JPS63305754A - Switching regulator circuit - Google Patents

Abstract

PURPOSE:To prevent the deterioration of overall efficiency, by a method wherein pulse width control is effected by a detecting output voltage and a switching frequency is reduced in accordance with a pulse width upon a high input voltage or a light load. CONSTITUTION:A push-pull switching regulator is constituted of a switching unit A, consisting of switching transistors Q1, Q2 and a transformer T, a rectifying and smoothing unit B, consisting of rectifying diodes D1, D2 and the like, and a pulse width control unit C. The control unit C is constituted of a serrated wave generator 1, a voltage control oscillator 2, an error amplifier 3, a comparator 4 and a driver 5. The oscillating frequency of the oscillator 2 is controlled by an input voltage or a load current so that switching frequency is elongated when an input voltage is increased or a load is reduced. According to this method, the title circuit is capable of coping with an input voltage having a large fluctuation range and the size as well as the weight of the circuit may be reduced.

Description

Detailed Description of the Invention (Technical Field to which the Invention Pertains) The present invention relates to a switching regulator circuit that stabilizes the output voltage by controlling the pulse width of the switching section according to fluctuations in the output voltage, especially in light load conditions. This invention relates to a switching regulator circuit that is suitable for applications where the input voltage has a wide variation range.

(Prior Art) As shown in the system diagram in FIG. 2(a), the conventional switching regulator circuit adjusts the switching section A via the pulse width control section C in accordance with the output voltage, and then converts the rectifying and smoothing circuit into a rectifying and smoothing circuit. The output voltage of B is stabilized. Therefore, when the input voltage is high and the load current is small, the switching pulse width becomes narrow, and the switching loss that accounts for the total loss of the circuit increases relatively, resulting in a decrease in overall efficiency.

Next, to explain using the switching waveform diagram in FIG. 2(b), the loss in the circuit in FIG. 2(a) is determined by the switching period T.
It is the sum of the losses for each interval a, b, c, d of a,
Section C is the switching section, section b is the ON section, and d is O.
This is the FF section. When the input voltage is high (and the load current is small, section d is long (and section b is short). Also, the loss in section d is extremely small compared to the loss in sections a, b, and c. When becomes shorter, the interval A becomes shorter than the interval A.

C becomes relatively long, and a accounts for the total loss in the entire section.
, the percentage of loss in section c increases, and the overall efficiency decreases. This is particularly undesirable when the load is often light and the input voltage has a wide fluctuation range.

(Specific Object of the Invention) The present invention prevents the drawbacks of conventional switching regulators that stabilize the output voltage only by controlling the switching pulse width, that is, the decrease in overall efficiency at high input voltages and light loads. The purpose is to
The output voltage is stabilized by controlling the pulse width based on the detected output voltage, and the switching frequency is lowered in response to high input voltage or light load to prevent a decrease in overall efficiency. The present invention will now be described in detail with reference to Examples.

(Structure and operation of the invention) FIG. 1(a) is a system diagram of a circuit according to an embodiment of the present invention in a push-pull switching regulator, in which Ql and Q are transistors that perform switching;
T is a transformer for transmitting switched power and at the same time performing necessary voltage transformation, and these form a switching section A. Further, D and D2 are rectifying diodes, and Ll and C6 are smoothing choke coils and capacitors, which form the rectifying and smoothing part B.
is the sawtooth wave generator required to perform pulse width control,
2 is a voltage-controlled oscillator whose oscillation frequency is controlled in response to the input voltage and load current that supply other high-frequency power for determining the switching frequency or cycle of the sawtooth wave generator 1; 3 is a reference; An error amplifier amplifies the difference voltage between the voltage ■□ and the output voltage; 4 is a comparator that takes out the difference between the output of the error amplifier 3 and the output of the sawtooth wave generator l; 5 is a transistor that converts the output of the comparator 4 This is a driver for converting signals suitable for driving Q, ,Q, and these 1゜2, 3
．． The pulse width control section C is formed in step 4.5.

FIG. 1(B) shows an example of a voltage waveform at each part in FIG. 1, and the horizontal axis represents time. a is the input voltage, 11 indicates the point at which the voltage becomes high, b is the output waveform of the voltage controlled oscillator 2, 12.13 indicates the period when the input voltage is low and high, respectively, C is the sawtooth shape Output waveform of wave generator l, d
is the input waveform of the comparator 4, the broken line is the output waveform of the sawtooth wave generator, and the solid line is the output waveform of the error amplifier 3, e
is the output waveform of the comparator 4, f is the collector waveform of Q, g is the rectified output waveform, and h is the output voltage waveform.

As is clear from the above explanation, the circuit of the present invention is not much different from the conventional switching regulator in its configuration.
The oscillator of the sawtooth wave generator is conventionally a fixed frequency oscillator, but the present invention is different in that it is a controlled oscillator whose oscillation frequency is controlled and varied by the input voltage and load current. . In addition, there is no difference in the original function of controlling the switching pulse width according to the output voltage to keep the output voltage constant, but as the input voltage increases or the load decreases, the switching period changes. The important difference is that it is longer. These differences bring about the following remarkable effects.

(Effect) In other words, the overall efficiency of a switching regulator is related to the overall loss of the circuit, and this is the sum of the loss in the switching transistor and the loss related to the load current, but the latter is related only to the load current and is dependent on the input voltage. is unrelated, but the former is proportional to the input voltage and switching frequency, as is well known. Therefore, in order to improve the overall efficiency, the only way to improve the overall efficiency is to reduce the loss in this switching transistor.Especially in burst communication radio equipment or breathtalk radio equipment, which has a particularly short transmission time, it is necessary to reduce the loss in this switching transistor. For relatively small-capacity switching regulators that have a short period of time, are often under light load conditions, and have a wide range of input voltage fluctuations, overall Preventing the increase in loss is an important matter, and it is unnecessary to explain that this invention can be achieved extremely easily by reducing the switching frequency, and the present invention exhibits excellent effects in practical use. It is.

[Brief explanation of the drawing]

FIGS. 1(a) and 1(b) are system diagrams of a circuit according to an embodiment of the present invention,
FIG. 2(a) Φ) shows a system diagram and a switching waveform diagram of a conventional switching regulator. Q,,Q,...switching transistor, T...
Transformer, DI, Dz... rectifier diode,
L, C... Smoothing choke coil and capacitor, 1.
... sawtooth wave generator, 2 ... voltage controlled oscillator, 3.
...Error amplifier that amplifies the difference voltage between the reference voltage and the output voltage, 4...Comparator, 5...Driver, A...
Switching section, B... Rectification and smoothing section, C... Pulse width control section. ! ! 11 Figure (a)

Claims (1)

[Claims] a switching section using a switching transistor;
In a switching regulator circuit that is composed of a rectifying and smoothing section and a pulse width control section of the switching section, and stabilizing the output voltage by controlling the pulse width, an oscillator for a sawtooth wave generator is a component of the pulse width control section. A switching regulator circuit characterized in that the oscillation frequency is controlled according to input voltage and load current.