Electricity: power supply or regulation systems – In shunt with source or load – Using choke and switch across source
Reexamination Certificate
2000-04-25
2001-03-06
Riley, Shawn (Department: 2838)
Electricity: power supply or regulation systems
In shunt with source or load
Using choke and switch across source
C323S901000, C323S284000
Reexamination Certificate
active
06198258
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a DC-DC converter of the chopper type, and more particularly to a DC-DC converter provided with soft starting function suitable for minimizing its size and reducing its manufacturing cost. The DC-DC converter of this type is suitable to be used for an electric power source or the like of portable devices adapted to be operated by a battery, and further it is suitable to drive an electromagnetic relay, a compact electric motor, an EL (Electro-Luminescence) or the like through a battery.
Hitherto, there are known a DC-DC converter provided with a soft starting circuit for the purpose of a restriction or the like for a rush current (JP-A-5-76167), and a DC-DC converter provided with not only a soft starting circuit but also an over current detection circuit (JP-A-7-298614). A PWM (Pulse Width Modulation) system for varying the width of a pulse for controlling a switching operation and a PFM (Pulse Frequency Modulation) system for varying the switching frequency are a precondition for those DC-DC converters.
Moreover, there is known a reference voltage generating circuit suitable to be easily structured by IC elements, which utilizes the band gap voltage power source with a precise voltage output but an insufficient output current. Such reference voltage generating circuit
5
, as shown in
FIG. 4
, is structured so that the reference voltage Vref generated by a band gap voltage power source
5
a
is amplified for current by a voltage follower
5
b
or the like in order to supply it to necessary circuits.
In contrast, since there is a boundary of minimizing the size and decreasing the manufacturing cost for the conventional DC-DC converters in which PWM and PFM are made precondition because of complexities of its circuit structure and its adjusting operation, there is presented by the same applicant as the present application, Japanese Application No. 10-322720 of the type (referred to as an oscillation stopping/restarting type hereinafter) in which the oscillation of an oscillation circuit for generating a fixed frequency is stopped suitably. According to the type, it is only sufficient to adapt an operation property of the circuit to a switching condition utilizing a predetermined frequency thereby enabling PWM and VCO unnecessary.
Namely, as shown in
FIG. 3
, for the purpose of boosting or decreasing an input voltage Vin from a DC primary electric power source
1
to a desired output voltage Vo to be supplied to a load
4
connected to a smoothing circuit
3
, the DC-DC converter
2
of the oscillation stopping/restating type is composed of an oscillation circuit
2
c for oscillating a predetermined frequency and generating a pulse signal A with a predetermined pulse width, a switching circuit
2
b
for chopping the inertia current I flowing into an inductance element section
2
a
on the basis of the input voltage Vin from the DC primary electric power source
1
, in accordance with the pulse signal A, and a feedback control circuit
2
d
for generating a feedback control signal B on the basis of the output voltage Vo obtained by smoothing the output from the switching circuit
2
b
, and feeding it to the oscillation circuit
2
c
thereby stopping/restarting the oscillation.
However, in the case where it is tried to provide a soft starting function for the DC-DC converter having the above-mentioned structure, it is difficult to adopt the conventional measure as it were and further it is not easy to provide the soft starting function therefor, because a switching control type as a premise is different form each other,
Therefore, it is a technical problem as to how the function for preventing and controlling the rush current and the over current is provided for the DC-DC converter of the oscillation stopping/restarting type.
SUMMARY OF THE INVENTION
The object of the present invention is to solve the technical problem as mentioned above, and to present a DC-DC converter having a simple structure and enabling a soft starting operation.
The DC-DC converter invented as a first solving means, which is made for the purpose of solving the conventional technical problem is composed of an oscillation circuit for oscillating a predetermined frequency and sequentially generating a pulse having a predetermined pulse width with the predetermined frequency if it is in a free running state, a switching circuit for chopping the current inputted from the Dc primary electric power source in accordance with the pulse, and feedback control means for stopping/restarting the oscillation of the oscillation circuit on the basis of the voltage that the output of the switching circuit is smoothed by a smoothing circuit which is installed within the system or the outside, wherein the operation of the oscillation circuit is controlled to stop so that the feedback control circuit compares the detected voltage with the reference voltage, and further means for slowly rising the reference voltage is provided within the reference voltage generating circuit for generating the reference voltage.
According to such DC-DC converter, the oscillation circuit for sequentially oscillating the pulse having a predetermined pulse width and with a predetermined frequency in the independent state in which no feedback signal is applied thereto, a feedback signal is applied to the oscillation circuit and the feedback signal is utilized for the switching circuit without modulating the oscillation signal and further the feedback to the oscillation circuit is performed by the voltage that the output is smoothed thereby enabling the oscillation of the oscillation circuit to be stopped and restarted, and therefore the frequency of the switching circuit becomes similar to that of PFM even if PWM and VCO are not used, thereby maintaining a suitable output.
Moreover, since the current inputted from the DC primary electric power source is chopped by the switching circuit and the switching control is performed in accordance with the pulse having a predetermined pulse width and a predetermined frequency from the oscillation circuit. Therefore, such switching operation is restored to the original state at a constant period corresponding to the pulse width in a normal condition, the switching condition is fixed substantially even if the switching system is similar to the PFM system.
As a result, the switching condition suitable to the operation property of the switching circuit or the like is established completely prior to a decision of the load condition, and therefore it becomes easy to design the system. Moreover, since PWM and VCO are unnecessary, the circuit construction becomes to be simple and the operation of the circuit becomes to be stable.
Moreover, when the output voltage is detected by the feedback control means, the detected voltage is compared with the reference voltage and further the stopping control of the oscillation circuit is performed on the basis of the result of the comparison. Therefore, since the reference voltage is adapted to be risen slowly, the feedback operation is achieved such that the output voltage is also increased slowly as the reference voltage rises slowly. Therefore, during some period from energization of the electric power source, namely during the transitional period until the reference voltage reaches a constant value, the stopping control for the oscillation circuit is performed more frequently than usual state, and therefore the chopped current is restricted from abrupt increment thereby slowly increasing to a normal state. The slow rise of the reference voltage is thus achieved, and its slow rise is achieved by a simple and local modification of the circuit such that a capacitance element or the like is added into the reference voltage generating circuit thereby restricting complexity of circuit to minimize extent.
As a result, there is presented a DC-DC converter provided with a soft starting function with maintaining the property that the PWM and VCO circuits are not necessary and it is easy to make the converter with a simple
Adachi Kengo
Ando Hiroaki
Hoshino Taichi
Morgan & Lewis & Bockius, LLP
Riley Shawn
Rohm & Co., Ltd.
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