Electricity: power supply or regulation systems – In shunt with source or load – Using choke and switch across source
Reexamination Certificate
2000-08-18
2001-07-10
Nguyen, Matthew (Department: 2838)
Electricity: power supply or regulation systems
In shunt with source or load
Using choke and switch across source
C363S124000
Reexamination Certificate
active
06259236
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a chopper type switching power supply for boosting input voltage and, more particularly, to a chopper type switching power supply in which an oscillation circuit for controlling the on/off operation of a switching element is formed by an oscillation circuit which performs the oscillating operation by using a pair of inductors coupled to each other.
As one of the chopper type switching power supplies capable of obtaining boosted DC output by using a simple circuit arrangement, there is a self-excited chopper type switching power supply in which a switching element forms a part of an oscillation circuit, as shown in the block 2 of
FIG. 2
of JP-A-62-48259. However, when obtaining the DC output exceeding 10 W, for example, by using the self-excited chopper type switching power supply, such a problem is apt to occur that the oscillating operation stops when the load changes. In contrast, when the constants of elements are set so that the oscillating operation stops scarcely, the conversion efficiency is likely reduced. Thus, when obtaining the DC output of relatively large electric power such as 10 W etc., a separately excited type arrangement is employed in which an oscillation circuit is provided separately from the switching circuit and the on/off operation of the switching element is controlled by the output of the oscillation circuit.
FIG. 4
shows the aforesaid chopper type switching power supply. That is, the chopper type switching power supply is provided with a triangular wave generation circuit
72
for generating a rectangular waveform signal and a comparator
71
having one terminal to which the rectangular waveform signal generated by the triangular wave generation circuit
72
is applied and the other terminal to which divided voltage of a DC output
73
is applied. Further, the chopper type switching power supply is arranged to perform the on/off control of a transistor
74
serving as a switching element by using the output of the comparator
71
.
However, the following problem arises when the aforesaid arrangement is employed. That is, the chopper type switching power supply changes a ratio between a time period where the transistor
74
is in an ON state and a time period where the transistor is in an OFF state thereby to control the DC output
73
to a predetermined voltage. Further, the period where the transistor
74
is turned on is same as the period of the triangular waveform signal generated by the triangular wave generation circuit
72
. Thus, the smaller the load is, the smaller the ratio of the time where the transistor
74
is in an ON state becomes. Accordingly, when the load becomes almost 0, the time period where the transistor
74
is in an ON state becomes quite short. As a result, there arises a phenomenon that the transistor
74
is turned off on the way where the transistor moves to the saturation state of ON state. Thus, there arises a problem that, when the load becomes smaller, the loss of the transistor
74
increases and hence the conversion efficiency is reduced.
SUMMARY OF THE INVENTION
Accordingly, the invention has been made in order to solve the aforesaid problem of the prior art, and an object of the invention is to provide a chopper type switching power supply which can prevent the reduction of the conversion efficiency even when the load becomes smaller in a manner that the on/off operation of a boosting switching element is controlled by using the output of an oscillation circuit for intermittent oscillation when the load becomes smaller.
In addition to the aforesaid object, another object of the invention is to provide a chopper type switching power supply which can employ an element with a low withstand voltage as a switching element for oscillation in a manner that current generated in an inductor when the switching element for oscillation is turned off is flown in a DC output through a diode thereby to suppress the increase of the voltage generated in the inductor.
In addition to the aforesaid object, still another object of the invention is to provide a chopper type switching power supply which can increase the conversion efficiency at the intermittent oscillation by applying the oscillation output to the gate of an FET through a PNP transistor.
In order to attain the aforesaid object, the chopper type switching power supply according to the invention is applied to the chopper type switching power supply in which a main switching element whose on/off operation is controlled by an output of an oscillation circuit opens and closes a connection between a ground level and other terminal of a main inductor whose one terminal is coupled to a DC power supply, and a DC output is taken out by using a rectifying and smoothing circuit coupled to the other terminal of the main inductor, the oscillation circuit is arranged to include
a first inductor coupled at its one terminal to the DC power supply;
an oscillation switching element for opening and closing a connection between the ground level and other terminal of the first inductor;
a second inductor, inductively coupled to the first inductor, for generating a feedback output for turning on the oscillation switching element when the oscillation switching element is turned on; and
a voltage stabilizing circuit for detecting an error voltage of a DC output outputted from the rectifying and smoothing circuit and, when the error voltage thus detected represents increase of a voltage of the DC output, for reducing a level of the feedback output induced to the oscillation switching element in correspondence to an amount of the increased voltage.
That is, when the load becomes small, the voltage of the DC output increases. Thus, the voltage stabilizing circuit reduces the level of the feedback output induced to the oscillation switching element and finally makes the level of the feedback output induced to the oscillation switching element zero. When such a phenomenon occurs, since the oscillation switching element can not be turned on, the oscillating operation stops. During the period where the oscillating operation stops, the voltage of the DC output decreases, and when a part of the feedback output outputted from the second inductor is induced to the oscillation switching element, the oscillating operation starts again. In this manner, the intermittent oscillating operation is performed. During the oscillation period of the intermittent oscillation, the electric power dissipated both in the oscillation period and the non-oscillation period is generated. In other words, the electric power generated during the oscillation period becomes large. Thus, the time period during which the oscillation switching element is in an ON state becomes sufficient time period. Therefore, the ratio of the transient time period during which the main switching element shifts from an ON state to an OFF state and vice versa with respect to the time period during which the main switching element is in the saturated ON state is a small value. This means that the switching loss of the main switching element scarcely increases despite that the load becomes small.
In addition to the aforesaid arrangement, the chopper type switching power supply is arranged to further include the clamping diode having the one terminal coupled to the other terminal of the first inductor and the other terminal coupled to the current path of an arbitrary DC output, wherein the clamping diode is arranged to such a direction that the clamping diode flows current therethrough when the oscillation switching element is turned off.
That is, when the oscillation switching element is turned off, the current generated at the other terminal of the first inductor flows into the DC output through the clamping diode. Thus, the voltage at the other terminal of the first inductor is suppressed to the voltage near the voltage of the DC output.
In addition to the aforesaid arrangement, the chopper type switching power supply is applied to one using the FET as the main switching element, and th
Crowell & Moring , L.L.P.
Funai Electric Co. Ltd.
Nguyen Matthew
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