Patent Description:
In a multi-output switched-mode power supply having a plurality of output ports, the power supply may convert an input voltage to multiple output voltages for powering a number of electronic apparatus such as light emitting diodes (LEDs), organic LEDs (OLEDs), integrated circuits (such as driver IC), lighting control systems, sensors, computers, server devices, fans, telecommunication devices, and other electronic devices. The input voltage may be an alternating current (AC) voltage or a direct current (DC) voltage, and the plurality of output voltages may include at least a high DC voltage and a low DC voltage. A typical isolated switched-mode power supply applying LLC resonant half-bridge topology with two output ports is shown in <FIG>. The primary circuit is not shown in detail and may vary. The AC input power in the source circuit <NUM> is coupled to a transformer circuit <NUM>. The transformer circuit <NUM> comprises a primary winding to be coupled to the source circuit <NUM> and a plurality of secondary windings to be coupled to the load circuit <NUM> with two output ports. The secondary circuit also comprises an inductor circuit <NUM> and a rectification circuit <NUM>.

In some applications, it is important to report whether the output ports are loaded. The conventional method for determining the presence or absence of a load is by detecting the current flowing through a load using a current detection resistor connected in series to the load at the output ports. However, such current detection resistors inevitably cause energy loss, which lowers the power efficiency of the circuit.

Other methods for detecting the output current at the output ports include methods using an operational amplifier, current transformer, or other similar electronic devices. The additional circuit for achieving an accurate measurement can be very complex, which can increase the cost and power consumption of the load detection and the accuracy for determining a low output current may not be adequate. <CIT> describes a load detection circuit having pull-up resistors connected to a feedback terminal so that resistance of the pull-up resistor is switched according to a change of load condition.

<CIT> describes an integrated circuit comprising a feedback terminal to receive a feedback signal and a voltage regulator having a power output in communication with an output terminal, wherein the voltage regulator is responsive to the feedback signal, to generate the power output.

Therefore, there is a need in the art to have a power supply with a function of detecting the presence or absence of a load at an output port accurately, even when a small load with a low output current is present. In particular, the additional components in the power supply are minimized so that the extra cost is relatively low, and the power dissipation for the detection is minimal.

Provided herein is a power supply for providing a plurality of voltage outputs at a plurality of output ports with a function of detecting presence or absence of a load at a first output port selected from the plurality of output ports. The power supply comprises a first voltage source for providing a first voltage at a first node; a first diode having a cathode coupled to the first output port, and having an anode directly or indirectly coupled to the first node for receiving the first voltage; a second voltage source for providing a second voltage at a second node; a second diode having a cathode coupled to a second output port selected from the plurality of output ports, and having an anode coupled to the second node for receiving the second voltage; and a bridging circuit having two terminals respectively connected to the first and the second output ports. The second voltage is higher than the first voltage such that when the load is not present at the first output port, the bridging circuit pulls up an output voltage at the first output port to reverse bias the first diode, thereby enabling the presence or absence of the load at the first output port to be detectable by detecting the output voltage at the first output port.

According to certain aspects, the power supply comprises a second voltage divider having a terminal coupled to the first output port, thereby a detection voltage is generated by the second voltage divider.

According to certain aspects, the power supply further comprises a first voltage divider having a terminal directly or indirectly coupled to the first node or the second node, thereby a reference voltage is generated by the first voltage divider. A ratio of the detection voltage to the reference voltage is used for determining the presence or absence of the load at the first output port.

According to certain aspects, the power supply comprises a processor configured to identify an increase in the ratio of the detection voltage to the reference voltage and generate one or more signals to signify the presence or absence of the load at the first output port.

According to certain aspects, the power supply comprises a third diode having an anode coupled to the first node, and having a cathode coupled to the anode of the first diode; and a first capacitor having a terminal electrically connected to the cathode of the third diode for stabilization. The bridging circuit is disconnected from the first capacitor by the first diode when the load is not connected to the first output port for achieving a fast detection of the load.

According to certain aspects, the power supply comprises a third diode having an anode coupled to the first node, and having a cathode coupled to the terminal of the first voltage divider; a first capacitor for stabilizing the first output port; and a second capacitor electrically connected to the cathode of the third diode for stabilization. The second capacitor has a substantially smaller capacitance than the first capacitor for minimizing a power consumption when the load is connected to the first output port.

According to certain aspects, the power supply comprises a multiple winding transformer comprising a first secondary winding and a second secondary winding, wherein the first secondary winding generates the first voltage source; and the second secondary winding generates the second voltage source.

According to certain aspects, the multiple winding transformer is configured in accordance with an isolated tapped winding flyback converter topology.

According to certain aspects, the multiple winding transformer is configured in accordance with an isolated boost topology.

According to certain aspects, the multiple winding transformer is configured in accordance with an isolated flyback converter topology.

According to certain aspects, the multiple winding transformer is configured in accordance with an isolated full-bridge or an isolated half-bridge converter topology.

According to certain aspects, the multiple winding transformer is configured in accordance with an isolated LLC resonant half-bridge converter topology.

According to certain aspects, the bridging circuit comprises a resistor, a combination of the resistor and a zener diode, a voltage-dependent resistor (VDR), or a combination of a zero-voltage-switching (ZVS) and the VDR.

According to certain aspects, the power supply comprises a combination of a zener diode and an alerting device for signifying whether the load is present, wherein the alerting device is an LED indicator, a beeping device, or a combination thereof.

According to certain aspects, the first diode and the second diode are Schottky diodes.

According to certain aspects, the load is one or more light emitting diodes (LEDs), an LED string, integrated circuits, lighting control systems, sensors, computers, server devices, fans, or telecommunication devices.

Other aspects and advantages of the present invention are disclosed as illustrated by the embodiments hereinafter.

The appended drawings, where like reference numerals refer to identical or functionally similar elements, contain figures of certain embodiments to further illustrate and clarify various aspects, advantages and features of an output load identification method and an apparatus incorporating such method as disclosed herein. It will be appreciated that these drawings and graphs depict only certain embodiments of the invention and are not intended to limit its scope. The output load identification method and apparatus as disclosed herein will be described and explained with additional specificity and detail through the use of the accompanying drawings in which:.

Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been depicted to scale.

The present disclosure generally relates to an output load identification method. More specifically, but without limitation, the present disclosure relates to the identification of a load on the output side of an isolated switched-mode power supply circuit. <FIG> shows a circuit diagram of a typical isolated switched-mode power supply. It should be appreciated that a vast number of variations for the power supply circuit exist. An objective of the present disclosure is to determine the presence or absence of a load at an output port accurately, even when a small load with a low output current is present.

<FIG> illustrates the issues to be addressed in the present disclosure. In a power supply <NUM> having a plurality of output ports, for example, a system with two output ports. The first output port <NUM> generates a lower voltage, and the second output port <NUM> generates a higher voltage. The power supply <NUM> may be a transformer-based power converter, a DC/DC converter, a voltage regulator, a switched mode power supply, a flyback converter, an isolated resonant half-bridge converter, or other types of power supply. In some applications, it is important to understand whether a load <NUM> is connected to the first output port <NUM>. In one embodiment, the load <NUM> is one or more light emitting diodes (LEDs), or an LED string. Information with respect to the presence or absence of a load <NUM> at a particular output port in a multi-output power supply can be coupled to a processor, such as a microcontroller unit (MCU), a field-programmable gate array (FPGA), an operational amplifier, or other programmable environments. This can facilitate the power generation, perform output power management, and detect system failure or fault for triggering over voltage protection (OVP), under voltage protection (UVP), over power protection (OPP), or short circuit protection (SCP). Other desirable use of the information may be attained by obtaining accurate information in relation to a presence or absence of a load.

In the following embodiments, the load detection circuit in an isolated switched-mode power supply is merely exemplary in nature and is not intended to limit the disclosure or its application and/or uses. It should be appreciated that a vast number of variations exist. The detailed description will enable those of ordinary skill in the art to implement an exemplary embodiment of the present disclosure without undue experimentation, and it is understood that various changes or modifications may be made in the function and arrangement of the circuit described in the exemplary embodiment without departing from the scope of the present disclosure as set forth in the appended claims. The circuits in the primary side of the transformer is not shown in the present disclosure for simplicity and clarity. The primary circuit may vary and is not limited to certain structures or topologies. The switching regulator for controlling the power converter is not shown, and the power supply may be configured in accordance with primary side regulation (PSR) or secondary side regulation (SSR). Other isolated switched-mode power supplies may apply the teaching of the present disclosure to determine the presence or absence of a load at an output port accurately.

The benefits, advantages, solutions to problems, and any element(s) that may cause any benefit, advantage, or solution to occur or become more pronounced are not to be construed as a critical, required, or essential features or elements of any or all of the claims.

For simplicity and clarity, relational terms such as "first," "second," "third," and the like, if any, are used solely to distinguish one from another entry, item, or device, without necessarily requiring any actual such relationship or order between such entries, items, or devices.

As used herein, the terms "coupled" and "connected," along with any variant thereof, covers any coupling or connection, either direct or indirect, between two or more elements, unless otherwise indicated or clearly contradicted by context.

Referring to <FIG>, a circuit diagram for performing load identification is depicted. In the figure, a complete circuit is not shown and the voltage generation circuits are omitted for clarity. At the node N1 and node N2, a first voltage and a second voltage are provided respectively. The first voltage and the second voltage may be generated from a power supply such as transformer-based power converter and DC/DC converter. A first diode (D1) <NUM> has a cathode coupled to the first output port (Vout1) <NUM> at node N3, and has an anode coupled to the node N1 for receiving the first voltage. Similarly, a second diode (D2) <NUM> has a cathode coupled to the second output port (V out2) <NUM> at node N4, and has an anode coupled to the node N2 for receiving the second voltage. The diodes used in the present disclosure may be any type, such as Schottky diode, P/N junction type diode, or a configured MOSFET.

For stabilizing the first output port <NUM>, a first capacitor (C1) <NUM> is electrically connecting node N3 to the ground (GND) as an energy storage capacitor. For stabilizing the second output port <NUM>, a second capacitor (C2) <NUM> is electrically connecting node N4 to node N3 as an energy storage capacitor. The first capacitor <NUM> and the second capacitor <NUM> may be polarized electrolytic capacitors, such as aluminum electrolytic capacitors or tantalum electrolytic capacitors. The voltage rating of the capacitors should be selected to correspond to the operating voltage of the power supply.

Advantageously, a bridging circuit (R CHARGE) <NUM> having two terminals connected to the first output port <NUM> and the second output port <NUM> respectively is used. The bridging circuit <NUM> may include a thin film resistor, a surface mounted chip resistor, or other types of resistor. The resistance can be selected to correspond to the two output voltages by minimizing the current across the bridging circuit <NUM>, thereby the power dissipation as a result of the additional bridging circuit <NUM> can also be minimized. When a load <NUM> is present at the first output port <NUM> while the power supply is in a normal operating state, the voltages at the first output port <NUM> and the second output port <NUM> are unchanged, which are equivalent to the voltages at the node N1 and node N2. When a load is absent at the first output port <NUM>, the bridging circuit <NUM> provides a resistive path from the second output port <NUM> to the first output port <NUM>, thereby the voltage at node N3 is pulled up, and the first capacitor <NUM> is charged to a higher voltage. As node N3 has a higher voltage than node N1, the first diode <NUM> is in reverse bias. Therefore, the bridging circuit <NUM> enables the presence or absence of the load <NUM> at the first output port <NUM> to be detectable by detecting the output voltage at the first output port <NUM>. The use of the bridging circuit <NUM> is simple to implement and so the impact to the component costs and power consumption is minimized. It is also apparent to those skilled in the art that the bridging circuit <NUM> can also be implemented using a MOSFET, transistors, or a switch in series with a resistor so that the resistive path between the first output port <NUM> and the second output port <NUM> is opened when the load identification is not needed. In certain embodiments, the bridging circuit <NUM> may comprise a combination of a resistor and a zener diode, a voltage-dependent resistor (VDR), a combination of zero-voltage-switching (ZVS) and VDR, or other combinations of electronic components that can provide a resistive path from the second output port <NUM> to the first output port <NUM> for charging the first capacitor <NUM>.

As shown in <FIG>, the power supply of the present disclosure may comprise a combination of a zener diode <NUM> and an alerting device <NUM> connected between the first output port <NUM> and the ground for signifying whether a load is present, and further comprises MOSFET or transistors for changing the alerting device to be active low, such that the alerting device is enabled when a load is absent. The alerting device <NUM> may be an LED indicator, a beeping device, or a combination thereof. For example, if the voltage at first output port <NUM> is 20V when a load is connected, and the voltage is increased to 30V when a load is not connected. An 18V zener diode <NUM>, together with an optional resistor and the alerting device <NUM> can be used.

This illustrates the fundamental structure and mechanism of the load identification structure in accordance with the present disclosure. The following describes further embodiments of the present disclosure in greater detail with reference to <FIG>. Each embodiment may show different benefits and advantages. For the convenience in description, similar reference numerals are given to components having the same or similar functions as the components described above.

As shown in <FIG>, the circuit diagram of the first design of a power supply with a function of detecting the presence or absence of a load is provided. Desirably, the voltages are generated by a transformer-based power converter, comprising a transformer with at least one primary winding (not shown in <FIG>) and at least two secondary windings <NUM>, <NUM>. The at least two secondary windings <NUM>, <NUM> are magnetically coupled to and isolated from the primary winding. The two secondary windings <NUM>, <NUM> are formed by tapping the winding at an intermediate location at node N1. The first secondary winding (T1-W1) <NUM> is the winding between node N1 and ground. The second secondary winding (T1-W2) <NUM> is the winding between node N2 and node N1.

The arrangement and properties of the diodes, capacitors, and the bridging circuit are the same as the circuit configurations in <FIG>. By tapping the secondary winding, a first voltage and a second voltage are generated at node N1 and node N2 respectively. A first diode (D1) <NUM> has a cathode coupled to the first output port (Vout1) <NUM> at node N3, and has an anode coupled to the node N1 for receiving the first voltage. Similarly, a second diode (D2) <NUM> has a cathode coupled to the second output port (Vout2) <NUM> at node N4, and has an anode coupled to the node N2 for receiving the second voltage. A first capacitor (C1) <NUM> is electrically connecting node N3 to the ground (GND), and a second capacitor (C2) <NUM> is electrically connecting node N4 to node N3, both preferably are polarized electrolytic capacitors functioned as energy storage capacitors.

A bridging circuit (R_CHARGE) <NUM> having two terminals connected to the first output port <NUM> and the second output port <NUM> respectively is used. This is a resistive path from the second output port <NUM> to the first output port <NUM>. When a load <NUM> is present at the first output port <NUM> while the power supply is in a normal operating state, the voltages at the first output port <NUM> and the second output port <NUM> are unchanged, which are equivalent to the voltages at the node N1 and node N2 respectively. When a load is absent at the first output port <NUM>, the voltage at node N3 is pulled up by the resistive path and the first capacitor <NUM> is charged to a higher voltage. As node N3 has a higher voltage than node N1, the first diode <NUM> is in reverse bias.

In order to determine the presence or absence of the load <NUM> at the first output port <NUM>, voltage dividers <NUM>, <NUM> are used. As shown in <FIG>, a first voltage divider <NUM> comprises at least a first resistor (R11) <NUM> and a second resistor (R12) <NUM>, with one terminal coupled to the node N4, and another terminal coupled to the ground. The node N4 is indirectly coupled to N2 through the second diode <NUM>. A reference voltage (Vdetect_1) <NUM> is generated by the first voltage divider <NUM> by tapping the two or more resistors at an intermediate location. The reference voltage <NUM> corresponds to the voltages generated by the secondary windings <NUM>, <NUM> for eliminating any inaccuracy caused by a fluctuation of voltage in the primary or secondary windings. A second voltage divider <NUM> comprises at least a third resistor (R21) <NUM> and a fourth resistor (R22) <NUM>, with one terminal coupled to the first output port <NUM>, and another terminal coupled to the ground. A detection voltage (Vdetect_2) <NUM> is generated by the second voltage divider <NUM> by tapping the two or more resistors at an intermediate location. The ratio of the detection voltage <NUM> to the reference voltage <NUM> can be used for determining the presence or absence of the load at the first output port <NUM>. When the load <NUM> is connected to the first output port <NUM>, the voltage at node N3 is pulled up, and so the detection voltage <NUM> is also pulled up. The voltage at node N4 is unaffected, so the ratio of the detection voltage <NUM> to the reference voltage <NUM> is increased.

Now referring to <FIG>, the circuit diagram of the second design of a power supply with a function of detecting the presence or absence of a load is provided. Desirably, the voltages are also generated by a transformer-based power converter, comprising a transformer with at least one primary winding (not shown in <FIG>) and at least two secondary windings <NUM>, <NUM>. The at least two secondary windings <NUM>, <NUM> are magnetically coupled to and isolated from the primary winding. The two secondary windings <NUM>, <NUM> are formed by tapping the winding at an intermediate location at node N1. The first secondary winding (T1-W1) <NUM> is the winding between node N1 and ground. The second secondary winding (T1-W2) <NUM> is the winding between node N2 and node N1.

By tapping the secondary winding, a first voltage and a second voltage are generated at node N1 and node N2 respectively. A third diode (D3) <NUM> has a cathode coupled to the node N5, and has an anode coupled to the node N1 for receiving the first voltage. A second diode (D2) <NUM> has a cathode coupled to the second output port (Vout2) <NUM> at node N4, and has an anode coupled to the node N2 for receiving the second voltage. A first diode (D1) <NUM> has a cathode coupled to the first output port <NUM> at node N3, and has an anode coupled to the node N5. A first capacitor (C1) <NUM> is electrically connecting node N5 to the ground (GND), and a second capacitor (C2) <NUM> is electrically connecting node N4 to node N5, both function as energy storage capacitors.

A bridging circuit (R_CHARGE) <NUM> having two terminals connected to the first output port <NUM> and the second output port <NUM> respectively is used. This is a resistive path from the second output port <NUM> to the first output port <NUM>. When a load <NUM> is present at the first output port <NUM> while the power supply is in a normal operating state, the voltages at the first output port <NUM> and the second output port <NUM> are unchanged, which are equivalent to the voltages at the node N1 and node N2 respectively. When a load is absent at the first output port <NUM>, the voltage at node N3 is pulled up by the resistive path. As node N3 has a higher voltage than node N5, the first diode <NUM> is in reverse bias. The bridging circuit <NUM> is disconnected from the first capacitor <NUM> by the first diode <NUM>. Therefore, the voltage at node N5 is not pulled up by the bridging circuit <NUM>, and the first capacitor <NUM> is not charged up to a higher voltage. As the capacitance of the first capacitor <NUM> is generally large, this circuit topology can advantageously achieve a fast detection of the load <NUM>.

In order to determine the presence or absence of the load <NUM> at the first output port <NUM>, voltage dividers <NUM>, <NUM> are used. As shown in <FIG>, a first voltage divider <NUM> comprises at least a first resistor (R11) <NUM> and a second resistor (R12) <NUM>, with one terminal coupled to the node N5, and another terminal coupled to the ground. The node N5 is indirectly coupled to N1 through the third diode <NUM>. A reference voltage (Vdetect_1) <NUM> is generated by the first voltage divider <NUM> by tapping the two or more resistors at an intermediate location. The reference voltage <NUM> corresponds to the voltages generated by the secondary windings <NUM>, <NUM> for eliminating any inaccuracy caused by a fluctuation of voltage in the primary or secondary windings. A second voltage divider <NUM> comprises at least a third resistor (R21) <NUM> and a fourth resistor (R22) <NUM>, with one terminal coupled to the first output port <NUM>, and another terminal coupled to the ground. A detection voltage (Vdetect_2) <NUM> is generated by the second voltage divider <NUM> by tapping the two or more resistors at an intermediate location. The ratio of the detection voltage <NUM> to the reference voltage <NUM> can be used for determining the presence or absence of the load at the first output port <NUM>. When the load <NUM> is connected to the first output port <NUM>, the voltage at node N3 is pulled up, and so the detection voltage <NUM> is also pulled up. The voltage at node N5 is unaffected, so the ratio of the detection voltage <NUM> to the reference voltage <NUM> is increased.

Now referring to <FIG>, the circuit diagram of the third design of a power supply with a function of detecting the presence or absence of a load is provided. Desirably, the voltages are also generated by a transformer-based power converter, comprising a transformer with at least one primary winding (not shown in <FIG>) and at least two secondary windings <NUM>, <NUM>. The at least two secondary windings <NUM>, <NUM> are magnetically coupled to and isolated from the primary winding. The two secondary windings <NUM>, <NUM> are formed by tapping the winding at an intermediate location at node N1. The first secondary winding (T1-W1) <NUM> is the winding between node N1 and ground. The second secondary winding (T1-W2) <NUM> is the winding between node N2 and node N1.

By tapping the secondary winding, a first voltage and a second voltage are generated at node N1 and node N2 respectively. A first diode (D1) <NUM> has a cathode coupled to the first output port <NUM> at node N3, and has an anode coupled to the node N1 for receiving the first voltage. A second diode (D2) <NUM> has a cathode coupled to the second output port (Vout2) <NUM> at node N4, and has an anode coupled to the node N2 for receiving the second voltage. A third diode (D3) <NUM> has a cathode coupled to the node N5, and has an anode coupled to the node N1 for receiving the first voltage. A first capacitor (C1) <NUM> is electrically connecting node N3 to the ground (GND), and a second capacitor (C2) <NUM> is electrically connecting node N4 to node N3, both are desirably polarized electrolytic capacitors functioned as energy storage capacitors. A third capacitor (C3) <NUM> is electrically connecting node N5 to the ground for stabilizing an internal port (Vout1A) <NUM>.

A bridging circuit (R_CHARGE) <NUM> having two terminals connected to the first output port <NUM> and the second output port <NUM> respectively is used. This is a resistive path from the second output port <NUM> to the first output port <NUM>. When a load <NUM> is present at the first output port <NUM> while the power supply is in a normal operating state, the voltages at the first output port <NUM> and the second output port <NUM> are unchanged, which are equivalent to the voltages at the node N1 and node N2 respectively. When a load is absent at the first output port <NUM>, the voltage at node N3 is pulled up by the resistive path. As node N3 has a higher voltage than node N1, the first diode <NUM> is in reverse bias. The absence of a load <NUM> will not affect the voltage at node N5, which is a separated path for generating a voltage for the internal port <NUM> to reflect the voltage at node N1. This circuit topology can also achieve high accuracy of detection, with an advantage of having no obvious high power loss as caused by the addition of the third diode <NUM> when compared with the second design in <FIG>. As the third capacitor <NUM> has a substantially smaller capacitance than the first capacitor <NUM>, the power consumption can be minimized when the load <NUM> is connected to the first output port <NUM>.

In order to determine the presence or absence of the load <NUM> at the first output port <NUM>, voltage dividers <NUM>, <NUM> are used. As shown in <FIG>, a first voltage divider <NUM> comprises at least a first resistor (R11) <NUM> and a second resistor (R12) <NUM>, with one terminal coupled to the internal port <NUM> at node N5, and another terminal coupled to the ground. The node N5 is indirectly coupled to N1 through the third diode <NUM>. A reference voltage (Vdetect_1) <NUM> is generated by the first voltage divider <NUM> by tapping the two or more resistors at an intermediate location. The reference voltage <NUM> corresponds to the voltages generated by the secondary windings <NUM>, <NUM> for eliminating any inaccuracy caused by a fluctuation of voltage in the primary or secondary windings. A second voltage divider <NUM> comprises at least a third resistor (R21) <NUM> and a fourth resistor (R22) <NUM>, with one terminal coupled to the first output port <NUM>, and another terminal coupled to the ground. A detection voltage (Vdetect_2) <NUM> is generated by the second voltage divider <NUM> by tapping the two or more resistors at an intermediate location. The ratio of the detection voltage <NUM> to the reference voltage <NUM> can be used for determining the presence or absence of the load at the first output port <NUM>. When the load <NUM> is connected to the first output port <NUM>, the voltage at node N3 is pulled up, and so the detection voltage <NUM> is also pulled up. The voltage at node N5 is unaffected, so the ratio of the detection voltage <NUM> to the reference voltage <NUM> is increased. As the detection voltage <NUM> and the reference voltage <NUM> are both generated from the same winding, the accuracy of the determination can be more accurate.

<FIG> provide the circuit diagrams of the secondary side of the power supply in various typical topologies. In these figures, only a part of the power supply on the secondary side forming the essential elements of the present disclosure is shown. It is easily understood by those skilled in the art that isolated power supplies using various topologies, such as flyback converter topology with PSR or SSR, LLC resonant half-bridge converter topology, forward converter topology, can also be used without departing from the purpose and the scope of the present disclosure. The aforementioned topologies are not intended to be exhaustive.

In <FIG>, the multi-output power supply using a multiple winding transformer for generating voltages at three output ports is depicted. An ioslated flyback converter topology is applied in the design of the power supply. The secondary windings <NUM>, <NUM>, <NUM> are arranged in series, and the output voltages are tapped from the secondary windings accordingly.

In <FIG>, another multi-output power supply using a multiple winding transformer for generating voltages at three output ports is depicted. An isolated boost converter topology is applied in the design of the power supply. The secondary windings <NUM>, <NUM>, <NUM> and the three diodes <NUM>, <NUM>, <NUM> are arranged alternately in series, and the output voltages are connected to the cathodes of the three diodes.

In <FIG>, another multi-output power supply using a multiple winding transformer for generating voltages at three output ports is depicted. An isolated flyback converter topology is applied in the design of the power supply. The secondary windings <NUM>, <NUM>, <NUM> are arranged in three separated flyback structures manner, and the output voltages are connected to the cathodes of the three diodes <NUM>, <NUM>, <NUM> of each flyback structure.

In <FIG>, another multi-output power supply using a multiple winding transformer for generating voltages at two output ports is depicted. An isolated full-bridge or an isolated half-bridge converter topology is applied in the design of the power supply. The secondary windings <NUM>, <NUM>, <NUM>, <NUM> are arranged in series, and the ground is tapped at the center of the secondary windings.

To better illustrate the present disclosure, as shown in <FIG>, a circuit diagram of a power supply for driving multiple LEDs with a function of detecting the presence or absence of an LED is presented. It should be understood that the present disclosure is not limited to be used in LED or lighting applications. Instead, it is apparent to one skilled in the art that the method can be applied to other applications, including but not limited to integrated circuits, lighting control systems, sensors, computers, server devices, fans, telecommunication devices, and other electronic devices. In this exemplary implementation, a full-bridge structure for driving a voltage output at LED1+ <NUM> is provided by the secondary windings 1001a, 1001b, which are above the LED- <NUM>, and the secondary windings 1004a, 1004b, which are below the LED- <NUM>. Similarly, another full-bridge structure for driving a voltage output at LED2+ <NUM> is provided by the secondary winding <NUM> above the LED-<NUM>, and the secondary winding <NUM> below the LED- <NUM>. Schottky diodes are used in this exemplary implementation. A bridging resistor (R57) <NUM> is connected between LED1+ <NUM> and LED2+ <NUM> as the bridging circuit between the two voltage outputs. A first voltage divider <NUM> is connected between LED2+ <NUM> and LED- <NUM> for determining a reference voltage. A second voltage divider <NUM> is connected between LED1+ <NUM> and LED- <NUM> for determining a detection voltage. In other to determine the presence or absence of a load at LED1+ <NUM>, a processor <NUM> is configured to identify an increase in the ratio of the detection voltage to the reference voltage and generate one or more signals to signify the presence or absence of the load at LED1+ <NUM>. The processor <NUM> used can be a microcontroller unit (MCU), a field-programmable gate array (FPGA), an operational amplifier, or other programmable environments.

The characteristics and performance of an exemplary design of the power supply of <FIG> are measured and evaluated. The experimental conditions and results are described below.

In a power supply with 60W output power, the high voltage range at LED2+ <NUM> and the low voltage range at LED1+ <NUM> are <NUM>-100V and <NUM>-59V respectively. The outputs for the LEDs are dimmable with current ranging from 10mA to <NUM>. The energy storage capacitors (C54, C58) are 82uF polarized aluminum electrolytic capacitors. The voltage divider <NUM> comprises two resistors R80 and R87, both having a resistance of <NUM> ohm. The second voltage divider <NUM> comprises two resistors R81 and R89, both having a resistance of <NUM> ohm. The bridging resistor R57 <NUM> is <NUM> ohm so that the power across the bridging resistor <NUM> can be limited to around <NUM>. The power dissipation on the resistor R87 is around <NUM>. 083W, and the efficiency loss as a result of the added components for the detection of the load is approximately <NUM>%. The LED identification threshold, as determined by the ratio of the detection voltage to the reference voltage, is defined as <NUM>%. When a load is present, the typical ratio is around <NUM>%-<NUM>%. When a load is absent, the ratio is expected to be increased to around <NUM>%-<NUM>%. The processor <NUM> can determine the presence or absence of the load by calculating the ratio of the detection voltage to the reference voltage.

Claim 1:
A power supply (<NUM>) for providing a plurality of voltage outputs at a plurality of output ports with a function of detecting presence or absence of a load (<NUM>) at a first output port (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>) selected from the plurality of output ports, the power supply (<NUM>) comprising:
a first voltage source for providing a first voltage at a first node;
a first diode (<NUM>, <NUM>, <NUM>, <NUM>) having a cathode coupled to the first output port (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>), and having an anode directly or indirectly coupled to the first node for receiving the first voltage;
a second voltage source for providing a second voltage at a second node;
a second diode (<NUM>, <NUM>, <NUM>, <NUM>) having a cathode coupled to a second output port (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>) selected from the plurality of output ports, and having an anode coupled to the second node for receiving the second voltage; and
a bridging circuit (<NUM>, <NUM>, <NUM>, <NUM>) having two terminals respectively connected to the first and the second output ports (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>);
wherein:
the second voltage is higher than the first voltage such that when the load (<NUM>) is not present at the first output port (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>), the bridging circuit (<NUM>, <NUM>, <NUM>, <NUM>) pulls up an output voltage at the first output port (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>) to reverse bias the first diode (<NUM>, <NUM>, <NUM>, <NUM>), thereby enabling the presence or absence of the load (<NUM>) at the first output port (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>) to be detectable by detecting the output voltage at the first output port (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>).