Patent Application
20090016091
The present invention relates generally to electronic circuits, and more particularly, to the use of half bridge and full bridge circuits for control of output power or power regulation in ultrasonic generators.
For years, half bridge and full bridge electronic circuits have been used as the output power generating topology for various ultrasonic and plasma generators in the frequency range of about 18 khz to 14 Mhz, with ultrasonic generators in the 350 khz to 10 Mhz range often referred to as megasonic generators. Typically, it is desired to set the output power of such generators to some desired value for a particular application, to change this power at will and/or to regulate this power to a constant value when outside factors would otherwise cause it to change. A basic output power control feature is needed to implement these features.
Prior art half bridge and full bridge generator circuits use several different methods to control output power. One commonly used configuration uses a variable voltage power supply to supply the +VDC voltage to a half bridge or full bridge circuit. In such a configuration, as the +VDC voltage is decreased, the output power of the half bridge or full bridge generator decreases. A second commonly used configuration uses variable duty cycle gate drive signals to half bridge or full bridge switching devices. In such a configuration, as the duty cycle of the gate drive signals is decreased, the output power of the half bridge or full bridge generator decreases. These prior art systems have certain disadvantages. For example, prior art variable voltage power supply systems are expensive and inefficient while variable gate drive duty cycle prior art systems lack the ability to linearly control power at low power levels.
With parenthetical reference to the corresponding parts, portions or surfaces of the disclosed embodiment, merely for purposes of illustration and not by way of limitation, the present invention is generally directed to circuits for control of output power or power regulation. According to one aspect of the invention, a regulator circuit and system allows the output power of a bridge generator to be controlled by inserting a voltage between the emitter or source of a lower switching device in a half bridge, or lower switching devices in a full bridge (this node will be referred to herein as the “bridge bottom” or −VDC) and the minus voltage supply (often ground) (this node will be referred to herein as “ground”).
According to one aspect of the invention, the improved circuit and system has high efficiency because, among other things, there are no resistors to cause IR losses. The operation of the circuit and system comprises, in one aspect, changing the duty cycle of the gate drive to the switching device in a regulator circuit or, in another aspect, changing both the frequency and duty cycle to the gate drive for more efficient switching of the switching device. Higher duty cycles develop a lower voltage at the bottom of the bridge generator; this gives a higher voltage drop across the bridge, which results in high output power and high amplitude. Lower duty cycles develop a higher voltage at the bottom of the bridge generator; this gives a lower voltage drop across the bridge, which results in low output power and low amplitude. In one aspect of the invention, a continuous range of output powers and amplitudes are produced over the continuous range of duty cycles to the base of the circuit's switching device.
Another advantage of the regulator circuit is that its maximum inefficiency is near the middle of the output power range from the bridge circuit. The regulator increases efficiency as the output power of the bridge is raised from about 50% to 100%. This advantage is especially important when compared to state of the art switching supplies that change the voltage to the +VDC supply of the bridge to regulate the output power. These prior art circuits dissipate maximum power at the full power output from the bridge, which is the condition when the bridge is dissipating the maximum power, causing maximum heating and loss at 100% power.
In one aspect of the invention, a regulator circuit comprises an inductor (13) in series with a switching device (12), for example, a power MOSFET, an IGBT (insulated gate bipolar transistor), or a NPN bipolar transistor; with the inductor (13) coupled to the bridge bottom (17) and the source (28) or emitter of the switching device coupled to ground (19). In one aspect, there is a diode (14) from the connection between the inductor and the switching device and the bridge's high voltage +VDC power supply (18). In yet another aspect, some capacitance (15) is connected from the bottom (17) of a bridge circuit (11) to a DC reference (for example 18) or ground (20); this capacitance can be a separate component, or this capacitance may exist as part of the bridge circuit. In another aspect, a resistor (16) may be coupled between the gate terminal (23) of the switching device and the drive terminal (29) which accepts a variable duty cycle waveform. In one aspect of the invention, a half bridge or full bridge circuit (11) is connected between the +VDC terminal (18) and the first terminal (17) of the regulator circuit.
The invention is next described further in connection with preferred embodiments, and it will become apparent that various additions, subtractions, and modifications can be made by those skilled in the art without departing from the scope of the invention.
The foregoing and other objects of this invention, the various features thereof, as well as the invention itself, may be more fully understood from the following description, when read together with the accompanying drawings in which:
At the outset, it should be clearly understood that like reference numerals are intended to identify the same parts, elements or portions consistently throughout the several drawing figures, as such parts, elements or portions may be further described or explained by the entire written specification, of which this detailed description is an integral part. The following description of the preferred embodiments of the present invention are exemplary in nature and are not intended to restrict the scope of the present invention, the manner in which the various aspects of the invention may be implemented, or their applications or uses.
In a preferred embodiment of the invention, the regulator circuit when used with a half bridge circuit is configured as follows: An electronic half bridge circuit with power regulation circuit referenced to system ground and driven by a variable duty cycle waveform comprising an electronic half bridge circuit with DC power supply terminals designated as +VDC and −VDC; a regulator circuit with a first terminal, a second terminal, a source terminal, and a gate terminal, the first terminal is coupled to the −VDC terminal of the electronic half bridge circuit, the second terminal is coupled to the +VDC terminal of the electronic half bridge circuit, the source terminal is coupled to the system ground, and the gate terminal is coupled to a variable duty cycle waveform or waveform generator. The regulator circuit in the preferred embodiment has (a) an inductive element with a first terminal and a second terminal, the first terminal of the inductive element coupled to the −VDC terminal of the half bridge circuit; (b) a switching device with a drain terminal, a source terminal and a gate terminal, the drain terminal of the switching device coupled to the second terminal of the inductive element, the source terminal of the switching device coupled to the system ground of the regulator circuit, and the gate terminal of the switching device coupled to the variable duty cycle drive waveform; (c) a diode with an anode terminal and a cathode terminal, the anode terminal coupled to the second terminal of the inductive element and the cathode terminal coupled to the +VDC terminal of the electronic half bridge circuit; and (d) a capacitive element with a first terminal and a second terminal, the first terminal of the capacitive element coupled to the −VDC terminal of the electronic half bridge circuit, and the second terminal of the capacitive element coupled to +VDC or system ground or both. In the preferred embodiment, the value of voltage at the −VDC terminal of the electronic half bridge circuit changes when the duty cycle of the variable duty cycle waveform changes.
The regulator circuit when used with a full bridge circuit is configured similarly to the configuration used with a half bridge circuit as is readily understood by a person skilled in the art.
Referring now to the drawings, and first, particularly, to
Half bridge 41 of
Full bridge 54 of
During operation of the preferred embodiment described herein, when the switching device 12 is on, charge from the capacitance 15 flows into the inductance 13 and is stored there as energy in the magnetic field; then, when the switching device is off, this energy in the inductor 13 flows through the diode 14 back to the +VDC power supply 18. According to one aspect of the invention, the higher the duty cycle of the switching device, the longer it is on, and therefore more energy is transferred from the node at the bottom of the bridge to the +VDC power supply. This lowers the voltage at the node at the bottom of the bridge which results in a higher voltage drop across the bridge and higher power produced by the bridge circuit. Lower duty cycles to the switching device transfer less energy and the voltage at the node at the bottom of the bridge builds up to a higher value resulting in less voltage drop across the bridge and therefore less power generated by the bridge. In the two extreme cases, that is, the switching device constantly off or fully on, the output power of the bridge circuit is zero power or full power, respectively. The switching device constantly off case can be understood by observing that the voltage of the capacitance at the node at the bottom of the bridge builds up to +VDC and therefore there is no voltage across the bridge. This is a zero power condition. The switching device fully on case can be understood by observing that the voltage of the capacitance at the node at the bottom of the bridge decays down to ground level because the inductor and the on switching device look like a short circuit to ground for this steady state condition. Therefore, there is maximum voltage across the bridge, that is +VDC. This is the maximum power condition.
To simplify the understanding and description of the regulator circuit, system ground was chosen and defined to be at the source terminal of the switching device. It is well known to those skilled in the art that any DC reference point in the circuit can be chosen as the system ground without changing the functionality of the circuit.
The bridge and regulator circuit of this embodiment were described using circuitry and devices where current flows from +VDC at the top of the bridge, through the bridge, through the regulator circuit and into ground or −V. This configuration generally requires switching devices such a N channel power MOSFETs, IGBTs or NPN bipolar transistors. It is readily understood by someone skilled in the art that equivalent operation can be realized with different direction current flow and/or different polarity voltage supplies by using P channel power MOSFETs or PNP bipolar transistors. Also many other switching devices, for example, GTOs (gate turn off thyristors) can be used in these circuits; however, currently the best choices are MOSFETs or IGBTs.
In another embodiment, the capacitive element of the inventive system is obtained from the power supply capacitors of the bridge circuit (half bridge or full bridge) rather than a separate capacitive element in the regulator circuit. For such embodiment, the following description applies: an electronic bridge circuit with first and second power supply lines connected to a power regulation circuit driven by a variable duty cycle waveform comprising: a series connected inductive element and a switching device connected in series with one power supply line of the bridge circuit, a diode element connected from the junction between the inductive element and the switching device to the second power supply line of the bridge circuit, wherein the value of voltage across the power supply lines of the electronic bridge circuit changes when the duty cycle of the variable duty cycle waveform changes. This embodiment may include a capacitive element connected between the first and second power supply lines, or a capacitive element connected between the first power supply line and system ground.
The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiments are therefore to be considered in respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of the equivalency of the claims are therefore intended to be embraced therein.
