ELECTRONIC CIRCUIT FOR USE IN A RECTIFIER

Abstract

 An electronic circuit (100) suitable for use in a rectifier circuit (200), the electronic circuit (100) having a MOSFET (Q1, Q2), a diode (D1, D2) and an impedance (R1, R2). The diode (D1, D2) is electrically connected across the gate terminal (124, 134) of the MOSFET and the drain terminal (120, 130) of the MOSFET, and the impedance (R1, R2) is electrically connected across the gate terminal (124, 134) and the source terminal (122, 132) of the MOSFET (Q1, Q2).

Description

Technical Field

[0001] The invention relates to an electronic circuit that may be used in a rectifier circuit, which may in turn be used in light emitting diode (LED) lamps and LED lighting, more particularly LED lamps suitable to replace a fluorescent lamp in a luminaire.

Background

[0002] Fluorescent lighting has been around for many years. This form of lighting started out as a highly efficient alternative for incandescent light bulbs, but has recently been surpassed by LED lighting in terms of efficiency and power consumption, and also in other aspects as set out below.

[0003] Fluorescent lamps generally comprise a tube filled with an inert gas and a small amount of mercury, capped at both ends with double pinned end caps. The end caps contain a glow wire to preheat the gasses inside the tube and to vaporize the mercury in order to assist with ignition of the fluorescent lamp. After the user turns on a main switch (e.g. a wall switch or a cord switch on the ceiling), the fluorescent lamp is ignited, and heat generated by the conducted current keeps the fluorescent lamp in operational condition. To facilitate starting of the lamp and to limit current through the lamp during operation, and thus limit the power consumed, a ballast is usually fitted in the fluorescent luminaire, connected between the mains power supply and the fluorescent lamp, and power is supplied to the lamp via the ballast. The ballast functions to limit the current through the fluorescent lamp and prevents the current from raising to a destructive level due to the negative differential resistance of the fluorescent lamp.

[0004] When first introduced, the only available ballasts were simple inductive or reactive elements placed in series with the power supply to the fluorescent lamp, which limit consumed power by limiting the AC current as a result of the frequency dependent impedance of the inductor. These types of ballasts are usually referred to as magnetic ballasts.

[0005] More recently other types of ballasts have been introduced, such as electronic ballasts. These ballasts usually first convert AC mains power into DC power, and subsequently convert the DC power into high frequency AC power to drive the fluorescent lamp (e.g. 100-1 10Vac at a frequency in the range from 20kHz to 70kHz).

[0006] Electronic ballasts can further be categorized into two types: constant current ballasts and constant power ballasts. Most electronic ballasts are constant current ballasts, designed to deliver current at a substantially constant amplitude. These ballasts can be modelled as a constant AC current source. A constant power ballast delivers power close to the original fluorescent lamp power and the output current will vary depending on the load to try to maintain the design power output. If the load voltage is below the design level, constant power ballasts usually try to increase the output current to come closer to the designed power level.

[0007] LED lamps are more efficient than fluorescent lamps, and have many other advantages. For example, no mercury is required for LED lamps, the light output from LED lamps is more directional, power can be more easily control or regulated, and the lifetime of LEDs is generally much longer than fluorescent lamps. Thus, replacing fluorescent lamps with LED lamps is often desirable, and it is also desirable to be able to fit replacement LED lamps into existing luminaires designed for fluorescent lamps without needing to modify the luminaire. However, an LED lamp typically operates differently when used with different types of ballasts. In some cases, a straightforward replacement of a fluorescent lamp by an LED lamp in a fluorescent luminaire results in a failure of the entire luminaire.

[0008] An LED lamp arrangement compatible with all three types of ballasts mentioned above (magnetic ballasts, constant current ballast, and constant power ballast), as well as when the luminaire does not have a ballast (e.g. a luminaire which was originally designed for a fluorescent lamp, but its ballast has been removed since it is too old or damaged) is described in applicant's US Patent No. 10 342 079, herewith incorporated by reference in its entirety. This LED lamp has a switched mode power supply for driving the LEDs, a ballast protection circuit comprising an inductor, and one or more sensing circuits for generating at least one output, in dependence on whether the electrical power received from the luminaire indicates that the electrical power is generated via a magnetic ballast, a constant current ballast, a constant power ballast, or not via a ballast. The lamp further has a plurality of switches for defining a plurality of operation modes of the LED lamp in which the components of the lamp (such as the switched mode power supply and the ballast protection circuit) are connected or disconnected in different ways, and for switching among the plurality of operation modes in dependence on the at least one output of the sensing circuits, which indicate that the electrical power is generated via a magnetic ballast, a constant current ballast, a constant power ballast, or not via a ballast.

[0009] An LED lamp arrangement equipped with a power regulation mechanism is described in applicant's PCT application published as WO 2020/084087 A1, herewith incorporated by reference. This LED lamp arrangement comprises a plurality of LEDs arranged in two or more groups connected in series, one or more rectifier circuits adapted for rectifying an electrical current received from the luminaire for supply to the LEDs, and a switch connected in parallel with one group of LEDs, which is bypassed when the switch is closed. The switch operates according to a duty cycle in dependence on the electrical current or electrical power received by or used by the LED lamp. This enables a precise control of the average power, allowing a uniform output power and light intensity from the LED lamp irrespective of the type of ballasts.

[0010] In the publications discussed above, a rectifier circuit is used to convert an AC voltage to a DC voltage, since the outputs of ballasts are based on an AC voltage while LEDs typically need to receive DC voltages as their inputs. An example of such a process (using so-called full-wave rectification) is shown in Fig. 1A-1E. A full-wave rectification allows the utilization of both positive voltage portion and negative voltage portion of an AC voltage input by effectively inverting the negative portion into positive. In this example, an AC input is first converted to a lower AC voltage by a transformer 10. A transformer 10 may be used when an electrical energy needs to be transferred from one electrical circuit to another electrical circuit. The output voltage of the transformer 10 is shown in Fig. 1B. This output is then processed by a rectifier circuit 20, which converts the input waveform to a constant polarity at its output, shown in Fig. 1C. In other words, the negative voltage portion of the input is converted, or inverted, into a positive voltage portion. This voltage is then further processed by a filter 30 (e.g. a capacitor) (Fig. 1D) to maintain a relatively high voltage with less fluctuation. A regulator 40 then process the DC voltage into a constant voltage (Fig. 1E) to supply to a load 50 such as LEDs.

[0011] Note that some of these elements may be omitted in some applications. Also note that in the context of the present application, the term "AC voltage" or "AC current" generally refers to a signal that changes its polarity (alternating between positive and negative) over time and is not limited to a sine wave or a fixed periodicity; outputs from magnetic ballasts and electronic ballasts are also to be understood as AC signals. Rectifiers are also not limited to full-wave rectification.

[0012] Typical rectifier circuits use one or more diodes. A electrical diode selectively allows the current from one polarity to pass. For example, one diode may be implemented as a half-wave rectifier allowing only half of an input AC voltage, i.e. either positive voltage of negative voltage, to pass for forming a DC voltage. Similarly, two or four diodes may be used to implement a full-wave rectifier circuit utilizing the entire AC voltage. These diodes are connected to conduct the current through the load in a defined direction, irrespective of the polarity of the input signal. Typically, so-called "power diodes" are used for this purpose. These diodes have a relatively large current rating (e.g. by forming a junction between heavily doped P⁺ and lightly doped N^- materials to increase the thickness of the depletion region), allowing these diode to withstand a large amount of forward current so that a large rectified current can flow through the rectifier.

[0013] A problem of using such diodes in a rectifier circuit, is that the responsivity of the rectifier circuit is limited by the transition time of the diodes. In other words, there is a reaction delay for a diode to switch between a conducting state and non-conduction state when the input signal changes its polarity. In a p-n junction diode for example, when the input signal switches from reverse biasing to forward biasing, it takes some time for the electrons and holes to move toward the depletion region. In addition, a sufficiently high voltage is required to overcome the barrier caused by the depletion region. Before the diode becomes conducting, heat will be generated and dissipated to the surroundings. Conversely, when the input voltage switches its polarity (so that the diode becomes reverse biased), there is usually a certain period of time (called reverse recovery time) before the current is blocked. During this period a significant amount of current can flow through the diode in an undesired direction and introducing losses.

[0014] When the input signal switches its polarity at a high frequency (such as 20 - 70 kHz in the case of electronic ballasts), these processes will repeatedly occur at a high frequency and generates a significant amount of heat. These issues can further be amplified by the measures in power diodes that achieve the high current rating (e.g. due to the enlarged depletion region). It has been observed by the inventor that in some cases, even for diodes advertised as having a recovery time of less than 100 ns, the diodes are still warmed to 148 °C in 45 °C ambient temperature and causes failure in the lamp. Using Schottky diodes allows for a faster reaction time but the heating problem nevertheless remains at a lesser degree. As it turns out, it appears that the high frequency and high peak current in combination result in a problem that cannot be effectively solved by (high speed) diodes.

[0015] It is also known that MOSFETs could be used to implement a rectifier. In such implementation, MOSFETs (typically enhancement-mode MOSFETs) are used as switches, i.e. actively turned on to allow current in one direction, and actively turned off to block current from flowing the other direction. The gate-source voltages of these MOSFETs represent the input voltage, which determines the state of the MOSFETs, so that these MOSFETs are turned on or turned off when needed as the input voltage changes. As MOSFETs can switch on and off quickly, this implementation allows for a suitable replacement of diodes in some high frequency applications.

[0016] However, in the applications of LEDs, the typical MOSFET rectifier implementation is problematic. As the input voltage from the main power source or ballasts is not a square wave but for example a sine wave, i.e. with an amplitude that gradually varies in time (or for example having a sine wave envelope), the gate-source voltages of the MOSFETs are not always sufficient to turn on the MOSFET switches when the input voltage switches. A different solution is therefore needed for rectifiers in the LED lamps.

Summary of the Invention

[0017] It is therefore an objective of the invention to provide a cost-effective electronic circuit suitable for use in a rectifier circuit in an LED lamp, in which high frequency operation based on a non-square wave input signal is envisaged.

[0018] The first aspect of the invention concerns an electronic circuit suitable for use in a rectifier circuit, the electronic circuit comprising:

• a MOSFET having a gate terminal, a source terminal and a drain terminal;
• a diode having an anode terminal and a cathode terminal; and
• an impedance,

wherein the diode is electrically connected across the gate terminal of the MOSFET and the drain terminal of the MOSFET, and the impedance is electrically connected across the gate terminal and the source terminal of the MOSFET.

[0019] In an embodiment, the MOSFET is an N-type MOSFET. In this embodiment, the anode terminal of the diode is electrically connected to the gate terminal of the MOSFET, and the cathode terminal of the diode is electrically connected to the drain terminal of the MOSFET.

[0020] In another embodiment, the MOSFET is a P-type MOSFET. In this embodiment, the cathode terminal of the diode is electrically connected to the gate terminal of the MOSFET, and the anode terminal of the diode is electrically connected to the drain terminal of the MOSFET.

[0021] The invention is based on an insight that a MOSFET could be used as a diode rather than a switch in a rectifier circuit. Most of the MOSFETs have an intrinsic diode in the device called body diode. This implementation takes advantage of the body diode in the MOSFETs.

[0022] Although MOSFETs are typically used as three-terminal transistors, it technically has four terminals, a source, a drain, a gate, and a base. The base is the bulk N-type or P-type material. In the three-terminal implementations, the source and the base are short-circuited by a hard-wired connection. Due to the P-N junction between the base and the drain and the additional connection between the source and the base, there is effectively a diode between the source and the drain. In most implementations, this intrinsic body diode is considered to be problematic.

[0023] The invention utilizes this body diode to have the MOSFET work as a diode in a rectifier. Unlike normal diodes, the behavior of the MOSFET body diode can be controlled by the voltages at the gate terminal. This enables the MOSFET to react quickly to the high frequency input signals and solves the problem of normal P-N junction diodes or Schottky diodes in the high frequency applications.

[0024] In embodiments according to the present invention, the diode and the impedance are configured to generate a voltage difference (V_GS) between the gate terminal and the source terminal of the MOSFET, the voltage difference (V_GS) having an opposite sign as the threshold voltage (V_T) of the MOSFET (e.g. in case the MOSFET is an N-type MOSFET, the V_GS is negative while the threshold voltage V_T is positive; in case the MOSFET is a P-type MOSFET, the V_GS is positive while the threshold voltage V_T is negative), when the diode is forward biased (when the voltage at the anode terminal of the diode is higher than the voltage at the cathode terminal of the diode). On the other hand, the diode and the impedance are configured to generate a substantially zero voltage (V_GS) across the gate terminal and the source terminal of the MOSFET, when the diode is reverse biased (when the voltage at the anode terminal of the diode is lower than the voltage at the cathode terminal of the diode). These ensure that the MOSFET is not turned on as a switch, but act as a diode to block the reverse current substantially throughout its operation.

[0025] When the MOSFET is an N-type MOSFET (an NMOS), for example, the diode is connected across its drain terminal (with the cathode of the diode) and gate terminal (with the anode of the diode), and the impedance is connected across its source terminal and gate terminal. This diode ensures that a negative gate-source voltage (V_GS) at the MOSFET when needed, ensuring that the MOSFET is not turned on irrespective of the voltage of the input signal. In addition, this negative gate-source voltage also increases the number of holes in the P-type material (body) and the electrons in the N-type material (drain). These additional holes and electrons improve the flow of electrons and holes and reduces the barrier in the depletion region, thereby providing a significant improvement of the reaction time of the MOSFET (which acts as a diode) when the input signal changes its polarity. Moreover, since this concept does not use MOSFETs as switches, it also does not suffer from the problem that a small forward biasing voltage (e.g. when a sine wave just switches its sign) does not switch on the current as described above. If the MOSFET is a P-type MOSFET (a PMOS), a similar arrangement and benefit apply, but the polarity of the diode is reversed to create a positive gate-source voltage (V_GS) at the MOSFET.

[0026] In a preferred embodiment, the gate-source voltage has an absolute value lower than the threshold voltage V_T of the MOSFET (but has an opposite sign as the threshold voltage). This value could be controlled by setting an appropriate value of the impedance. The optimum value of the impedance depends on several factors (such as the voltage/current level and frequencies of external power source, the threshold voltage V_T of the MOSFET, etc.) and can be empirically determined on a case by case basis. Under typical conditions, the impedance value (e.g. in an embodiment, the impedance is a resistor, in which case the impedance value is the resistance of the resistor) is preferably in a range 100-2500 Ohm, more preferably in a range 500 - 1500 Ohm.

[0027] In a preferred embodiment, the MOSFET is an N-type MOSFET (NMOS). Compared to P-type MOSFETs, N-type MOSFETs are generally less expensive, faster, and more effective (i.e., lower drain-source on-resistance R_DS(ON)). The N-type MOSFETs also typically create less heat than P-type counterparts.

[0028] The electronic circuit of the first aspect of the invention described above is suitable for use in a rectifier circuit. It may also be used in other converters, such as in a switching mode power supply, e.g. Buck, Boost, Flyback, Forward, etc. Basically, the electronic circuit could take the place of a diode in any circuits where a diode is typically used, with the advantage of high-speed reaction and low temperature of the invention.

[0029] The second aspect of the invention concerns a rectifier circuit suitable for use in an LED lamp arrangement, the rectifier circuit comprising:

• a first circuit comprising a first MOSFET, a first diode and a first impedance, connected with each other in accordance with the first aspect of the invention;
• a second circuit comprising a second MOSFET, a second diode and a second impedance, connected with each other in accordance with the first aspect of the invention;
• a third circuit comprising a third MOSFET, a third diode and a third impedance, connected with each other in accordance with the first aspect of the invention; and
• a fourth circuit comprising a fourth MOSFET, a fourth diode and a fourth impedance, connected with each other in accordance with the first aspect of the invention.

[0030] The first circuit, second circuit, third circuit and fourth circuit are connected with each other to receive an AC current and to output a rectified AC current. For example, the anode of the first diode in the first circuit may be electrically connected to the cathode of the fourth diode in the fourth electronic circuit, and the cathode of the second diode in the second circuit may be electrically connected to the anode of the third diode in the third electronic circuit. These connections may function to receive an AC current, e.g. from the ballast. On the other hand, the cathode of the first diode in the first circuit may be electrically connected to the cathode of the third diode in the third electronic circuit, and anode of the second diode in the second circuit may be electrically connected to the anode of the fourth diode in the forth circuit. These connections may function to supply a rectified AC current, e.g. to LEDs.

[0031] The third aspect of the invention concerns an LED lamp arrangement for replacing a fluorescent lamp in a luminaire having a ballast, the LED lamp arrangement comprising:

• a plurality of LEDs;
• two or more electrodes for releasably connecting to the luminaire and for receiving a current from the ballast; and
• two or more electronic circuits according to the first aspect of the invention (e.g. to form one or more rectifier circuits according to the second aspect of the invention), configured to for rectify the received current and supply a rectified current to the LEDs.

Brief Description of the Drawings

[0032] The advantages of the invention will be apparent upon consideration of the following detailed disclosure of exemplary non-limiting embodiments of the invention, especially when taken in conjunction with the accompanying drawings.

Figs. 1A-1E illustrate a known process of full-wave rectification.

Fig. 2A and 2B describe embodiments of the electronic circuit 100 according to the first aspect of the present invention.

Figs. 3A-3C describe an underlying theory of the present invention developed by the inventor.

Figs. 4A and 4B show embodiments putting the theory of the present invention into practice.

Fig. 5A shows an known configuration of a rectifier circuit using four diodes.

Fig. 5B illustrates an embodiment of a rectifier circuit 200 according to the second aspect of the present invention.

Fig. 6 illustrates an embodiment of an LED lamp arrangement 500 according to the present invention.

Description of Illustrative Embodiments

[0033] The following is a more detailed explanation of exemplary embodiments of the invention.

[0034] Fig. 2A illustrates an embodiment of an electronic circuit 100 according to the first aspect of the present invention, which may be used in a rectifier circuit. The electronic circuit may comprise a first terminal 101 and a second terminal 102 and comprises a MOSFET Q1, a diode D1 and an impedance such as a resistor R1.

[0035] The MOSFET Q1 has a gate terminal 124, a source terminal 122, and a drain terminal 120 is shown. The MOSFET Q1 shown in Fig. 2A is N-type. The source terminal 122 is electrically connected to a first terminal 101 and the drain terminal 120 is electrically connected to a second terminal 102. An anode terminal of a diode D1 is electrically connected to the gate terminal 124 of the MOSFET Q1. An impedance R1 is electrically connected across (in parallel with) the gate terminal 124 and the source terminal 122.

[0036] Fig. 2B shows another embodiment, in which the MOSFET Q2 is a P-type MOSFET. To create a positive gate-source voltage (V_GS) at the MOSFET Q1, the polarity needs to be reversed. The drain terminal 130 in this case is electrically connected to the first terminal 101, while the source terminal 132 is electrically connected to the second terminal 102. The cathode terminal of the diode D2 is electrically connected to the gate terminal 134. The anode terminal of the diode D2 is electrically connected to the drain terminal 130. The impedance R2 is electrically connected across the gate terminal 134 and the source terminal 132 of the MOSFET Q2.

[0037] The invention is based on an insight that MOSFETs could be used as a diode rather than switches in a rectifier circuit. The MOSFET Q1, Q2 are turned off throughout its operation and acts as a diode, allowing current to flow from the first terminal 101 to the second terminal 102. This is based on the intrinsic (body) diode in the MOSFET Q1. It has been tested by the inventor that, when configured in accordance with the present invention, the MOSFETs (acting as diodes) can react more quickly to the high frequency input signals compared to normal P-N junction diodes or Schottky diodes, and demonstrate a lower temperature during the high frequency applications.

[0038] Without being bound by theory, an underlying principle of the present invention according to the understanding of the inventor is described below. Fig. 3A shows the structure of a typical MOSFET, where an N-type MOSFET is used as an example. The gate terminal 124 is connected to a conductor layer 201 (e.g. metal or polysilicon), which is separated with the body semiconductor material (P-type in the case of NMOS) by an insulator layer 202 (e.g. oxide or other dielectrics). The source terminal 122 and drain terminal 126 are connected to regions of a different type of semiconductor material than the body (N-type in the case of NMOS). Typically, an N-type MOSFET is turned on by exerting a positive gate-source voltage on the gate terminal 124, forming a channel underneath the insulator layer 202 so that electrons can flow between the source terminal 122 and drain terminal 120, to form a current.

[0039] But there is another way to conduct a current between the source terminal 122 and drain terminal 120. As can been seen in Fig. 3A, in addition to the gate terminal 124, source terminal 122 and drain terminal 120, a MOSFET has a fourth terminal 126 called "base". The base is the bulk material (P-type in the case of NMOS). As shown in Fig. 3A, the source terminal 122 and the base terminal 126 are typically short-circuited with each other. Due to the P-N junction between the base and the drain and the additional connection between the source and the base, there is effectively a diode between the source and the drain. When the voltage at the source terminal 122 is sufficiently higher than the voltage at the drain terminal 120, current can flow from the source terminal 122 to the base terminal 126, then through this body diode to the drain terminal 120.

[0040] If the voltage difference between the gate terminal 124 and source terminal 122 is zero (V_GS = 0), as shown in Fig. 3B, there will be a limited number of holes (illustrated as empty circles) and electrons (illustrated as solid circles). In this case, the body diode behaves like a normal diode, which acts relatively slowly compared to a rapid change in input voltage at high frequency. In this case, similar problem occurs as in the case of typical diode rectifiers in high frequency operations.

[0041] However, if a negative voltage is applied between the gate terminal 124 and source terminal 122 (V_GS < 0), as shown in Fig. 3C, the negative voltage attracts holes in the bulk P-type material to the region underneath the insulator layer 202, i.e. close to the P-N junction. This in turn attracts the electrons in the drain terminal 120 to come closer to the P-N junction.

[0042] The invention utilizes this body diode to have the MOSFET work as a diode in a rectifier. Unlike normal diodes, the behavior of the MOSFET body diode can be controlled by the voltages at the gate terminal. This enables the MOSFET to react quickly to the high frequency input signals and solves the problem of normal P-N junction diodes or Schottky diodes in the high frequency applications. The controlled voltage can increase the number of holes in the P-type material (body) and the electrons in the N-type material (drain). These additional holes and electrons improve the flow of electrons and holes and reduces the potential barrier in the depletion region, thereby providing a significant improvement of the reaction time of the MOSFET (which acts as a diode) when the input signal changes its polarity.

[0043] Figs. 4A and 4B shows how the electronic circuit 100 according to the invention utilizes the insight described above, using the embodiment of Fig. 2A as an example. When the voltage at the first terminal 101 becomes larger than the voltage at the second terminal 102 (i.e. V₁₀₁ > V₁₀₂), the diode D1 becomes forward biased and allows current I₁ to flow through it, as shown in Fig. 4A. This current creates a voltage (I₁ × R₁) across the gate terminal 124 and the source terminal 122, where the voltage at the source terminal 122 is higher. As a result, the gate-source voltage V_GS of the MOSFET Q1 becomes negative, so that the MOSFET Q1 acts as a fast diode as described above in Fig. 3C. The MOSFET Q1 then conducts a parallel forward current I₂. Since the impedance R₁ limits the current flowing through diode D1, most of the current coming into the first terminal 101 will flow through the MOSFET Q1 acting as a diode as the input voltage increases. At the same time, by limiting the current I₁, the negative V_GS can also be controlled (preferably set at an absolute value lower than the threshold value V_T of the MOSFET Q1) so that the MOSFET operates at an optimum condition.

[0044] When the polarity is reversed, the voltage at the first terminal 101 becomes smaller than the voltage at the second terminal 102 (i.e. V₁₀₁ < V₁₀₂). In that case, both the diode D1 and the MOSFET Q1 react quickly to block the reverse current, as shown in Fig. 4B. For the MOSFET Q1, since it acts as a fast diode (as described in Fig. 3C), the carriers around the depletion region can move quickly in response to the changes in voltages V₁₀₁ and V₁₀₂; for the diode D1, it can also react quickly as the forward current I₁ has been limited by the impedance R₁. The diode D1 then blocks the current that would flow from the second terminal 102, as visually represented in Fig. 4B as a broken circuit in the place of the diode D1.

[0045] By blocking the current through the diode D1, the diode further functions to ensure that the MOSET Q1 is not switched on as the voltage at the second terminal 102 further increases. As shown in Fig. 4B, due to the series connection between the diode D1 and the impedance R1, the current through the impedance R1 is also blocked. This ensures that the gate-source voltage V_GS across the gate terminal 124 and source terminal 122 of the MOSFET Q1 is substantially zero during the entire period when the voltage at the first terminal 101 becomes smaller than the voltage at the second terminal 102 (i.e. V₁₀₁ < V₁₀₂), so that the gate-source voltage V_GS is always smaller than the threshold voltage V_T of the MOSFET without turned on, so that the MOSFET continues to act as a diode to block the reverse current.

[0046] As can be seen from the above, by connecting the diode D1 across the gate terminal 124 of the MOSFET Q1 and the drain terminal 120 of the MOSFET Q1, and connecting the impedance R1 across the gate terminal 124 and the source terminal 122 of the MOSFET Q1, these elements work together to ensure that the MOSFET Q1 acts as a diode with a high efficiency. When (forward) current needs to be conducted through the MOSFET Q1, the diode D1 and the impedance R1 together create a negative V_GS to increase the efficiency of the body diode; when (reverse) current needs to be blocked, the diode D1 across the gate terminal 124 of the MOSFET Q1 and the drain terminal 120 of the MOSFET Q1 ensures that the voltage across the impedance R1 (V_GS) is substantially zero, so that the MOSFET continues to act as a diode to block the current. The same principle applies when the MOSFET is a PMOS (see Fig. 2B). In this way, the present invention successfully utilizes these elements to effectively create a high speed, high efficiency diode that can handle a large current with a high frequency, which for example is come across in LED lamps.

[0047] Fig. 5B describes an embodiment of a rectifier circuit 200 according to the invention. This rectifier circuit comprises four sets of MOSFETs Q1a - Q1d, diodes D1a - D1d, and impedances R1a - R1d, each connected into a circuit according to the electronic circuit 100 shown in Fig. 2A and replacing a respective diode 401 - 404 in the known rectifier circuit shown in Fig. 5A.

[0048] In the embodiment shown, the source terminal 122a of the first MOSFET Q1a in the first circuit is electrically connected to the drain terminal 120d of the fourth MOSFET Q1d in the fourth circuit, and the drain terminal 120b of the second MOSFET Q1b in the second circuit is electrically connected to the source terminal 122c of the third MOSFET Q1c in the third circuit. These connections function to receive an AC current from a power source, which may be a voltage source V1 as shown in Fig 5B, a current source (e.g. such as in the case of a constant current ballast), or a combination of these (such as in the case of a constant power ballast).

[0049] In the embodiment shown, the drain terminal 120a of the first MOSFET Q1a in the first circuit is electrically connected to the drain terminal 120c of the third MOSFET (Q1c) in the third circuit, and the source terminal 122b of the second MOSFET Q1b in the second circuit is electrically connected to the source terminal 122d of the fourth MOSFET (Q1d) in the fourth circuit. These connections functions to supply a rectified AC current to a load 410, such as LEDs.

[0050] In the embodiment shown in Fig. 5B, all the MOSFETs are N-type MOSFETs. Some or all these MOSFETs may be replaced with P-type MOSFETs and use the configuration shown in Fig. 2B (turned 90°).

[0051] Fig. 6 shows an embodiment of an LED lamp arrangement 500 according to the invention. This embodiment comprises a plurality of LEDs 501, 502, 503, a plurality of electrodes 511a, 511b, 511c, 511d, and a plurality of electronic circuits 100 connected to rectify the received current.

[0052] The LED lamp arrangement 500 needs at least two electrodes to conduct current from one end of the lamp to another end. For replacing a fluorescent lamp, it is preferred that the LED lamp arrangement 500 comprises four electrodes as shown in Fig. 5. Typically, a fluorescent lamp has four pins. When connecting to a luminaire, two pins are connected to the ballast (called hot ends), and the other two pins are connected to other elements such as a capacitor for stability (called cold ends). Using four electrodes in the LED lamp arrangement 500 like in an fluorescent lamp has an advantage that, irrespective of how the lamp is connected to the luminaire, current can conduct from one electrode to another electrode.

[0053] In line with this, two rectifier circuits 200a, 200b (in accordance with the embodiment shown in Fig. 5B) are used in this embodiment, although it is also possible to use only one rectifier circuit and possible to connect the two or more electronic circuits 100 with each other in a different way. If electrodes 511a and 511b are connected to hot ends, current will flow from electrode 511a to 511b or vice versa, depending on the polarity of the input current at the time. When current flows from electrode 511a to electrode 511b, it first flows through the MOSFET Q1a (acting as a diode) in the first rectifier circuit 200a, through the LEDs 501, 502, 503, then through the MOSFET Q1f in the second rectifier circuit 200b to the electrode 511b. Conversely, when current flows from electrode 511b to electrode 511a, it first flows through the MOSFET Q1g, then through the LEDs 501, 502, 503, and then through the MOSFET Q1d. When the other two electrodes 511c and 511d are connected to the hot end, the current similarly flows between these electrodes through different MOSFETs. In all these cases, all MOSFETs act like diodes, while responding to changes in the input signal faster and demonstrating lower temperature compared to normal diodes.

[0054] The diodes D1 and D2 described above may be any diodes that conduct when it is forward biased, such as a normal P-N junction diode or a Schottky diode, such as Microsemi's UPSC600. Preferably, diodes D1/D2 has a short forward/reverse recovery time to quickly react to changes in input voltages. A high current rating of the diode D1/D2 is not required, as most of the forward current will flow through the MOSFET Q1/Q2. Schottky diodes are suitable choices for this purpose, including those which are not power diodes. For example, the diode could also have a low current rating typically limited to signalling purposes. Preferably, diodes D1 and D2 are not Zener diodes.

[0055] Note that the first terminal 101 and second terminal 102 do not require physical electrodes or pins. Any part of the circuit that allows an electrical connection with another circuit may function as the first terminal 101 and second terminal 102. When multiple copies of the circuit 100 are present (see e.g. Fig. 5B and 6), the first and/or second terminal 101, 102 of one copy of the circuit 100 may be embodied in the same wiring as a first and/or second terminal 101, 102 of another copy of the circuit 100.

[0056] In preferred embodiments of the present invention, as described with respect to Figs. 2-6, the MOSFETs (NMOS and PMOS) are enhancement type, which is turned off when the gate-source voltage V_GS is zero. The so-called depletion type MOSFETs, which is turned on when V_GS is zero and is turned off by changing the V_GS, may also be used. But in that case, other measures (such as an additional voltage source) may be needed to ensure that the MOSFET is turned off.

[0057] It will be appreciated by the skilled person that features described in relation to one embodiment may be used with or combined with features of the other embodiments. While the principles of the invention have been set out above in connection with specific embodiments, it is to be understood that this description is merely made by way of example and not as a limitation of the scope of protection, which is determined by the appended claims.

Claims

1. An electronic circuit (100) suitable for use in a rectifier circuit (200), the electronic circuit (100) comprising:

- a MOSFET (Q1, Q2) having a gate terminal (124, 134), a source terminal (122, 132) and a drain terminal (120, 130);

- a diode (D1, D2) having an anode terminal and a cathode terminal; and

- an impedance (R1, R2),

wherein the diode (D1, D2) is electrically connected across the gate terminal (124, 134) of the MOSFET and the drain terminal (120, 130) of the MOSFET, and the impedance (R1, R2) is electrically connected across the gate terminal (124, 134) and the source terminal (122, 132) of the MOSFET (Q1, Q2).

2. The electronic circuit (100) according to claim 1, wherein the diode (D1, D2) and the impedance (R1, R2) are configured to generate a voltage difference (V_GS) between the gate terminal (124, 134) and the source terminal (122, 132) of the MOSFET (Q1, Q2), the voltage difference (V_GS) having an opposite sign as the threshold voltage (V_T) of the MOSFET (Q1, Q2), when the diode (D1, D2) is forward biased.

3. The electronic circuit (100) according to claim 2, wherein the diode (D1, D2) and the impedance (R1, R2) are configured to generate a substantially zero voltage (V_GS) across the gate terminal (124, 134) and the source terminal (122, 132) of the MOSFET (Q1, Q2), when the diode (D1, D2) is reverse biased.

4. The electronic circuit (100) according to any of the preceding claims, wherein the MOSFET (Q1) is an N-type MOSFET, the anode terminal of the diode (D1) is electrically connected to the gate terminal (124) of the MOSFET (Q1), and the cathode terminal of the diode (D1) is electrically connected to the drain terminal (120) of the MOSFET.

5. The electronic circuit (100) according to any of claims 1-3, wherein the MOSFET (Q2) is a P-type MOSFET, the cathode terminal of the diode (D2) is electrically connected to the gate terminal (134) of the MOSFET (Q2), and the anode terminal of the diode (D2) is electrically connected to the drain terminal of the MOSFET (Q2).

6. The electronic circuit (100) according to any of the preceding claims, wherein the diode (D1, D2) is not a Zener diode.

7. The electronic circuit (100) according to any of the preceding claims, wherein the diode (D1, D2) is a Schottky diode.

8. The electronic circuit (100) according to any of the preceding claims, wherein the impedance (R1, R2) is a resistor.

9. The electronic circuit (100) according to any of the preceding claims, wherein the impedance (R1, R2) has an impedance value in a range 100-2500 Ohm, preferably in a range 500-1500 Ohm.

10. a rectifier circuit (200) suitable for use in an LED lamp arrangement (500), the rectifier circuit (200) comprising:

- a first circuit comprising a first MOSFET (Q1a), a first diode (D1a) and a first impedance (R1a), connected with each other in accordance with any of the preceding claims; and

- a second circuit comprising a second MOSFET (Q1b), a second diode (D1b) and a second impedance (R1b), connected with each other in accordance with any of the preceding claims;

- a third circuit comprising a third MOSFET (Q1c), a third diode (D1c) and a third impedance (R1c), connected with each other in accordance with any of the preceding claims; and

- a fourth circuit comprising a fourth MOSFET (Q1d), a fourth diode (D1d) and a fourth impedance (R1d), connected with each other in accordance with any of the preceding claims,

wherein the first circuit, second circuit, third circuit and fourth circuit are connected with each other to receive an AC current and to output a rectified AC current.

11. An LED lamp arrangement (500) for replacing a fluorescent lamp in a luminaire having a ballast, the LED lamp arrangement comprising:

- a plurality of LEDs;

- two or more electrodes for releasably connecting to the luminaire and for receiving a current from the ballast; and

- two or more electronic circuits (100) according to any of claims 1-9, configured to rectify the received current and supply a rectified current to the LEDs.

12. The LED lamp according to claim 11, comprising four or more electronic circuits (100), the four or more electronic circuits (100) forming one or more rectifier circuits according to claim 10.

Drawing