Electric power conversion systems – Current conversion – Including automatic or integral protection means
Reexamination Certificate
2001-10-15
2003-04-01
Vu, Bao Q. (Department: 2838)
Electric power conversion systems
Current conversion
Including automatic or integral protection means
C363S019000, C363S056090, C363S056110
Reexamination Certificate
active
06542388
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an intermittent switching power supply circuit which stabilizes output from a secondary output winding by controlling periodic oscillation intervals of a primary winding. More specifically, the present invention relates to an intermittent switching power supply circuit that avoids output excessive power from its secondary output winding during element malfunction.
2. Description of the Related Art
It is known that some types of intermittent switching power supply circuits are used as stabilized power supplies in AC adapters and battery chargers.
Referring now to
FIG. 4
, an example of a prior art intermittent switching power supply circuit
100
includes an input side and an output side. Simply stated, intermittent power supply circuit
100
enables oscillation of an oscillator when output voltage and/or current drop below thresholds, and inhibits oscillation when output voltage and/or current increases beyond slightly higher thresholds. During oscillation, power is stored in reactive (capacitive/inductive) components. The stored power is then fed as DC power to using circuits including times when oscillation is stopped.
On the input side, a direct current power supply
1
, illustrated as a battery, is an unstable power supply whose output voltage varies depending on load. Direct current power supply
1
includes a high-voltage terminal
1
a
and a low-voltage terminal
1
b.
A transformer
2
includes a primary winding
2
a
and a secondary output winding
2
b
. One end of primary winding
2
a
is connected to high-voltage terminal
1
a
. An intermittent oscillator
3
is connected between the second terminal of primary winding
2
a
and low-voltage terminal
1
b.
Intermittent oscillator
3
includes the conventional elements of an oscillator, a control element, and a switching element (all not shown). The switching element alternately turns on and turns off current to primary winding
2
a
of transformer
2
. Intermittent oscillator
3
oscillates at a fixed frequency. Intermittent oscillator
3
stops oscillation when a stop control signal, in the form of a fixed current, is received at a control terminal
3
a.
A photocoupler receiver element
39
is photocoupled to a photocoupler emitter element
35
disposed on the output side. Photocoupler receiver element
39
is connected between control terminal
3
a
of intermittent oscillator
3
and low-voltage terminal
1
b
of direct current power supply
1
. When photocoupler receiver element
39
is energized by an optical signal from photocoupler emitter element
35
, it applies the, required fixed current to control terminal
3
a
to turn off oscillation. In the absence of energization of photocoupler receiver element
39
, intermittent oscillator
3
is enabled to oscillate.
A rectifier diode
4
and a smoothing capacitor
13
form a rectifying/smoothing circuit. The rectifying/smoothing circuit rectifies and smooths the AC signal from output winding
2
b
. Energy stored in the reactive elements are fed to the remainder of the circuit during periods of non-oscillation of intermittent oscillator
3
. The smoothed result is connected to a high-voltage output line
20
a
and a low-voltage output line
20
b
. A Zener diode
14
provides an output voltage clamp to limit the voltage across smoothing capacitor
13
to the breakdown voltage of Zener diode
14
.
An output monitoring circuit is disposed between output lines
20
a
,
20
b
. The output monitoring circuit includes a voltage monitoring circuit and a current monitoring circuit, described later. The output monitoring circuit energizes photocoupler emitter element
35
when the output voltage or the output current exceeds a predetermined reference voltage or current. Energization of photocoupler emitter element
35
turns of oscillation of intermittent oscillator
3
, as described above.
The voltage monitoring circuit includes a pair of voltage divider resistors
30
,
31
connected in series between high-voltage output line
20
a
and low-voltage output line
20
b
. An intermediate tap
32
obtains divided output voltage. The divided output voltage is connected to an inverse input terminal of an error amplifier
33
a.
A DC voltage monitoring reference power supply
34
a
, illustrated as a battery, is connected between an uninverted input terminal of error amplifier
33
a
and low-voltage output line
20
b.
Error amplifier
33
a
is a threshold circuit which compares the first comparison voltage input to the uninverted input terminal with the divided output voltage input to the inverted input terminal. The output of error amplifier
33
a
switches between its high and low values when the value of the voltage fed to its inverted input becomes more or less than the divided value fed to its uninverted input. The point at which the switch takes place is set by adjustment of the resistance values of voltage divider resistors
30
,
31
or by adjustment of the first comparison voltage of monitoring reference power supply
34
a.
The output of error amplifier
33
a
is connected to an anode of photocoupler emitter element
35
. Photocoupler emitter element
35
is connected through a resistor
36
to high-voltage output line
20
a
to provide it with a power supply. A resistor
37
a
and a capacitor
38
a
, connected in series, serve as an AC negative feedback element to provide stable operation of error amplifier
33
a.
The output of error amplifier
33
a
switches between a voltage near the voltage of low-voltage output line
20
b
and a voltage near the voltage of high-voltage output line
20
a
. When the output of error amplifier
33
a
is high (near the voltage of high-voltage output line
20
a
), insufficient voltage exists across photocoupler emitter element
35
for energization thereof. In this condition, oscillation of intermittent oscillator
3
is enabled. When the output of error amplifier
33
a
is low (near the voltage of low-voltage output line
20
b
), substantially the entire voltage difference between high-voltage line
20
a
and low-voltage output line
20
b
(minus voltage drops in resistor
36
, and other elements) is available to energize photocoupler emitter
35
. As a result, oscillation of intermittent oscillator
3
is inhibited.
The current monitoring circuit operates in a manner similar to the voltage monitoring circuit described above. A current detection resistor
43
is connected in series with low-voltage output line
20
b
. One end of current detection resistor is
43
connected to an inverted input terminal of an error amplifier
33
b
. The second end of current detection resistor
42
is connected to the uninverted input terminal through a current monitoring reference power supply
34
b
(illustrated as a battery).
The potential difference between the terminals of current detection resistor
43
is proportional to the output current flowing through low-voltage output line
20
b
. Error amplifier
33
b
compares voltage across current detection resistor
43
with a second comparison voltage from current monitoring reference power supply
34
b
to determine whether a predetermined reference current has been exceeded. The value of the reference current may be set by either adjusting the resistance of current detection resistor
43
or by adjusting the second comparison voltage of current monitoring reference power supply
34
b.
The output of error amplifier
33
b
is connected to a connection point between the output of error amplifier
33
a
(monitoring the output voltage), and photocoupler emitter element
35
. In a manner identical to voltage error amplifier circuit
33
a
, current error amplifier circuit
33
b
energizes and de-energize photocoupler emitter element
35
in response to the current in the low-voltage output line
20
b
being greater or less than, respectively, the selected threshold voltage.
Serially connected resistor
37
a
and capacitor
38
a
, along with a resistor
37
b
and a capacitor
38
b
, serve as AC negative feedback elements
Darby & Darby
SMK Corporation
Vu Bao Q.
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