CN108923639A - A kind of circuit for eliminating primary side feedback Switching Power Supply audio-frequency noise - Google Patents
A kind of circuit for eliminating primary side feedback Switching Power Supply audio-frequency noise Download PDFInfo
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- CN108923639A CN108923639A CN201810985965.9A CN201810985965A CN108923639A CN 108923639 A CN108923639 A CN 108923639A CN 201810985965 A CN201810985965 A CN 201810985965A CN 108923639 A CN108923639 A CN 108923639A
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M1/00—Details of apparatus for conversion
- H02M1/44—Circuits or arrangements for compensating for electromagnetic interference in converters or inverters
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
- H02M7/02—Conversion of ac power input into dc power output without possibility of reversal
- H02M7/04—Conversion of ac power input into dc power output without possibility of reversal by static converters
- H02M7/12—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
- H02M7/21—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
- H02M7/217—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only
- H02M7/219—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only in a bridge configuration
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Abstract
The invention discloses a kind of circuit for eliminating primary side feedback Switching Power Supply audio-frequency noise, primary side feedback Switching Power Supply is based on AC-DC primary-side-control converter topologies, it is characterised in that：The system that oscillator, clear circuit, noise detecting circuit, time voltage converter, switch capacitor filter, voltage-current converter circuit and peak current detection circuit are constituted is set, closed loop is constituted with controlled primary side feedback Switching Power Supply, achieve the purpose that control system frequency by the peak point current of regulating system, in high power load, the transmission energy of Switching Power Supply is high, making system operating frequency, clamper works except audio zone in 20KHz or more always；When small-power, the transmission energy of Switching Power Supply is extremely low, without enough energy production audio-frequency noises, finally eliminates the audio-frequency noise in the entire loading range of Switching Power Supply.
Description
Technical field
The present invention relates to a kind of Switching Power Supply of primary side feedback control, in particular to a kind of elimination primary side feedback Switching Power Supplies
The circuit of audio-frequency noise, belongs to technical field of integrated circuits.
Background technique
The AC signal of high pressure can be converted to the direct current signal of low pressure by the Switching Power Supply of primary side feedback control, because of its periphery
System device is few, at low cost, advantages of simple structure and simple, is widely used in charger, adapter, the fields such as LED driving.City at present
Many IC for using primary side feedback control technology are proposed on field, these IC use pulse frequency modulated mode (pulse
Frequency modulation, abbreviation PFM), the working frequency and load current of Switching Power Supply are linear, when output is negative
When carrying current reduction, the switching frequency of Switching Power Supply is also decreased, in order to reduce the no-load standby power losses of system, it will usually
Working frequency is fallen too low, when the switching frequency of system is as low as audio zone (20Hz~20KHz), if system operating power mistake
Height seriously affects equipment use since the mechanical oscillation of the external devices such as transformer, capacitor and resistance can generate audio-frequency noise.
Summary of the invention
The purpose of the present invention is to solve traditional primary side feedback AC-DC switching power source chip working frequencies to be lower than
When 20KHz, audio-frequency noise is led to the problem of into audio range.For this purpose, the present invention provides a kind of elimination primary side feedback switches
The circuit of power supply audio-frequency noise achievees the purpose that accuracy-control system frequency by the peak point current of regulating system, high-power
When load, the transmission energy of Switching Power Supply is high, make system operating frequency always clamper in 20KHz or more, work audio zone it
Outside；When small-power, system frequency passes through rapidly audio zone, and the transmission energy of Switching Power Supply is extremely low, without enough energy productions
Audio-frequency noise finally eliminates the audio-frequency noise in the entire loading range of Switching Power Supply.
The technical solution adopted by the present invention is that：A kind of circuit for eliminating primary side feedback Switching Power Supply audio-frequency noise, primary side are anti-
It presents Switching Power Supply and is based on AC-DC primary-side-control converter topologies, including rectifier bridge, input filter capacitor, primary side winding NP
And primary side switch pipe and sampling resistor R5, auxiliary winding NA and partial pressure output resistance, vice-side winding NS and rectifier diode and
Output resistance R0With capacitor C0, the negative terminal for the voltage signal connection error amplifier that auxiliary winding NA is exported by electric resistance partial pressure, accidentally
The anode of poor amplifier connects 2V voltage, and the output of error amplifier controls primary side switch after PFM modulator and driving circuit
The grid of pipe；It is characterized in that：Oscillator, clear circuit, noise detecting circuit, time voltage converter, switching capacity are set
The system that filter, voltage-current converter circuit and peak current detection circuit are constituted, with controlled primary side feedback Switching Power Supply
Constitute closed loop；Peak current detection circuit passes through the peak-current signal CS connection comparator that primary side switch pipe sampling resistor obtains
The anode of COMP, reference voltage VREF connect the negative terminal of comparator COMP after connecting by resistance R3 with R4, comparator COMP's
Output connection PFM modulator, oscillator generate the periodic square wave clock signal clk that duty ratio is 50%, frequency-invariant, noise
Detection circuit receives the square-like clock signal CLK of oscillator output as clock signal, handles by counter and logic circuit,
Calculate the difference signal T of system switching frequency Yu 25KHz frequencydetect, it is defeated that time voltage converter receives noise detecting circuit
Difference signal T outdetect, the voltage value V_DETECT directly proportional to the time is converted thereof into, clear circuit receives PFM modulation
The PFM signal of device output, for noise detecting circuit and time voltage converter provide each period start when clearing resetting believe
Number RESET, the control signal of switch capacitor filter are the PFM signal of PFM modulator output, the voltage value directly proportional to the time
V_DETECT exports filtered voltage V_SCF by switch capacitor filter, is connected to electricity by voltage-current converter circuit
The connecting pin of R3 and R4 is hindered, the pull-down current with input voltage linear change is exported, which drags down peak current detection circuit
Peak point current comparative threshold voltage, control system frequency is reached by the peak point current of regulating system, in high power load,
The transmission energy of Switching Power Supply is high, and making system operating frequency, clamper always works in except audio zone in 20KHz or more always；
When small-power, the transmission energy of Switching Power Supply is extremely low, without enough energy production audio-frequency noises, finally eliminates Switching Power Supply
Audio-frequency noise in entire loading range.
The noise detecting circuit includes T trigger T1, T trigger T2, T trigger T3, T trigger T4, set-reset flip-floop
D1, set-reset flip-floop D2, phase inverter INV1, phase inverter INV2, phase inverter INV3, NAND gate NAND1 and XOR gate XOR1；T triggering
The end the SET connection of square-like clock signal CLK, the T trigger T1 of the input end of clock CK connection oscillator output of device T1 resets weight
One of the input end of clock CK and NAND gate NAND1 of the output end Q connection T trigger T2 of confidence RESET, T trigger T1
Input terminal, the end SET of input end of clock CK, the T trigger T3 of the output end Q connection T trigger T3 of T trigger T2, which connects, to reset
Reset signal RESET；The input end of clock CK's and NAND gate NAND1 of the output end Q connection T trigger T4 of T trigger T3 is another
One input terminal, the end S of the output connection set-reset flip-floop D2 of NAND gate NAND1, the SET termination cycles of T trigger T4 are set again
The end the SET connection of the input of the output end Q connection phase inverter INV1 of position signal RESET, T trigger T4, T trigger T4 resets weight
The end S of the output end connection set-reset flip-floop D1 of confidence RESET, phase inverter INV1, the end the R connection of set-reset flip-floop D1 reset resetting
The end the R connection of an input terminal of the output end Q connection XOR gate XOR1 of signal RESET, set-reset flip-floop D1, set-reset flip-floop D2 is clear
Another input terminal of the output end Q connection XOR gate XOR1 of zero reset signal RESET, set-reset flip-floop D2, XOR gate XOR1's
The input of output connection phase inverter INV2, resets reset signal RESET through delay control circuit Delay connection phase inverter INV3's
Input terminal.
The time voltage converter includes current source IP1, switch K1, switch K2 and capacitor C1, the input of current source IP1
End connection power vd D, one end of the output end connection switch K1 of current source IP1, one end of switch K1 other end connection switch K2
Output end with one end of capacitor C1 and as time voltage converter exports the voltage value V_DETECT directly proportional to the time,
The other end of switch K2 and the other end of capacitor C1 are grounded, phase inverter in the control terminal connection noise detecting circuit of switch K1
The output of INV2, the control terminal of switch K2 connect the output of phase inverter INV3 in noise detecting circuit.
The switch capacitor filter includes switch K3, switch K4, phase inverter INV4, capacitor C2 and capacitor C3；Time electricity
One end of the voltage value V_DETEC connection switch K3 directly proportional to the time of pressure converter output, the other end connection of switch K3
Switch capacitor filter is simultaneously made in one end of switch K4 and one end of capacitor C2, one end of the other end connection capacitor C3 of switch K4
Output end exports filtering voltage V_SCF, and the other end of capacitor C2 and the other end of capacitor C3 are grounded, the control terminal of switch K3
The PFM signal of PFM modulator output is connected, the control terminal of switch K4 connects the output end of phase inverter INV4, phase inverter INV4's
Input terminal connects the PFM signal of PFM modulator output.
The voltage-current converter circuit includes operational amplifier A1, resistance R1, NMOS tube M1, PMOS tube M2, PMOS tube
M3, NMOS tube M4 and NMOS tube M5；The output voltage V_ of the non-inverting input terminal connection switch capacitive filter of operational amplifier A1
The source electrode of the negative-phase input connection NMOS tube M1 of SCF, operational amplifier A1 and one end of resistance R1, another termination of resistance R1
Ground, operational amplifier A1 output end connection NMOS tube M1 grid, NMOS tube M1 drain electrode connection PMOS tube M2 drain electrode and
The grid of grid and PMOS tube M3, the source electrode of PMOS tube M2 and the source electrode of PMOS tube M3 are all connected with power vd D, PMOS tube M3's
The drain and gate of drain electrode connection NMOS tube M4 and the grid of NMOS tube M5 pipe, the source electrode of NMOS tube M4 and the source of NMOS tube M5
It is extremely grounded, output end of the drain electrode of NMOS tube M5 as voltage-current converter circuit connects electricity in peak current detection circuit
Hinder the connecting pin of R3 and R4.
The clear circuit generates quenching pulse signal, output when the PFM signal of input becomes the rising edge of high level
Reset signal for noise detecting circuit provide each period start when clearing reset signal RESET；In the PFM signal of input
When becoming low level failing edge, quenching pulse signal is generated, the reset signal of output provides for time voltage converter by week
The clearing reset signal of phase.
Advantages of the present invention and remarkable result：The Switching Power Supply audio that the present invention can effectively eliminate primary side feedback control is made an uproar
Sound achievees the purpose that accuracy-control system frequency, in high power load, Switching Power Supply by the peak point current of regulating system
It is high to transmit energy, making system operating frequency, clamper works except audio zone in 20KHz or more always；When small-power, system frequency
Rate passes through rapidly audio zone, and the transmission energy of Switching Power Supply is extremely low, without enough energy production audio-frequency noises, finally eliminates
Audio-frequency noise in the entire loading range of Switching Power Supply.
Detailed description of the invention
Fig. 1 is a kind of circuit system block diagram for eliminating primary side feedback Switching Power Supply audio-frequency noise of the present invention；
Fig. 2 is the connection circuit diagram of the oscillator and noise detecting circuit and time voltage converter in Fig. 1；
Fig. 3 is the switch capacitor filter circuit diagram in Fig. 1；
Fig. 4 is the voltage-current converter circuit and peak current detection circuit in Fig. 1；
Fig. 5 is noise detecting circuit control sequential figure.
Specific embodiment
Such as Fig. 1, a kind of circuit for eliminating primary side feedback Switching Power Supply audio-frequency noise of the present invention, primary side feedback Switching Power Supply base
In AC-DC primary-side-control converter topologies, including rectifier bridge, input filter capacitor, primary side winding NP and primary side switch pipe
With sampling resistor R5, auxiliary winding NA and partial pressure output resistance, vice-side winding NS and rectifier diode and output resistance R0With
Capacitor C0, the negative terminal for the voltage signal connection error amplifier that auxiliary winding NA is exported by electric resistance partial pressure, error amplifier
Anode connects 2V voltage, and the output of error amplifier controls the grid of primary side switch pipe after PFM modulator and driving circuit；Its
It is characterized in that：Oscillator, clear circuit, noise detecting circuit, time voltage converter, switch capacitor filter, voltage are set
The system that current converter circuit and peak current detection circuit are constituted constitutes closed loop with controlled primary side feedback Switching Power Supply；Peak
It is worth the anode for the peak-current signal CS connection comparator COMP that current detection circuit is obtained by primary side switch pipe sampling resistor,
Reference voltage VREF connects the negative terminal of comparator COMP after connecting by resistance R3 with R4, the output of comparator COMP connects PFM
Modulator, oscillator generate the periodic square wave clock signal clk that duty ratio is 50%, frequency-invariant, and noise detecting circuit connects
The square-like clock signal CLK exported by oscillator calculates system by counter and logic circuit processing as clock signal
The difference signal T of switching frequency and 25KHz frequencydetect, time voltage converter, which receives the difference that noise detecting circuit exports, to be believed
Number Tdetect, the voltage value V_DETECT directly proportional to the time is converted thereof into, clear circuit receives the PFM of PFM modulator output
Signal, for noise detecting circuit and time voltage converter provide each period start when clearing reset signal RESET, reset
Circuit generates quenching pulse signal when the PFM signal of input becomes the rising edge of high level, and the reset signal of output is noise
Detection circuit provides clearing reset signal RESET of each period when starting；Become low level decline in the PFM signal of input
Along when, generate quenching pulse signal, the reset signal of output provides the clearing reset signal of Cycle by Cycle for time voltage converter.
The control signal of switch capacitor filter is the PFM signal of PFM modulator output, the voltage value V_DETECT directly proportional to the time
Filtered voltage V_SCF is exported by switch capacitor filter, is connected to resistance R3 and R4 by voltage-current converter circuit
Connecting pin, output with input voltage linear change pull-down current, the electric current drag down peak current detection circuit peak value electricity
Comparative threshold voltage is flowed, control system frequency, in high power load, Switching Power Supply are reached by the peak point current of regulating system
Transmission energy it is high, making system operating frequency, clamper always works in except audio zone in 20KHz or more always；When small-power,
The transmission energy of Switching Power Supply is extremely low, without enough energy production audio-frequency noises, finally eliminates Switching Power Supply and entirely loads
Audio-frequency noise in range.
Such as Fig. 2, noise detecting circuit includes T trigger T1, T2, T3, T4, set-reset flip-floop D1, D2, phase inverter INV1,
INV2, INV3, NAND gate NAND1 and XOR gate XOR1；The square wave clock letter of the input end of clock CK connection oscillator output of T1
The end the SET connection of number CLK, T1 reset reset signal RESET, the input end of clock CK of output end Q (f1) the connection T2 of T1 and with
The end the SET connection of an input terminal of NOT gate NAND1, the input end of clock CK, T3 of the output end Q connection T3 of T2 resets resetting letter
Number RESET；Another input terminal of the input end of clock CK and NAND gate NAND1 of output end Q (f2) the connection T4 of T3, NAND gate
The end S of output (f4) the connection D2 of NAND1, the SET termination cycles of T4 set signal RESET again, the output end Q connection of T4
The input of INV1, the end the SET connection of T4 reset reset signal RESET, and the end S of output (f3) the connection D1 of INV1, the end R of D1 connects
It connects and resets reset signal RESET, the end the R connection of an input terminal of output end Q (f20) the connection XOR gate XOR1 of D1, D2 is clear
Another input terminal of output end Q (f25) the connection XOR gate XOR1 of zero reset signal RESET, D2, the output of XOR gate XOR1
The input of INV2 is connected, input terminal of the reset signal RESET through delay control circuit Delay connection INV3 is reset.
Time voltage converter includes current source IP1, switch K1, switch K2 and capacitor C1, and the input terminal of current source IP1 connects
Connect power vd D, one end of the output end connection switch K1 of current source IP1, one end of switch K1 other end connection switch K2 and electricity
Hold one end of C1 and the output end as time voltage converter, exports the voltage value V_DETECT directly proportional to the time, switch
The other end of K2 and the other end of capacitor C1 are grounded, phase inverter INV2 in the control terminal connection noise detecting circuit of switch K1
Output, the control terminal of switch K2 connect the output of phase inverter INV3 in noise detecting circuit.
In Fig. 2, CLK pass through the counter that is made of T trigger T1~T4 generate Cycle by Cycle time be 40us (f25) and
The switch power supply system working frequency of the clock signal of 50us (f20), primary side feedback control is reduced with the reduction of load, when
When working frequency is lower than 25KHz (corresponding gate time is 40us), the output of INV2 becomes high level, K1 closure, constant-current source
IP1 starts to charge with constant electric current to capacitor C1, the output voltage values V_DETECT of generation time electric pressure converter.Switch electricity
Source system operating frequency is lower, and K1 closing time is longer, and V_DETECT voltage value is also higher.System operating frequency is reduced to 20KHz
When, K1 is opened, and V_DETECT voltage reaches maximum value.
Such as Fig. 3, switch capacitor filter includes switch K3, switch K4, phase inverter INV4, capacitor C2 and capacitor C3；Time
The other end of one end of the voltage value V_DETEC connection switch K3 directly proportional to the time of electric pressure converter output, switch K3 connects
One end of switch K4 and one end of capacitor C2 are connect, switch capacitor filter is simultaneously made in one end of the other end connection capacitor C3 of switch K4
Output end, export filtering voltage V_SCF, the other end of capacitor C2 and the other end of capacitor C3 be grounded, the control of switch K3
The PFM signal of end connection PFM modulator output, the output end of the control terminal connection phase inverter INV4 of switch K4, phase inverter INV4
Input terminal connection PFM modulator output PFM signal.Capacitance needed for switch capacitor filter is small, can save chip area,
It is at low cost, and have processing speed fast, structure is simple, advantage with high accuracy.When PFM is high level, switch K3 closure is opened
It closes K4 to open, the voltage value of V_DETEC is transferred to capacitor C2, and when PFM is low level, switch K3 is opened, switch K4 closure, electricity
Hold the charge transfer of C2 storage to C3, generates filtering voltage value V_SCF.The transmitting speed of the higher switch capacitor filter of PFM frequency
Degree is faster, and the speed that V_DETEC is transmitted to V_SCF is faster.
Such as Fig. 4, voltage-current converter circuit includes operational amplifier A1, resistance R1, NMOS tube M1, PMOS tube M2, PMOS
Pipe M3, NMOS tube M4 and NMOS tube M5；The output voltage of the non-inverting input terminal connection switch capacitive filter of operational amplifier A1
The source electrode of the negative-phase input connection NMOS tube M1 of V_SCF, operational amplifier A1 and one end of resistance R1, the other end of resistance R1
Ground connection, the grid of the output end connection NMOS tube M1 of operational amplifier A1, the drain electrode of the drain electrode connection PMOS tube M2 of NMOS tube M1
With the grid of grid and PMOS tube M3, the source electrode of PMOS tube M2 and the source electrode of PMOS tube M3 are all connected with power vd D, PMOS tube M3
Drain electrode connection NMOS tube M4 drain and gate and NMOS tube M5 pipe grid, the source electrode of NMOS tube M4 and NMOS tube M5's
Source grounding, output end of the drain electrode of NMOS tube M5 as voltage-current converter circuit, connects in peak current detection circuit
The connecting pin of resistance R3 and R4.M2, M3 are current mirror duplicate circuit, by adjusting the breadth length ratio of M2, M3, available current mirror
The proportionality coefficient of duplication.The drain electrode of PMOS tube M3 connects drain electrode, grid and the M5 tube grid of NMOS tube M4, NMOS tube M4, M5
Source electrode ground connection.M4, M5 are current mirror duplicate circuit, by adjusting the breadth length ratio of M2, M3, the ratio of available current mirror duplication
Coefficient.Voltage-current converter circuit, which is realized, is converted to electric current I_CS for input voltage V_SCF.
Peak current detection circuit is as shown in figure 4, include resistance R3, R4, comparator COMP, the one end resistance R3 connects benchmark
Voltage VREF, the other end connect the drain electrode of NMOS tube M5 and one end of resistance R4, the negative input of another termination comparator of R4
End, peak current detection signal CS meet the normal phase input end of comparator, output signal Cout.The Vth=as I_CS=0
VREF, when I_CS becomes larger, Vth becomes smaller and (is less than VREF), and CS is flipped output signal Cout when smaller, i.e. peak value
Electric current becomes smaller, and output signal is the shutdown that Cout controls PFM signal.
The working principle of circuit of the present invention is as follows：Primary side feedback Switching Power Supply based on PFM mode, power transmission equation
For：
Wherein, P is switch power supply system output power, VOAnd IORespectively system output voltage and electric current, η turn for system
Change efficiency, LmFor transformer inductance, fsFor system switching frequency, IpkFor the peak point current of each periodic system primary side inductance.
By (1) formula it is found that PFM modulating system for constant peak current control mode, LmFor definite value, IpkIt is fixed
Value, the working frequency and load current of Switching Power Supply are linear, when output load current reduces, i.e. IOWhen reduction, open
The switching frequency f in powered-down sourcesAlso it decreases, as the switching frequency f of systemsBeing reduced to audio zone (20Hz~20KHz) can generate
Audio-frequency noise.In order not to allow system to be down to audio range, under identical power condition, changes system operating mode, reduce IpkIt can
Promote fs。
As shown in Fig. 2, becoming the rising edge of high level as the starting point of a cycle using PFM signal, clear circuit is in PFM
Become generating quenching pulse signal RESET when the rising edge of high level, reset signal RESET triggers T trigger T1~T4, SR
Device D1~D2 is zeroed out, and the CLK that oscillator generates later, which passes through, starts timing by the counter that T trigger T1~T4 is constituted,
If system switching frequency is greater than 25KHz, the logic output of counter disconnects K1 always, and then V_DETECT is zero, V_
SCF is zero, I_CS zero, and VREF is equal to Vth, and system works in constant peak current-mode.If system load electric current persistently drops
It is low, so that system operating frequency is reduced to 25KHz hereinafter, the CLK that oscillator generates passes through the frequency dividing being made of T trigger T1~T4
When device timing to 40us (corresponding frequency is 25KHz), f25 becomes low level, and f20 is high level, different by logic gates
Or high level is exported after door XOR1 and phase inverter INV2 operation, it is closed K1, constant-current source IP1 starts with constant electric current to electricity
Hold C1 charging, by capacitance equation
It is available, time voltage converter output voltageWherein I is the electric current of constant-current source IP1, t
For K1 closing time, C is the capacitance of capacitor C1.
By (3) it is found that t can also be expressed as the system duty cycle timeWith the difference of the noise measuring time 40us of setting
Value.V_DETECT accesses switch capacitor filter circuit.As shown in figure 3, when PFM is high level, switch K3 closure, switch K4
It opens, the voltage value of V_DETEC is transferred to capacitor C2, and when PFM is low level, switch K3 is opened, switch K4 closure, capacitor C2
The charge transfer of storage generates filtering voltage value V_SCF to C3.The transmission speed of the higher switch capacitor filter of PFM frequency is more
Fastly, V_DETEC be transmitted to V_SCF speed it is faster, by the transmitting V_DETEC=V_SCF in several periods.V_SCF is as electricity
The input of current voltage conversion circuit, as shown in figure 4, V_SCF is by operational amplifier A1, NMOS tube M1, PMOS tube M2, resistance R1 group
At voltage-current converter circuit be converted into electric current I1,
The current value of I1 can be obtained by formula (4), I2 is accurately multiple by the current mirror being made of PMOS tube M2 and PMOS tube M3
The electric current of I1 processed, I_CS are accurately replicated the electric current of I2 by the current mirror being made of NMOS tube M4 and NMOS tube M5, can finally obtained
I_CS accesses peak current detection circuit, as shown in figure 4,
Vth=VREF-I_CS × R3 (5)
The linear relationship of the comparative threshold voltage Vth and pull-down current I_CS of CS known to formula (5).
The peak point current I known to formula (6)pkWith the relationship of CS comparative threshold voltage and detection resistance R5.
It can be obtained by formula (2) (3) (4) (5) (6)
By formula (7) it is found that the present invention is converted to the peak point current of the Switching Power Supply of primary side feedback mode and system switching
The function of frequency dependence, switching frequency fSValue it is smaller, IpkIt is smaller.
It can be obtained by formula (1) (7)
If load current continues to reduce, when system operating frequency being made to be reduced to 20KHz, the CLK that oscillator generates passes through
For the counter counts being made of T trigger T1~T4 when 50us (respective frequencies 20KHz), f25 is low level, and f20 becomes
Low level exports low level after logic gates XOR gate XOR1 and phase inverter INV2 operation, opens K1, constant-current source
IP1 stops charging to C1, and the voltage on C1 reaches maximum value, corresponding I at this timepkReach minimum value, noise detecting circuit control
Timing is as shown in figure 5, power by (8) Shi Ke get at this time
R3, R1, R5, the parameter of C1, so that switching frequency 20KHz, I are rationally set known to (9) formulapkWhen reaching minimum value
System output power P it is sufficiently small, as low as be not enough to generate sound in audio section even if generated transmission energy
Frequency noise.System switching frequency is being less than 25KHz to IpkBetween minimum value always clamper in 20KHz or more.Load current later
Continue to reduce, system enters pulse frequency modulated (PFM) operating mode, and system switching frequency is lower than 20KHz, due to power at this time
Sufficiently small, the transmission energy of Switching Power Supply is extremely low, even if being lower than without enough energy production audio-frequency noise system switching frequencies
20KHz will not generate audio-frequency noise.
The whole system course of work is divided into three phases：(1) working frequency is greater than 25KHz, and system is using constant peak electricity
The pulse frequency modulated mode (PFM) of stream, audio-frequency noise will not be generated by not entering into audio section.(2) working frequency is less than
25KHz eliminates the circuit of Switching Power Supply audio-frequency noise by the switching frequency fs real-time control peak point current of detection system, make be
System working frequency always works in 20KHz or more, and until peak point current is minimized value, this stage does not enter into audio section will not
Generate audio-frequency noise.(3) working frequency is less than 20KHz, works in the pulse frequency modulated mode of low peak current, at this time power
Sufficiently small, the transmission energy of Switching Power Supply is extremely low, without enough energy production audio-frequency noises, even if system switching frequency is lower than
20KHz will not generate audio-frequency noise.
In conclusion the circuit for the Switching Power Supply audio-frequency noise that elimination primary side feedback of the invention controls, can accurately examine
Examining system switching frequency, by control peak point current, make system when high-power, system operating frequency always clamper in 20KHz
More than, when small-power, the transmission energy of Switching Power Supply is extremely low, and without enough energy production audio-frequency noises, final realize is eliminated
The purpose of audio-frequency noise.
Claims (6)
1. a kind of circuit for eliminating primary side feedback Switching Power Supply audio-frequency noise, primary side feedback Switching Power Supply are based on the control of AC-DC primary side
Converter topologies processed, including rectifier bridge, input filter capacitor, primary side winding NP and primary side switch pipe and sampling resistor R5,
Auxiliary winding NA and partial pressure output resistance, vice-side winding NS and rectifier diode and output resistance R0With capacitor C0, auxiliary winding
NA connects the negative terminal of error amplifier by the voltage signal that electric resistance partial pressure exports, and the anode of error amplifier connects 2V voltage,
The output of error amplifier controls the grid of primary side switch pipe after PFM modulator and driving circuit；
It is characterized in that：Oscillator, clear circuit, noise detecting circuit, time voltage converter, switch-capacitor filtering are set
The system that device, voltage-current converter circuit and peak current detection circuit are constituted is constituted with controlled primary side feedback Switching Power Supply
Closed loop；Peak current detection circuit passes through the peak-current signal CS connection comparator COMP that primary side switch pipe sampling resistor obtains
Anode, reference voltage VREF by resistance R3 connect with R4 after connection comparator COMP negative terminal, the output of comparator COMP
PFM modulator is connected, oscillator generates the periodic square wave clock signal clk that duty ratio is 50%, frequency-invariant, noise measuring
Circuit receives the square-like clock signal CLK of oscillator output as clock signal, handles by counter and logic circuit, operation
The difference signal T of system switching frequency and 25KHz frequency outdetect, time voltage converter receive noise detecting circuit output
Difference signal Tdetect, the voltage value V_DETECT directly proportional to the time is converted thereof into, it is defeated that clear circuit receives PFM modulator
PFM signal out, for noise detecting circuit and time voltage converter provide each period start when clearing reset signal
RESET, the control signal of switch capacitor filter are the PFM signal of PFM modulator output, the voltage value V_ directly proportional to the time
DETECT exports filtered voltage V_SCF by switch capacitor filter, is connected to resistance by voltage-current converter circuit
The connecting pin of R3 and R4, exports the pull-down current with input voltage linear change, which drags down peak current detection circuit
Peak point current comparative threshold voltage reaches control system frequency by the peak point current of regulating system, in high power load, opens
The transmission energy in powered-down source is high, and making system operating frequency, clamper always works in except audio zone in 20KHz or more always；It is small
When power, the transmission energy of Switching Power Supply is extremely low, and without enough energy production audio-frequency noises, it is whole finally to eliminate Switching Power Supply
Audio-frequency noise in a loading range.
2. the circuit according to claim 1 for eliminating primary side feedback Switching Power Supply audio-frequency noise, it is characterised in that：It is described to make an uproar
Sound detecting circuit includes T trigger T1, T trigger T2, T trigger T3, T trigger T4, set-reset flip-floop D1, set-reset flip-floop D2,
Phase inverter INV1, phase inverter INV2, phase inverter INV3, NAND gate NAND1 and XOR gate XOR1；The clock of T trigger T1 inputs
The end the SET connection of square-like clock signal CLK, the T trigger T1 of CK connection oscillator output is held to reset reset signal RESET, T touching
Send out an input terminal of the input end of clock CK and NAND gate NAND1 of the output end Q connection T trigger T2 of device T1, T trigger T2
Output end Q connection T trigger T3 input end of clock CK, T trigger T3 the end SET connection reset reset signal RESET；T
Another input terminal of the input end of clock CK and NAND gate NAND1 of the output end Q connection T trigger T4 of trigger T3, and it is non-
The end S of the output connection set-reset flip-floop D2 of door NAND1, set signal RESET, T are touched the SET termination cycles of T trigger T4 again
The input of the output connection phase inverter INV1 of device T4 is sent out, the end the SET connection of T trigger T4 resets reset signal RESET, phase inverter
The end S of the output end connection set-reset flip-floop D1 of INV1, the end the R connection of set-reset flip-floop D1 reset reset signal RESET, set-reset flip-floop
The end the R connection of an input terminal of the output end Q connection XOR gate XOR1 of D1, set-reset flip-floop D2 resets reset signal RESET, SR
The output of another input terminal of the output end Q connection XOR gate XOR1 of trigger D2, XOR gate XOR1 connects phase inverter INV2
Input, reset input terminal of the reset signal RESET through delay control circuit Delay connection phase inverter INV3.
3. the circuit according to claim 1 for eliminating primary side feedback Switching Power Supply audio-frequency noise, it is characterised in that：When described
Between electric pressure converter include current source IP1, switch K1, switch K2 and capacitor C1, the input terminal of current source IP1 connects power vd D,
One end of the output end connection switch K1 of current source IP1, one end of switch K1 other end connection switch K2 and one end of capacitor C1
And the output end as time voltage converter, export the voltage value V_DETECT directly proportional to the time, the other end of switch K2
And the other end of capacitor C1 is grounded, the output of phase inverter INV2, switch in the control terminal connection noise detecting circuit of switch K1
The output of phase inverter INV3 in the control terminal connection noise detecting circuit of K2.
4. the circuit according to claim 1 for eliminating primary side feedback Switching Power Supply audio-frequency noise, it is characterised in that：It is described to open
Closing capacitive filter includes switch K3, switch K4, phase inverter INV4, capacitor C2 and capacitor C3；The output of time voltage converter
One end of the voltage value V_DETEC connection switch K3 directly proportional to the time, one end of the other end connection switch K4 of switch K3 and
One end of capacitor C2, one end of the other end connection capacitor C3 of switch K4 and the output end for making switch capacitor filter, output filter
The other end of wave voltage V_SCF, capacitor C2 and the other end of capacitor C3 are grounded, and the control terminal of switch K3 connects PFM modulator
The PFM signal of output, the output end of the control terminal connection phase inverter INV4 of switch K4, the input terminal of phase inverter INV4 connect PFM
The PFM signal of modulator output.
5. the circuit according to claim 1 for eliminating primary side feedback Switching Power Supply audio-frequency noise, it is characterised in that：The electricity
Current voltage conversion circuit includes operational amplifier A1, resistance R1, NMOS tube M1, PMOS tube M2, PMOS tube M3, NMOS tube M4 and
NMOS tube M5；The output voltage V_SCF of the non-inverting input terminal connection switch capacitive filter of operational amplifier A1, operational amplifier
The source electrode of the negative-phase input connection NMOS tube M1 of A1 and one end of resistance R1, the other end ground connection of resistance R1, operational amplifier
The grid of the output end connection NMOS tube M1 of A1, the drain and gate and PMOS tube of the drain electrode connection PMOS tube M2 of NMOS tube M1
The grid of M3, the source electrode of PMOS tube M2 and the source electrode of PMOS tube M3 are all connected with power vd D, and the drain electrode of PMOS tube M3 connects NMOS tube
The drain and gate of M4 and the grid of NMOS tube M5 pipe, the source electrode of NMOS tube M4 and the source grounding of NMOS tube M5, NMOS
Output end of the drain electrode of pipe M5 as voltage-current converter circuit, connects the connection of resistance R3 and R4 in peak current detection circuit
End.
6. the circuit according to claim 1 for eliminating primary side feedback Switching Power Supply audio-frequency noise, it is characterised in that：It is described clear
Zero circuit generates quenching pulse signal when the PFM signal of input becomes the rising edge of high level, and the reset signal of output is to make an uproar
Sound detecting circuit provides clearing reset signal RESET of each period when starting；In the case where the PFM signal of input becomes low level
Drop along when, generate quenching pulse signal, the reset signal of output is that time voltage converter provides the clearing resetting of Cycle by Cycle and believes
Number.
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| CN112542954A (en) * | 2020-12-16 | 2021-03-23 | 南京微盟电子有限公司 | Adaptive soft drive control circuit suitable for DCM |
| CN112564511A (en) * | 2020-12-16 | 2021-03-26 | 南京微盟电子有限公司 | Self-adaptive soft drive control circuit suitable for CCM |
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| CN112822818A (en) * | 2019-11-15 | 2021-05-18 | 华润微集成电路(无锡)有限公司 | Circuit structure for realizing stepless dimming function |
| CN114679053A (en) * | 2022-04-15 | 2022-06-28 | Oppo广东移动通信有限公司 | Power supply system, control method thereof and electronic equipment |
| CN114697593A (en) * | 2020-12-31 | 2022-07-01 | 广州艾美网络科技有限公司 | Power supply system of audio and video integrated machine |
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Address after: 210042 4th floor, building 1, Xuzhuang Software Park, 699-8 Xuanwu Avenue, Xuanwu District, Nanjing City, Jiangsu Province Patentee after: NANJING MICRO ONE ELECTRONICS Inc. Country or region after: China Address before: 210042 4th floor, building 1, Xuzhuang Software Park, 699-8 Xuanwu Avenue, Xuanwu District, Nanjing City, Jiangsu Province Patentee before: NANJING MICRO ONE ELECTRONICS Inc. Country or region before: China |