Electricity: power supply or regulation systems – Input level responsive
Reexamination Certificate
1999-02-17
2001-08-28
Han, Jessica (Department: 2838)
Electricity: power supply or regulation systems
Input level responsive
C363S041000
Reexamination Certificate
active
06281668
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a switching regulator(hereinafter referred to as a “SW regulator”) control circuit and an SW regulator of the PFM (pulse frequency modulation) type which can supply a large current to a load even with a low-input power supply voltage in accordance with a value of an input supply voltage of a SW regulator, and which is small in ripple voltage even with a high input power supply voltage.
As a conventional PFM SW regulator control circuit, there has been known an SW regulator control circuit shown in a circuit diagram of FIG.
5
. That is, there is provided a comparator
13
that compares a reference voltage value Vref of a first reference voltage circuit
10
with a voltage at a node of bleeder resistors
11
and
12
that divide an output voltage Vout of an output terminal
5
of the SW regulator. Assuming that the output voltage of the reference voltage circuit
10
is Vref, and the voltage of the node of the bleeder resistors
11
and
12
is va, if Vref>Va, an output Vcomp of the comparator
13
becomes high in level, but conversely, if Vref<Va, the output Vcomp becomes low in level. The output Vcomp of the comparator
13
is supplied to one input terminal of an AND gate
17
, and an output Vosc of a second the comparator
16
is supplied to the other input terminal of the AND gate
17
. The output Vosc of the second comparator
16
compares triangular wave Vos outputted from an oscillator circuit
14
with a reference voltage value Vref
2
of a second reference voltage circuit
15
to produce a rectangular wave having a given duty ratio (hereinafter referred to as “duty ratio”). The ratio of turning on a switch element used in the SW regulator to the oscillating period is a PFM-DUTY ratio. In other words, when the output voltage is lower than a normal voltage, an output Vcomp of the first comparator
13
becomes high in level, and the second output Vosc of the comparator
16
is made equal to the output Vand of the AND gate
17
with the result that the switch element used in the SW regulator is turned on/off by the output Vosc. Conversely, when the output voltage is higher than the normal voltage, the output of the first comparator
13
becomes low in level, and the output Vand of the AND gate
17
becomes low in level with the result that the switch element used in the SW regulator is kept in an off state.
FIG. 6
shows the voltage waveforms of the respective portions of the SW regulator shown in
FIG. 5
with the axis of abscissa representing time.
In general, in the SW regulator, as a period of time during which the SW is on is long, a capacity for supplying an electric power to the load becomes higher. Accordingly, in case of the SW regulator of the PFM system, even if the load is heavy to some degree, the PFM-DUTY ratio is set at a certain value of about 50 to 90% so that an energy can be supplied sufficiently. The PFM-DUTY ratio is always held to a constant value regardless of the supply voltage.
However, the conventional SW regulator of the PFM type suffers from the following problems. That is, because the PFM-DUTY ratio is held constant regardless of the supply voltage, if the PFM-DUTY ratio is set to be small, when the supply voltage is low, the energy in a coil used in a PFM to switching power supply is small so that a large load current cannot be supplied. Also, if the PFM-DUTY ratio is set to be large, when the supply voltage is high, because energy in a the coil of the switching power supply is large, a large ripple voltage occurs in the output voltage.
In view of the above, in order to solve the conventional problems, an object of the present invention is to impart a supply voltage dependency to the PFM-DUTY ratio of the SW regulator of the PFM type so as to set the PFM-DUTY ratio to be large when the supply voltage is low, and to set the PFM-DUTY ratio to be small when the supply voltage is high, so that an energy can be sufficiently supplied to a load even at a low supply voltage, and a ripple voltage is suppressed when the supply voltage is high.
SUMMARY OF THE INVENTION
In order to solve the above problems, according to the present invention, there is provided an SW regulator control circuit of the PFM system in which a supply voltage dependency is imparted to the PFM-DUTY ratio, thereby being capable of suppressing a ripple voltage when the supply voltage is high.
REFERENCES:
patent: 4437769 (1984-03-01), Shida et al.
patent: 5260645 (1993-11-01), Williams et al.
patent: 5319174 (1994-06-01), Omori et al.
Adams & Wilks
Han Jessica
Seiko Instruments Inc.
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