CA2331916A1 - Dc power supply - Google Patents

Abstract

A power supply circuit uses a simplified design for converting AC to DC and powering a flyback transformer. The switch of the flyback transformer operates at a high frequency and the time of the transformer is controlled to achieve a high power factor. The flyback transformer is fed a rectified AC signal which has not been smoothed in the traditional manner using a bulk hold-up capacitor and in rush limiting resister. Any filtering to smooth the output current or voltage is carried out on the secondary side. In some cases, no smoothing of the output current or voltage is necessary. The time on of the switch is changed if necessary, slowly, relative to the pulsating input signals powering the primary winding. With a fixed Ton, or slowly varying Ton, a high input power factor can be achieved.

Description

WH-10,757-2CA
TITLE: DC POWER SUPPLY
FIELD OF THE INVENTION
The present invention relates to a power supply for DC
devices and in particular, to a power supply for converting from an AC input to a DC output while maintaining a high power factor.
BACKGROUND OF THE INVENTION
Recent advances in rechargeable batteries have greatly extended the number of products that can be powered by a relatively small battery. Furthermore, the number of electronic devices that do not use batteries but operate using DC power generated by a built in AC to DC power supply continue to grow. In many of these products it is desirable to have a charging circuit associated with the product to allow convenient recharging of the battery. As most of these devices are portable, weight and size of the power supply and charging circuits are important factors, and from a marketing point of view, the cost of the circuit is also important.
The growth in numbers of these electronic devices as well as rechargeable battery operated devices have also forced electric utilities to reconsider specifications for AC to DC power supplies as well as charging circuits as many of the early designs had relatively poor power factor correction. As the number of products increase, this has become a concern for the utilities and thus, the specification, with respect to recharging circuits is changing.
In the past switching power supply devices of a type without power factor correction have been used. These devices rectify an AC voltage and process the rectified AC
voltage using a bulk holdup capacitor to smooth it to a DC
voltage. This smoothed DC signal is then provided to a WH-10,757-2CA
flyback transformer circuit that is cc>ntrolled by a switch.
The feedback circuitprovides relatively fast response to maintain an output having low ripple.
The smoothing of the rectified AC.' signal has the advantage that the signal provided to the primary winding for powering thereof is more constant, and thus, the charging current provided by the secondary winding is more consistent. The charging current may be closely monitored and fast correction of variations in the charging current is provided by the feedback mechanism and a control arrangement associated with the switch. of the flyback transformer. Unfortunately, this design has a relatively poor power factor. In addition, the design includes a number of bulky and expensive components for smoothing of the input signal, which further increases, the cost of the charging circuit.
The present invention provides a simplified circuit, which has desirable characteristics with respect to achieving a predetermined power factor, has improved space utilization, and is cost effective.
SUMMARY OF THE INVENTION
A power circuit according to the present invention comprises means for receiving an AC input signal, means for rectifying the AC input signal to produce a non constant DC
signal and providing said non constant DC signal to an input of a flyback transformer circuit. The flyback transformer circuit comprises a primary winding in series with a switch, and a secondary winding associated with said primary winding, and having a diode. The secondary winding produces a current for powering of a DC device. A control arrangement controls the opening and closing of the switch and thereby defines a time on and time off of the switch.
The control arrangement controls the time on as required to meet a predetermined power factor specification.

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The power circuit of the invention recognizes that the rectified AC signal can advantageously be used for powering of the primary winding without any extensive smoothing of the signal. Such smoothing of the signal typically has been accomplished in prior art devices using a large, relatively expensive bulk holdup capacitor.
With the present invention, the tame on is controlled to achieve or meet a predetermined power specification.
The time on, in some applications, can. be constant or where it is desired to vary the time on to appropriately increase or decrease the output power, the time on is varied slowly and thus, high power factor correction. is possible.
The present invention recognizes that the input signal to the primary winding can vary, and the resulting instantaneous output power can vary in each cycle and that satisfactory operation of a DC device is possible. Many DC
devices are quite tolerant to variation in the output power. In many applications, the output power is only controlled to be below some maximum level. Therefore, the time on can be set to achieve a desired maximum output power for the maximum voltage provided by the input signal. By controlling the time on to achieve the acceptable characteristics for the output power, effective operation of the device can occur. The power circuit of the present invention is quite simple in design and has relatively few components. This combination is space efficient, weight efficient, and has a controllable power factor correction. This is also highly desirable for portable products.
A power circuit supply according to an aspect of the invention, has the control arrangement control the rate of change of time on to meet the predetermined power factor specification.
According to yet a further aspect of the invention, the circuit includes an input arrangement for entering a

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voltage output specification and the control arrangement varies the time on to meet the power output specification.
A power supply circuit according to the present invention has the rectified AC signal applied directly to the primary winding and this signal continuously varies from 0 volts to a maximum voltage and the output power produced by the secondary winding continuously varies as a function of the rectified AC signal.
A power supply circuit according to an aspect of the invention allows for considerable variation in the instantaneous output power and this output power can vary at least 25 per cent during each cycle. The changing output power can be smoothed if desired by processing after the secondary winding.
According to yet a further aspect: of the invention, the rectified AC signal used to power the primary windings pulses and the output power produced by the secondary winding varies as a function of the rectified AC pulsating signal.
Another aspect of the invention includes a second flyback transformer. This second transformer may share the same control circuit and switch or uses a separate switch or a separate control circuit and separate switch. The second flyback transformer includes a hold-up capacitor that the first flyback transformer charges. The second flyback transformer then uses the more or less constant voltage from this hold up capacitor to provide a DC output that has low ripple and is well regulated. The feedback for this circuit is allowed to be fast providing a low ripple output.
A power supply circuit according to the present invention that includes a second flyback transformer and one or more devices to reduce the harmonic line currents that are even harmonics of the AC input.

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According yet another aspect of this invention where the flyback transformer that has pulsating DC applied to its primary may operate for a portion of the pulsating DC in a continuous mode. In this aspect of the invention T
on may be varied by the control circuit in order to maintain a high degree of power factor'. Continuous mode is that condition when the energy stored in the primary of the transformer is not fully transferred to the secondary during T off but a portion remains within the flyback transformer when it begins the next T on cycle.
A further aspect of this invention may use a flyback transformer that has multiple secondaries providing multiple outputs of the same or different voltages.
A power supply according to this invention may be comprised of multiple parallel flyback transformers that may share the same switch, use separate switches or use separate control circuits and separate switches. These multiple flyback transformers may each. may have one of more secondaries that share the same or have different output filter circuits.
Additional aspects of this invention may use a battery instead of a DC device. The battery in this aspect maybe single or multiple with a single or multiple secondary circuits providing the recharging power. The type of battery includes ni-cad, lithium, lead acid or other battery types that can accept the output current generated by the secondary circuit.
An embodiment of this invention that uses a battery and DC device in combination on the secondary may use one or more secondaries that may be isolated or connected in part with each other. Further this embodiment may use an additional active circuit in the secondary for special control of the battery and DC device combination.

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The power supply circuit of the present invention is advantageously used in combination with the powering of DC
devices where power correction is desired.
BRIEF DESCRIPTION OF THE DRAWINGS
Preferred embodiments of the invention are shown in the drawings, wherein:
Figure 1 shows a simplified power supply circuit;
Figure 2 is a schematic of a simplified power supply circuit with some additional components;
Figure 3 shows various signals of the signal;
Figure 4 shows a modified DC power supply circuit.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The power supply circuit 2 of Figure 1 receives an AC
input signal at 4, filters out high frequency noise from switch 14, then rectifies the AC signal at 6 to produce a pulsating rectified AC signal generally shown at 7. This signal is provided to a flyback transformer circuit comprising the primary winding 10, the controlled switch 14, the secondary winding 24, and the current rectifying diode 16. The secondary winding 24 provides power for a DC
device 30. This DC device can be a rechargeable battery 33, lamp, input for another DC to DC power supply, input for a DC to an AC conversation device, and numerous other DC devices that use power of this type.
A feedback arrangement 29 preferably provides feedback with respect to the present voltage of the DC device as well as the output current. This information can be provided to the control arrangement 18. The control arrangement opens and closes switch 14 in a predetermined manner and defines an on time of the switch (Ton), indicated as 19, and an off time of the switch (Toff) indicated as 21. The on time charges the primary winding

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and is discharged during the off time. This is the typical operation of the flyback transformer.
The rectified AC signal has a frequency of typically but not limited to 120 Hz and the switch 14 is opened and closed at a rate at least 10 times this frequency. The control arrangement 18 can vary the output power provided to the DC device 30 by varying the on time. In order to provide a high power factor, the rate of change of time on is slow relative to the rectified AC signal 7. A very high power factor close to unity can be obtained if the rate of change of time on is 25 Hz or less, and preferably, 12 Hz or less. This slow rate of change of Ton is quite acceptable for charging of the battery 30 as well as a number of DC devices 30.
As can be seen from the circuit of Figure 1, the traditional flyback transformer and charging circuit, does not include a bulk hold capacitor nor an in rush resistor to smooth the DC signal that is provided to the primary winding 10. This modification of the circuit significantly reduces the cost of the circuit due to a reduction in relatively expensive components and also allows for the improved power factor.
The feedback arrangement 29 for some application may provide very little feedback, if any. For example, for some applications, it may be sufficient to use a constant Ton such that the DC device 30 is exposed to the same output power throughout normal operation. For a battery device 33, the charging cycle can be stopped once the battery achieves a predetermined voltage. For other applications, it will be desirable to have a battery charging profile. Such profiles are desirable with some nickel cadmium batteries, as well as lithium batteries. In this case, a predetermined battery charging profile can be provided to the control arrangement 18 as indicated by the profile 32. Such a profile can be a battery voltage relates to maximum charging current relationship and the control arrangement 18 can vary Ton relatively slowly to on WH-10,757-2CA
average, achieve a desirable charging current. In this way, the maximum charging current is maintained below a certain level. For other DC devices, the profile 32 may be external control of power output, output voltages or output current.
It can be appreciated from the circuit of Figure 1 that the pulsating signal provided to the primary winding will result in a pulsating output current for operating 10 of the DC device. Some smoothing of that output current can be provided if desired with the addition of a filter 30 on the secondary side, however, for some DC applications, this is not necessary. In any event, the recognition that the pulsating input current to the primary winding 10 is satisfactory allows vast improvement in the power factor, excellent control of the operating characteristics of the DC device, reduction in costs of the circuit due to fewer components, as well as reduced space requirements due to lesser components.
The power supply circuit 2a of Figure 2 merely includes some additional components but basically operates in the same manner as Figure 1. On th.e input side, a small capacitor 31 has been provided to reduce high frequency noise signals caused by the opening and closing of the switch 14. This is not a bulk hold capacitor. It merely prevents the high frequency signal being fed back to the power system. The primary side of the circuit has also been modified to include a circuit branch 33 across the switch 14, which acts as a clamp for flyback protection of switch 14 protecting it against over voltage.
The circuit of Figure 2 also shows an auxiliary power arrangement 41 used to provide power to the control arrangement 18. It also shows another winding 45 that may be used for auxiliary power or, a filter arrangement 43 is shown which can modify and smooth the output current to the DC device 30, if necessary. A feedback arrangement 29 is also provided. The DC device 30 maybe replaced with a battery 33.
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The simplified power supply circuit of Figures 1 and 2 has particular application for applications up to 250 to 300 watts. This power limitation is primarily determined by the availability of suitable components for the circuit at reasonable costs. If there is an application for higher power requirements, rather than increasing the circuit components, it may be preferably to parallel the design with one or more power supply circuits using combined feedback and control.
The power factor is easily controlled as the rate of change of Ton necessary to achieve a particular output power to a DC device is quite tolerant, and thus the feedback arrangement can be slow, relative to the input signal. This allows an average or dampened feedback response and avoids wide variations in Ton. Most of the benefits with respect to the power factor correction have been achieved due to the elimination of the in rush resistor and the bulk hold capacitor of the traditional flyback transformer charging circuit.
Basically, the design accepts the pulsating DC signal provided to the primary winding and if necessary or desired, suitable filtering of the output current or output voltage can occur on the secondary side of the circuit.
It can fully be appreciated that the electronic power switch shown as 14 can be any of the traditional devices such as bi-polar transistor Mosfet transistor, IGBT
transistor, etc. The circuit design of Figures 1 and 2, allows for variation of the duration of Ton, however, any changes therein are relatively slow. This, to a large extent, provides the circuit with a generally constant duty signal. The power factor specification is met by slowly varying any change in Ton. Basically, Ton is constant as the input signal to the primary winding varies from one minimum through a maximum, to the next minimum. In fact, in the preferred embodiments, Ton would not change for WH-10,757-2CA
several cycles of this signal. Ton can also be controlled by distinct steps and is general constant between steps.
The transferred power to the DC device generally follows the following equation.
(Vin x Ton) 2 x Freauencv Power Supply Power Out = 2 x (Primary Inductance of T1) Where:
x means multiply Vin is the instantaneous voltage across T1 and the Electronic Switch Ton is the on time, in seconds Frequency is the frequency of the electronic switch operation .in Hertz Primary Inductance of Tl is the primary inductance of Tl Power Supply Power Out is the power delivered to the DC device ignoring losses V~hen Vin, the instantaneous rectified line voltage is integrated over one complete line cycle, the output power of the power supply is Power Supply Power Out = (Line voltage in rms)2 x constant The power factor correction will occur so long as the duty of the control circuit maintains nearly a constant duty when averaged over one half cycle of the AC input line voltage.
The output filter circuit of the flyback converter is designed to reduce as required the output ripple voltage as seen by the DC device being powered. It can be nothing, a filter capacitor, combination of passive devices or may even include some form of active electronic circuit. The feedback circuit monitors the output of the power supply, sends a signal back to the electronic switch control WH-10,757-2CA
circuit and adjusts the duty to increase or decrease the output power delivered to the DC device.
The operation of the power supply circuit has been described with respect to a feedback arrangement where Ton is slowly varied relative to the input. signal. It is also possible to vary the frequency of the switch 14 to thereby vary the output power for the DC device. It is also possible to use a combination of the variation of the frequency and the variation of Ton to achieve a desired charging characteristic. Varying the time on of the switch is more traditional and easier to accomplish, and as such, is the preferred control.
Modulation of time on or the switching frequency will result in the modulation of the input source current, thereby degrading the power factor.
If time on and frequency are held constant, a high power factor (better than .98) in practical implementation of the circuit is achieved. Power factors of better than .95 are easily obtained with slow modulation of time on or switching frequency.
In many cases, the switch 14 will. operate at a frequency in the order of 100 kHz. The feedback for variation of Ton is preferably of the order of 10 Hz. It is also possible to have different profiles for Ton that vary as a function of time. The important thing is that Ton over a number of cycles of the input signal does not widely vary and as such, a high power factor power is achieved. If certain applications do not require a high power factor correction, then the rate of change of Ton can approach the frequency of the input signal. Therefore, the rate of change of time on and/or frequency of the switch is controlled to meet a particular power factor specification.
Figure 3 shows various signals of the circuit.

WH-10,757-2CA
Two set of signals have been given one set shows typical signals that are present for Continuous mode operation and the second shows a typical Discontinuous operation. In both examples the following signals are represented as follows.
Vsw is the Voltage that would be seen across the switch.

Ip is the current in the primary of the flyback transformer.

Vs is the voltage across the flyback transformer secondary winding.

Is is the current that would be seen in the secondary winding.

Control Logic is the signal telling the switch to open or close where in this case High means the switch is closed.

The power supply has particular application for charging batteries, however, it can be used as a power supply for many DC devices. One particular application is providing DC power to solid state lamps such as LED's (light emitting diode). These solid state lamps have a very long life and are being used for traffic light signals and other lighting applications. The power circuit is suitable for powering any DC device which can accept the degree of regulation and ripple that this circuit generates. It can also be appreciated that some signal conditioning on the secondary side can be used to broaden the applications. Further, a filtered output may be used as an input for another DC power supply which then provides a well regulated output voltage.
Figure 4 shows a modified application where a second switch-mode power supply, right of line A-B, has been added after the power factor correction circuit, left of line A-B, to provide a low ripple well regulated DC output. The circuit design is unique in that the switch-mode power supply section right of line A-B has in common the switch 110, control 109 and feedback 125 with the power factor WH-10,757-2CA
correction front-end left of line A-B. This new technique uses less components than current designs, which results in a smaller, lower cost and simpler design. For ease of understanding, Figure 4 only shows the principle elements and additional components can be added, depending upon the final application.
The power supply receives an AC input signal at 100 which then goes through a noise filter 101, which attenuates the noise generated by switch 110 below a predetermined level. The signal then goes to an AC
rectifier 102 where it is converted to a pulsating DC 103.
The pulsating DC 103 is applied to capacitor 104, which is used to reduce the switching noise of switch 110, it does not act as a bulk hold-up capacitor anal does not smooth the pulsating DC 103, the same as used in Figure 2. The pulsating DC 103 is then applied across the primary winding 106 of a flyback transformer, diode 112 resistor 111 and switch 110. Diodes 112 and 113 block the flyback voltage that will occur when primary 106 and primary 121 flyback when switch 110 opens. These diodes 112, 113 isolate the two primary windings 106 and 121 from each other when switch 110 opens. The voltage across switch 110 will be the greater of the flyback voltage of primary 106 or 121.
V~hen switch 110 is closed, the pulsating DC 103 flows into primary winding 106. V~Then the switch 110 opens, this energy is then transferred to secondary winding 107 which is rectified by diode 108 and stored as a DC voltage across capacitor 119, which is a hold-up capacitor. Hold-up capacitor 119 provides power to primary 121 when the pulsating DC 103 approaches a minimum as the power delivered by secondary winding 107 would be also a minimum.
The power delivered by secondary 107 behaves the same as in Figures 1 and 2. This output power delivered by secondary winding 107 is a function of the pulsating DC 103.
The voltage present across capacitor 119 is applied to the primary winding 121, diode 113, resistor 111, then switch 110, and returns to capacitor 119 through resistor r, ,, WH-10,757-2CA
116. V~hen switch 110 closes current from C119 flows into the primary winding 121 storing energy. When switch 110 opens this energy stores in the primary winding 121 is then transferred to the secondary winding 122 then trough diode 123 to capacitor 124, feedback 125 and. the DC devices 126 that are being operated by the power supply. With the voltage across hold-up capacitor 119 constant in value, the power transferred through primary winding 121 and secondary winding 122 to capacitor 124 is constant with low ripple.
The fast feedback 125 then adjusts the Ton to regulate the output, correcting for variances in the AC input 100 and the power drawn by the DC devices 126. Multiple secondary with separate isolated voltage outputs are possible but only one secondary is shown for simplicity.
Switch 110 then does two jobs, it. controls the amount of power transferred to capacitor 119 from the pulsating DC
103 and it transfers the energy stored. in capacitor 119 to the output capacitor 124 and the DC devices 126. The feedback circuit 125 is fast, typically a few kHz, much faster than the feedback used in Figures 1 and 2. The advantage of this is that a well regulated, low ripple voltage output across DC devices 126 is created.
The disadvantage of a fast feedback 125 is that currents, which are harmonics of the AC input 100, are created and appear at the AC input 100, degrading the power factor. Resistor 111 is used to reduce the AC input harmonic currents that are created by the fast feedback 125. It does this by creating voltage equal and opposite to the ripple voltage, across capacitor 119 seen by primary winding 121 of T2. The voltage drop across resistor 111 is caused by the currents that flow from the primary 106 and primary 121. The current in primary 106 is in phase with the ripple voltage across capacitor 119. By choosing an appropriate value of resistance, a voltage drop can be created equal to the voltage rise that appears on the hold-up capacitor 119, when the pulsating DC 103 across primary winding 106 approaches maximum.

WH-10,757-2CA
The circuit 115 comprising resistor 116 and transformer T3 comprised of primary winding 117 and secondary winding 118 are an improved method of compensating for the ripple voltage that is present across capacitor 119. T3 reverses the phase of the current flowing in secondary winding 107 and creates a compensating voltage, equal and opposite in magnitude to that across capacitor 119, across resistor 116. The circuit 115 purpose is the same as resistor 111, t.o reduce the currents that are even harmonic of the AC input. 100 created through the action of using a fast feedback 125. These harmonic currents are not desirable and two methods of harmonic current reduction, other than using an. extremely large value for capacitor 119, have been demonstrated.
Switch 110 maintains nearly a constant Ton and is 10 changed by the feedback 125, which provides a signal to the control 109, maintaining a well-regulated output. The feedback 125 in this case operates fast, such that a high quality regulated output is generated. As the DC devices 126 demand more power, the feedback will cause the control to increase the Ton of switch 110. The increased Ton will transfer more power through primary winding 106 from the pulsating DC 103 to hold-up capacitor 119. The increased Ton will also cause an increase in the power transferred from the hold-up capacitor 119 through primary winding 121 to secondary winding 122, then output filter capacitor 124.
This power is then available to the DC devices 126 as required. With both transformers T1 and T2 being flyback in design, the relationship of power transferred is the same, relative to Ton. This creates a simple to control power supply with power factor and well regulated using just a single switch.
It can be appreciated that power supplies maybe designed using multiple switches as well as paralleling multiple circuits for higher power output.

WH-10,757-2CA
Although various preferred embodiments of the present invention have been described herein i.n detail, it will be appreciated by those skilled in the art, that variations may be made thereto without departing from the spirit of the invention or the scope of the appended claims.

Claims (24)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A power supply circuit comprising means for receiving an AC input signal, means for rectifying said AC signal to produce a non constant DC signal and providing said rectified signal to an input of a fly back transformer circuit, said fly back transformer circuit comprising a primary winding in series with a switch and a secondary winding associated with said primary winding and having a diode, said secondary winding providing an output current for charging a battery or other DC device, a control arrangement controlling the opening and closing of said switch and thereby define a time on and a time off of said switch, said control arrangement controlling said time on as required to provide an acceptable power factor specification.

2. A power supply circuit as claimed in claim 1 wherein said control arrangement controls the rate of change of time on to provide the acceptable power factor specification.

3. A power supply circuit as claimed. in claim 1 wherein the rate of change of time on is slow relative to the frequency of the AC input signal.

4. A power supply circuit as claimed in claim 3 wherein the rate of change of time on is slowly varied by said control arrangement to provide said power factor specification and to met a predetermined power output specification.

5. A power supply circuit as claimed. in claim 4 wherein said circuit includes an input arrangement for entering a power output specification and said control arrangement varies time on to met the power output specification.

6. A power supply circuit as claimed. in claim 1 wherein said rectified AC signal applied to said primary winding continuously varies from about zero volts to a maximum voltage and an output current produced by said secondary winding continuously varies as a function of said rectified AC signal.

7. A power supply circuit as claimed. in claim 6 wherein the percentage variation of said power current during each time off is at least 25%.

8. A power supply circuit as claimed in claim 1 wherein said rectified AC signal is used to power said primary windings to expose the windings to the pulsating characteristic of said rectified signal and an output current produced by said secondary winding varies as a function of said rectified AC signal.

9. A power supply circuit as claimed in claim 1 used in combination with a solid state DC device with said power supply circuit powering sad solid state DC device.

10. A power supply circuit as claimed in claim 9 wherein said rectified AC signal is used to power said primary windings to expose the windings to the pulsating characteristic of said rectified signal and an output current produced by said secondary winding varies as a function of said rectified AC signal.

11. A power supply circuit as claimed in claim 1 used in combination with a solid state DC traffic light device or other lighting device with said circuit powering said solid state DC device.

12. A power supply circuit as claimed in 1 including at least one further secondary winding and diode, with each secondary winding and diode providing power to a separate DC device.

13. A power supply circuit as claimed in 12 wherein each secondary winding has associated therewith an independent filter.

14. A power supply circuit as claimed in 12 wherein each secondary winding has associated therewith but a separate feedback circuit and the combined feedback of said feedback circuits is used to control the opening and closing of said switch.

15. A power supply circuit as claimed in 14 wherein each secondary winding has associated therewith an independent filter.

16. A power supply arrangement comprising a plurality of power supply circuits where each power supply circuit comprises means for receiving a AC signal, means for rectifying said AC signal to produce a non constant DC
signal and providing said rectified signal to an input of a fly back transformer circuit, said fly back transformer circuit comprising a primary winding in series with a switch and a secondary winding associated with said primary winding and having a diode, said secondary winding providing an output current for charging a battery or other DC device, a control arrangement controlling the opening and closing of said switch and thereby define a time on and a time off of said switch, said control arrangement controlling said time on as required to provide an acceptable power factor specification.

17. A power supply arrangement as claimed in 16 wherein said power supply circuits are in parrallel and each circuit includes its own output filter associated with the secondary winding.

18. A power supply arrangement as claimed in 16 wherein said power supply circuits are in parrallel and each circuit includes its own feedback circuit associated with said respective control arrangement.

19. A power supply arrangement as claimed in 16 wherein the control arrangement of said circuits are combined.

20. A power supply circuit as claimed in 1 in combination with a second power supply, said second power supply receiving as an input the output of said supply circuit whereby said second power supply provides a regulated output voltage for operating other do devices.

21. A power supply circuit as claimed in 1 wherein the do device is a common do power bus capable of operating a single or multiple number of do devices.

22. A power supply circuit as claimed in 1 wherein the DC
device is another fly back transformer that shares the same switch and provides a well regulated do power output for operating other do devices.

23. A power supply circuit as claimed in 22 including a circuit to reduce even harmonic distortion of the AC input.

24. A power supply circuit as claimed in 1 wherein said control arrangement is operated in a manner that the energy stored in the flyback transformer does not always decrease to zero during the time the switch is open.