TWI323396B - Switching regulator having energy saving circuit and energy saving control method - Google Patents

Description

1323396 VB : feedback signal Vc : energy saving signal VREF2 : second reference voltage VSAW : sawtooth signal

Vfb: output signal Vrefi: first reference voltage VS2: auxiliary control signal VIII. If there is a chemical formula in this case, please disclose the chemical formula that best shows the characteristics of the invention: IX. Invention description: [name of invention]: switching type with energy-saving circuit BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a power-saving switching regulator, a power supply, and a power converter. [Prior Art] A switching regulator utilizes a control switching signal to provide an adjustable output voltage and current. Based on the need for power savings, power utilization in electronic products must comply with power management and energy efficiency regulations. Referring to the first figure, it is a schematic diagram of a conventional-switching regulator, and a switching switch is connected to the switching regulator input terminal VIN. Through the -component Τι, the NAND (3) transmits power to the -output V of the switching regulator. . - Auxiliary shredding_2_ to provide a synchronous rectification or half-bridge circuit architecture, the auxiliary switching can be selected to enable or disable... The coupler 50 system is connected to the cut-down regulator _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ The (4) circuit is switched to the _ connector 5G to receive the output signal Vfb'. The field-switching signal and the auxiliary switching signal SW2 are used to select the (4) gamma. The _ signal ^ system (4) switches on or off for the turn-on, for the stable output of the output of the switching regulator. And the supplement _ exchange number SW2_ to control the auxiliary switch open secret.

The main power loss of the switching regulator is the loss of iron of the magnetic element 1 and the switching loss of the switching switch Qi. At light load, the main power loss of the switching regulator is proportional to the switching signal SW1. Switch fresh Fs. In addition, the other power loss of the switching regulator comes from the power secret of the control circuit. The switching signal Sw丨 _ switching cycle thief and its switching frequency inversion ratio, Ts 1 / Fs - Tgn + TgFF. The towel Tgn picks up the on-time of the switching signal Sw丨, and τ(10) is the wearing time of the switching nickname SW1. The power loss can be reduced by increasing the switching period Ts. However, in order to reduce the volume of the magnetic H element T, the switching type must perform the switching operation 0 in the - (four) switching period 1, and the switching frequency Fs cannot be reduced without limitation, and must be appropriately limited. In order to avoid saturation of the neodymium 1± component ^, the maximum on-time t〇n will be limited. Therefore, the switching period A can be extended by increasing the cut-off time T 〇 FF under light load and no load conditions, and the power loss of the cut surface (4) can be reduced. The switching regulator may generate audio noise when the fine-tuning & reduction audio band is reduced. SUMMARY OF THE INVENTION It is an object of the present invention to provide a lion-replacement type m supplier and an electric multiplexer, which can turn off some circuits under light load and no planting to save energy and improve system efficiency. A switching regulator includes a switching switch for controlling power transfer to the output of the switching regulator. A feedback unit outputs a feedback signal according to the load condition; in order to achieve energy saving and improve the system efficiency of the switching regulator under light load, a first control unit outputs a signal according to the change of the feedback signal. Oscillation signal and a provincial signal. A second control unit receives the feedback signal and the oscillation signal for outputting a switching signal to control the switching switch. As the load decreases, the cutoff time of the switching signal increases. The energy-saving signal is used to turn off the circuit in the switching regulator that does not need to work during the switching signal cut-off period, so the energy-saving effect can be achieved under light load. When the switching frequency of the switching signal falls before the audio band, the switching signal is disabled to avoid audio noise. When the output load increases, the switching rate of the switching signal exceeds the tone solution and the switching signal is defeated by the back. The present invention proposes a switching regulator with a Wei circuit 'in the city and down, to achieve energy saving effect and optimize power mussel consumption' and to reduce the switching regulator (4) audio noise. In order to make the present invention (the above and other objects, advantages and advantages of the invention are better understood, the following detailed description of the preferred embodiments, together with the accompanying drawings, will be described in detail below. [Embodiment] Referring to the second figure, A schematic diagram of the control unit 10 of the switching regulator of the present invention. A biasing unit 6 generates a -first reference voltage ¥_, a second reference voltage Vref2, and a bias current Ι〇·Ιν. - The feedback unit 8 〇 passes through the secret device 50 to the "output terminal V" of the switching device, to receive-output the signal VFB, and according to the input Jij load condition - the signal Vb. The control unit 9 Receiving the second reference f voltage VREF2|| the shouting Vb for transmitting the __vibration PLS, a cat tooth signal vSAW, a provincial energy signal vG and an auxiliary control signal Vs2. A second control unit 7〇 according to the feedback signal vB, the sawtooth wave signal vSAw, the auxiliary control signal, the provincial energy signal Vg and the oscillation signal PLS, for outputting a switching signal Swi and an auxiliary switching signal Swz for control-switching Switch Q1 and - assist switch open _q2. The switch is connected to the switch mode The input terminal of the device is used to control the power transmission to the output terminal v of the switching regulator. A cutoff time T〇Fr of the switching signal swl increases as the load decreases. The signal Vc is used to turn off the circuit in the switching regulator that does not need to work during the switching signal Swi cutoff time t〇ff, so as to achieve energy saving under light load and no load. There are many circuits in the switching regulator that are in standby and do not need to work under light load and no load. When the cutoff time τ 〇砰 is extended to a certain extent, in order to comply with the power management and energy saving specifications, the present invention The switching regulator starts to turn off some circuits that do not need to work, that is, no power supply is provided to save energy. When the wheel load is reduced, the switching frequency Fs falls before the audio band, so that the switching signal Swi is disabled. In order to avoid audio noise, when the output load increases and the switching frequency FS exceeds the audio band, the switching signal 8 is enabled by the feedback signal ¥8. Once the switching signal Twi of the switching signal S12 is increased, ' With output For the lowering of the load, the auxiliary control signal VS2 is used to cut off the auxiliary switching switch q2. Please refer to the third figure, in conjunction with the second figure, which is a schematic diagram of the biasing unit 60 of the preferred embodiment of the present invention. 〇 generating the first reference voltage Vrefi, the second reference voltage and the bias current 1〇In.·- the reference voltage circuit 110 generates the first reference voltage 丫_ and the second reference voltage V〆 - a reference voltage system - a pair of electrical converters, the first __ return current converter is composed of - operational amplifier 112, - resistor 113 and _ transistor 114. The first voltage to current converter is reduced The first reference voltage VreF1, the rib output __ constant current 1114... the first current mirror circuit is composed of transistors 115, II6, m, 118, 119, etc., receives the constant current 匕 for outputting the bias voltage Current Ι〇 · · Ι ν · · ' The first current mirror circuit is expected to provide the various components of the electrical material exchange regulator. The bias current is 1〇, Ir. It is coupled to some circuits that need to work under various loads. The bias current is ΙΝ1Ν+1. It is lightly connected to some circuits that do not need to work under light load and no load. The activation and deactivation of the bias currents In, In+i.. are controlled by switches 123, 124, etc., respectively, for energy saving purposes. The turning on or off of the switches 123, 124, etc. 4 is controlled by the energy saving signal yG. Therefore, under light load and no load, the energy-saving signal VG is low, and the circuit that does not need to be operated in the switching regulator can be turned off. Please refer to the fourth figure, which is a schematic diagram of the second control unit 7 according to a preferred embodiment of the present invention. An input of a flip-flop 78 is coupled to a supply voltage Vcc, which is supplied to the input of the flip-flop 78 via an inverter 71. The input terminals of the AND gate 79 are respectively coupled to an output of the flip-flop 78, an output of the inverter 71, and the energy-saving signal Vc. An output of the AND gate 79 produces a switching signal Sw丨. According to the falling edge of the oscillation signal pls (from high potential to low potential), the switching signal SWA is enabled (high potential). The switching signal SW1 is deactivated according to the enable (high potential) of the oscillation signal PLS and the activation (low potential) of the provincial energy signal %. An input of a reverse gate 76 is coupled to the output terminal of the AND gate 79 for outputting the auxiliary switching signal Sw2 at an output of the inverse gate 76. The phase of the auxiliary switching signal Sw2 is thus opposite to the switching signal sw1. The other input of the inverse gate 76 is coupled to the auxiliary control signal VS2. The auxiliary switching signal SW2 is turned off according to the enable (high potential) of the auxiliary control signal VS2 to reduce power loss and save energy. A negative terminal of a comparator 72 is coupled to the sawtooth signal VSAW. A positive terminal of the comparator 72 is coupled to the feedback signal VB for feedback loop control. An input end of the gate 73 is coupled to an output end of the comparator 72. The other input end of the gate 73 is coupled to a round output of a protection circuit 75. Terminal 1323396 connects her to the reset terminal of the flip-flop 7S. The % of the contradiction has over-, over-discriminate and over-temperature protection mechanisms to protect the switch-type bumper and its peripheral circuits. The switching signal Sw丨 can be turned off by the protection circuit 75 or the feedback signal vB. Referring to the fourth diagram, the bias current In+1 provides power to the comparator 72, and the bias current (4) provides power to the protection circuit 75. During light load and no load period, the province's energy signal % is low, so that the bias current IN+1 dragon test current In+2 is cut off, and the circuit does not need to work under the fiber (such as the taste) The device 72 and the protection circuit 75) are used to reduce mystery and achieve energy saving. Please refer to the fifth figure, which is the switching signal Sm and the provincial signal % waveform of the present invention. ~ The table indicates that the switching signal is not overloaded, and Swi^ indicates the switching signal under light load. When the oscillating signal pLS is enabled (high), the switching signal SW1 is turned off to provide a programmable cut-off time. 〇 〇 _ indicates the cut-off time under heavy load, and 1 ^ is called the thief end of the table. The maximum on-time τ〇ν of the secret reduction is fixed to avoid saturation of the magnetic components. * month refers to the sixth figure, which is a schematic diagram of the feedback unit 8 of the preferred embodiment of the present invention. The feedback unit is 5 error amplifier 81'. The error amplifier 81 is a trans_conductance amplifier, and the end surface is connected to the first reference voltage, and the negative end is tied to the turn. The output of the connector is known as the nickname VFB. A resistor 82 is coupled in series with a capacitor 83 and coupled to an output terminal COMV' of the error amplifier 81 for frequency compensation. The inter-electrode of a level shifting transistor % is drawn to the output terminal COMV' of the error amplifier 81. The source is secretly connected by a resistor 86 and 87 to form an attenuator for outputting the feedback 峨VB. When the memory vFB becomes larger, the Vb^ is turned smaller, and the bias voltages ml2 and IN+3 provide power to the error amplifier 81. During light load and no load, the provincial signal Vc It is low, and the bias current IN+3 is turned off to save the power loss of the error amplifier 81. Please refer to the seventh figure, in conjunction with the second figure, the first control unit 90 is a schematic diagram of the preferred embodiment of the present invention. The first control unit 90 includes a modulator 1 〇〇, an oscillating circuit and a province. Can circuit. The modulator 1 receives the second reference voltage VREF2 and the feedback signal Vb for generating a discharge current 1〇, a light load signal VD and the auxiliary control signal vsz. The oscillating circuit comprises a charging current source 15A, a switch, a switch 154, a capacitor 155, a discharge current source 16A and an oscillating control circuit for generating the oscillating signal PLS and the sawtooth wave signal VsAW. The energy saving circuit can be implemented by a reverse gate 167. The reverse gate 167 is connected to the light signal PSD and the light load signal VD to generate the energy saving signal VG. The discharge current source 160 is implemented by a second current mirror circuit composed of transistors 151 and 152. The discharge current 1D is coupled to one of the input terminals of the second current mirror circuit. The switch 153 is coupled between the charging current source 150 and the capacitor 155. The switch 154 is coupled between the capacitor 155 and an output of the second current mirror circuit. The oscillation control circuit includes a comparator 161, a comparator 162, a reverse gate 163, and a reverse gate 164.

With an inverter 165. The comparator 161 has a high threshold voltage VH, the comparator 162 has a low threshold voltage VL, and the comparators 161 and 162 are coupled to the capacitor 155. The output terminals of the comparators 161 and 162 are connected to a latch circuit ‘ formed by the NAND gates 163 and 164 for outputting the oscillation signal pls. The oscillation signal PLS controls the on or off of the switch 154. A wheel-in end of the inverter 165 is coupled to the oscillation signal PLS. An output of the inverter 165 controls the on or off of the switch 153 to achieve an oscillating action. As the load decreases, the discharge current ID decreases, and the activation time of the oscillation signal PLS increases. Once the load is below a threshold value, the light load signal VD is enabled. The enable signal VG is generated according to the light load signal vD and the activation of the vibration signal PLS. The charging current source 150 provides a charging current and a voltage valley of the valley 155 ???the maximum conduction time T〇n of the switching signal Swi. The discharge current 1 〇 and the capacitance 155 determine the off time T0FF of the switching signal SW1. The charging current IA is a constant current, and the discharging current Id changes in proportion to the change in the load. Referring to the eighth figure, there is shown a schematic diagram of the modulator 100 in accordance with a preferred embodiment of the present invention. The modulator 1A includes a second voltage-to-current converter, a third current mirror circuit, a fourth current mirror circuit, a fifth current mirror circuit, a buffer 205, and an inverting buffer 207. An inverter 206. The second voltage-to-current converter is composed of a transistor 185, a resistor 183, an operational amplifier 181, and an operational amplifier 182. The operational amplifier 182 is coupled to the feedback signal Vb. The second reference voltage VREn is coupled to the second reference voltage VREn. The second voltage produces a current core 85 to the current converter. When the load is reduced, the output signal vFB is increased and the feedback signal vB is decreased. Once the feedback signal 丫8 is lower than the second reference voltage Vref2, the current ilfJS is increased as the feedback signal vB is decreased. The third current mirror circuit is composed of a transistor i86 and a slave 7. The third current mirror circuit is coupled to the power for taking off a current. The constant current source is supplied by a bias current of 1 耦, and the constant current source is coupled to one of the input terminals of the fourth current mirror circuit, and the fourth current mirror circuit is composed of transistors 188, 189, 190 and 196. Composition to generate a current of 9 13233,96

Iiw, a current of 1] 9 〇 and a current of 1 丨 96. The fifth current mirror circuit is composed of transistors 191, 192, 193, 194 and 195. One input end of the fifth current mirror circuit is coupled to one of the gates of the transistor 187 and the transistor 189. A difference current I(9) between the electrodes and the current lm is not used to generate a current Im at a drain of the transistor 192, and a current is generated at a drain of the transistor 193. A current I1M is generated at a drain of the transistor 194 and a current η% is generated at a drain of the transistor 195. The drain of the transistor 192 is coupled to the gate of the transistor 190. The gate of the transistor 193 is coupled to a drain of the transistor 196. An input of the inverting buffer 207 is coupled between a drain of one of the transistors 193 and a drain of the electrical body 196. When the current I 丨 M is less than the current I, the voltage of an input of the buffer 2 〇 5 will be a low level, and the inverter 2 〇 6 will receive the low level voltage and output a high level. The light-loaded signal %> is used to output a low-level energy-saving signal ¥ (;, to turn off some of the circuits that do not need to be operated under light load to save energy. When the current I1W is less than the current, the inverting buffer The input voltage of the input terminal of the second buffer 7 is low, so that the output of the inverting buffer 207 generates a high level of the auxiliary control signal Vs, thereby causing the auxiliary switching signal SW2 to be disabled and turned off. The auxiliary switch Q2 is coupled between one of the drains of the transistor 194 and the input end of the buffer 2〇5. A switch 2〇2 is coupled to one of the transistors. The pole is used to provide the discharge current Id, wherein the discharge current 1〇 is provided by the current 1. The output terminal of the buffer 205 controls the on or off of the switches 2〇1 and 2〇2. The 2〇6 system is connected to the buffer|§2〇5 输 输 M, 帛 丨 载 载 载 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 'To avoid audio noise. The discharge current is switched by the mosquito to switch the signal~. When the switching signal SW1_ fine red scale, the system 2, the city, the Mizaki discharge current Id and the switching signal Swi In order to avoid audio noise... When the load is increased, and the switching frequency of the switching signal ^ is changed, the discharging current Id is used by the fine-tuning city %. According to the embodiment of the present invention, Switching facet implementation - the Weipu method includes the following steps: detecting a load change of the switching regulator, the feedback unit 80 is coupled to the negative reference of the switching regulator, the second and sixth figures The feedback unit 8 〇, the load 'and the feedback signal Vb is generated according to the load change; 1323396 uses the feedback signal vB to determine the light load condition, referring to the first control unit 9 〇 ' shown in the second and seventh figures The first control unit 90 receives the feedback signal νΒ, and generates an activation time of the oscillation signal pls according to the feedback signal vB to generate the light-load signal VD and the oscillation signal PLS′ as the load decreases. And light load signal VD and oscillation The PLS will determine the activation of the energy-saving signal VG. According to the feedback signal VB, the switching signal SW1 is generated to control the load transmitted to the switching regulator. Referring to the second and fourth figures, the second The control unit 7 is configured to receive the oscillation signal PLS and the energy-saving signal VG to determine a duty cycle of the switching signal Swi, wherein the oscillation signal PLS determines the cutoff of the switching signal Sw] During the period, but the maximum on time of the switching signal 8^^ is a fixed value;

During the off period of the switching signal swi, the power supply signal Vg is used to turn off the power of part of the circuit of the switching regulator under light load conditions. BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings are for the purpose of clearly describing the present invention, and are incorporated by reference to the detailed specification. The following figures are in the form of the present invention. The principles of the invention. The first figure is a schematic diagram of a conventional switching regulator. The second figure is a schematic diagram of the control circuit of the switching regulator of the present invention. The third figure is a schematic diagram of the biasing unit of the preferred embodiment of the present invention in the second figure. The fourth figure is a schematic diagram of the second control unit of the preferred embodiment of the present invention in the second figure. The fifth figure is the waveform diagram of the switching signal and the Wei signal of the present invention in the second figure. Figure 6 is a schematic diagram of the feedback unit of the preferred embodiment of the present invention in the second diagram. Figure 7 is a schematic diagram of the _ control unit of the preferred embodiment of the present invention in the second diagram. Figure 8 is a schematic view of the modulator of the present invention in the seventh diagram. 11 1323396 [Key component symbol description]

10: control circuit 50: coupler 60: bias unit 70: second control unit 71, 165, 206: inverter 72, 161, 162: comparator 73, 79: and gate 75: protection circuit 76: reverse OR gate 78: flip-flop 80: feedback unit 81: error amplifier 82 '86 ' 87 ' 113 ' 183 : resistors 83, 155: capacitors 85, 114 - 119, 151, 152, 185 - 196 : transistor 90: First control unit 100: modulator 110: reference voltage circuit 112, 181, 182 • operational amplifier 123, 124, 153, 154, 201, 202: switch 150: charging current source 160: discharging current source 163, 164, 167 : Inverting gate 205: Buffer 207: Inverting buffer COMV: Output terminals I〇, II, Ijs, Ιν+1, ΪΝ+2, In+3: Bias current Ια: Charging current Id: Discharge current PLS : oscillation signal Q!: switching switch Q2: auxiliary switching switch Svvi: switching signal S\V2: auxiliary switching signal T, magnetic element T〇FF: cut-off time T〇N: on-time Vb: feedback signal vcc: supply voltage vD: light load signal Vfb: output signal vG: energy saving signal Vim: input terminal 12 1323396 « , · V〇: output VSAW: mine Tooth signal VreF2: second reference voltage VS2: auxiliary control signal VREF丨: first reference voltage

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Claims (1)

9 fee 8^2 evaluation (more> positive replacement page '98T-8-2D----^10. Patent application scope: 1. A switching regulator, comprising: a switch, coupled to the An input end of the switching regulator is configured to control power transmission to a round of the switching regulator; a feedback unit coupled to the output of the switching regulator is based on a load condition The first control unit includes: a modulator, which receives the The feedback signal is used to output a discharge current and a light load signal; a Zhenbao circuit includes a charging current source, a discharge electric mf μ, a discharge switch, a capacitor, and a vibration control circuit for outputting impurities. The discharge current source mirrors the discharge current for discharging the capacitor; and an energy-saving circuit 'connects the money signal and the training call to read the provincial energy signal; The current is reduced according to the decrease of the load; according to the discharge current Decrease, the start of the oscillation signal (4) is riding; if it is negative - the critical value, the miscellaneous message is activated, the scale is lightly transferred to the Lai, the Wei Mi (4) provincial Wei; and The first unit j unit receives the feedback signal and the vibration signal for outputting a switching signal to control the switching switch; s. the cut-off time of the sub-signal is increased according to the load-lowering; During the cut-off period of the signal, the province can slap the __-type _ sub-circuit; and the switching signal is disabled before the switching signal is switched to the human audio band to avoid audio. Noise. ' ° 2 · If you apply for the switch type of the suspension tube described in the chest, the load is increased when t, and the switching signal is switched to the super-shooting woman. The switching regulator according to claim 1, wherein the domain signal is provided according to the use of the vibration and the rib of the vibration. Switching signal--planable cut-off; the maximum on-time of the switching signal is constant to avoid magnetic The saturation occurs. : : £ extra 83⁄4 § Transfer the magnetic page j 98-8-20 — 4. The switching stability described in the scope of the patent application, wherein the modulator comprises: a first operation The amplifier receives the feedback signal; the first one is different from the amplification voltage, and is connected to a threshold voltage; the electric current converter is controlled by a transistor, the first operation, and the second operation (four) The operational amplifier is configured to output a first current; when the feedback signal is lower than the threshold voltage, the first current is increased according to the decrease of the feedback signal; the first current mirror circuit is steadily - current for outputting _second current; a constant current source; - second current mirror circuit 'secret to the constant current source for generating - third current and - fourth current; - second current mirror circuit 'light Connected to the first current mirror circuit and the second current mirror circuit, the third current mirror circuit receives a difference between the second current and the third current for outputting a fifth current and a sixth current a seventh current; a first switch, the first end of which is a second current is supplied by the seventh current, and a second end is used to output the discharge current; and a buffer circuit is configured to receive the fifth a current and a difference current of the fourth current are simultaneously secreted to a second end of the first switch; one of the round ends controls the first switch and the second switch to be turned on or off; and an inverter And coupled to the output end of the buffer circuit for outputting the light load signal. 5. The switching regulator as described in claim 1 further comprising: an auxiliary switching switch coupled to the switching switch. 6. The switching regulator of claim 5, wherein the first control unit outputs an auxiliary control signal, and the off-time of the switching signal is increased according to a decrease in the load, the auxiliary control signal It is used to cut off the auxiliary switch. ο日给 (more) replacement page 98-8-20, flyback conversion 2 If you apply for a patented fine needle Gu Jieqing fiber reducer, it can be a rotary converter or a half bridge power supply topology. 8. A power saving control circuit, used in a power converter, comprising: and outputting a back according to a change of a load - a feedback unit coupled to a load of the power converter, a signal number; For example, the first control unit receives the feedback signal, and the first control unit includes: a modulator that receives the feedback signal for rotating a light load Signal; - Zhenbao circuit, including - charging current source, - discharging current source ' _ charging off, a discharge switch, - capacitor and - vibration | control circuit for outputting a vibration signal; and - energy saving circuit 'Take the thief vibration i message 黯 载 υ 四 四 四 四 四 四 四 四 四 四 四 四 四 四 四 四 四 四 四 四 四 四 四 四 四 四 四 四 四 四 四 四 四 四 四 四 四 四 四 四 四 四 四 四 四 四 四 四 四 四And the second control unit receives the feedback signal for outputting a switching signal to control the power transmission to the load of the power conversion H; and the + provincial energy signal is turned over and cut, and Turn off part of the circuit of the power converter; The second control unit in the switching frequency of the switching signal falls before the audio zone, the switching signal is disabled, in order to avoid audio noise. 9. The energy saving control circuit of claim 8, wherein the switching nickname is for controlling a switching switch, and the switching switch is coupled to an input of the power converter. 10. A power saving control method implemented in a switching regulator, comprising: detecting a load change of the switching regulator to generate a feedback signal; using the feedback signal to determine a light load condition, Generating a provincial energy signal; generating a switching signal according to the feedback signal to control the load transmitted to the switching regulator; and 16~乃ο t Μ» . - · 丨··11··1— 11 I r :ββ f.*·,ττ i τ_^5 f i33⁄4 ,3⁄4 〇曰 ( (more) 正普换页 I 98-8-20 During the cut-off period of the switching signal, use the provincial energy signal in the light planting The power of part of the circuit of the switching regulator is turned off, and the switching signal is deactivated before the switching frequency of the switching signal falls into the audio band. 11. The energy-saving control method according to claim 10, further comprising: generating an oscillation signal according to the feedback signal, and determining, by the oscillation signal, a cut-off period of the switching signal, and The maximum on time of the switching signal is a fixed value. 17