Off-line converter with digital control

Details Off-line converter with digital control Off-line converter with digital control

2002-03-06

2003-08-19

Han, Jessica (Department: 2838)

Electricity: power supply or regulation systems

Output level responsive

Using a three or more terminal semiconductive device as the...

C323S285000, C363S131000

Reexamination Certificate

active

06608471

ABSTRACT:

BACKGROUND
1. Field of the Invention
The present inventions pertain to the field of power supplies, and among other things to the regulation of power supplies.
2. Background
Accurate regulation of power supplies is important in many areas. For instance in sensitive electronic devices such as computers and televisions maintaining a constant power supply is important for the operation of the computer or television. Additionally, the advantages of accurate power supply regulation include reduced overall power consumption and reduced damage to equipment by preventing voltage spikes during start up and operation.
Power supplies are regulated by keeping either a current or voltage delivered to a load within a specified range. A power supply is deemed to be in regulation if the load current or voltage is within the specified range and is deemed to be out of regulation if the load current or voltage is outside the specified range.
Problems associated with out of regulation conditions include damage to the load, improper load functioning, and the consumption of power when no power is necessary to operate the load. Therefore, power supplies that regulate output power provided to the load are desired.
A known regulated power supply is depicted in FIG.
1
. The regulated power supply of
FIG. 1
includes an EMI filter
10
that receives an AC mains voltage. The output of the EMI filter
10
is coupled to rectifier
15
that rectifies the AC mains voltage and then provides the rectified voltage to capacitor
20
. Capacitor
20
provides a substantially DC voltage to a primary winding
25
of transformer
30
.
A monolithic power supply control chip
40
includes a MOSFET
45
tat is controlled by pulse width modulator
50
. When MOSFET
45
is conducting, primary winding
25
has current flowing through it allowing transformer
30
to store energy. When MOSFET
45
is not conducting, the energy stored in the transformer
30
induces a voltage across the secondary winding
55
which is transferred to a load
60
connected at output terminals
65
. A capacitor
70
is coupled to secondary winding
55
in order to maintain the voltage that is being supplied to the load
60
when MOSFET
45
is on.
A feedback circuit
75
is coupled to the load
60
. The feedback circuit
75
includes a resistor
80
, zener diode
85
and an optocoupler
90
. A bias winding
95
is magnetically coupled to primary winding
25
and is used to supply power to the output of the optocoupler
90
. When the voltage at load
60
is above combination of the reverse bias voltage of zener diode
85
and the forward voltage drop of light emitting diode
100
, a current is generated in the phototransistor
105
by light emitting diode
100
. The phototransistor
105
current flows from the bias winding
95
to the control terminal
110
of monolithic power supply control chip
40
. The current provided to the control terminal
110
of monolithic power supply control chip
40
controls the duty cycle of MOSFET
45
. When the control terminal
110
current increases the duty cycle of MOSFET
45
decreases and the amount of current through primary winding
25
decreases. Therefore, the power provided to the load
60
decreases. As the power supplied to the load
60
decreases, the load voltage decreases which in turn reduces the optocoupler
90
current increasing the duty cycle of MOSFET
45
. Thus, the output voltage is regulated at a voltage equal to zener
85
reverse breakdown voltage plus the forward drop of LED
100
in an analog closed loop. Resistor
80
controls the gain of the analog loop.
It should be noted that pulse width modulator
50
is switching at some duty cycle to provide power to the feedback circuit
75
even when there is no load connected to the output terminals
65
. This will cause power consumption from switching losses occurring at the operating frequency of the MOSFET
45
.
The regulated power supply of
FIG. 1
is able to maintain the voltage at the load at a reasonably constant level, while reducing voltage transients due to load and line variations. However, the addition of a feedback winding and pulse width modulation controller makes application of the regulated power supply of
FIG. 1
expensive for many power suppliers operating at low powers, especially those below five (5) watts. Additionally, the use of analog pulse width modulation feedback control requires compensation circuitry to stabilize the circuit and to prevent oscillations. The compensation circuit limits the bandwidth of the control loop to one (1) or two (2) kilohertz. The Pulse Width Modulated feedback circuit while effective at regulating the voltage still has time periods when the voltage is above and below the desired level, because of the limited bandwidth of the feedback loop which is in the range of one (1) or two (2) kilohertz even though the switching frequency of the MOSFET
45
may be as high as one hundred (100) kilohertz.
It is therefore desired to create a power supply that is cost effective for low power solutions.
It is further desired to create a power supply that utilizes the minimum amount of components possible.
It is additionally desired to create a power supply that can respond quickly to load transients without losing output regulation.
SUMMARY OF THE INVENTION
A presently preferred DC to DC converter comprises an energy storage element that receives a first power level and that provides a second power level, a feedback circuit coupled to the energy storage element, and a regulator circuit coupled to the feedback circuit and to the energy storage element. When a feedback signal is above a threshold the regulator circuit is disabled and when the feedback signal is below said threshold level the regulator circuit is enabled.
In another embodiment a power supply comprises a transforming element that transfers energy and is coupled to receive a first power level and a regulator circuit coupled to the transforming element. The regulator circuit controlling input of the first power level to the transforming element. When an output voltage or current of the transforming element is above a threshold level the regulator circuit is disabled and when output voltage or current of the transforming element is below a threshold level the regulator circuit operates.
In yet another embodiment a regulator circuit comprises a feedback input, a switch operating when a control signal is received at its control terminal, an oscillator that provides a duty cycle signal comprising a high state and a low state. The control signal is provided when no feedback signal is provided and the duty cycle signal is in said high state.
In a further embodiment a power supply comprises an energy storage element coupled to receive a first power level and a regulation circuit coupled between the energy storage element and a source of the first power level. The regulation circuit prevents the energy storage element from receiving the first power level when a current or voltage at the input of the energy storage element is at or above a predetermined threshold level.
In an additional embodiment a power supply comprises a transforming element coupled to receive a first power level and a regulation circuit coupled between the transforming element and a source of the first power level. The regulation circuit prevents the transforming element from receiving the first power level when a current or voltage at the input of the transforming element is at or above a predetermined threshold level.
It is an object of an aspect of the present inventions to create a power supply that is accurately regulated with a minimum amount of time spent out of regulation.
It is another object of an aspect of the present inventions to create a power supply that is cost effective for low power solutions.
It is a further object of the present inventions to create a power supply that utilizes the minimum amount of components possible.
It is also an object of the present inventions to create a power supply that is low cost.
This and other objects and aspects of the presen

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