knli, then K
m, n=0.11 Therefore, if the impulse ratio of the transistor 4 is changed from 0.11 to 0.8 for an input voltage of 1 ov to 380 volts, the DC output voltage can be theoretically stabilized. Also, the primary inductance of the converter transformer 3 is calculated as I, and the collector peak current of the J-transistor 4 is calculated as I. p, the switching period is T, and the output power on the secondary side is Po, then 2, L I ap 7r = p0−・−・−・−・<1
). From the above two equations, if L is eliminated, Io
There is a relationship between p. From this, V, = 10V, aaov.

Substituting Km0.8 and 0.11 respectively, Iap
(atloV)=0°26PO Iap(at380V)=o-o6P.

Therefore, at the minimum value and maximum value of the input voltage, transistor 4
The collector peak current of changes by a factor of 6.

Therefore, the base current of the transistor 4 must be provided with an amount sufficient to saturate the transistor 4 at the minimum input voltage of 10V. Therefore, when the input voltage is at its maximum value of 380V, the collector current of transistor 4 decreases to %.
This has the drawback of creating an excessive base current state, increasing the storage time, and as a result, narrowing the dynamic range.

In addition, the vcEo of transistor 4 needs to be more than twice the maximum value of the input voltage, and in such a high voltage transistor, the DC amplification factor is also large and the change with respect to the collector current is large, so the minimum value of the input voltage is , the required base current varies greatly depending on the maximum value.

From the above results, it is theoretically possible to use the conventional flyback switching regulator shown in Figure 1 to stabilize the DC output over a wide range of input voltages, but In practice, this is difficult to realize due to the large amount of accumulated charge and the large change in DC amplification factor.

In view of such points, the present invention provides a tap in the primary winding of the converter transformer, or a tap in the primary winding of the converter transformer, or two separate windings.
The output DC voltage is stabilized by providing a secondary winding, in effect using two primary windings, one in contact with low input and the other operating in response to high input. It is something that we are trying to change. The present invention will be explained below based on the embodiments shown in FIGS. 2 and 3. First, in Figure 2,
1a and 1b are input terminals, 2a and 2b are output terminals, and 6.6 is a driving circuit and a rectifying and smoothing circuit similar to those explained in FIG. 1, respectively. 7 is a converter transformer, the primary wire of which has a tap T, so that the primary windings are essentially two primary windings 7a and 7b. Here, the primary winding (tap T) is the primary winding 7b
At the beginning of winding, the first transistor 4 for switching
It is connected to the collector of a. On the other hand, the end of the primary winding 7b is connected to the collector of the second switching transistor 4b, and the emitters of each of the first and second transistors 4a and 4b are connected to the input terminal 1b. In addition, each base is connected to a changeover switch circuit 8 consisting of a semiconductor switch or relay. A switching drive signal from the drive circuit 6 is applied to the bases of the transistors 4a and 4b via the changeover switch circuit 8. Reference numeral 9 denotes a low input detection circuit that detects when a low input is applied between the input terminals 1a and Ib and causes the changeover switch circuit 8 to perform a switching operation. Next, the operation of this embodiment will be explained.

The changeover switch circuit 8 connects the base of the normal transistor 4b to the output side of the drive circuit 6, and performs a stabilizing function when a high input is applied to the input terminals 1a and 1b. There is. On the other hand, input terminals 1a and 1b
When the voltage applied between them becomes a low input, the low input detection circuit 9 operates, and the drive circuit 6 is connected to the base of the transistor 4a.
The changeover switch circuit 8 performs a switching operation so as to provide a drive signal from. At this time, the transistor 4b requires a high withstand voltage, but a low withstand voltage can be used for the transistor 4a, and such a transistor generally has a large DC amplification factor and can operate with a relatively small base current. becomes. Therefore, as explained in the conventional example of FIG.

Even if the peak current of the transistor changes six times over a wide input range, it is possible to sufficiently operate the transistor 4a with the base current necessary to drive the high voltage transistor 4b. Further, the embodiment shown in FIG. 2 is characterized by a low input detection circuit 9 and a changeover switch circuit 8, which allow the input terminal 1a to be connected to the input terminal 1a.

Even if the input applied between 1b and 4a changes over a wide range, transistor 4a will automatically change depending on the low or high input.
and 4b are switched, so there is no trouble in switching at all.

FIG. 3 shows another embodiment of the invention, which is 7a in FIG.
It uses a converter transformer 7' that has two separate primary windings 7a' and 7b' corresponding to Suitable for equipment that uses high input power supplies and low input power supplies. In addition, in FIG. 3, 1a and 1b are input terminals for low input,
1a' and 1b are input terminals for high input, and since the operation of the circuit and the effects obtained are essentially the same as those of the embodiment shown in FIG. 2 described above, a description thereof will be omitted here.

As described above, the switching regulator of the present invention has
By using a converter transformer with essentially two primary windings and switching the primary winding to be driven depending on low and high input conditions, it is sufficiently stable over a wide input range. It has the excellent feature of being able to obtain high DC output.

[Brief explanation of the drawing]

FIG. 1 is a circuit configuration diagram of a conventional switching regulator, and FIGS. 2 and 3 are circuit configuration diagrams of an embodiment of the present invention, respectively. 1a, 1a', 1b---Input terminal, 2a, 2b
...... Output terminal, 4a, 4b... Switching transistor, 6... Drive circuit, 6... Rectification and smoothing circuit, 7, 7'... ...Converter transformer, 7a, 7a', 7b, 7b'--
-..., primary winding, 7a-... secondary winding, 8.
...changeover switch circuit, 9...low input detection circuit. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 2

Claims (1)

[Claims] A converter transformer having substantially two low-input primary windings, a high-input primary winding, and a secondary winding, and a collector-emitter path between the input terminals of the low-input one.
The first winding is connected in series with the secondary winding and the high input primary winding.
and a second switching transistor;
and a drive circuit that outputs a drive signal for switching a second switching transistor, and selects the drive signal to either the base of the first switching transistor or the base of the second switching transistor. a changeover switch circuit that provides
The circuit includes a circuit that rectifies and smoothes the AC output obtained from the secondary winding of the converter transformer, and operates one of the first and second switching transistors depending on the input applied to the input terminal. 1. A switching regulator configured to switch and operate said changeover switch circuit as the changeover occurs.