FORM - 2
THE PATENTS ACT, 1970 (39 of 1970)
COMPLETE SPECIFICATION (Section 10, rule 13)


"Ultra-Wide AC/DC Input-Range Multiple Isolated-Output
Power Supply"

Forbes Marshall Pvt. Ltd.
with Corporate office at Forbes Marshall Pvt. Ltd., A-34/35, MIDC Pimpri, H Block,
Pune 400 018, Maharashtra, India.
an Indian Company registered under the provisions of the Companies Act, 1956,
THE FOLLOWING SPECIFICATION PARTICULARLY DESCRIBES THE INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFORMED: -



FIELD Of INVENTION
This invention relates to Power Supply.
Particularly, this invention relates to Multiple Output Power Supply. More particularly, this invention relates to an Ultra-Wide Input-Range Multiple-Output Power Supply with isolated Outputs.
Further, this invention relates to an Ultra-Wide AC or DC Input-Range Multiple-Output Power Supply with isolated Outputs.
Also, this invention relates to an Ultra-Wide AC or DC Input-Range fed through a common pair of conductors and Multiple-Output Power Supply with isolated Outputs.
BACKGROUND OF THE INVENTION
Present day power shortage has forced the industries to move towards battery-operated system; however the need for input supply varies with the application. Most of the process instruments used in any industry need universal power input (90 VAC 10 260VAC) for operating the instrument, such that the problem of low line input voltage and variations of normal 230 VAC supply can be resolved. Modern technology enables us to design the Power Supply for universal input. Soirre industries are using 24 V battery input or a DC supply input to fulfill the input power requirement. Such variation in input supply requirement results in design of two different versions of Power Supply mostly known as DC version and AC version. This increases the cost of manufacturing and testing for a single instrument. Installation of wrong version causes failure of the whole instrument, which unnecessarily increases the overhead costs related to repairs or replacement. Overcoming this problem is the most demanding need of the industry.
Modern switching technology provides a low cost, compact switched mode Power Supply to cater to the power demand of industry. Integrated switching technology provides reliable low cost Power Supply but has some limitations when it comes to the input range of the Power Supply. This invention provides a solution to designing a wide input range Power Supply.
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Power Suppl) units are usually available with a variety of configurations to cater to different power needs of the industry. Most of the instruments used in the process industry are required to operate on a universal input power supply of 90 VAC to 265 VAC.
The need for un-interrupted Power Supply has forced the industry to move towards the battery-fed systems. The input power supply in such cases is a DC supply. Besides, some of the industrial environments employ a battery (DC supply) to address the power requirement. Such variation in the input power supply results in two different versions of the Power Supply, namely the DC version and the AC version. Maintaining two versions increases time to design the two different versions, the operational cost for a single instrument and the manufacturing cost. Further, the use of incorrect version (AC version used with a DC input supply and DC version used with a AC input supply) causes failure of the instrument.
Currently available Power Supply units with such wide input range use either external conirol circuit or automatic switching mechanism to control the ultra wide input range; thereby making the power supply unit bulkier and dependent on external control circuit thereby increasing the cost.
The outcome of the earlier attempts to address this problem resulted in costly and bulkier Power Supply, which required clubbing two different converters or using a multi-tapped transformer with external control circuitry.
Therefore, there is a need to design a 'universal' Power Supply that is capable to operate from either AC or DC input supply supply and across the available input supply range.
PRIOR ART
US patent 4389702 describes switching Power Supply having constant output for wide range input supply. This Power Supply is single transistor having unidirectional clamp consist of clamp diode, capacitor and a resistor. Although it accepts the universal input range of 85 VAC to 265 VAC it does not operate at lower DC input.
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US patent 5097402 describes a Power Supply operable from a mains voltage generally within two voltage ranges according to which Power Supply automatically switches between full wave and voltage doublers. This provides a response to a rapid change of input mains voltage.
US patent 5534768 discloses the Power Supply design, which accepts either AC or DC input but having limitation of input range. This design accepts either 48 VDC or 117 VRMS input and generates multiple isolated outputs using traditional technology. This consists of an external MOSFET and PWM controller to drive the MOSFET and uses the MOSFET based post-regulator to regulate the auxiliary windings. It accepts AC or DC input but has a limited range of 38 VDC to 190 VDC. Input exceeding 190VDC destroys the circuit and below 38 VDC the Power Supply will not switch-on.
This Power Supply has limited use in telecom applications and does not address the lower range battery feed inputs like 24 VDC or lower AC range.
Attempts were made to design low cost, lightweight, wide range input Power Supply but these resulted in either having an external control circuitry or controller based system for achieving a wide input range.
OBJECTS OF THE INVENTION
An object of this invention is to provide Power Supply, typically a versatile universal Power Supply.
Another object of this invention is to provide a wide range of AC or DC input including low level DC input, fed via a pair of input conductors as applicable to a typical Power Supply.
Another object of this invention is to provide a dual mode operable Power Supply, typically a wide input range.
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Yet another object of this invention is to provide a wide input range through a common pair of input terminals; typically for a Power Supply.
Another object of this invention is to provide Power Supply operable over a universal AC input range and a lower DC input range typically a battery feed input, through a common pair of terminal or pair of conductor.
Further object of this invention is to provide a Power Supply with no external control circuit to achieve the wide input supply range.
Still another object of this invention is to provide uninterrupted Power Supply.
Further object of this invention is to provide a means to prevent failure of Power Supply arising from the use of incorrect version of the Power Supply.
Still further object of the present invention is to provide a cost effective and compact Power Supply.
SUMMARY OF THE INVENTION
The invention envisages an Ultra Wide AC-DC Input Range Isolated Multiple Output Power Supply that accepts either AC (20 VAC to 260VAC) or DC input (22 VDC to .575 VDC), through same pair of conductors and capable of delivering the power with isolated multiple outputs, without using any external control circuitry to control such ultra wide input range.
Such Power Supply can operate at universal AC input range or lower DC range like battery feed input such as 24 volt or 48 volt through the same terminal or pair of conductor.
The Power Supply in accordance with this invention is with no external control circuit making it reliable, compact and manufacturable at a reduced cost.
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BRIEF DESCRIPTION OF THE DRAWINGS
The invention will now be described with reference to the accompanying drawings in which:
Figure 1 ol'the accompanying drawings illustrates the Block diagram of Ultra-Wide AC or DC Input-Range fed through a common pair of conductors and Multiple-Output Power Supply with isolated Outputs in accordance with this invention where:
Numeral I: Input termination and EMC filter to remove electromagnetic
interference.;
Numeral 2: Input bridge rectifier and filter capacitor;
Numeral 3: Transformer wound on Ferrite core;
Numeral 4: Output rectifier and filter capacitor;
Numeral 5: Output termination;
Numeral 6: Output sampling network and error amplifier;
Numeral 7: Optimized feedback network;
Numeral 8: Opto coupler;
Numeral 9: PWM controller TOPXXXX; and
Numeral 10: Input Range expander (UV/OV circuit of TOPXXXX).
DETAILED DESCRIPTION OF THE DRAWINGS
The accompanying drawings illustrates a typical fly back converter. Energy stored in
the primary winding during switch-on mode is transferred to the secondary during
switch-off mode. Fly-back topology works either in continuous or discontinuous
mode of conduction, however the choice of mode depends on the output power level
and core size. This design operates in discontinuous as well as continuous mode of
conduction.
Continuous mode of conduction:
Vin/Vo=(l-dll,ilJ/dmilx ...(1)
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In continuous mode of conduction, energy is still stored in the transformer at the end of the switching period. Dead time is zero in this mode of conduction.
Discontinuous mode of conduction:
The Power Supply has been designed using the basic discontinuous mode of conduction. The transformer equation can be described as follows. The total time T is considered as summation of maximum TON. TRand TD times -
T = TDN+TR + N ...(2)
Where TR is the reset time and TD is the dead time. Dead time is considered to be 20 %. So the equation (2) can be rewritten as -
0.8T = T()N+TR ...(3)
The operating period is 80 % of total period. This ensures that any sudden change in load current does not force the converter into continuous mode of conduction, until the change is corrected by the internal negative feed back loop. In the continuous mode of conduction, there is no dedicated dead time. The Switch of the PWM Controller block is turned ON before the inductor current decreases to zero, leaving some current in the primary.
The advantages of the continuous mode are small core size and lower peak current, whereas the discontinuous mode requires a larger core size and high primary current. Taking advantage of both the modes, it is possible to achieve wide input range Power Supply. The Power Supply operates in continuous mode at lower input voltage and in discontinuous mode at higher voltage, thereby achieving a wide input range.
Numeral I consists of input terminations, EMC filters, and fuse and inrush current limiter.
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Numeral 2 consists of full bridge rectifier and input filter capacitor to store the energy.
Numeral 3 consists of gapped transformer, which steps down the input voltage as per the primary-secondary turns-ratio and also provides primary-secondary isolation. The transformer works in fly back mode.
The detailed design procedure of the transformer follows:
The energy stored in the fly-back transformer is defined by Equation 4. This energy is
delivered to the secondary side during the OFF time.
E=l/2*Lp*Ipp*lpp ...(4)
I PPrimary Inductance lpp= Primary peak current
Power in Watt can be defined as follow:
P- E/T
Where T=Total time
To achieve wide range of input without saturating the core, it is important to determine the turns-ratio for the transformer to operate at desired switching frequency. The maximum T0„ time can be calculated as follows:
Io„_max = (V„+Vd)*N*(0.8T)/(V min)+( (V0+Vd)*N)... (5)
V„=Desired output voltage Vd=Oiitput diode forward voltage drop
N=Nr/Ns
['^Switching frequency
T=l/F, which ensures the discontinuous mode of conduction at higher input.
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Duty cycle of operation is given by
L' max ~ ' on' I

...(6)

Primary inductance value is calculated as follows -
Lp— Vln niin L)„m/Ipp I un ...(7)
lpP=Peak primary current.
Core saturation is calculated as follows -
1W= Lp *lpp/Np*Ac ..,(8)
Np= Number of Primary Turns
Bmax=Maximum flux density.
Likewise, for known Bmax and AC value from core datasheet at required operating frequency, the Primary turns can be calculated by equation 8
Required AL value can be obtained by -
AL=LP/Np: ...(9)
If core AL value is too low; one can recalculate the primary turns by increasing the switching frequency of Power Supply. This completes the basic design of Transformer.
Numeral 3 consists of transformer with specific calculated gap to increase the magnetic path length; the inductance value of the primary coil is adjusted to obtain a lower value inductor without saturating the core. The turns-ratio of the transformer is adjusted by keeping duty cycle well below the specified duty cycle max limit of the PWM Controller. It is necessary to verify the saturation of the core by using equation 8 for the calculated turns-ratio. The turns-ratio should be such that: - the secondary reflected voltage should not be so high that it over-stresses the MOSFET on the primary side


- output power level is maintained at required levels
Numeral 4 consists of output rectifier and filter. Transformer output is rectified by the diode 4.1. The rectifier selection is done on the basis of turns-ratio, during off time the voltage across the diode should not cross the P1V limit of the diode. During off time the stored energy in the transformer charges the output capacitor and provides the load current. During on time the output capacitor 4.2 provide the necessary load current. Output capacitor should be selected on the basis of ESR (Equivalent Series Resistance)value and secondary RMS (Route Mean Square) current. The desired capacitance and its HSR value can be achieved by connecting capacitors in parallel thereby improving the ripple. Post LC filter may be required to keep ripple level below the specified limit.
Numeral 5 consists of output terminations for connecting the load. It may be necessary to add dummy load on each output to keep the regulation of other auxiliary outputs within the specified limit.
Numeral 6 consists of feedback network resister divider 6.1 and error amplifier 6.2. Resistors divide the output voltage down to 2.5V which is compared against a fixed internal reference using comparator 6.2 and generating an error voltage. This error voltage is proportional to the change in the output voltage due to change in the load current and / or the input line voltage. One has to set the Gain of error amplifier to avoid oscillation at the output. Gain of the error amplifier 6.2 is made high at lower frequency and low at higher frequency. Three pin terminal TL431 is used as error amplifier.
Numeral 7 consists of the optimized feedback network. This is a proposed feedback network which may require. This network consists of a capacitor in series with the gain limiting resistor to give phase boost.
Numeral 8 consists of the Opto isolator. Opto coupler 8.1 is used to couple electrical signal from secondary to primary. Change in the output voltage causes the error current to flow in LED of Opto-coupler 8.1. This current is transferred to the primary
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with some current gain. This current then establishes the duty cycle and corrects the change in the output voltage
Numeral 9 consists of PWM controller 9.1 TOP2XXX. This PWM controller senses the line input voltage through line resistor. The internal current source connected between drain and control pin charges the control pin capacitor. On reaching 5.8V, the control circuit increases the duty cycle to maximum value approximately in 10 milliseconds. The function of this block is to control the PWM pulses and to maintain the output at a constant level.
Numeral 10 consists of range expander circuit. This circuit in which the under voltage lockout of the \C is disabled - is recommended as part of the Power Integration TOP specs manual.
Circuit Description:
When input is applied (20 VAC to 260 VAC or 22 VDC to 360 VDC) to block 1 it is rectified by diode 2.1 and filtered by capacitor 2.2. The rectified voltage is sensed by TOP switch 9.1 of Numeral 9 via Range expander circuit of block 10. Internal circuit of TOP switch increases the duty cycle from minimum to maximum value. Primary of Transformer 3.1 is connected to drain pin of TOP switch 9.1. Raw DC applied to primary winding of transformer 3.1 is connected to the top switch. The current ramps up to the designed value, based on the inductance value of Transformer. This energy stored in the gap of the transformer 3.1 is delivered to the secondary side by turns-ratio of transformer 3.1. The inductance value of the transformer determines the energy stored in transformer as defined in equation 4. Transformer is designed in such a way that this will not saturate at higher input and still operate at lower input voltages. The turns-ratio of the transformer determines the duty cycle and hence the reflected voltage on primary side. Using a high clamping voltage device across the primary winding, the energy transfer to the secondary can be obtained with minimum loss. Energy transferred to the secondary is rectified by diode 4.1 and filtered by capacitor 4.2. Output voltage is sampled by sampling network 6.1 which is a resister divider network. The output is sampled and brought down to 2.5 volt and compared with the fixed internal value and error signal is generated by error amplifier 6.2. The

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output of error amplifier is connected to opto- coupler 8.1 and current flow through the opto-coupler is transferred to secondary with some current gain. This current flows through the control pin capacitor of TOP switch 9.1 and charges the capacitor to value 5.2 V. Excess current will be shunted by internal circuit of TOP switch 9.1 and Hows through the internal resistor which sets the PWM gain for TOP switch. Optimized feedback network of Block 7 helps perform phase boost and avoids oscillations. This block may not be required. Once the value of the control pin capacitor reaches appropriate value, the feedback loop is closed and the Power Supply starts functioning normally. Any change in load and line is corrected by the error amplifier by changing the Ton time.
Accurate turns-ratio keeps the duty cycle in specified range and specific gap placed in transformer core does not allow the transformer to saturate at higher input voltage. Transformer does play an important role in this invention. To achieve such a wide range, the transformer turns-ratio is required to be designed in such a way that it will not saturate at higher input voltages. Equation 1 determines the turns-ratio for the transformer. Inductance value should be selected such that the Power Supply will work in continuous mode of conduction at lower input range. Power Supply will work in discontinuous mode of conduction at higher input voltage.
A correct transformer primary inductance value successfully switches on the Power Supply at lower input voltage and also avoids the saturation at higher input voltage.
The integrated switching technology adds value to the Power Supply design. High end integrated switches like those from TOP switch 9.1 are used in this design. Their specifications indicate that it is possible to use the TOP switch well below 36 VDC however, the control pin charging current reduces which impacts the start up time and auto restart function.
Using OV (over voltage) mode of TOP switch it is possible to switch on the power supply at lower voltage. However, to switch on the TOP switch at lower voltage, the charging capacitor current reduces. This can be achieved by placing a appropriate value resistor across the secondary side of the opto-coupler. This ensures the control pin capacitor charges to specified voltage 5.8V which switches on the TOP switch and hence the power supply at said low input voltage.
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The desired inductance value can be obtained by placing gap in transformer 3.1 which stores the energy. Accurate turns-ratio sets the correct value of the duty cycle. This ensures that duty cycle will swing within its defined range, over the complete line voltage of very lower value of 22 VDC to higher value of 375 VDC achieving required line regulation. Duty cycle will be maximum at lower line voltage and minimum at higher line voltage, thus achieving the wide input range. Optimized feedback network ensures the stability of Power Supply for large variation in input voltage. The correct choice of TOP is dependent upon the Primary current.
Accurate turns-ratio wound around a high frequency ferrite material core, optimized feedback loop and correct value of control pin charging current of TOP switch enables the switching on of TOP switch at lower value of 22 VDC. A correct choice of the current value and selecting the correct TOP switch together made this design different, without using any external circuit to control the range.
Voltage stored in capacitor 2.2 is sensed by block 10 and TOP2XXX starts increasing the duty cycle of the Power Supply. Turns-ratio of transformer 3.1 sets the correct output voltage at secondary by storing the energy in to the gap of the transformer. Inductance value of the primary can also be achieved by using higher volume core.
fhe designed Power Supply has five outputs delivering into a total load of 6 watts. This Power Supply functions from 22 VDC to 375VDC (20 VAC to 260VAC).
In view of the wide variety of embodiments to which the principles of the present invention can be applied, it should be understood that the illustrated embodiments are exemplary only. The illustrated embodiments should not be taken as limiting the scope of the present invention. While various elements of the preferred embodiments have been described as being implemented, other embodiments implications may alternatively be used, and vice-versa.
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We claim.■
I.A multiple output Power Supply system, adapted for providing an output
independent of the input voltage, said multiple output Power Supply system
comprising:
- Input jnrush current limited input filter means adapted to receive input voltage signal and further adapted to provide a filtered output signal;
- input rectifier means adapted to provide a unipolar rectified output signal of said filtered output signal;
- capacitor means adapted to store said rectified output signal;
- transformer means adapted to work in fly-back mode, having a pre-defined number of turns and a pre-defined gap, for providing isolation between said rectified input signal at the primary windings of said transformer and the transformed output signal at the secondary windings of said transformer;
- output rectifier means adapted to provide a rectified filtered output signal of said transformed output signal;
diimm> load adapted to maintain a regulated output signal;
- feedback network means adapted to provide a specific gain by providing a feedback from the secondary side to the primary side; and
- modulation means adapted to provide an output signal at a constant level.

2. A system as claimed in claim I wherein, said filter means in an EMC filter means.
3. A system as claimed in claim 1 wherein, said transformer means is a gapped
transformer means.
4. A system as claimed in claim I wherein, said transformer includes a gap changing
means adapted to change the magnetic path length of said gap transformer.
5. A system as claimed in claim 1 wherein, said feedback network means includes a
resistor network means and an amplifier means adapted to define the gain of the output signal.
6. A system as claimed in claim I wherein, said feedback network means includes
capacitor in series with gain limiting resistor to provide a phase boost.
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7. A system as claimed in claim I wherein, said feedback network means is an opto-
coupler feedback with a correct value of resistor parallel to the secondary side of the opto coupler which ensures a specific control pin charging current to switch on the TOP switch and hence the power supply at said low input voltage.
8. A system as claimed in claim 1 wherein, said modulation means is a pulse width
modulation means.