Electric power conversion systems – Current conversion – Including d.c.-a.c.-d.c. converter
Reexamination Certificate
2001-09-06
2003-10-28
Sterrett, Jeffrey (Department: 2838)
Electric power conversion systems
Current conversion
Including d.c.-a.c.-d.c. converter
C363S021090, C363S021110, C363S097000
Reexamination Certificate
active
06639812
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a power supply control circuit, power supply and power supply control method for converting an existing power supply at a first voltage and power rating to a secondary voltage and power rating.
2. Description of the Related Art
In a portable electronic device, such as a notebook size personal computer, an AC adapter or automobile battery adapter, etc. can be used for an external power supply. The automobile battery adapter is called a power supply. The power supply provides an output power by adjusting the power from the car battery to the power required for the portable electronic device.
The capacity of the power supply and the AC adapter generally determine the maximum output voltage and the maximum output current. This maximum output voltage and the maximum output current are defined as the rated output. The power supply always operates to compensate to the rated output even if the input power varies. Therefore, when an input voltage is high, an input current is small. On the other hand, when an input voltage is low, an input current becomes large.
FIG. 1
is a schematic diagram of a power supply circuit of the related art. The circuit includes a noise eliminating filter section
10
, a voltage converting section
20
for converting an input power to an output power, a rectifying section
30
for rectifying an output of the secondary side, an output detecting section
40
for monitoring an output of the secondary side and a coupler
50
for transmitting the condition of an output detecting circuit in the secondary side to the voltage converting circuit in the primary side.
The filter section
10
is formed of a coil L
1
and a capacitor C
1
. The filter section
10
is a circuit for preventing propagation of noise generated in the voltage converting section
20
to the input side.
The voltage converting section
20
includes a transformer T
1
for voltage conversion, a transistor Tr
1
for shutting off a current flowing through the transformer T
1
and a control circuit
60
for controlling the transistor Tr
1
.
The rectifying section
30
includes a rectifying diode D
1
for rectifying a current outputted from the voltage converting section
20
and a capacitor C
2
for smoothing the rectified current.
The output detecting section
40
includes a sense resistor R
0
for detecting an output current value of the power supply and a sense circuit
70
for detecting a voltage value across both ends of the sense resistor R
0
.
The coupler
50
is a circuit for transmitting an output of the sense circuit
70
to the control circuit
60
. In the coupler
50
, a photo-coupler is used in general to electrically insulate the primary side and secondary side.
In
FIG. 1
, when the transistor Tr
1
is ON, an input current flows in the primary side coil of the transformer T
1
. When the transistor Tr
1
is OFF, an output current flows in the secondary side of the transformer T
1
. The circuit explained above is defined as an RCC type switching regulator.
In the RCC type switching regulator, when an output voltage value is Vout, input voltage value is Vin, the ON time of transistor Tr
1
is Ton and the OFF time of transistor Tr
1
is Toff, the relationship is defined by Vin×Ton=Vout×Toff. However, when the number of turns of the primary coil of the transformer T
1
is assumed to be identical to the number of turns of the secondary coil, this formula can be modified so that Vout=(Vin×Ton)/Toff. Moreover, it can be modified by the period of ON/OFF of the transistor Tr
1
replacing T, producing Vout=(Vin×Ton)/(T−Toff).
As indicated in the above formula, the input current can be adjusted by controlling the ON time of transistor Tr
1
while the output voltage is kept constant. Thus, even when the load connected to the output terminal of the power supply varies, the value of Vout can be maintained constant using the feed-back control that controls the ON time of the transistor Tr
1
by monitoring the output voltage Vout.
FIG. 2
is a schematic diagram of another power supply circuit of the related art. The circuit of
FIG. 2
is different from the RCC type switching regulator in that the voltage converting and rectifying section
80
is formed by integrating the voltage converting section
20
and rectifying section
30
of FIG.
1
. Rectifying section
80
is therefore provided in place of individually providing a voltage converting section and a rectifying section.
In
FIG. 2
, when the transistor Tr
1
is ON, an input current flows through the primary side coil of the transformer T
1
. This causes the output current to flow through the secondary side coil of the transformer T
1
. This type of circuit is defined as a FORWARD type switching regulator.
In
FIG. 2
, the transformer T
1
operates as a switch circuit. The transformer T
1
does not operate as a voltage converting circuit. Therefore, a choke coil L
2
and a flywheel diode DO are required for voltage conversion in addition to the transformer T
1
. In the circuit of
FIG. 2
, the relationship of the voltage to the time the transformer T
1
is ON is Vout=(Vin×Ton)/(Ton+Toff)=(Vin×Ton)/T.
In addition, the current flowing through L
2
also flows in the output detecting section
40
and the noise eliminating filter section
10
while the transistor Tr
1
is ON. Moreover, current flowing through L
2
is supplied via D
1
while the transistor Tr
1
is OFF. Therefore, an average input current Iin to the power supply circuit becomes equal to a product of an output current lout and the ON time of transistor Trn. Accordingly, the relationship of current to the time transistor Tr
1
is ON is Iin=(Iout×Ton)/T.
As indicated in the above formula, controlling the ON time of the transistor Tr
1
can cover variation of the input voltage. Moreover, even when the capacity of the load connected to the output of the power supply is varied, Vout can be maintained constant by having the feedback control vary the ON time of the transistor Tr
1
in accordance with the output voltage Vout.
FIG. 3
is a schematic diagram illustrating details of the sense circuit
70
and control circuit
60
that monitor the output power in the circuit illustrated in
FIG. 1
or FIG.
2
. The sense circuit
70
includes a voltage amplifier AMP
11
, a couple of error amplifiers ERA
11
, ERA
12
and reference voltage sources e11, e12. The control circuit
60
includes a triangular wave oscillator
66
, a PWM comparator
62
and a drive circuit
68
.
The reference voltage source e11 is the reference voltage used to determine the output current value. The reference voltage source e12 is the reference voltage used to determine the output voltage value.
The voltage amplifier AMP
11
measures a voltage drop generated by a current flowing through the sense resistor R
0
. The voltage amplifier AMP
11
outputs a voltage that is proportional to a current value flowing through the sense resistor R
0
. The error amplifier ERA
11
compares an output voltage value with the reference voltage value e11. The error amplifier ERA
11
outputs a low level when a large current flows through the sense resistor R
0
or a high level when a small current flows through the sense resistor R
0
.
Similarly, the error amplifier ERA
12
compares an output voltage value of the power supply with the reference voltage value e12. The error amplifier ERA
12
outputs a low level when the power supply outputs a high output voltage value or a high level when the power supply outputs a low output voltage value.
The PWM comparator
62
is a voltage comparator including one inverting input and a plurality of non-inverting inputs. Namely, the PWM comparator
62
illustrated in
FIG. 3
is a voltage pulse width converter for controlling the ON time of an output pulse depending on an input voltage value. The PWM comparator
62
compares the minimum voltage value among a plurality of non-inverting inputs shown by a +, with the voltage valu
Matsuda Kouichi
Nakazawa Shigeaki
Ozawa Hidekiyo
Saeki Mitsuo
Tanaka Shigeo
Fujitsu Limited
Staas & Halsey , LLP
Sterrett Jeffrey
LandOfFree
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