Control method for reducing standby power consumption of switching power supply

Abstract

The invention discloses a control method for reducing standby power consumption of a switching power supply. According to the method, when it is detected that the AC-DC switching power supply is connected to the mains supply but the output end is not connected with the electric equipment, the standby power consumption of the system can be effectively controlled to be 100 mW or below, and the no-load loss of 1 W or above of a conventional switching power supply is remarkably lower than that of the conventional switching power supply. According to the technology, the electric energy loss in the standby state is greatly reduced, so that the power utilization cost of a user is reduced, and energy is saved; meanwhile, the reduction of the power consumption of the system during no-load or light-load also reduces the heating of elements, thereby facilitating the prolonging of the service life of the switching power supply.

Description

Technical Field

[0001] This invention belongs to the field of switching power supply technology, specifically relating to a control method for reducing the standby power consumption of a switching power supply under no-load or light-load conditions. Background Technology

[0002] Switching power supplies are widely used in mobile phone chargers, laptop adapters, home appliances, and industrial equipment due to their high efficiency, small size, and light weight. However, when a switching power supply is connected to mains power but is in an unloaded or lightly loaded state, its internal high-frequency switching transistors, inductors, diodes, and other circuits are still working and consuming energy. This energy is ultimately converted into heat, which not only wastes energy but also accelerates the aging of components.

[0003] The industry commonly uses a "hiccup mode" to reduce power consumption under no-load or light-load conditions. The principle is as follows: under no-load or light-load conditions, the control chip stops outputting the PWM drive signal, causing the output voltage to drop; when the output voltage is detected to be below a set threshold, the PWM signal is restarted. By periodically shutting down the PWM, losses can be reduced to some extent. However, this method has significant drawbacks: firstly, the PWM start-stop frequency is typically in the 20Hz-20kHz audible range, which can easily cause audible noise from the transformer or inductor, creating interference; secondly, it degrades light-load performance, leading to increased output ripple and poorer dynamic response. Summary of the Invention

[0004] The purpose of this invention is to provide a control method for reducing standby power consumption of switching power supplies. This method detects the output current of the standby power consumption control circuit and controls the switching on and off of the power factor correction (PFC) and subsequent buck circuits, enabling the PFC and buck circuits to achieve near-zero power consumption operation when no DC load is connected to the switching power supply. This significantly reduces system losses under no-load or light-load conditions and extends the lifespan of key components such as power switches, high-frequency inductors, and fast recovery diodes in the PFC and buck circuits.

[0005] To achieve the above objectives, the technical solution provided by this invention is as follows: (1) Current sampling circuit: The current transformer T1 is connected to the source of the power MOSFET Q1 in the power path of the PFC+ step-down circuit to collect the DC load current signal. This signal is further applied to the sampling resistor Rs and converted into a corresponding voltage signal. (2) RC filter circuit: The voltage signal is processed by the RC filter circuit to filter out the high-frequency interference generated by the switching power supply, and then transmitted to the differential amplifier circuit. (3) Differential amplifier circuit: The two voltage signals after filtering form a differential input, which is amplified by the operational amplifiers respectively, and outputs a differential signal with a specific proportional relationship. (4) Proportional-integral amplifier circuit: The differential output signal V BL and V ALConnect to the inverting input and non-inverting input of an operational amplifier respectively. When the load current is greater than zero, the PI amplifier circuit outputs a positive voltage signal; otherwise, its output voltage is zero. (5) Standby detection circuit: The output voltage of the PI amplifier circuit is connected to the non-inverting input of comparator OP2B and compared with the reference voltage preset by MCU (U2) at the inverting input of OP2B to determine whether the load current exists. (6) Light load detection circuit: The output voltage of the PI amplifier circuit is simultaneously connected to the non-inverting input of comparator OP2A and compared with another reference voltage preset by MCU (U2) at the inverting input of OP2A to determine whether the load current is lower than the set light load threshold. (7) MCU unit and isolation drive circuit: When the MCU detects no load current or the load current is less than the light load threshold through the above circuit, its control terminal Vctrl outputs a low level, which is isolated by optocoupler U3 and then turns off the field effect transistor Q1.

[0006] Specific Implementation Method 1 (No-Load State): When no DC load is connected, the N-channel MOSFET Q1 is turned off, and its power consumption is negligible; no current flows through the current transformer T1 and the sampling resistor Rs, so they consume virtually no energy; the operational amplifier OP1 and comparator OP2 are powered by 5V, and their quiescent currents are each less than 1mA; the DC / DC auxiliary power supply outputs 5V under no-load conditions, with a current loss of approximately 1mA; the MCU is in sleep mode, only intermittently waking up to perform current detection, with an instantaneous operating current of approximately 15mA; the isolation optocoupler U3 is in the off state and does not consume energy. At this time, the maximum instantaneous power consumption of the entire control circuit is less than 90mW, far lower than the 1-2W no-load loss of a conventional switching power supply.

[0007] Specific Implementation Method Two (Example under Load): Taking a 1000W DC load as an example, the N-channel MOSFET Q1 is turned on, with an on-resistance of approximately 30mΩ and a conduction loss of approximately 367mW at a current of approximately 3.5A. The total loss of the current transformer T1 and sampling resistor Rs is less than 100mW. The RC filter circuit has a loss of approximately 5mW. The differential amplifier, proportional-integral amplifier, standby, and light-load detection circuits each have a loss of approximately 15mW. The DC / DC auxiliary power supply provides 5V, with a load current of approximately 3mA and a loss of approximately 20mW. The MCU is in operation, with a current of approximately 20mA and a loss of approximately 100mW. The isolation optocoupler U3 has an operating current of approximately 3mA and a loss of approximately 15mW. At this time, the total instantaneous maximum power consumption of the entire control circuit is less than 667mW, which is still far below the no-load loss level of a conventional power supply.

[0008] The input port of the standby power consumption control circuit is connected to the output port of the full-bridge rectifier circuit, and its output port is connected to the input port of the power factor correction (PFC) circuit. The control circuit includes: a current sampling circuit, an RC filter circuit, a differential amplifier circuit, a proportional-integral circuit, a standby detection circuit, a light-load detection circuit, an MCU unit, an isolation drive circuit, an N-channel MOSFET Q1, and a DC / DC auxiliary power supply.

[0009] The current sampling circuit includes a current transformer T1 and a sampling resistor Rs. T1 is connected on the connection line between the PFC+ step-down main circuit and the source of Q1; the sampling resistor Rs is connected in parallel to the secondary output terminal of the transformer T1.

[0010] The RC filter circuit includes resistors R5 and R6, and capacitors C1 and C2. One end of resistor R5 is connected to a common node of the sampling resistor Rs and the current transformer, and the other end is connected to capacitor C1 and the non-inverting input of operational amplifier OP1B; the other end of capacitor C1 is connected to floating ground AGND. One end of resistor R6 is connected to the other common node of the sampling resistor Rs and the current transformer, and the other end is connected to capacitor C2 and the non-inverting input of operational amplifier OP1A; the other end of capacitor C2 is connected to floating ground AGND.

[0011] The differential amplifier circuit includes operational amplifiers OP1A and OP1B, and resistors R7, R8, R9, R10, and R11. The non-inverting input of OP1B is connected to the common point of R5 and C1, the inverting input is connected to the common point of R7 and R8, and the output is connected to the common point of R8 and R9. The non-inverting input of OP1A is connected to the common point of R6 and C2, the inverting input is connected to the common point of R7 and R10, and the output is connected to the common point of R10 and R11. Resistor R7 is connected between the inverting inputs of OP1B and OP1A. Resistor R8 is connected between the inverting input and output of OP1B. Resistor R9 is connected between the output of OP1B and the node of the subsequent PI circuit (the common point of R12 and R13). Resistor R10 is connected between the inverting input and output of OP1A. Resistor R11 is connected between the output of OP1A and the non-inverting input of the subsequent PI circuit operational amplifier OP1C.

[0012] The proportional-integral (PI) circuit includes an operational amplifier OP1C, resistors R12 and R13, and capacitor C3. The non-inverting input of OP1C is connected to resistor R11, the inverting input is connected to the common point of resistors R9, R12, and R13, and the output is connected to the common point of resistors C3, R13, R14, and R15. R12 is connected between the inverting input of OP1C and capacitor C3. R13 is connected between the inverting input and output of OP1C. Capacitor C3 is connected between resistor R12 and the output of OP1C.

[0013] The standby detection circuit includes a comparator OP2B, resistors R14 and R16. The inverting input of OP2B is connected to R14, the non-inverting input is connected to the MCU's reference voltage output Vnoload, and the output is connected to R16 and the MCU's detection input Snoload. R14 is connected between the PI circuit output node and the inverting input of OP2B. R16 acts as a pull-up resistor, connected between the OP2B output and the +5V power supply.

[0014] The light load detection circuit includes a comparator OP2A, resistors R15 and R17. The inverting input of OP2A is connected to R15, the non-inverting input is connected to the MCU's reference voltage output Vlightload, and the output is connected to R17 and the MCU's detection input Slightload. R15 is connected between the PI circuit output node and the inverting input of OP2A. R17 acts as a pull-up resistor, connected between the OP2A output and the +5V power supply.

[0015] The MCU unit is based on U2 (LPC832M101DH20) and includes its necessary peripheral circuits. The DC / DC auxiliary power supply uses the U1 (LP3210) integrated chip to achieve isolated step-down, outputting +5V power and floating ground AGND to power the entire control circuit.

[0016] The isolation drive circuit includes an optocoupler U3 (EL317), resistors R1, R2, R3, and R4, and a field-effect transistor Q1. On the input side of optocoupler U3: pin 1 is connected to the MCU control terminal Vctrl via R4, and pin 2 is connected to AGND via R3. On the output side: pin 3 is connected to the gate of Q1 via R1, and pin 4 is connected to the main circuit node (the common point of A1 and A2) via R2. The source of Q1 is connected to the main circuit, and the drain is connected to the drive resistor R1.

[0017] The input port of the DC / DC auxiliary power supply is connected to the full-bridge rectifier output ports A1 and B1, and its output +5V power supply powers all active devices such as the microcontroller, optocoupler, operational amplifier and comparator.

[0018] The beneficial effects of this invention are as follows: By adding the control module to a traditional switching power supply architecture, this invention can effectively control the system's no-load loss to below 100mW, far lower than the no-load loss level of over 1W in conventional switching power supplies. This technology can significantly reduce energy waste in standby mode, helping to reduce electricity costs for users and businesses and save social energy. Simultaneously, the reduction in no-load and light-load power consumption also reduces component heat generation, which is beneficial for extending the overall lifespan of the switching power supply. Attached Figure Description

[0019] Figure 1 A block diagram of a control method for reducing standby power consumption of switching power supplies

[0020] Figure 2 Standby power consumption control circuit block diagram

[0021] Figure 3 Schematic diagram of standby power consumption control circuit Specific implementation methods

[0022] When the power supply is initially connected to 220V AC mains, the MCU unit U2 is powered on, and its control pin Vctrl outputs a high level, turning on the switching transistor Q1. At this time, the potential difference between A2 and B2 is equal to the potential difference between A1 and B1.

[0023] Current sampling circuit: When the power supply is under no-load for a long time, there may be a small standby current in the circuit. The current transformer T1 collects this current signal and converts it into a weak voltage signal across the sensing resistor Rs.

[0024] RC filter circuit: The sampled voltage signal passes through a first-order RC filter circuit composed of R5, R6 and C1, C2 to filter out high-frequency noise before being input to the differential amplifier circuit.

[0025] Differential amplifier circuit: two filtered voltage signals V AL and V BL The differential voltage signal in standby mode is amplified by the differential amplifier circuit consisting of operational amplifiers OP1A and OP1B and resistors R7, R8, R9, R10, and R11.

[0026] Proportional-integral circuit: The above differential amplification signal (V) H and V L The signal is then processed by a proportional-integral (PI) circuit consisting of operational amplifier OP1C, resistors R12, R13, and capacitor C3, outputting a voltage signal V that is on the same order of magnitude as the power supply voltage but slightly lower. PI .

[0027] Standby detection circuit: Proportional-integral output voltage V PI The voltage is sent to the inverting input of comparator OP2B via resistor R14 and compared with the reference voltage Vnoload provided by MCU unit U2 (connected to the non-inverting input of OP2B). (1) If the voltage at the inverting input of OP2B is higher than the voltage at the non-inverting input (Vnoload), OP2B outputs a low-level signal Snoload to the MCU, indicating that current flows through the switching power supply. (2) If the voltage at the inverting input of OP2B is lower than the voltage at the non-inverting input, OP2B outputs a high-level signal Snoload to the MCU, indicating that no current flows through the switching power supply.

[0028] Light load detection circuit: Proportional-integral output voltage V PIAt the same time, the voltage is sent to the inverting input of comparator OP2A via resistor R15 and compared with another reference voltage Vlightload provided by MCU unit U2 (connected to the non-inverting input of OP2A). (1) If the voltage at the inverting input of OP2A is lower than the voltage at the non-inverting input (Vlightload), OP2A outputs a high-level signal Slightload to the MCU, indicating that the current flowing through the switching power supply is less than the set light load threshold. (2) If the voltage at the inverting input of OP2A is higher than the voltage at the non-inverting input, OP2A outputs a low-level signal Slightload to the MCU, indicating that the switching power supply is in normal working condition (load current is higher than the light load threshold).

[0029] MCU Processing and Standby Operation: When the MCU detects that Snoload is low and Slightload is high, it determines that it is under light load, and its control pin Vctrl outputs a low level. When the MCU detects that Snoload is high, it determines that it is under no-load, and its control pin Vctrl outputs a low level. This low-level signal, through the isolation drive circuit composed of optocoupler U3 and resistor R1, turns off the switching transistor Q1. At this time, the potential difference between A2 and B2 is zero, thereby cutting off the power supply to the subsequent power factor correction (PFC) and buck circuit, significantly reducing its standby power consumption. Subsequently, the MCU enters sleep mode and wakes up periodically (sending a "heartbeat" signal) to briefly turn on Q1 to re-detect the load status.

[0030] Load connection and power restoration: When a DC load is connected at a certain moment, the current transformer T1 detects a large load current and converts it into a higher voltage signal on the detection resistor Rs. This signal is processed sequentially through the aforementioned RC filter circuit, differential amplifier circuit, and proportional-integral circuit. (1) The standby detection circuit (OP2B and R14) outputs a low-level signal Snoload (indicating that there is current). (2) The light load detection circuit (OP2A and R15) outputs a low-level signal Slightload (indicating that the current exceeds the light load threshold). After receiving these two low-level signals, the MCU outputs a high level on its control pin Vctrl, which turns on the switching transistor Q1 through the isolation drive circuit. At this time, the potential difference between A2 and B2 is restored to the same as the potential difference between A1 and B1, thereby restoring the power supply to the subsequent PFC and buck circuit.

Claims

1. A control method for reducing standby power consumption of a switching power supply, characterized in that: The standby power consumption control circuit detects that the load current of the switching power supply is less than the preset value of the microcontroller, determines that there is no DC load connected to the switching power supply, and thus enters the no-load mode and cuts off the main circuit for DC load power supply to reduce the no-load loss of the system.

2. The standby power consumption control method according to claim 1, characterized in that: The input port of the standby power consumption control circuit is connected to the output port of the full-bridge rectifier circuit, and its output port is connected to the input port of the power factor correction circuit.

3. The standby power consumption control method according to claim 1, characterized in that: The standby power consumption control circuit includes a current sampling circuit, an RC filter circuit, a differential amplifier circuit, a proportional-integral circuit, a standby detection circuit, a light load detection circuit, an MCU unit, an isolation drive circuit, and an N-channel MOSFET Q1, and is equipped with a DC / DC auxiliary power supply.

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