The invention disclosed herein relates to a power circuit for providing electrical power to a load. Furthermore, this invention can be applied to provide an uninterruptible power supply.

The problem to which this invention is directed relates to providing a circuit which can be used to transform a first electrical input supply from a first voltage to a second voltage. The first voltage is substantially an Alternating Current (AC) or a varying voltage signal, whereas the second voltage is rectified and is preferably substantially a Direct Current (DC). This second voltage can, if required, be used for storage means charging. Furthermore, this second voltage can be either used directly to provide a DC to a load or alternatively the voltage can be processed to provide a useful output which is substantially an AC.

In addition to the above, the second voltage can be sustained, if required, when the input supply is removed. This is achieved by the storage means providing the second voltage.

Conventionally previous approaches have involved power circuit apparatus which were adapted to be supplied with an AC power at a first voltage and the apparatus is then adapted to effect through a transformer a voltage reduction of this incoming power, and then effect a rectification at the second voltage. This approach requires relatively heavy transformers, depending upon the application, and this can lead to substantial power loss which results in heat being generated in the transformer. In addition to the extra bulk caused by the transformer this heat must be dispensed by some cooling means thus adding to the cost and complexity of the power circuit.

It is the intended object of this invention to overcome the abovementioned problems or at least provide the public with an useful alternative.

According to one form of this invention, although this need not be the only or the broadest form, there is proposed a means of converting a first voltage into a rectified second voltage without the use of a transformer or a substantial

voltage drop across a series resistor, wherein the second voltage has a substantially different Root Mean Squared (RMS) Value to the first voltage.

Alternatively, according to another form of this invention, although this need not be the only or the broadest form, there is proposed a means of converting a first voltage into a rectified second voltage without the use of a transformer in which the second voltage has a substantially smaller RMS Value than the first voltage, wherein the first voltage is an alternating supply voltage of a frequency within the range 20 to 100 Hertz.

Alternatively, according to another form of this invention, although this need not be the only or the broadest form, there is proposed a means of converting a non-DC into a substantially DC of a desired voltage including: a rectifying means for rectifying the non-DC voltage to provide a rectified voltage; a reducing means for reducing the alternating component of the rectified voltage to provide a substantially DC voltage; a sensing means for sensing a voltage proportional to the substantially DC voltage, the sensing means being adapted to provide a feedback voltage; a processing means for providing a pulse width modulated signal dependent upon the feedback voltage; and a regulating means for regulating the amplitude of the substantially DC voltage, the regulating means being controlled by the pulse width modulated signal.

Alternatively, according to another form of this invention, although this need not be the only or the broadest form, there is proposed a means of converting a first voltage into a rectified second voltage including: a rectifying means adapted to be connected directly onto a mains supply to provide a rectified voltage; a voltage feedback means to provide a feedback signal dependent upon the voltage of the rectified voltage; a processing means for processing the feedback signal to provide a control signal, the control signal being a frequency of varying width pulses the width of which is dependent upon the feedback signal; and a switching means adapted to regulate the voltage of the rectified voltage, the switching means being controllable by the control signal.

Alternatively, according to another form of this invention, although this need not be the only or the broadest form, there is proposed a means of converting a first voltage into a rectified second voltage including: a rectifying means adapted to be connected directly onto a mains supply to provide a rectified voltage; a reducing means for reducing the alternating component of the rectified voltage to provide a substantially DC voltage; a voltage feedback means to provide a first feedback voltage dependent upon the voltage of the DC voltage; a processing means for processing the first feedback voltage to provide a control signal, the control signal being a frequency of varying width pulses the width of which is dependent upon the first feedback voltage; and a switching means adapted to regulate the voltage of the DC voltage, the switching means being controllable by the control signal.

Alternatively, according to another form of this invention, although this need not be the only or the broadest form, there is proposed a means of converting a first voltage into a rectified second voltage including: a rectifying means adapted to be connected directly onto a mains supply to provide a rectified voltage; a voltage feedback means to provide a first feedback voltage dependent upon the voltage of the rectified voltage; a processing means for processing the first feedback voltage to provide a control signal, the control signal being a frequency of varying width pulses the width of which is dependent upon the first feedback voltage; and a switching means adapted to regulate the voltage of the rectified voltage, the switching means being controllable by the control signal.

In preference, referring to any of the above relevant forms, the processing means includes a comparison means adapted to compare the first feedback voltage against a reference voltage to give a result, wherein the result of the comparing affects the width of the control signal.

In preference, referring to any of the above relevant forms, the processing means is adapted to process the control signal such that it is a pulse width modulated signal.

In preference, referring to any of the above relevant forms, there is a reducing means adapted to substantially remove the alternating component of the rectified voltage and provide a substantially DC voltage.

In preference, referring to any of the above relevant forms, there is a battery means adapted to be charged by the DC voltage.

In preference, referring to any of the above relevant forms, there is a current feedback means for providing a second feedback voltage dependent upon the current flowing into the battery means, the processing means is adapted to further process the second feedback voltage, wherein the pulse width of the control signal is adapted to be varied by the values of the first feedback voltage, reference voltage and second feedback voltage.

In preference, the processing means is adapted to limit the width of the control signal's pulses, the limiting being dependent upon the second feedback signal.

In preference, referring to any of the above relevant forms, the means of converting is adapted to be an uninterruptible power supply such that upon the mains supply failing the battery means can be used to supply a load.

In preference, referring to any of the above relevant forms, the output of the means of converting is connected to a DC to AC Converter adapted to supply the load.

in preference, referring to any of the above relevant forms, the means of converting is adapted to allow the supply power factor to be above 0.8.

In preference, referring to any of the above relevant forms, there is an isolation means adapted to isolate the battery means from the supply when the supply voltage falls below a threshold voltage level.

Alternatively, according to another form of this invention, although this need not be the only or the broadest form, there is proposed a method of converting an AC into a substantially DC of a desired voltage, the method including the steps of: rectifying the non-DC voltage to provide a rectified voltage;

processing the rectified voltage to provide a substantially DC voltage; sensing a voltage proportional to the substantially DC voltage to provide a feedback voltage; providing a pulse width modulated signal dependent upon the feedback voltage; and regulating the amplitude of the substantially DC voltage, the regulating being controlled by the pulse width modulated signal.

According to one form of this invention, although this need not be the only or the broadest form, there is proposed a method of voltage conversion, without the use of a transformer, including the steps of: rectifying a mains supplied voltage by a rectifying means, the mains supplied voltage being connected to the rectifying means without voltage transformation; and receiving a voltage wherein the second voltage has a substantially different RMS Value to the first voltage.

Alternatively, according to another form of this invention, although this need not be the only or the broadest form, there is proposed a method of converting an AC mains supply into a substantially DC, the method including the steps of: rectifying the supply to provide a rectified voltage; reducing the alternating component of the rectified voltage to provide a substantially smoothed rectified voltage; sensing the changes in the substantially smoothed rectified voltage to provide a feedback signal; processing the feedback signal in combination with a reference level to provide a control signal for controlling a semiconductor switch; and controlling the semiconductor switch to compensate for changes in the rectified voltage.

In preference, the method is further characterised by the substantially smoothed rectified voltage being substantially a DC.

In preference, the method is further characterised by the processing including the steps of: comparing the feedback signal voltage level against a reference voltage to provide a control voltage; and

modifying the pulse width of the control signal, wherein the pulse width is dependent upon the control voltage.

In preference, the method is further characterised by the control signal being a pulse width modulated signal.

In preference, the method is further characterised by the step of charging a battery means, the battery means being charged by the substantially smoothed rectified voltage.

In preference, the method is further characterised by the steps of: sensing variations in current flowing into the battery means; effecting a second feedback signal; and processing the second feedback signal to provide a means of limiting the width of the control signal's pulses.

In preference, the method is further characterised by the steps of: supplying a load with the substantially smoothed rectified voltage; and supplying the load with the battery means' charge upon the removal of the mains supply voltage.

In preference, the method is further characterised by the substantially smoothed rectified voltage or battery means' charge being converted into an AC and supplying the load.

In preference, the method is further characterised by the power factor of the mains supply being above 0.8.

In preference, referring to any of the above relevant forms, there is an isolation means adapted to isolate the battery means from the supply when the supply voltage falls below a threshold voltage level.

Alternatively, according to another form of this invention, although this need not be the only or the broadest form, there is proposed an apparatus adapted such that an incoming voltage which can be an AC power supply is directed immediately into the rectifiers without transformation so that the output of the rectifiers is a substantially untransformed voltage from the input voltage, the substantially untransformed voltage from the rectifiers then being converted

using DC techniques from a second voltage to a third voltage which voltage is useful for charging an electrical storage means, and an inverting means adapted to invert the DC voltage to a further substantially AC output of the third voltage.

In preference there is a power circuit including an input means adapted to connect to a first source of electrical power, a rectifying means connected to the input means and adapted to rectify current drawn from the first source of electrical power into DC electrical power at a first voltage.a first voltage regulating means connected to the rectifying means adapted to produce an output at a second voltage characterised by being of substantially constant voltage, a second voltage regulating means connected to the output of the first voltage regulating means and adapted to provide a source of AC electrical power as an output, the power circuit being characterised such that the output of the second voltage regulating means being substantially independent of variations in the first source electrical power.

In preference, in one form of the invention, the power circuit is characterised by a battery means connected across the output of the first voltage regulating means, the first voltage regulating means being further adapted to charge the battery means, the first source of electrical power being characterised by an AC of a first frequency, the second switched voltage regulating means being adapted such that the output of the second voltage regulating means is characterised by a second AC of substantially the same frequency as the first frequency and of a substantially constant peak voltage, and the second voltage regulating means being adapted to draw power from either the output of the first regulating means or the battery means to produce the output of the second switched voltage regulating means for a period of time substantially independent of the source of the first source of electrical power; in this arrangement the battery means is used to supply the power circuit load during times of power failure of the AC mains whilst under normal conditions the electrical power is supplied from AC mains; thus in this configuration the power circuit forms part of an uninterruptible power supply.

in preference, in one form of the invention, the power circuit is characterised by the first source of electrical power being characterised by an AC of a first frequency, the second voltage regulating means being adapted such that the output of the second voltage regulating means is characterised by a second

AC of substantially the same frequency as the first frequency, and the output of the second regulating means being characterised by an alternating voltage substantially of constant frequency and peak voltage when the power circuit input is connected to a source of AC mains; in this configuration without the battery means the power circuit is being used as part of a mains line conditioner.

In preference, in one form of the invention the power circuit is characterised by the second voltage regulating means producing the output of the second voltage regulating means in response to an audio frequency electrical signal, and the power circuit is adapted to produce at the output of the power circuit a power amplified representation of the audio frequency electrical signal.

Preferably the power circuit is adapted to have an output power capability greater than 50 Watts.

In preference the power circuit is characterised by the first voltage regulating means including a switch or switches the conducting state of which are controlled by a pulse width modulated signal, the width of the resultant conduction pulse of the switch or switches increase with increase load on the output first voltage regulating means, and the second voltage regulating means being characterised by including a switch or switches the conducting state of which are controlled by a further pulse width modulated signal.

Alternatively, the invention may be said to reside, not necessarily in the broadest or only form, in a power circuit including an input adapted to be connected to a source of AC, first circuitry connected to the input adapted to convert AC into DC, second circuitry connected to the output of the first circuitry adapted to convert a first DC voltage into a second DC voltage, and third circuitry connected to the output of the second circuitry adapted to convert the second DC voltage into an AC which is the output of the power circuit.

In preference the power circuit includes battery means connected to the output of the first circuitry, the power circuit being adapted to charge the battery means and adapted to provide the AC output of the power circuit when the input of the power circuit is not connected to a source of AC from energy stored within the battery means.

In another preferred form the invention may be said to reside, again not necessarily in the broadest or only form, in a circuit adapted to perform the steps including rectifying an electrical input to form a first DC voltage by rectifying means, converting the first DC voltage by a DC to DC converter into a second DC voltage, converting the second DC voltage into a first AC voltage exhibiting predefined voltage characteristics by a DC to AC invertor, and where the first AC voltage is substantially independent of any variations in the electrical input.

Preferably the power circuit is characterised by the frequency of the output of the second voltage regulating means being different to the first frequency of the AC of the first source of electrical power.

Preferably the power circuit is adapted to provide an uninterruptable power supply for computers.

Circuits exhibiting the invention have a number of advantages compared with known systems. First, due to the DC stage filtering of the mains supply is relatively easily and effectively achieved. Secondly, due to the lack of an input transformer the circuit, within limitations of the specific components used, is substantially independent of the mains voltage or frequency or variations to these characteristics. The output of the circuit is independent of the source of electrical power characteristics.

The invention will now be described with reference to the accompanying figures illustrating a preferred embodiments of the invention in which:

FIG. 1 illustrates a preferred embodiment of the invention in block diagram form;

FIG. 2 illustrates the power circuit without the details of the feedback control circuitry;

FIG. 3 is a schematic diagram of the feedback control circuitry;

FIG. 4 is an example of a load which can be supplied by the power circuit;

FIG. 5 is an example of another load which can be supplied by the power circuit; and

FIG. 6 illustrates a further embodiment of the power circuit which improves the power factor of the input to the circuit.

It will be appreciated that FIG. 1 does not show the details of the circuitry or necessary control circuits. As such it is only intended to provide an overview. It will be appreciated that the term load, unless the context indicates differently, will be used to refer to the effective load on the output of the power circuit.

Considering FIG.1 the input voltage, in this embodiment a mains AC 1 , is rectified by rectifiers 2 to form a DC voltage 3. The DC voltage 3 is converted by a DC to DC converter 4 to a voltage 5 adapted to supply a load 8 and preferably may also charge a battery 6. A feedback signal dependent upon the voltage at 5 provides a feedback signal to the regulator controller 9.

Furthermore, the current flowing into the battery can be monitored to provide a further feedback signal to the regulator controller 9. The output of the regulator and controller 9 provides a control signal for controlling the voltage 5 at the output of the DC to DC converter.

When the mains AC 1 is available the battery charge is maintained and the voltage 5 is controlled to supply the battery 6 and load 8. When the mains AC 1 is interrupted the load is supplied by the charge stored in the battery 6.

Referring to FIG. 2. The power circuit is preferably adapted to be connected to the mains input. However, other input voltages can be applied. In the embodiments described herein a single phase version is disclosed but it will be appreciated that a three phase version could also be implemented. Further, whilst switched voltage regulators are used in the embodiments other suitable types of regulators may be used.

Consider the power circuit connected to the mains supply, in Australia or the United Kingdom typically 240 Volts AC at 50Hz. The mains supply is applied to the filter network comprising varistors 10, 11 and 12, resistors 13 and 14, and capacitor 15. This filter substantially protects against over voltage noise spikes and also substantially filters out high frequency noise.

SUBSTJTUTE SHEET (Rule 26)

After filtering the mains is rectified by bridge rectifier 16. The output of the rectifier is across capacitor 17 which is substantially a DC voltage of approximately 340 Volts. At this point filtering is conducted by capacitors 17, 18 and 19, and inductor 20. This filtering is intended to remove high frequency variations, some low frequency variations can be tolerated as these are removed by the input regulator which includes the semiconductor switch 21 and inductor 25.

The DC voltage across the capacitor 18 is reduced by the input regulator. This is a switched voltage regulator providing DC to DC conversion from approximately 340 volts to, for example in this embodiment, approximately 39.6 volts under normal operating conditions. The input regulator comprises a semiconductor switch 21 and inductor 25. The output voltage of the input regulator is generated across capacitors 26. This is used to provide a feedback signal to control the "on" state of semiconductor switch 21. Across capacitors 26 are three 12 volt batteries 27. The current flowing into the batteries 27 is also preferably used to control the "on" state of semiconductor switch 21.

The "on" state of the semiconductor switch 21 is controlled so that the output voltage of the input regulator applied across the batteries 27 is limited to 39.6 volts or to a lower voltage when the batteries 27, typically during charging, are drawing a current of 3 A. By such means the input regulator maintains charge of the batteries 27. The effect of a load on the power circuit is to lower the voltage across the batteries 27 and so in an indirect way this affects the "on" state of the semiconductor switch 21.

The input regulator control circuitry is illustrated in FIG. 3 and includes an input regulator controller 22, feedback control operational amplifier circuits 23 and 24. Note that two voltage references, ground or zero voltage, are used in this control circuit. Voltage feedback is achieved by sensing the voltage across capacitors 26 to provide a feedback signal F1 which is applied to the operational amplifier circuitry 23. The voltage across capacitors 26 is effectively subtracted from a reference signal. The output is applied to the voltage feedback input of a switch mode power supply controller integrated circuit which forms the input regulator controller 22. The output of the input regulator controller 22 is buffered before being applied to the semiconductor switch 21 by the control signal Cl. This output is a pulse width modulated

signal of a frequency preferably in the range of 1 kHz to 100 kHz. The width of these pulses is dependent upon the feedback input voltage (FBACK) and the frequency can be altered by selecting values of the controller's 22 relevant capacitors and resistors.

Current flowing into the batteries is sensed by detecting the voltage drop across the resistor 32 to provide a feedback signal F2. This voltage is buffered, scaled and subtracted from the feedback signal. However, other forms of processing may be used. The output due to this processing is provided by the operational amplifier circuitry 24 which is merged with the output from the operational amplifier circuit 23 to provide the FBACK to the input regulator controller 22. As an alternative the output from the operational amplifier circuitry 24 can be connected to the current limit input of the input regulator controller 22. The effect of the current limit voltage supplied by the output from the operational amplifier circuit 23 is to limit the maximum width of the pulses of the pulse width modulated signal.

The voltage across capacitor 17 is also used to power the input regulator control circuitry. This is done by forming a 12 volt power source by resistors 28 and Zenner diode 29.

The output of the voltage feedback circuit 23 is also applied to a comparator 30 which is used to the control relay 31. The circuitry is adapted to close the relay when there is a mains supply. When the mains supply fails the relay 31 is open which ensures isolation of the output and the input regulators.

The result of this arrangement is that the output of the input regulator and the batteries are effectively connected in parallel. Under normal operating conditions the batteries are maintained in a charged state by power flowing from the mains through the input regulator to the batteries. The control circuitry of the input regulator is powered from the mains AC and is therefore only operable if the mains supply is available.

The batteries and the output of the input regulator are adapted to supply substantially DC to a load. The load may be a simple resistive, digital electronic or other load which can be directly driven by a substantially DC. However, if the load requires an AC then the load driving circuits of either FIG. 4 or FIG. 5 can be used to convert the substantially DC Output (+VE and -VE)

to a substantially AC. This is achieved by the semiconductor switches (as illustrated in FIG. 5 or FIG. 6) being alternately selected. The selected semiconductor switch is switched "on" and "off" for example using a pulse modulated signal. This provides half the waveshape applied to the transformer. The other half of the waveshape is supplied by selecting the other semiconductor switch and switching it "on" and "off" by a pulse modulated signal. To provide a further controlling effect feedback points can be supplied from F3 and F4 to a controller which modifies the pulse modulated signal and therefore this adjusts the amplitude of the current flowing into the transformer.

In some circumstances when the invention, as illustrated in the preferred embodiment of FIG. 2, is connected to the mains supply, the power factor requirements of the supply authority may be contravened. This is due to the 110 microFarad capacitors 17 and 18 in series with the 125 microHenry inductor being connected across the output of the bridge rectifier. As a result it may cause the mains power factor to be below 0.8 and probably even as low as 0.6. Consequently, the circuit of FIG. 2 can be modified so that the capacitors 17 and 18 are removed. This, however, will affect the ripple voltage across the output (+VE and -VE). Consequently, the control input Cl can be modified to compensate for the ripple voltage fluctuations.

It will be appreciated that there are a number of ways of implementing the invention other than that described herein. As such all of these would fall within the spirit of the invention. It will further be appreciated that there are circuit details which can be modified to suit specific applications as desired all of which would be apparent to a person skilled in the art.