AC-DC Converter

Abstract

Describe an AC-DC conversion system. The conversion system consists of a control circuit and an electronic switch for providing a controlled pulsed power supply to a storage device, which supplies power to a load at a preselected or manually or automatically selectable voltage while ensuring that the voltage drop across the switch is minimized to reduce the power consumed through the switch itself, thereby significantly improving efficiency and reducing heat loss. The minimum version of the AC-DC converter consists of a pair of N-MOSFET transistors, a voltage divider, a storage element, and a pair of diodes. The design achieves high efficiency with the minimum number of components that can be fully integrated on silicon.

Description

[0001] Cross - Reference to Related Applications

[0002] This application claims priority to U.S. Provisional Application No. 62 / 987,045, entitled "Zero Voltage Switching AC Direct Power Regulator and Discriminator," filed on March 9, 2020. The two applications include common inventors and are currently under examination.

[0003] Statement Regarding Federally Sponsored Research or Development

[0004] Not applicable. Technical Field

[0005] The present invention relates to a power management system and method for providing low-voltage DC current from an AC mains with very high efficiency. Background Art

[0006] Traditional ways of providing DC power from a primary AC power source (mains) are through analog circuits, which include step-down transformers, diode rectifiers, and filters containing electrolytic capacitors and resistors. The output voltage mainly depends on the turns ratio of the transformer, and the circuit efficiency is moderate. However, the size and weight of the magnetic structures required for low-frequency transformers rule out the use of this method in micro devices.

[0007] Subsequent methods that do not use transformers involve direct rectification of the AC mains, where the rectified waveform is directly applied to a voltage regulation circuit including active solid-state devices connected in series or parallel. Shunt regulators operate by providing a current path across the rectified mains output through a variable resistance device, thereby shunting current from the load. In the simplest implementation of a shunt regulator, a Zener diode is connected in parallel with the load, and a resistor is connected in series with this parallel branch. Any rectifier output voltage exceeding the Zener voltage will drop across the resistor, causing excess power to be dissipated as heat. Therefore, this regulator configuration is very inefficient. Since the Zener current must be greater than the load current to maintain regulation through the Zener effect, the efficiency of this regulator circuit is much less than the ratio of the output voltage to the rms value of the rectified supply voltage.

[0008] An improved method uses solid-state devices connected in series, such as bipolar or field-effect transistors, to buffer the Zener voltage reference. The active devices are connected in a source-follower or emitter-follower configuration, with the load connected to the source or emitter and the Zener reference connected to the gate or base. The Zener current can be much smaller than in the parallel configuration, so the total current is mainly the current supplied to the load. Therefore, the efficiency of this circuit is generally not better than the ratio of the input voltage to the output voltage.

[0009] A further refinement of this circuit functionality is called a switched-mode power supply. Many such designs are known in the art, but the common denominator is an input rectifier, a switching element that operates at high speed to switch a storage element, inductor, or capacitor into or out of the power supply. If isolation of the input and output is desired, a high-speed transformer can be introduced, which also serves to isolate and regulate the output voltage. An RC filter is included to reduce ripple in the output. Switched-mode power supplies have the advantage of increased efficiency because the power loss mechanisms of earlier linear systems are largely eliminated. However, if isolation is required, then transformer losses result in reduced efficiency. In addition, high-speed switches are a significant source of RF noise and introduce greater losses in conductors due to the skin effect. In specially designed systems, high efficiency can be and has been achieved in theory. Efficiencies as high as 95% have been reported, but in low-cost isolated systems, the actual efficiency is typically 60% to 70%.

[0010] The drawback of all systems known heretofore is that they cannot be easily integrated. Except for limited special applications, the designs of existing AC-DC converters cannot be integrated with other system functions on a chip. The power consumed in individual circuit elements is too large for integration at the system-on-chip level. Components such as the required type of transformer are simply not available for integration on silicon.

[0011] Common electronic devices and subsystems typically operate at 3.3 or 5 volts. The requirement to convert a 120-volt or 240-volt AC mains to these low operating voltages places a strain on the efficiency of power converters available heretofore. For both linear and switched-mode power supplies, the greater the difference between the input voltage and the output voltage, the lower the efficiency. There is a need for high-efficiency and low-voltage power supplies to power numerous low-power, low-voltage consumer devices. Electronic products are proliferating in "smart" cars and "smart" homes. There is a need for small, efficient power supplies that can support always-on sensors and networks. An increasing number of homes, factories, and office buildings, both new construction and retrofit, are adopting electronic sensors to control all power usage for increased efficiency. There is a need for a low-voltage, integrated, high-efficiency power supply to support both new and retrofit homes, factories, and office buildings with their existing electrical grids. The power supply must be able to be integrated into sensors and control electronics so that these devices can be physically installed within the footprint of a plug and socket for local power delivery. There is a need for high efficiency to avoid heat dissipation within the walls of homes, offices, and factories and within the electrical grid. There is a need for power converters with efficiencies in the range of 99% to 100%. There is a need for a compact power converter that can be installed in a wide range of devices rather than existing as a bulky box external to the device. There is a need for a power converter that can be integrated. SUMMARY OF THE INVENTION

[0012] Describe an AC-DC power conversion system. The system and related devices address the need for a compact, integrated, low-cost design that is efficient and provides for the use of low voltages to drive typical silicon-based electronics used in home sensors and networks, smart vehicles, etc. In one embodiment, the system includes an efficient electronic switch for disconnecting the input of a series voltage regulator circuit from a rectified AC mains power supply to reduce the power consumed within the series regulator. To optimize efficiency, the voltage across the open switch is minimized when the switch is closed and energy is accumulated and stored in a shunt energy storage element. The electronic switch is opened when the rectified AC mains waveform exceeds a threshold. When the switch is open, the energy storage element supplies energy to the load through the regulator circuit. In this way, the benefits of the regulator circuit accrue to additional load circuits while significantly reducing the power consumed within the regulator circuit compared to the prior art. In another embodiment, the rectifier is removed and the switch is synchronized with one half-cycle of the AC mains waveform.

[0013] A comparator is used to control the electronic switch. In one embodiment, the comparator includes an operational amplifier and a reference voltage source. In another embodiment, the comparator includes a MOS field-effect transistor. In one embodiment, the MOS field-effect transistor is controlled by a voltage divider. In another embodiment, the voltage divider is replaced by a reference voltage source. In other embodiments, the reference voltage is adjustable.

[0014] The specific examples are not intended to limit the inventive concept to the example applications. Other aspects and advantages of the present invention will be apparent from the accompanying drawings and the detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 is a schematic diagram of a prior art AC-DC converter.

[0016] Figure 2 is a schematic diagram of a prior art AC-DC converter with current limiting.

[0017] Figure 3A is a schematic diagram showing the function in an improved circuit.

[0018] Figure 3B is a schematic diagram showing without a full-wave rectifier Figure 3A of the circuit

[0019] Figure 4 is a schematic diagram showing an improved AC-DC converter.

[0020] Figure 5 is a schematic diagram of an embodiment of an improved circuit using a MOS field-effect transistor Figure 4 in

[0021] Figure 6 is Figure 5 a schematic diagram of a simplified version of

[0022] Figure 7 showing the drain - source voltage and drain current waveforms of the MOSFET switches generated by a circuit simulation program in Figure 6

[0023] Figure 8 a schematic diagram of an embodiment of a zero - voltage - switching circuit using MOS field - effect transistors.

[0024] Figure 9 showing the drain - source voltage and drain current waveforms of the MOSFET switches generated by a circuit simulation program in Figure 8

[0025] Figure 10 a schematic diagram of an alternative embodiment of a zero - voltage - switching circuit using MOS field - effect transistors.

[0026] Figure 11A showing the AC mains voltage waveform and drain current waveform of the MOSFET switches during circuit startup in Figure 10

[0027] Figure 11B showing the drain - source voltage and drain current waveforms of the MOSFET switches in steady state generated by a circuit simulation program in Figure 10

[0028] Figure 12 is Figure 8 a schematic diagram of a preferred embodiment of a zero - voltage - switching circuit of , including output current limiting and negative - feedback stabilization of the output voltage.

[0029] Figure 13 is Figure 10 a schematic diagram of a preferred embodiment of a zero - voltage - switching circuit of , including output current limiting, output voltage regulation, and negative - feedback stabilization of the output voltage.

[0030] Figure 14 is Figure 13 a schematic diagram of a zero - voltage - switching circuit of where the output voltage can be manually adjusted.

[0031] Figure 15 is Figure 13 a schematic diagram of a zero - voltage - switching circuit of where the output voltage can be electronically adjusted.

[0032] Figure 16 a block diagram of a third embodiment of a zero - voltage - switching circuit.

[0033] Figure 17 isFigure 16 Schematic diagram of an embodiment.

[0034] Figure 18 Showing the prior art of an AC - DC converter, including isolating the load from the power supply.

[0035] Figure 19 Showing an embodiment of the AC - DC converter of the present invention, including isolating the load from the power supply.

[0036] Figure 20 Showing an embodiment of the AC - DC converter of the present invention, including isolating the load from the power supply and further including feedback control from the load to the AC - DC converter. Detailed implementation

[0037] Figure 1 Showing a schematic diagram of a prior art AC - DC converter circuit. The single - phase AC mains waveform 101 is sinusoidal and is full - wave rectified by a diode bridge 102, and the resulting time - varying DC voltage waveform is smoothed by a capacitor 103 (usually an electrolytic capacitor). Note that there is no control for the charging of this capacitor 103. The rectified line voltage is applied to this capacitor, so a capacitor with a large capacitance value and a rated voltage greater than the peak value of the rectified AC mains waveform is required. The smoothed voltage waveform is applied to the input of a series regulator circuit, which includes a bias resistor 104, a Zener diode 105 with a characteristic Zener voltage V Z and a transfer transistor 106, where the transfer transistor 106 is shown as an enhancement - mode metal - oxide - semiconductor field - effect transistor (MOSFET) with a characteristic threshold voltage V T . The regulator output is applied to the load 107.

[0038] In operation, the transfer transistor 106 dynamically adjusts its drain - source voltage to hold the load voltage at V Z - V T . In other words, the transfer transistor 106 forms a source - follower circuit buffering the Zener voltage V Z . Since the full load current passes through the transfer transistor 106 and assuming the Zener bias current is negligible, the efficiency of this regulator circuit is simply the ratio of the load voltage to the rms value of the supply voltage. Thus, if the required load voltage is nominally 3.3V and the supply voltage is 120Vrms, the efficiency is less than 3%. Additionally, if the load only requires a few tens of milliamperes of current, the transfer transistor 106 must continuously dissipate several watts of power as heat. This dissipation typically results in an unacceptable temperature rise in a micro - enclosed device.

[0039] Figure 1Another limitation of the circuit is that it does not provide protection against output current transients that may damage the transfer transistor 106. Such transients can occur as a result of an accidental short circuit at the output terminal during operation or testing, or as a result of capacitive load impedance components. Figure 2 FIG. shows a schematic diagram of a prior art AC-DC converter that includes additional components to limit the output current, thereby protecting the transfer transistor 106. In Figure 2 FIG., a current sensing resistor 201 with a small resistance value is placed in series with the load, and a current limiting bipolar transistor 202 is connected between the gate of the transfer transistor 106 and the load that forms a protection current limiting circuit. Now, if the voltage drop across the resistor 201 exceeds approximately 0.7V (for a silicon bipolar transistor), the transistor 202 begins to conduct, which reduces the gate-source bias on the transfer transistor 106, thereby reducing the output current. However, compared to Figure 1 the circuit shown in FIG., the efficiency of this improved circuit remains substantially unchanged.

[0040] To improve the efficiency of these prior art series regulator circuits, the power dissipated in the transfer transistor must be significantly reduced. In one embodiment of the present invention, the transfer transistor is disconnected from the rectified supply voltage when not needed. Figure 3A FIG. shows a schematic diagram of an improved rectifier circuit that includes an AC mains 101, a diode bridge 102, and a filter capacitor 103, but an additional circuit is inserted between the output of the diode bridge 102 and the filter capacitor 103. The waveform of the output of the diode bridge 102 is merely a full-wave rectified sine waveform, which typically varies from 0V to a peak value of approximately 170V for a conventional AC mains with an rms value of 120V. However, note that the following described method applies to any periodic power waveform, assuming appropriate adjustment of the numerical specifications of the affected components. Additionally, if the power waveform is less than the reference voltage described below, the power waveform may include a DC offset.

[0041] The additional circuit includes a comparator circuit 302, the inverting input of the comparator circuit 302 is connected to the output of the diode bridge 102, and a voltage reference 301 is connected to its non-inverting input, wherein the comparator 302 controls a series switch 303. If the diode bridge output voltage exceeds the reference voltage V R , the series switch 303 disconnects the diode bridge output from the subsequent circuit (opens the switch 303). On the other hand, when the reference voltage V RWhen the voltage exceeds the output voltage of the diode bridge, switch 303 closes, and capacitor 103 is charged through series diode 304. When the output voltage of the diode bridge decreases, diode 304 prevents capacitor 103 from discharging back through switch 303. The combination of diode 304 and capacitor 103 forms a "peak detector" circuit that stores energy during each half of the AC line cycle to supply subsequent regulator circuits and load 305. Different from the prior art examples, the voltage across capacitor 103 only needs to be large enough to meet the energy requirements of the subsequent regulator circuits and load 305. Compared with the rms value of the AC line, the input voltage to the series regulator is significantly reduced. The operation of the "peak detector" circuit ensures that the peak voltage stored on capacitor 103 is always V R , regardless of the fluctuations in the peak voltage of the AC line, as long as the voltage of the AC line remains greater than V R . This embodiment of the switching circuit itself operates as a voltage regulator circuit. Since the operation of switch 303 uses negligible energy, the efficiency of the overall improved AC-DC converter circuit shown in Figure 3A is much greater than the efficiency seen in the prior art circuits of Figure 1 and Figure 2 . An additional benefit is a significant reduction in operating temperature rise. Although comparator 302 is a well-known analog circuit component, other analog or digital circuits can also be used to implement the desired threshold function required to operate switch 303.

[0042] In one embodiment, the reference voltage VR is fixed. In another embodiment, the reference voltage can vary. In another embodiment, the reference voltage is selectable. In one embodiment, Figure 3A the circuit is connected to the load, and the regulator aspect of the circuit is used to control the voltage supplied to the load. In another embodiment, an additional regulator is used in series with Figure 3A the circuit and the load.

[0043] As described above, the operation of this circuit does not depend on the availability of a full-wave rectified AC line waveform. In fact, assuming that the specifications of components 301 to 305 are sufficient to handle the negative offset of the AC line waveform, diode bridge 102 can be removed, and the switching and regulating components can be directly connected to the AC line, resulting in the embodiment shown in Figure 3B . Note that when switch 303 is about to close, peak detector diode 304 also blocks the reverse current through the load during the negative half-cycle of the AC line. Compared with Figure 3A shown, the only drawback of this embodiment is that the total maximum power available to the load is halved.

[0044] Figure 4A schematic diagram showing an improved rectifier circuit interconnected with series regulators 103, 104, 105, 106 and a load 107 is provided, and it provides a convenient basis for establishing relationships between design variables in the new rectifier circuit described below. The voltage supplied to the comparator passes through a voltage divider network of resistors 401, 402. Comparators 301 to 304 are as described above. To maintain regulation of the output voltage, the voltage across capacitor 103 must exceed the Zener 105 voltage V Z . However, due to the nominally constant current supplied to the load 107, capacitor 103 will discharge linearly with time during the half cycle of the AC mains. Therefore, capacitor 104 must first be charged to the peak voltage V peak = V Z + I load * t MAINS / (2 * C103), where t MAINS is the period of the AC mains waveform. This gives the value of capacitor 103 as a function of the difference between V peak and V Z . A higher value of V peak will also result in higher power dissipation in the transfer transistor 106, and this can be traded off against the maximum practical value of capacitor 103. The efficiency of the regulator is the ratio of the power delivered to the load divided by the total power consumed in the circuit, given by 2 * (V Z - V T ) / (V Z + V peak ). Since the minimum value of V peak is V Z , the best-case efficiency is simply 1 - V T / V Z .

[0045] Figure 5 A schematic diagram showing an improved rectifier circuit is presented, where an enhancement-mode MOSFET 505 is used to implement switch 303. Additionally, an enhancement-mode MOSFET 504 characterized by a threshold voltage V T1 and a load resistor 503 are used to implement the comparator circuit as a single common-source amplifier stage. Thus, when the output of the voltage divider network including resistors 501 and 502 exceeds the threshold voltage V T1 of MOSFET 504, the gate of MOSFET switch 505 is pulled to the ground point, thereby opening switch 505. When the output of the voltage divider network 501, 502 is less than V T1 , the gate of MOSFET 505 is connected to its drain, thereby closing the switch. However, MOSFET 505 is not an ideal switch and may experience significant power dissipation when it is in the on state. Therefore, the efficiency of the circuit implemented using MOSFETs will be lower than Figure 4as high as that ideally obtained. The efficiency issue stems from the fact that as the drain and gate voltages of MOSFET 505 increase during the positive half-cycle of the source 101, when the gate voltage exceeds the source voltage by the threshold voltage V of MOSFET 505 T2 at which point, the drain current Id(t) flows from the drain to the source, and the source voltage of MOSFET 505 rises to the threshold voltage V of its gate voltage T2 within. When MOSFET 505 is turned off by MOSFET 504, the drain current stops. Therefore, during the charging current transient, the drain-source voltage of MOSFET 505 is also approximately its threshold voltage V T2 , and for a power FET, the threshold voltage V T2 is typically around 4 to 6V. Therefore, during the charging current transient, the instantaneous power consumed in MOSFET 505 is merely Id(t)*V T2 , which is perceptible compared to the power transferred to the load through the same current transient.

[0046] In addition, as a result of its manufacturing process, a power MOSFET typically includes a parasitic source-drain diode 506 associated with MOSFET 505, and a parasitic source-drain diode 507 associated with MOSFET 504. Note that diode 506 can allow capacitor 103 to discharge when MOSFET 505 is "off", but the series tracking and holding diode 304 blocks this spurious discharge path. The presence of parasitic diodes 506 and 507 is assumed in the subsequent schematic diagrams. In one embodiment, Figure 5 all components of Figure 5 are fabricated on a single semiconductor chip. In another embodiment, all components of

[0047] Figure 6 except for capacitor 103 Figure 5 are fabricated on a single semiconductor chip.

[0048] Assume the AC mains frequency is 60Hz, Figure 6 the SPICE simulation results of the circuit are as Figure 7 shown, Figure 7 showing the waveforms of the drain-source voltage 701 (Vds) and drain current 702 (Id) of the switching MOSFET 505 within one cycle of the AC mains 101. Note that the amplitude of the base 703 is approximately V T2, i.e., the threshold voltage of MOSFET 505, is consistent with the drain current transient on the Vds waveform 701. The efficiency is the ratio of the average power delivered to the load 107 (Id * Vload) divided by the average power delivered by the AC mains to the switching circuit (Id * VAC), which is 68%. All 30% of the power provided by the AC mains is consumed in the switching MOSFET 505.

[0049] To overcome this V T2 “overhead”, Figure 8 A higher efficiency circuit includes a current limiting resistor 801 and a zener diode 802, which are shunted by a capacitor 803 connected between the gate and source of MOSFET 505. During the negative half cycle of the power supply 101, current starts from the ground point, flows through the body diode 507 of MOSFET 504, flows through the added components 801 to 803 and returns to 101 through the body diode 506 of MOSFET 505, causing the zener voltage Vz of the diode 802 to be stored on the capacitor 803. Note that this stored voltage applies a positive bias equal to Vz on the gate of 505 relative to its source, and this positive bias can be greater than V T2 . Therefore, when MOSFET 505 conducts again at the start of the positive half cycle of 101, its drain-source voltage can be much smaller than V T2 , limited only by the inherent channel resistance rds of MOSFET 505 (usually much less than 1 ohm). The SPICE simulation results of this “zero voltage” switching circuit are as Figure 9 shown, again showing the waveforms of the drain-source voltage 901 (Vds) and the drain current 902 (Id) of MOSFET 505 over one cycle of the AC mains. Note that during the drain current transient 903, the Vds waveform is almost zero. The efficiency of this circuit is 89%, and less than 2% of the power provided by the AC mains is consumed in MOSFET 505.

[0050] Since the capacitor 803 is pre-charged to the zener voltage of the diode 802 during the negative half cycle of the AC mains to provide gate bias for MOSFET 505, the resistor 503 is no longer needed to provide it. Figure 10 Another embodiment of the zero voltage switching circuit shown removes the load resistor in the drain circuit of MOSFET 504 ( Figure 8 item 503 in Figure 8The duration of the drain current transient in the circuit. Further, the bias resistor 501 is disconnected from the AC mains 101 and is directly connected to the DC output node at the junction of the diode 304, the load resistor 107, and the capacitor 103. Thus, when the DC output node voltage reaches the threshold established by the resistors 501 and 502 and the threshold voltage of the MOSFET 504, the MOSFET 504 conducts, thereby turning off the switching MOSFET 505. The SPICE simulation results of this circuit are as Figure 11A and Figure 11B shown. Figure 11A Shows three initial cycles 1100 of the AC mains 101 (Vac) and the drain current 1102 (Id) of the MOSFET 505 at the start of circuit startup, and shows that the drain current transient 1102 reaches a steady state after the first negative half-cycle of the AC mains 1100. Figure 11B Again shows, in the steady state, the waveforms of the drain-source voltage 1101 (Vds) and the drain current 110 (Id) of the MOSFET 505 over one cycle of the AC mains. Because of the relatively large drain current transient duration 1103, the total power delivered to the load increases by 25%. The efficiency of this zero-voltage switching circuit increases to 90%, and less than 1% of the power supplied by the AC mains is consumed in the MOSFET 505.

[0051] Figure 10 Shows Figure 8 a first embodiment 1000 of a zero-voltage switching circuit, which now includes a bias resistor 501 connected between the DC output node 1005 and the gate 1001 of the MOSFET 504.

[0052] The first embodiment includes: an AC-DC conversion system for supplying energy from an alternating current (AC) power source (101) to an electronic load (107) in direct current (DC) at an output node (1005), comprising:

[0053] a. A voltage divider (501, 502) connected to span the load (107), and

[0054] b. A first switch (504) having an input (1001) and an output (1002), connected to the voltage divider through its input (1001), and

[0055] c. A second switch (505) having an input (1003) and an output (1004), whose input (1003) is connected to the output (1002) of the first switch (504), and

[0056] d. A storage capacitor (103) connected to the output (1004) of the second switch (505) through a diode (304), and

[0057] e, f, A Zener diode (802) having a Zener voltage is connected between the input (1003) and the output (1004) of the second switch (505) to clamp the voltage between the input (1003) and the output (1004) of the second switch (505) to the Zener voltage of the Zener diode (802), and

[0058] g, An electronic load (107) is connected to the storage capacitor (103).

[0059] In the first embodiment, as Figure 10 shown, switches 504 and 505 are N-MOSFET transistors. In another embodiment, functionally equivalent to Figure 10 , but not shown, switches 504 and 505 are bipolar transistors.

[0060] In Figure 12 shown another embodiment, the AC-DC converter includes an overcurrent protection circuit inserted between the output 1004 of the MOSFET switch 505 and the input of the diode 304. The protection circuit consists of a series resistor 201 with a very small value and a bipolar transistor 202, where the base terminal is connected to the switch output 1004, the emitter terminal is connected to the input of the diode 304, and the collector is connected to the input 1003 of the MOSFET switch 505.

[0061] In Figure 13 shown another embodiment, the AC-DC converter includes a regulation circuit having elements 104, 105, and 106 inserted between the pre-output terminal 1005 and the load 107 at the new DC output terminal 1301.

[0062] Figure 14 is a schematic diagram of an embodiment of a zero-voltage switching circuit using MOSFETs, where the output voltage at the output 1005 can be manually adjusted. Figure 12 The resistor 502 in

[0063] Figure 15 is replaced by a potentiometer 1401, and the potentiometer 1402 can be manually adjusted to change the voltage waveform applied to the gate 1001 of the MOSFET 504, thereby changing the voltage stored on the capacitor 103. Figure 12 The resistor 502 in Cis applied to the gate of MOSFET 501, thereby changing the voltage applied to the gate 1001 of MOS FET 504 and changing the voltage stored on the capacitor 103.

[0064] In another embodiment, the AC-DC converter 1600 generally includes Figure 16 the elements shown and the methods implied by these elements. Non-limiting specific examples of circuit elements are as Figure 17 shown. Referring to Figure 16 , the AC source 1601 is connected to the surge protection element 1602. In one embodiment, the surge element includes a resistor element in the line and the neutral point of the AC power supply. In another embodiment, in cases where higher power and efficiency are required, the surge protection includes a switching element that provides a high resistance at startup and switches the resistor element out of the circuit during steady-state operation. After the surge protection, for control purposes, a scaled copy of the waveform of the AC source 1601 is formed using the sampling element 1603. In one embodiment, the sampling element 1603 includes resistors configured as a voltage divider network. One embodiment is the voltage divider as Figure 5 shown and discussed. In another embodiment, the sampling element includes a reference voltage source and a comparator as Figure 4 shown. In another embodiment, the sampling element 1603 can be manually adjusted as Figure 14 shown. In another embodiment, the sampling element can be as Figure 15The electronic regulation shown. The sampled voltage is used as an input to the switch driver element 1604. In a preferred embodiment, the switch driver element 1604 receives a feedback voltage signal 1609 from the storage element 1606 and controls the voltage applied to the gate of the switching element in the control switch and the clamping element 1605 based on the voltage signal, thereby opening and closing the control switch 1605 to supply power to the storage element 1606 and ultimately to the load 1608. In one embodiment, in the absence of feedback 1609, the AC-DC converter is a feed-forward converter, where the charging of the storage element 1605 is controlled from the forward side 1603, 1604, and 1605. The addition of the feedback control 1609 provides means for both feed-forward control and feedback control. In one embodiment, the balance between feed-forward control and feedback control is determined by selecting elements in the voltage sampling element 1603 and the feedback line 1609. In one embodiment, the balance between feed-forward control and feedback control is determined by the resistive elements in the sampling element 1603 and the feedback 1609. In another embodiment, variable elements are used such that the feed-forward control and feedback control can be adjusted. In a preferred embodiment, the switch driver 1604 includes a voltage divider and a switch. The switch, current limiting, and clamping element 1605 controlled by the switch driver 1604 supplies pulsed power to the storage element 1606 at a fixed maximum current. In a preferred embodiment, the switch, current limiting, and clamping element 1605 includes an N-MOSFET, a current sensing resistor, and a bipolar peak current limiting transistor as well as a Zener diode, whose source is connected to the gate to clamp the peak gate-source voltage during the negative half-cycle of the AC source 1601, thereby providing a zero voltage switching feature for the circuit. The power from the switch and clamping element including a preselected peak current pulse is supplied to the storage element 1606. In one embodiment, the voltage on the storage element 1606 (including a capacitor and a diode used as an energy storage element) is fed back 1609 to the switch driver 1604 through a voltage divider circuit, thereby maintaining a constant charge on the capacitor. The output from the storage element is fed to the load 1608 through a voltage regulator 1607. In another embodiment, the AC-DC converter further includes a current isolation element 1610. In another embodiment, the AC-DC converter further includes an element 1611 capable of enabling feedback from the load 1608. In a preferred embodiment, the feedback circuit 1611 also includes current isolation between the control element 1604 and the load 1608.

[0065] Figure 17 A preferred embodiment of a zero voltage switching AC-DC converter is shown. The operation of each component of the circuit is the same as that of many of the circuit components already described in Figures 5 to 15 There are many similarities. The elements 1701 to 1708 correspond respectively to Figure 16Components 1601 to 1608 therein. The AC source 1701 is connected to the surge protection circuit 1702 included in this preferred embodiment of resistors R1 and R2. In another embodiment (not shown), the surge protection includes a switch such that current flows through resistors R1 and R1 at startup and bypasses the resistors once steady-state operation is reached. In another embodiment, the surge control uses inductors; that is, inductors L1 and L2 are used in place of components R1 and R2. The output from the surge protection goes to switch Q2 of the switch, the current limiting and clamping circuit 1705, and the voltage sampling element 1703. The voltage sampling element 1703 includes resistors R3 and R4 that sample the voltage from the storage capacitor C1. The values of R3 and R4 are selected such that the voltage to the gate of switch Q1 in the switch driver element 1704 turns on and off switch Q1, thereby turning off and on switch Q2 synchronously, and thus providing a preselected time output pulse from switch Q2 to the charge storage element C1. Resistor R4 provides a feedback path regarding the charge on capacitor C1 and thus provides the output voltage to the voltage sampling circuit 1703 and thus to the control circuit 1704. The switch, current limiting and clamping element 1705 includes switch Q2, current sensing resistor R10, bipolar transistor Q4, zener diode D1, capacitor C3, and resistor R7. Switch Q2 is controlled by the switch drive circuit 1704. Based on the selected value of the current sensing resistor R10, the peak output current of switch Q2 is limited to a preselected maximum value. Capacitor C3 is charged to the zener voltage of diode D1 during the negative half-cycle of the AC source 1701 and provides a gate-source bias on Q2 that minimizes the gate-source voltage of Q2 during the charging current transient. This pulsed output from switch Q2 is connected to the voltage regulator 1706, which maintains the storage capacitor C1 at a constant charge through feedback from R4 to voltage sampling 1703 and the switch driver 1704. The control element switch Q1 and thus the power switch Q2 are activated, either turned off or on, synchronously with the AC input 1701. The AC-DC converter provides a low-voltage output with pulse modulation at the frequency of the input AC source. The switches are activated, either turned off or on, at a voltage within the threshold of components Q1 and Q2 near the zero-crossing of the AC source. The output then goes to the voltage regulator 1707 and then to the load 1708. The voltage regulator 1707 includes switch Q3, zener diode D3, resistor R9, and capacitor C2. The circuit components D3, Q3, R9 act as a voltage regulator equivalent to Figure 1 the voltage regulators described respectively for circuit elements 105, 104, 106 therein. Capacitor C2 provides storage capacity to buffer and thus smooth the output from the AC-DC converter to the load 1708.

[0066] Figure 16 and Figure 17The AC-DC converter in the preferred embodiment includes elements of a surge protection 1602, a voltage sampling 1603, a switch driver 1604, a switch and a clamp 1605, a storage element 1606, and a voltage regulator 1607. The selection of components in the voltage sampling 1603 determines the timing of the switch driver 1604. The selection of elements in the switch and the clamp determines the peak voltage and current of the output pulse. The power output is controlled by selecting both the peak current and the pulse timing. Feedback from the storage element through the voltage sampling is used to select the pulse timing. The AC-DC converter operates synchronously with the AC source.

[0067] Figure 16 and Figure 17 The preferred embodiment of typically includes a voltage divider 1603 connected to a power supply 1601, a first switch 1604 whose input is connected to the voltage divider, a second switch 1605 whose input is connected to the output of the first switch, a storage capacitor C1 whose output is connected to the second switch through a diode, a sense resistor 1609 connected between the storage capacitor and the voltage divider to provide feedback control for a zero-voltage-switch AC direct-to-DC extraction conversion system, a Zener diode D1 connected between the input and output of the second switch, and an electronic load 1608 connected to the storage capacitor C1. The switches 1604, 1605 can be any electronically actuated switch. In one embodiment, the switch is an N-MOSFET. In another embodiment, the switch is a bipolar transistor, and in another embodiment, the switch is a microelectromechanical switch.

[0068] Figure 18 An AC-DC converter system of the prior art is shown, which includes current isolation between an AC source 1808 and a load. A typical prior art AC-DC converter includes a full-wave rectifier 1802, which provides a grounded 1809 DC source that is filtered 1803, includes a controller 1804, which is typically a pulse controller that controls the output through a transformer 1806 using a switch 1805 to provide a DC voltage to the load 1808. A diode 1807 prevents current from flowing back from the load to the transformer 1806. Typically, the transformer also acts as a step-down transformer to control the voltage required by the load 1808. Note that the high-voltage side of the transformer 1806 operates at the rectified voltage of the AC source 1801. Although the transformer does provide current isolation, the high voltage connected to the transformer thus requires a transformer that can operate at that high voltage.

[0069] In contrast, the power supply of the present invention is in Figure 19is shown in the first embodiment. The AC source 1901 is connected to the load 1905 via the AC-DC converter 1902 through the isolation device 1904. The ground point 1906 on the AC-DC converter 1902 is not necessarily at the same level as the ground point 1907 on the load 1905. In the preferred embodiment, the AC-DC converter 1902 is as Figure 12 and Figure 13 shown. The AC-DC converter 1902 includes clamping the output voltage provided to the storage capacitor ( Figure 13 C1), so that the isolation device 1904 sees at most the clamped voltage. In Figure 16 and Figure 19 the preferred and comparative embodiments, the isolation device is located between the block elements 1607 and 1608.

[0070] Figure 20 Another embodiment shown also includes feedback from the load 1905 to the AC-DC converter 1902. The feedback is provided to the AC-DC converter through the sensing line 2002 passing through the isolator 2001 and through the isolated sensing line 2003. In one embodiment, one of the sensing lines 2003 is grounded and the other is fed to the voltage sampling circuit 1303, which has much in common with the sensing lines Figure 17 shown and is fed from the capacitor C1 through the resistor R8. In one embodiment, the isolator 2001 is an optical isolator as shown. In another embodiment (not shown), a transformer is used for the isolator instead of the optical isolator.

[0071] Figure 16 、 Figure 17 、 Figure 19 and Figure 20An AC-DC converter that can be fully integrated on silicon is shown. Not all components shown in the figures are required for a fully functional device. In one embodiment, the AC-DC converter consists of a voltage divider (1703) that is connected to an AC source 1701 to sample it and is further connected to the base of a first switching transistor Q1. The values of the resistors in the voltage divider control the voltage seen by Q1, thereby providing feedforward control of Q1 and thus the output of the AC-DC converter. The drain of Q1 is correspondingly connected to the base of a second switching transistor Q2, and the second switching transistor Q2 provides a pulsed current to a storage device C1. Diode D2 prevents the capacitor C1 from discharging through switch Q2. A sense line connects from the storage element C1 through a resistor R8 to the voltage divider 1703 and provides feedback control to prevent the storage capacitor C1 from discharging completely. A Zener diode D1 connected between the gate and source of Q2 clamps the gate-to-source voltage seen by Q2 to the Zener voltage of diode D1, and the bias voltage of diode D1 is stored on capacitor C3. An inductor or a low-resistance wirewound resistor R1 connected in series in the AC line filters transients and limits the current seen by Q2. Thus, a fully functional AC-DC converter is considered to consist of a voltage divider, two switches, a storage device, a Zener diode, a conventional diode, and an inductor, where the switches are N-MOSFETs and the storage device is a capacitor. In another embodiment, the AC-DC converter further includes surge control 1702. In one embodiment, the surge control consists of a resistor connected in series between the line and the neutral point of the AC source. In another embodiment, the AC-DC converter further consists of a voltage regulator. In one embodiment, the voltage regulator consists of a switch Q3 connected to the output line of the storage device C1. The switch is controlled by a Zener diode D3 connected from a capacitor C2 to its base. The output of the voltage regulator is connected to a load 1708. In another embodiment, the AC-DC converter further includes current isolation, where the current isolation is an isolation transformer connected to the output of the voltage regulator. In another embodiment, there is no voltage regulator, and the isolation transformer is connected between the storage capacitor C2 and the load 1708. Another embodiment further includes feedback from the load to the voltage divider 1703. The feedback from the load is fed to the voltage divider 703 through a second isolation device 2001.

[0072] Summary

[0073] Describe an AC-DC conversion system. The conversion system consists of a control circuit and an electronic switch for providing a controlled pulsed power supply to a storage device. The storage device supplies power to a load at a preselected or manually or automatically selectable voltage, while ensuring that the voltage drop across the switch is minimized to reduce the power consumed through the switch itself, thereby significantly improving efficiency and reducing heat loss. The minimum version of the AC-DC converter consists of a pair of N-MOSFET transistors, a voltage divider, a storage element, and a pair of diodes. The design achieves high efficiency with the minimum number of components that can be fully integrated on silicon.

Claims

1. An AC-DC conversion system for providing energy from an alternating current (AC) power supply (101) to an electronic load (107) in direct current (DC) at an output node (1005), the AC-DC conversion system comprising: a. A first switch (504), the first switch being a MOSFET, having its gate as an input (1001), its source connected to the return line of the electronic load, and its drain as an output (1002), the first switch being connected via its input (1001) to a voltage divider (501, 502), and b. A second switch (505), the second switch being a MOSFET, having its gate as an input (1003), its source connected to the line side of the AC power supply, and its drain as an output (1004), the input (1003) of the second switch being connected via a current limiting resistor (801) to the output (1002) of the first switch (504), c. A storage capacitor (103), the storage capacitor being connected via a diode (304) to the output (1004) of the second switch (505), d. The voltage divider (501, 502), connected at a first end after the second switch (505) and before the storage capacitor (103), and at a second end to the return line of the AC power supply and thus connected across the load (107), e. A Zener diode (802) and a shunt capacitor (803), the Zener diode having a Zener voltage, the Zener diode being connected between the input (1003) and the output (1004) of the second switch (505), the shunt capacitor (803) being connected in parallel with the Zener diode to clamp the voltage between the input (1003) and the output (1004) of the second switch (505) to the Zener voltage of the Zener diode (802), and f. The electronic load (107), the electronic load being connected across the storage capacitor (103).

2. The AC-DC conversion system according to claim 1, wherein, All semiconductor devices are fabricated on a single integrated circuit chip.

3. An AC-DC conversion system for providing energy from an alternating current (AC) power supply (101) to an electronic load (107) in direct current (DC) at an output node (1005), the AC-DC conversion system comprising: a. A first switch (504), the first switch being a MOSFET, having its gate as an input (1001), its source connected to the return line of the electronic load, and its drain as an output (1002), the first switch being connected via its input (1001) to a voltage divider (501, 502), and b. A second switch (505), which is a MOSFET, having its gate as an input (1003), its source connected to the line side of the AC power supply, and its drain as an output (1004), the input (1003) of the second switch being connected to the output (1002) of the first switch (504) through a current-limiting resistor (801), c. A storage capacitor (103), which is connected to the output (1004) of the second switch (505) through a diode (304), d. The voltage divider (501, 502), being connected at a first end after the second switch (505) and before the storage capacitor (103), and at a second end to the return line of the AC power supply, and thus being connected across the load (107), e. A Zener diode (802) and a shunt capacitor (803), the Zener diode having a Zener voltage, the Zener diode being connected between the input (1003) and the output (1004) of the second switch (505), the shunt capacitor (803) being connected in parallel with the Zener diode so as to clamp the voltage between the input (1003) and the output (1004) of the second switch (505) to the Zener voltage of the Zener diode (802), f. The electronic load (107), which is connected across the storage capacitor (103), and g. A series voltage regulator circuit, which is inserted between the storage capacitor (103) and the electronic load (107), The series voltage regulator circuit consists of a transfer transistor (106), a bias resistor (104) and a Zener diode, The transfer transistor (106) is connected to the load (107) and has a characteristic threshold voltage V T , The bias resistor (104) is connected across the transfer transistor, and The Zener diode is connected to the bias resistor and has a Zener voltage Vz, Keep the output voltage of the load at V Z –V T .

4. An AC-DC conversion system for supplying energy from an alternating current (AC) power supply (101) to an electronic load (107) as direct current (DC) at an output node (1005), the AC-DC conversion system consisting of: a. A first switch (504), which is a MOSFET, having its gate as an input (1001), its source connected to the return line of the electronic load, and its drain as an output (1002), the first switch being connected to a voltage divider (501, 502) through its input (1001), and b. A second switch (505), which is a MOSFET, having its gate as an input (1003), its source connected to the line side of the AC power supply, and its drain as an output (1004), the input (1003) of the second switch being connected to the output (1002) of the first switch (504) through a current-limiting resistor (801), c. A storage capacitor (103) connected to the output (1004) of the second switch (505) through a diode (304), d. The voltage divider (501, 502) connected at a first end after the second switch (505) and before the storage capacitor (103), and at a second end to the return line of the AC power supply and thus connected across the load (107), e. A Zener diode (802) and a shunt capacitor (803), the Zener diode having a Zener voltage, the Zener diode being connected between the input (1003) and the output (1004) of the second switch (505), the shunt capacitor (803) being connected in parallel with the Zener diode to clamp the voltage between the input (1003) and the output (1004) of the second switch (505) to the Zener voltage of the Zener diode (802), f. The electronic load (107) connected across the storage capacitor (103), and g. A current limiting circuit inserted between the second switch and the storage capacitor to limit the current flowing through the second switch, The current limiting circuit consists of a sense resistor (201) and a bipolar transistor (202), The sense resistor (201) is connected to the output of the second switch and the load (107), and The bipolar transistor (202) is connected between the load and the input of the second switch.

5. An AC-DC conversion system for providing energy from an alternating current (AC) power supply (101) to an electronic load (107) in direct current (DC) at an output node (1005), the AC-DC conversion system consisting of: a. A first switch (504), which is a MOSFET, having its gate as an input (1001), its source connected to the return line of the electronic load, and its drain as an output (1002), the first switch being connected through its input (1001) to a voltage divider (501, 502), and b. A second switch (505), which is a MOSFET, having its gate as an input (1003), its source connected to the line side of the AC power supply, and its drain as an output (1004), the input (1003) of the second switch being connected to the output (1002) of the first switch (504) through a current limiting resistor (801), c. A storage capacitor (103) connected to the output (1004) of the second switch (505) through a diode (304), d. A potentiometer (1401) connected at its first end after the second switch (505) and before the storage capacitor (103), and at its second end to the return line of the AC power supply and thus connected across the load (107), such that the input voltage to the first switch is manually adjustable, e. A Zener diode (802) and a shunt capacitor (803), the Zener diode having a Zener voltage, the Zener diode being connected between the input (1003) and the output (1004) of the second switch (505), the shunt capacitor (803) being connected in parallel with the Zener diode to clamp the voltage between the input (1003) and the output (1004) of the second switch (505) to the Zener voltage of the Zener diode (802), and f. The electronic load (107), the electronic load being connected across the storage capacitor (103).

6. An AC-DC conversion system for providing energy from an alternating current (AC) power supply (101) as direct current (DC) to an electronic load (107) at an output node (1005), the AC-DC conversion system comprising: a. A first switch (504), the first switch being a MOSFET having its gate as an input (1001), its source connected to the return line of the electronic load, and its drain as an output (1002), the first switch being connected through its input (1001) to a voltage divider (501, 502), and b. A second switch (505), the second switch being a MOSFET having its gate as an input (1003), its source connected to the line side of the AC power supply, and its drain as an output (1004), the input (1003) of the second switch being connected through a current limiting resistor (801) to the output (1002) of the first switch (504), c. A storage capacitor (103), the storage capacitor being connected through a diode (304) to the output (1004) of the second switch (505), d. A control MOSFET (1501) and a resistor (501) connected at its first end after the second switch (505) and before the storage capacitor (103), and at its second end to the return line of the AC power supply and thus connected across the load (107), and an external DC control voltage applied to the input of the control MOSFET (1501) to change the voltage applied to the input of the first switch and the voltage stored on the storage capacitor, e. A Zener diode (802) and a shunt capacitor (803), the Zener diode having a Zener voltage, the Zener diode being connected between the input (1003) and the output (1004) of the second switch (505), the shunt capacitor (803) being connected in parallel with the Zener diode so as to clamp the voltage between the input (1003) and the output (1004) of the second switch (505) to the Zener voltage of the Zener diode (802), and f. The electronic load (107), the electronic load being connected across the storage capacitor (103).

Images