CLIAMS:We claim:

1) A system for converting voltage source to a current source without the need for a switching technology, comprising a triode structure with an electron emitter wherein emission of electrons is controlled by a gate voltage; a collector; and a gate interposed between said electron emitter and collector such that the flow of electrons from the electron emitter creates a current source based on the gate voltage.

2) The system as claimed in claim 1 wherein the current source is again converted to a voltage source when electrons from the collector are shielded from flowing back to the electron emitter thereby charging the collector to a higher or lower voltage as required.

3) The system as claimed in claims 1 and 2 wherein the electron emitter is a large array of sharp tips or carbon nanotubes.

4) The system as claimed in claims 1 and 2 wherein the gate is a grid or a mesh and the collector is an anode.

5) The system as claimed in claims 1 and 2 wherein the system further comprises at least one actuator to actively control properties such as gate to electron emitter spacing, gate to collector spacing and anode capacitance thereby resulting in flexible and dynamically tunable voltage conversion.

6) The system as claimed in claims 1 to 5 wherein the system is fabricated on a micro-scale level or nano-scale level.

7) The system as claimed in claim 6 wherein the system is used for a power device.

8) A method for converting voltage source to a current source by a triode structure, the method comprising:

converting input voltage into a flow of electrons by an electron emitter;
controlling the emission of electrons by a gate voltage thereby creating a current source based on gate voltage but independent on the output voltage;
shielding the electrons from flowing back from the collector by a gate;
charging the collector to the desired higher or lower voltage.

9) The method as claimed in claim 8 wherein the current source is again converted to a voltage source when electrons from the collector are shielded from flowing back to the electron emitter thereby charging the collector to a higher or lower voltage as required.

10) The method as claimed in claims 8 and 9 further comprising controlling actively the properties such as gate to electron emitter spacing, gate to electron spacing and anode capacitance by an actuator or plurality of actuators.
,TagSPECI:FIELD OF THE INVENTION

[0001] The present invention relates generally to a method and system for converting a voltage source to a current source and back to a voltage source at a different voltage level.

BACKGROUND OF THE INVENTION

[0002] DC to DC converters find many applications in electronics. Typical examples occur in most PCB implementations of electronics and embedded systems where there are sub-circuits that require different voltage levels from the primary power source. A microcontroller may operate at, say 5 Volts, while a modem in a different sub-circuit may operate at 2.8 Volts. Given that there will typically be only one power supply available at a voltage of, say, 12 Volts, this voltage will need to be down-converted to all required voltages for the various sub-circuits. There are other applications where voltage will need to be up-converted as well. For example, MEMS electrostatic actuators need extremely low power to operate but need high voltages of the order of 60-90 Volts. This is because electrostatic force is proportional to the square of voltage and force hence increases significantly with voltage. The power supply on the board may be much lower, especially if a battery is used. In these applications the voltage needs to be significantly boosted from the battery voltage.

[0003] The above refers to DC to DC converter needs for applications that use fairly low power. There are many applications in high power where DC conversion is required. Such converters my operate at high voltage levels such as 100's of volts to kiloVolts and also at higher power levels such as 50 Watts to several kiloWatts or even higher. Typical applications include DC battery chargers, drives for electric vehicles, DC power implementations such as solar cells, power supplies for high power equipment etc.

[0004] There are several existing technologies to design solid-state DC-DC converters. Some primary techniques are described below:

[0005] LDO: These are linear regulators and can only convert a higher voltage to a lower voltage. Unfortunately, these are very lossy as they dissipate power equal to the product of the voltage difference and the current. These converters are hence used in situations where the required voltage change and/or the current are minimal.

[0006] Switched mode: In this technique, the energy is temporarily stored at one voltage and then released at a different voltage. The storage of energy could be implemented through multiple technologies such as capacitive, magnetic etc. As an example of the principle, charge Q = CV could be stored in a capacitor of capacitance C at Voltage V. Through a switching technique, the capacitance could be reduced to half by connecting two capacitors in series. When energy is released from this configuration, the voltage will be doubled as charge is conserved. Capacitance configuration is thus continuously switched, while providing a buffer at the output and a mechanism to prevent backflow of charge to the input. In this technique, the conduction and switching losses of the switching device are limiting factors for efficiency.

[0007] Electromechanical: By coupling the shaft of a DC motor to a DC generator, it is possible to convert one DC voltage to another. This technique is good for high power applications and the mechanical inertia of the motor-generator set works as a fly-wheel or the equivalent of a capacitor, thus providing smooth flow of energy through load fluctuations. However, this technique typically requires a brushed DC motor to be entirely electromechanical. This could pose potential reliability issues. While the efficiency of motors and generators is quite high today, further work is required towards increasing the efficiency of the motor generator combination for DC applications.

[0008] MEMS: There have been attempts to make a DC-DC converter using MEMS technology - these basically use principles already discussed above but at the microscale. There are a few but limited references in this area. We refer to the following publication: Microsyst Technol (2012) 18:1801-1806, Multiple-output MEMS DC/DC converter: a system modeling study, A. Chaehoi et.al. A MEMS device based on capacitance charge storage was designed, fabricated and tested. As shown in Fig. 1, this device consists of two sets of drive electrodes Cd1 and Cd2. The output electrodes are on the sides, labelled C1 and C2. This device is driven at resonance through the driving capacitors. The input voltage that needs to be converted is applied across the pump charge capacitors. As the drive electrodes move to and fro, the spacing between the pump charge electrodes alternately increases and decreases. When the gap between plates in the pump charge electrodes decreases, capacitance increases and charge increases at constant input voltage. When the gap between the plates subsequently decreases, the capacitance decreases and the excess charge has to leave the capacitor. This charge is held in a reservoir (diodes prevent backflow of charge to the input source) such as a higher voltage capacitor. The obvious drawbacks of this technique are many: The driving electrodes need to be driven by an AC source, which has to be provided separately or converted from the DC input voltage. This requires the use of electronic circuitry to perform this conversion. Secondly, the use of diodes creates an unwanted forward drop and hence a further efficiency loss. Thirdly, the reported output power of this device is only 56 pW. Though this work was not performed for a power device, it is perhaps possible to scale the number of capacitor fingers in order to increase the power performance.

[0009] There is a recognized need in the art for a voltage converter that does not suffer from the drawbacks of conventional solid-state converters such as (including but not limited to) forward drop, excessive conduction and switching losses, the requirement for an added driver circuit etc. We should also not suffer the drawbacks of electromechanical converters such as the reduced reliability of brushed systems and the efficiency loss in the multi-conversion chain involving Electrical to magnetic to mechanical (motor) and further from mechanical to magnetic and back to electrical (generator). The present invention overcomes the above disadvantages and fulfills this long standing need in the art.

SUMMARY OF THE INVENTION

[00010] An object of the present invention is to provide a system and method for converting a voltage source to a current source and back to a voltage source at a different voltage level and to implement this without the need for a switching technology.

[00011] An object of the present invention is to provide a voltage converter that does not suffer from the drawbacks of conventional solid-state converters such as (including but not limited to) forward drop, excessive conduction and switching losses, the requirement for an added driver circuit etc.

[00012] Another object of the present invention is to provide a voltage converter that does not suffer the drawbacks of electromechanical converters such as the reduced reliability of brushed systems and the efficiency loss in the multi-conversion chain involving Electrical to magnetic to mechanical (motor) and further from mechanical to magnetic and back to electrical (generator).

[00013] Accordingly, to meet the objects of the invention, disclosed herein is a system for converting voltage source to a current source without the need for a switching technology, comprising a triode structure with an electron emitter wherein emission of electrons is controlled by a gate voltage; a collector; and a gate interposed between said electron emitter and collector such that the flow of electrons from the electron emitter creates a current source based on the gate voltage. The current source can again be converted to a voltage source when electrons from the collector are shielded from flowing back to the electron emitter thereby charging the collector to a higher or lower voltage as required. The electron emitter may be a large array of sharp tips or carbon nanotubes. The gate can be a grid or a mesh and the collector can be an anode. The system further comprises at least one actuator to actively control properties such as gate to electron emitter spacing, gate to collector spacing and anode capacitance thereby resulting in flexible and dynamically tunable voltage conversion. The system can be fabricated on a micro-scale level or nano-scale level. The system can be used for a power device.

[00014] Losses are minimized in type of DC-DC converter by the following two primary mechanisms among others: 1) Designing the gate grid material and geometry and the gate to collector spacing such that a very small number of electrons are captured by the gate and consequently reducing gate current and hence reducing power loss at the input and 2) Designing the gate grid material and geometry such that the gate effectively shields the collector from emitter voltage so that even though the current flowing into the collector is large, the electric field and hence the voltage drop between gate and collector is nearly zero.

[00015] Accordingly, to meet the objects of the invention, disclosed herein is a method for converting voltage source to a current source by a triode structure, the method comprising converting input voltage into a flow of electrons by an electron emitter; controlling the emission of electrons by a gate voltage thereby creating a current source based on gate voltage but independent on the output voltage; shielding the electrons from flowing back from the collector by a gate; charging the collector to the desired higher or lower voltage. The current source can again be converted to a voltage source when electrons from the collector are shielded from flowing back to the electron emitter thereby charging the collector to a higher or lower voltage as required. The properties such as gate to electron emitter spacing, gate to collector spacing and anode capacitance can be actively controlled by an actuator or plurality of actuators.

BRIEF DESCRIPTION OF THE DRAWINGS

[00016] Referring now to the drawings wherein the showings are for the purpose of illustrating embodiments of the inventions only, and not for the purpose of limiting the same.

[00017] Fig. 1 shows a conventional MEMS capacitive DC to DC converter.
[00018] Fig. 2 shows a block diagram for a DC-DC converter.
[00019] Fig. 3 shows a triode vacuum tube
[00020] Fig. 4 shows a diamond tip field emitter
[00021] Fig. 5 shows a large array of very sharp tips created through thermal oxidation of silicon
[00022] Fig. 6 shows a schematic diagram of DC to DC converter device showing electron emitter, grid and anode (electron collector) in accordance with an exemplary embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION

[00023] Definitions unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

[00024] The present invention will be described herein below with reference to the accompanying drawings. The present invention discloses a system and method for converting the voltage source to a current source and once the voltage is converted into current, the current can be converted back to different voltage.

[00025] Fig. 2 shows a block diagram for a DC-DC converter.
[00026] In an embodiment of the present invention, the input voltage is converted into a flow of electrons without a significant forward drop in the process of conversion. One such way is to make an electron emitter that emits electrons in proportion to the applied voltage. Other ways may be used consistent with the spirit of the invention. This emission of electrons has to be proportional to the input voltage only and should not depend on the output voltage. In other words, the output voltage should be "independently" controllable. For this purpose, a triode vacuum tube valve is used consistent with the spirit of the invention. It can be fabricated on a micro-scale level or a nano-scale level. The triode has an electron emitter where the emission of electrons is controlled by the "gate" voltage. The "gate" is a grid or mesh that is placed in fair proximity with the emitter and can influence the flow of electrons from the emitter (the emitter current). The gate performs a second function of shielding these electrons from the collector. Hence this arrangement effectively creates a current source based on gate voltage. In conventional vacuum tubes, there is a separate power source to power the emitter for thermionic emission, but this is not strictly necessary and can potentially be replaced by an emitter that is driven by the input voltage itself.
[00027] Figure 3 shows a triode vacuum tube with emitter (cathode), gate (grid) and collector (anode). The two symbols in the bottom show two configurations - one where the filament is separate from the cathode and the second, where the filament is the cathode itself. Note that the term filament is primarily used for thermionic devices.
[00028] According to a preferred embodiment, low work function materials are used as field emitters. Though field emission will be our primary approach, thermionic emission is also a possibility. Through micro scale / MEMS fabrication techniques, it is possible to make extremely sharp tips and also space them very close to a grid - both of these factors will ensure an extremely high electric field for a reasonable voltage, thus making the case for field emission as the first choice of emitter technology. Thermionic emission has the advantage that it can be used to emit a very large number of electrons but with the added overhead of heating a filament. The ability to produce high temperatures is small thermal masses has been previously demonstrated.
[00029] In a preferred embodiment, there is a large array of sharp tips, a grid above this array that will serve as a gate and an electrode above the gate that will serve as the collector. Fig. 4 shows a diamond tip field emitter. Fig. 5 shows a large array of very sharp tips created through thermal oxidation of silicon.
[00030] This triode structure may potentially be realized in the lateral direction as well.
[00031] Figure 6 shows a schematic diagram of DC to DC converter device showing electron emitter, grid and anode (electron collector) in accordance with an embodiment of the present invention.

[00032] The architecture shown in Figure 6 is inherently scalable. The number of tips and the size of the grid and anode can be scaled, without limit to increase the current output (and hence power handling) of the device. The anode is made thick and highly conductive to reduce any ohmic conduction losses at the output. Low work function coatings on the emitter array will ensure that the voltage required for starting emission will be minimal (or tunable based on the requirement of the power application). Carbon nanotubes may also be used as a field emitter, consistent with the spirit of the invention. Further extension to the triode structure are possible such as a 4-electrode, 5-electrode (pentode) structure etc.

[00033] The Fowler Nordheim equations predict the current density from in field emission. Here we refer to practical implementations of field emitters such as those found in the following reference: Electrical and field emission investigation of individual carbon nanotubes from plasma enhanced chemical vapour deposition, W.I. Milnea et.al., Diamond and Related Materials 12 (2003) 422–428. In this work, a practical field emission current of 10µA is obtained from carbon nanotubes. It is also known through several references that a very high density of nanotubes is possible on a chip - numbers in the several million nanotubes per square centimetre have been achieved. For thermal applications, even higher densities have been reported, of the order of 10 million to 1 billion tubes per sq.mm. Indeed, for interconnect applications, current densities of the order of 10 million Amps per sq. cm are being quoted. Properties such as gate to emitter spacing, gate to collector spacing and anode capacitance may be actively controlled through MEMS actuators thus resulting in flexible and dynamically tunable voltage conversion devices.

[00034] In view of the above, a DC-DC converter can be realized and when two such devices are used back to back, it can be used for AC as well.

[00035] The Target End User Applications are given below:
i) Power device
ii) On-board, rack-mounted and discrete power supplies
iii) DC motor drives
iv) Automotive power electronics. Eg: Supply for power steering from battery voltage
v) Electric vehicles - both EV and HEV
vi) Battery chargers
vii) Higher voltage applications (Solid-state devices are often voltage limited, but the valve concept can be adapted to much higher voltages)
viii) Solar power conversion applications
ix) Aviation and Space applications in the future

[00036] The foregoing description is for preferred embodiments of the present invention. It should be appreciated that these embodiments are described for purpose of illustration only, and that numerous alterations and modifications may be practiced by those skilled in the art without departing from the spirit and scope of the invention. It is intended that all such modifications and alterations be included insofar as they come within the scope of the invention as claimed or the equivalents thereof.

[00037] Other modifications will be apparent to those skilled in the art and, therefore, the invention is defined in the claims.