HYBRID POWER SUPPLY SYSTEM
Field of invention:
The present invention provides a hybrid power supply system. The present invention is particularly useful in the power supply section of low power consuming electronic devices. Low power devices require very low operating voltages and operating currents, which can be provided by using miniature solar panels.

Background of invention;
Power supply is an essential section in an electronic device. The power supply apart from its function, of powering up the device also helps in isolating the secondary side circuits (such as microcontroller section, memory section, communication section etc.) form high voltage surges, electro fast transients etc, for protection of the equipment. The modern day product compliances impose requirements that the product should withstand high levels of voltage surges, the value of which depends on the product class and the standard to which it complies. In a regular power supply the galvanic isolation is provided either by SMPS transformers or by linear transformers, the size of which increases with the increase in the galvanic isolation requirement. The galvanic isolation prevents electric shocks, arc flashes, thermal burns, etc.

This galvanic isolation is required to ensure that the electrical/electronic products that are connected to the secondary power supply system remain safe from the transients that appear on the raw input supply line which can go upto several kilovolts. Another factor which is also taken care by the galvanic isolation is the safety of the user. If the galvanic isolation is compromised there is a good amount of chance that the electronic/electrical product is damaged permanently or there can be conditions such that the transients travel through the electronic devices and damages any other devices to which it is connected such as computers or any communication devices etc.

One common technique for achieving the safety isolation, i.e., the galvanic isolation between the input and output of a power supply is by using a transformer in the power convertor. The disadvantage associated with the technique of inclusion of transformer in the power converter increases the complexity and power supply design tends to become bulky as the galvanic isolation requirements increase. This is because for attaining higher isolation using conventional transformers, the quantity, i.e. the number of layers of insulating tape has to be increased, and the creepage (i.e. the distance between adjacent pins and layers) has to be increased, which can be attained by using a bigger sized bobbin. All these factors tend to increase the overall transformer size and the size of the PCB on which it is mounted. Moreover using more layers of insulating tape/ creepage will tend to increase the leakage inductance of the transformer and efficiency of the transformer reduces drastically also it poses a threat to the life of the switching device.

With a view therefore to overcome the disadvantages associated with conventional transformer based power supply system, the inventors felt the need to develop a novel hybrid power supply system which aims in providing higher galvanic isolation while keeping the overall size of the power supply small. The invention helps in eliminating the SMPS or the linear transformer from the power supply design.

In the present invention the primary power supply unit is provided with an array of light emitting devices electrically connected to an AC voltage source, while the secondary power supply unit is provided with a photovoltaic device optically coupled with said array of light emitting devices. A galvanic isolation block disposed between said primary power supply unit and said secondary power supply unit.

The alternative method to achieve benefits of the present invention would perhaps be to use a direct DC supply from devices such as batteries etc. But such system cannot be used with AC power supply.

Heat energy may be an alternative way of generating DC power by coupling it with a thermocouple. But there may be risk of overheating the electrical/electronic components attached to the secondary power source and thereby damaging them. Also the chances of electrical fire cannot be ruled out.
One might think of using a dynamo to generate the DC power required to operate the equipment. But a system using dynamo requires inductive coupling and it required moving components to be incorporated in the system. The set up of a power generating system using dynamo is a complicated setup.

US patent document US7453710B2 discloses a transformerless safety isolation in a power supply. Here the isolation relies on the dielectric material used in the capacitor. The disadvantage associated with US 7453410B2 is that the size of the capacitor increases with the increase in the dielectric. Moreover, the property of the dielectric material used deteriorates with usage.

In the present invention no transformer has been used. This eliminates the use of inductive coupling between the primary power supply unit and secondary power supply unit and thus the filtering components used in the primary power supply unit has been reduced because the noise has been reduced. The secondary power supply unit outputs pure DC voltage which does not require any AC noise filtering; thereby reducing the number of components in the secondary power supply unit.

The present invention is particularly applicable in low powered devices. However, the present invention can also be used to power electronic devices which require high operating power. This can be achieved by optimizing the photovoltaic devices and light emitting devices. The present invention can be used by the electronic device manufactures, who design products which are to be used with the mains power supply. The present invention is applicable to the equipments falling under the CAT III class of equipments and also a few devices falling under the CAT II classification.

Summary of the invention:
Accordingly the present invention provides a hybrid power supply system, and a galvanic isolation block disposed between said primary power supply unit and said secondary power supply unit,
wherein said primary power supply unit comprises: input terminals connected to an AC voltage source,

- an array of light emitting devices electrically connected to said AC voltage source via a driver circuit, said array of light emitting devices being configured to emit monochromatic light energy of predefined waveband/frequency band, and wherein said secondary power supply unit comprises :

- a photovoltaic device optically coupled with said array of light emitting devices, said photovoltaic device being configured to receive said monochromatic light energy emitted from array of light emitting devices and provide predefined DC voltage as output upon converting the light energy into electrical energy,

- a voltage regulator to regulate the DC voltage output from said photovoltaic device, and

- output terminals connected to said voltage regulator.
According to a preferred embodiment of the invention said driver circuit for said array of array of light emitting devices comprises, a full wave rectifier unit for rectifying the AC voltage received from said AC voltage source and thereupon providing rectified DC voltage as output, a filtering circuit connected with said full wave rectifier unit for filtering off noise components from said rectified DC voltage,
a switching device fed with said rectified DC voltage to control the current flowing through said array of light emitting devices,
a brightness control circuit for presetting the current flowing through said array of light emitting devices to user defined values, and

a protection circuit to protect said switching device in cases of open circuit or short circuit fault conditions.

According to a another embodiment of the invention each of said light emitting devices is provided with a lens for focusing and directing the emitted light towards said photovoltaic device.

According to a further embodiment of the invention each of said light emitting devices is provided with a reflector for focusing and directing the emitted light towards said photovoltaic device.

According to another preferred embodiment of the invention said photovoltaic device comprises of an array of solar panels.
In the present invention said galvanic isolation block may be in the form of an air gap or in the in the form of transparent glass sheets or in the form of transparent mica sheets or in the form of in the form of transparent polyester film. In other words, air gap between the LEDs and the solar panels may be bridged using a transparent insulating material such as glass, mica sheets or polyester film etc, which can increase the isolation in the order of kilo volts.

According to yet another preferred embodiment of the invention said AC voltage source of the primary power supply unit is in the range between 85 VAC to 265 VAC. In other words, the invention works on universal power supply range i.e., 85 VAC to 265 VAC. According to a further embodiment of the invention the secondary power supply unit is provided with a plurality of energy storage capacitors.

According to one embodiment of the invention, said filtering circuit is a CR circuit comprising of at least a pair of capacitors and a resistor.

According to another embodiment of the invention, said full wave rectifier unit comprises of at least a pair of diodes biased oppositely with respect to each other.

According to yet another embodiment of the invention, said brightness control circuit comprises a capacitor and a variable resistor.

According to still another embodiment of the invention, said said protection circuit comprises a pair of reversely biased diodes, a first diode and a second diode, and a forwardly biased Zener diode, and wherein said first diode is connected in series with said Zener diode and said second diode is connected in parallel with said Zener diode.

According to a still further embodiment of the invention said switching device, said brightness control circuit, said protection circuit and said array of light emitting devices are electrically connected to form a closed loop circuit which for maintaining a constant current in said closed loop circuit and thereby maintain a constant brightness of said array of light emitting devices.

Preferably each of said light emitting devices is a white light emitting diode (LED).
In the invented hybrid power supply system, said device may be provided with a resistor divider network for providing voltage feedback to said switching device.
Preferably in the invented hybrid power supply system said switching device is in the form of a switcher IC.
In the invented hybrid power supply system, said photovoltaic device may be comprised of an array of solar panels. Preferably, said array solar panels said array of solar panels is configured to output DC voltage of 5V and output current of 60 mA.
The alternative method to achieve the said benefits would be to use a direct DC supply from devices such as batteries etc. but here the equipment cannot be used with AC power supply.
Heat energy is another way to generate DC power by coupling it with a thermocouple. But it introduces the risk of overheating the nearby components and thereby damaging them also chances of electrical fire also increases.
The concept of a dynamo can be used to generate the DC power required to operate the equipment. But it again has inductive coupling and also it introduces moving components into the device which is a complicated setup.
Currently the idea finds its application in low powered devices. This can further scale up to be used with electronic devices which require high operating power. This can be achieved by optimizing the solar panels and LED's.
Brief description of the drawings:
For better understanding various embodiments of the invention will now be described with reference to the accompanying drawings. It will, however, be appreciated that the embodiments exemplified in the drawings are merely illustrative and not limitative to the scope of the invention, because it is quite possible, indeed often desirable, to introduce a number of variations in the embodiments that have been shown in the drawings. In the accompanying drawings:
Figure 1 is a schematic block diagram of the invented hybrid power supply system according to a particular embodiment of the invention.

Figure 2 schematically illustrates the circuit diagram of the invented hybrid power supply system, according to a preferred embodiment of the invention.
Figure 3 graphically illustrates ON/OFF control of the switcher IC control to regulate the output current, according to a particular embodiment of the invention.
Figure 4 graphically illustrates the relation between the luminous intensity of the LEDs and the output power of the solar panels, according to a particular embodiment of the invention.
Detailed description of the drawings:
Referring to figure 1 of the accompanying drawings, the invented hybrid power supply system (100), according to a particular embodiment of the invention, comprises a primary power supply unit (102), a secondary power supply unit (104), and a galvanic isolation block (106) disposed between the primary power supply unit (102) and the secondary power supply unit (104).
The primary power supply unit (102) comprises:
- input terminals (108) connected to an AC voltage source (not shown in figure 1),
- a full wave rectifier unit (110) for rectifying the AC voltage received from said AC voltage source and thereupon providing rectified DC voltage as output,
- a filtering circuit (112) connected with said full wave rectifier unit (110) for filtering off noise components from said rectified DC voltage,
- an array of light emitting diodes (114),
- a switching device (116) fed with said rectified DC voltage to control the current flowing through said array of light emitting diodes (LEDs) (114),
- a brightness control circuit (118) for presetting the current flowing through said array of LEDs (114) to user defined values, and
- a protection circuit (120) to protect said switching device (116) in cases/events of open circuit or short circuit fault conditions.
The secondary power supply unit (104) comprises:
- a solar panel block (122) optically coupled with said array of LEDs (114),
- a voltage regulator (124) to regulate the DC voltage output from said solar panel block (122), and
- output terminals connected to said voltage regulator (124).
The AC voltage source can vary between 85 VAC to 265 VAC. This input AC voltage has noise and other transients which need to be filtered off.

The full wave rectifier unit (110) is used to rectify the AC voltage in to DC voltage and the filtering circuit (112) is used to filter off all the noise components.
The switching device (116) controls the current flowing through the array of LEDs (114). This switching device (116) shuts off in events of short circuit in the circuit of the array of LEDs (114).
The brightness control circuit (118) is configured to preset the required current passing through the array of LEDs (114).
The galvanic isolation block (106) may be formed of air gap. This air gap isolation can be reinforced by using glass sheet, mica sheets or transparent polyester tapes. This sort of an arrangement can provide isolation to very high levels. Unlike electrical transformers the galvanic isolation block (106) does not have any sort of inductive coupling.
The solar panel block (122), consists of miniature solar panels. The solar panel block (122) is configured to receive the monochromatic light energy emitted from array of LEDs (114) and provide predefined DC voltage as output upon converting the light energy into electrical energy. The solar panels (122), for example, may be of 4cm x 4cm size with an output voltage of 5V and output current of 60mA. The output obtained from the solar panel block (122) is pure DC voltage. These solar panels (122) have very long life, which make them suitable for continued operation. These solar panels (122) have high efficiency when exposed to bright white light. This ensures that no rectification or filtering of the output voltage is required. Only a voltage regulator (124) along with storage capacitors (not shown in figure 1) may be used to provide the required voltage to the secondary circuits (126). As seen in figure 1, the switching device (116), the protection circuit (120), the brightness control circuit (118) and the array of LEDs (114) are connected in such a way to forms a closed loop circuit which helps the switching device (116) _ to maintain a constant current in the closed loop circuit and thereby maintain a constant brightness of the array of LEDs (114).
According to a preferred embodiment of invented power supply system (200), as seen in figure 2 of the accompanying drawings, the primary power supply unit (202) comprises:
an input terminals connected to an AC voltage source,
- an array of light emitting diodes (D6,D7,D8,D9,D 10 and D11), and
- a driver circuit (228) for generating a constant current output for driving the LEDs (D6,D7,D8,D9,D10 and Dl 1) irrespective of the variations in the AC input voltage
The driver circuit (228) comprises a full wave rectifier circuit (210), a filtering circuit, a switching device in the form of switcher IC (216), a brightness control circuit (218) and a protection circuit (220). The full wave rectifier circuit (210) is formed of the diodes Dl and D2, the filter circuit is an RC circuit formed of comprising of the capacitors CI, C2, the

resistor R2. Inductor LI is used for charge storage. The protection circuit (220) is formed of the diodes D3, D4 and the Zener diode D5. The diodes D3 and D4 are reverse biased and the Zener diode D5 is forward biased. The diode D4 is connected in series with the Zener diode D5 while the diode D3 is connected parallel with respect to the Zener diode D5.The brightness control circuit (218) comprises of the capacitor C4 and the resistor R6.
As seen in figure 2 a buck-boost topology IC generates a constant current output for driving the LEDs (D6,D7,D8,D9,D10 and Dll). However, any other form of driving circuit for the LEDs (D6,D7,D8,D9,D10 and Dll) can be used for the same purpose.

The secondary power supply unit (204), as seen in figure 2, comprises of a pair of solar panels (222-1,222-2). The solar panel 222-1 is provided with the voltage regulator 224-1 while the solar panel 222-2 is provided with the voltage regulator 224-2.
The primary power supply unit (202) and the secondary power supply unit (204) are galvanically isolated by the transparent insulator layer (206).

The method/technique by which the driver circuit (228) generates constant current output will now be explained with reference to figure 2.

The AC input, fed through the resistor Rl, is rectified by the diodes Dl and D2. The diodes Dl and D2 improve both line surge withstand and conducted electromagnetic interference (EMI). The rectified voltage contains noise components which are filtered by the RC circuit. The resistor Rl should be fusible and flameproof type, whereas R2 may be flameproof type only.

Referring to figure 2, the switcher IC (216) uses On/Off control to regulate the output current. The internal clock (not shown in figure 2) of the switcher IC (216) runs all the time. At the beginning of each clock cycle, the switcher IC (216) samples the feedback pin (FB) to decide whether or not to implement a switch cycle and based on the sequence of samples over multiple cycles, it determines the appropriate current limit. The capacitor C3 is used for noise filtering on the bypass pin (BP) of the switcher IC (216). The capacitor C5 is used for filtering any surge current that might appear near the LEDs (D6, D7, D8, D9, D10 and Dll) due to the switcher IC (216). The resistors R3 and R5 forms a resistor divider network for giving voltage feedback to said switcher IC (216).

At high loads, the state machine sets the current limit to its highest value. At lighter loads the state machine sets the current limit to reduced value. At near maximum load the switcher IC (216) will conduct nearly all of its clock cycle. At slightly lower load switcher IC (216) will 'skip' additional cycle in order to maintain current regulation at the power supply output.

The response time of the ON/OFF control scheme is very fast to control the current. The switcher IC (216) only takes the required power form the mains supply. This reduces the wastage of power and also makes sure that the LEDs (D6, D7, D8, D9, D10 and Dl 1), glow with required brightness. The relation between the luminous intensity of the LEDs (D6, D7, D8, D9, D10 and Dll) and the output power of the solar panels (222-1,222-2) has been graphically illustrated in figure 4 of the accompanying drawings. The ON/OFF control of the switcher IC (216) has been graphically illustrated in figure 3.

When the current into the feedback pin (FB) exceeds a fixed limit (depending on the component), the switching in the switcher IC (216) is disabled for the next switching cycle. The voltage across R6, which is averaged by C4 represents the output current. The voltage across R6 sets the current for the (D6, D7, D8, D9, D10 and Dl 1) for the required brightness. This current limiting action of the brightness control circuit (218) ensures minimal wastage of power and also ensures that the customer is safe from high power. If any of the LEDs (D6, D7, D8, D9, D10 or Dl 1) is disconnected or shorted, no feedback is provided and the switcher IC (216) restarts. The diode D4 and the Zener diode D5 protect the circuit from open load condition.

The LEDs (D6, D7, D8, D9, D10 and Dll) and the solar panels (222-1,222-2) are arranged such that the light emitted from the LEDs (D6, D7, D8, D9, D10 and Dl 1) falls perpendicular on to the solar panels (222-1,222-2). This will ensure optimum performance of the solar panels (222-1,222-2). The array of LEDs (D6, D7, D8, D9, D10 and Dl 1) are configured to emit monochromatic light. The array of LEDs (D6, D7, D8, D9, D10 and Dl 1) are placed in such a manner that the total light emitted from the LEDs (D6, D7, D8, D9, D10 and Dl 1) is focused directly on the solar panels block (222-1, 222-2). The brightness of the LEDs (D6, D7, D8, D9, D10 and Dl 1) is directly proportional to the current flowing through them.

Preferably, the LEDs (D6, D7, D8, D9, D10 and Dll) used are white light LEDs, because their wavelength has a very broad spectrum. Each of the LEDs (D6, D7, D8, D9, D10 and Dl 1) are provided with lens/reflector which allows focusing the light in a particular direction. The operating voltage range for these LEDs (D6, D7, D8, D9, D10 and Dl 1) lie below 5V and the current requirement for complete brightness is below 50mA. These surface mount LEDs are ideal for frequent ON/OFF cycling, and they achieve their full brightness within a microsecond. In contrast to other light sources, LEDs radiate very little heat in the form of IR, this ensures that the nearby electronic components are not damaged. The effective lifetime of these LEDs typically range between 35,000 to 50,000 hours.

Presetting the resistor R6 allows the required current to flow through the LEDs (D6, D7, D8, D9, D10 and Dl 1) and thereby the brightness of the LEDs (D6, D7, D8, D9, D10 and Dl l)is controlled and the output of the solar panels is regulated. The solar panels (222-1,222-2) produce DC voltage without any AC noise components; hence the need for any kind of filtering is eliminated. The bulk capacitors C6, C7, C8 and C9, as seen in figure 2, are used for energy storage which is required in events of momentary changes in the power requirement at the secondary side. The regulated DC voltages appearing on the outputs of voltage regulators (224-1,224-2) are used to power up the various secondary side circuits.

As already mentioned the foregoing description is illustrative of the invention and not limitative to its scope; because it will be apparent to persons skilled in the art to devise other alternative embodiments without departing from the broad ambit of the disclosures made herein.

We claim:

1. A hybrid power supply system comprising a primary power supply unit, a secondary power supply unit, and a galvanic isolation block disposed between said primary power supply unit and said secondary power supply unit, wherein said primary power supply unit comprises: input terminals connected to an AC voltage source,

an array of light emitting devices electrically connected to said AC voltage source via a driver circuit, said array of light emitting devices being configured to emit monochromatic light energy of predefined waveband/frequency band, and wherein said secondary power supply unit comprises :

- a photovoltaic device optically coupled with said array of light emitting devices, said photovoltaic device being configured to receive said monochromatic light energy emitted from array of light emitting devices and provide predefined DC voltage as output upon converting the light energy into electrical energy,

- a voltage regulator to regulate the DC voltage output from said photovoltaic device, and

- output terminals connected to said voltage regulator.

2. The hybrid power supply system as claimed in claim 1, wherein said driver circuit comprises,

a full wave rectifier unit for rectifying the AC voltage received from said AC voltage source and thereupon providing rectified DC voltage as output,

a filtering circuit connected with said full wave rectifier unit for filtering off noise components from said rectified DC voltage,

a switching device fed with said rectified DC voltage to control the current flowing through said array of light emitting devices,

a brightness control circuit for presetting the current flowing through said array of light emitting devices to user defined values, and

a protection circuit to protect said switching device in cases of open circuit or short circuit fault conditions.

3. The hybrid power supply system as claimed in any of the above claims , wherein each of said light emitting devices is provided with a lens for focusing and directing the emitted light towards said photovoltaic device.

4. The hybrid power supply system as claimed in any of the above claims, wherein each of said light emitting devices is provided with a reflector for focusing and directing the emitted light towards said photovoltaic device.

5. The hybrid power supply system as claimed in any of the above claims, wherein said galvanic isolation block is in the form of an air gap.

6. The hybrid power supply system as claimed in any of the above claims 1 to 4, wherein said galvanic isolation block is in the form of transparent glass sheets.

7. The hybrid power supply system as claimed in any of the above claims 1 to 4, wherein said galvanic isolation block is in the form of transparent mica sheets.

8. The hybrid power supply system as claimed in any of the above claims 1 to 4, wherein said galvanic isolation block is in the form of transparent polyester film.

9. The hybrid power supply system as claimed in any of the above claims, wherein said secondary power supply unit is provided with a plurality of energy storage capacitors.

10. The hybrid power system as claimed in any of the above claims, wherein said filtering circuit is a CR circuit comprising of at least a pair of capacitors and a resistor.

11. The hybrid power system as claimed in any of the above claims, wherein said full wave rectifier unit comprises of at least a pair of diodes biased oppositely with respect to each other.

12. The hybrid power system as claimed in any of the above claims, wherein said brightness control circuit comprises a capacitor and a variable resistor.

13. The hybrid power system as claimed in any of the above claims, wherein said protection circuit comprises a pair of reversely biased diodes, a first diode and a second diode, and a forwardly biased Zener diode, and wherein said first diode is connected in series with said Zener diode and said second diode is connected in parallel with said Zener diode.

14. The hybrid power system as claimed in any of the above claims wherein said switching device, said brightness control circuit, said protection circuit and said array of light emitting devices are electrically connected to form a closed loop circuit which for maintaining a constant current in said closed loop circuit and thereby maintain a constant brightness of said array of light emitting devices.

15. The hybrid power supply system as claimed in any of the above claims, wherein each of said light emitting devices is a white light emitting diode.

16. The hybrid power supply system as claimed in any of the above claims, wherein said switching device is provided with a resistor divider network for providing voltage feedback to said switching device.

17. The hybrid power supply system as claimed in claim 16, wherein said switching device is in the form of a switcher IC.

18. The hybrid power supply system as claimed in any of the above claims, wherein said photovoltaic device comprises of an array of solar panels.

19. The hybrid power supply system as claimed in claim 18, wherein said array of solar panels is configured to output DC voltage of 5 V and output current of 60 mA.

20. The hybrid power supply system as claimed in any of the above claims, where said AC voltage source is in the range between 85 VAC to 265 VAC.