Utility model content
The purpose of this utility model is to provide a kind of excellent PWM switching power source control circuits of anti-electromagnetic interference capability,
It is excellent with anti-electromagnetic interference capability, the advantages of the efficiency of Switching Power Supply can be improved, reduce the energy loss of Switching Power Supply.
The above-mentioned technical purpose of the utility model technical scheme is that:
The excellent PWM switching power source control circuits of a kind of anti-electromagnetic interference capability, including power supply and drive module, protection mould
Block and multi-mode control module;
The power supply and drive module, including internal starting module, reference voltage module, current sampler, error amplification
Device, output driving module;
The protection module, including overheating protection module, overload protection module, overvoltage protective module and overcurrent protection mould
Block;
The multi-mode control module, including feedback input end, oscillator, frequency, load detecting for changing switch
Module, zero current detecting circuit are used to implement valley conduction pattern, the lowest point detector and mode selector, for several work
The switching of operation mode.
By using above-mentioned technical proposal, since Switching Power Supply needs constantly to carry out charge and discharge to coil in practical applications
Electricity, the presence of this rush of current cause electromagnetic interference than more serious.Research shows that the ripple size of electric current is about V/2Lfk,
Wherein V is voltage, and L is coil inductance, fkFor switching frequency.It can be seen that current ripples are directly proportional to voltage.
Supply voltage cannot be too low in practical application, and in order to reduce electromagnetic interference, switching frequency cannot be too low, that is, improves and open
Current ripples can be reduced by closing frequency, but can so increase switching loss, and energy conversion efficiency reduces.Therefore switching frequency
Selection must take into consideration factors, and compromise.The utility model uses variable switching frequency with according to different situations tune
Switching frequency needed for section.
The utility model employs zero current detecting circuit to optimize the conducting of switching tube.The of switching tube drain-source power supply
Position where one minimum value causes the MOSFET to turn on, and the current spike that can cause conducting is minimum.The circuit provides letter
Number driving switch pipe into open-minded, that is, realizes valley conduction when its drain terminal voltage difference is relatively low.The current spike so turned on will
Can be minimum, so as to substantially reduce the electromagnetic interference of entire Switching Power Supply.
Further set:The load detecting module is connected with internal starting module, for starting in internal starting module
Afterwards, detect external loading situation and electric signal fed back into mode selector, mode selector for changing control circuit work
Operation mode.
Further set:Metal-oxide-semiconductor is connected with outside the power supply and drive module, operating mode starts zero current detection after determining
Circuit, the lowest point detector, power supply and drive module start metal-oxide-semiconductor, generate sampled voltage, internal logic electricity is equipped in control circuit
Road, compared with predetermined value, sampled voltage is closed or opened metal-oxide-semiconductor.
Further set:Output voltage compared with reference voltage, is passed through error amplifier by the current sampler
Error amplification signal is converted into electric current by optocoupler, and is injected in feedback input end, to adjust the size of output voltage.
Further set:The oscillator uses multi-frequency generator, and for passing through, to change capacitance constant in charging and discharging currents
In the case of adjust frequency, and duty cycle can be changed by adjusting the charging and discharging currents in charging and discharging circuit.
By using above-mentioned technical proposal, due to the influence of inductance, capacitance in switch power supply system, Switching Power Supply control electricity
Road can introduce electric current and voltage higher harmonic components during the work time, i.e., with the presence of the noise band that peak value is very high on frequency spectrum,
So as to generate serious electromagnetic interference.The utility model uses " frequency conversion " technology so that and switching frequency is not fixed, but
Variation in a certain range so as to which the frequency band of each harmonic of the voltage and current in Switching Power Supply is obtained broadening, is opened with reducing
Powered-down source control circuit electromagnetic interference.
Further set:The interior current sampling circuit for being equipped with to control switching current of the control circuit.
By using above-mentioned technical proposal, during switching power circuit designs, in order to reduce electromagnetic interference, simultaneously
Reduce switching loss, improve high conversion efficiency, reduce to a certain extent in the utility model switching tube cut-off current and
Load current to reduce the loss in the course of work, improves transfer efficiency.
In conclusion the utility model has the advantages that:
The utility model employs the method for a variety of reduction electromagnetic interferences, the control after the design of multiple electromagnetism interference
The anti-electromagnetic interference capability of circuit is preferable, can application monitor/LCD TV/set-top box power supply, can be used for it is various exchange/
DC power source adapter and various chargers.
Switching Power Supply frequency can be smoothly varying in external world's load variation for the utility model, that is, embodies " soft bending "
The characteristics of, therefore with traditional switch power supply electromagnetic interference is reduced compared to switching loss is substantially reduced.
By using Valley-Switching pattern, it is smaller to turn it on formed current spike, so as to reduce entire switch electricity
The electromagnetic interference in source improves transfer efficiency.In addition in addition to reducing electromagnetic interference and switching loss, transfer efficiency is improved, it is right
Switching current has carried out effective control.
In actual application, the utility model not only can largely save peripheral circuit, moreover it is possible to greatly improve power supply
Transfer efficiency reduces switching loss.
Specific embodiment
Specific embodiment of the present utility model is described further below in conjunction with the accompanying drawings.
Technical solution is used by the utility model:
The excellent PWM switching power source control circuits of a kind of anti-electromagnetic interference capability, as shown in Fig. 2, function module includes supplying
Electricity and drive module, protection module and multi-mode control module.
Power supply and drive module include internal starting module, reference voltage module, current sampler, error amplifier, defeated
Go out drive module.
Protection module, including overheating protection module, overload protection module, overvoltage protective module and overcurrent protection module.
Multi-mode control module, including feedback input end, oscillator, frequency, load detecting module for changing switch,
Zero current detecting circuit is used to implement valley conduction pattern, the lowest point detector and mode selector, for several operating mode
Switching.
So it can realize the raising of circuit anti-electromagnetic interference capability by four kinds of modes.
1st, using multi-operation mode
The principle of multi-operation mode is:As shown in Fig. 2, after system electrification, internal activation circuitry is filled to VCC ends external capacitor
Electricity, when VCC voltages rise to certain value, internal circuit is started to work, and oscillator also sends trigger signal, the inspection of load detecting module
External loading is surveyed, mode selection circuit starts, and different working modes are respectively enterd according to different loads situation.
Zero current detecting circuit, the lowest point detector are started to work afterwards, when eligible, into quasi-resonance Valley-Switching mould
Formula opens metal-oxide-semiconductor through drive control module.Line voltage charges to primary inductance, primary inductance electric current linear rise.
Inductive current flows through metal-oxide-semiconductor, and electric current generates sampled voltage after mirror image on internal sampling resistor in proportion, when inductive current rises
To when sampled voltage being made to be more than preset value, current comparator is overturn, and triggers internal logic circuit, closes metal-oxide-semiconductor.When shaking
It swings device next cycle to come temporarily, MOS is again turned on.
After a series of activities cycle, output voltage, which is opened, to be risen, and internal control circuit is by output voltage and benchmark
Reference voltage is compared and enlarged, and error amplification signal is converted into electric current by optocoupler, by the injection circuit of FB ports
The feed back input module in portion.
When output voltage raises, the electric current increase of FB ports injection, the pressure drop which generates on internal resistance increases,
Current comparator is overturn so that the pressure drop that primary inductance electric current generates on internal resistance reduces, i.e., primary inductance is electric
Stream reduces, and being thus relayed to secondary energy will reduce, and output voltage will reduce, so as to form the stability series of a negative-feedback
System.Conversely, when output voltage reduces, degeneration factor will automatically adjust the electric current of FB ends injection, raise input voltage, from
And obtain a highly stable output voltage.When the electric current of FB ends injection is close to zero, primary inductance electric current is up to
Maximum.
The operating mode of the utility model is as shown in figure 3, in full load, when the input power is low, the IC works
Make in fixed frequency CCM(Continuous Condition Mode)Pattern, the fixed frequency are 50KHz or so;And it is inputting
When power is higher, quasi-resonant mode is operated in, at this moment low-limit frequency is clamped down in Flow;Both the above pattern can reach very high
Efficiency.
Under normal load condition, the utility model is in quasi-resonant mode(Quasi-Resonant Mode)Lower work.In order to
Switching loss is reduced, the highest switching frequency under quasi-resonant mode will be any limitation as, and be clamped down in this circuit in Fhigh, value is
90KHz or so meets EMI standards.The pwm control circuit is oscillated at first trough in power supply and opened in QR patterns, switching tube
It is logical, start next cycle.By quasi-resonance operating mode, the switching loss and EMI of system substantially reduce.
When the load decreases, the utility model is in PFM(Pulse Frequency Modulation)It works under pattern, with
Reach more than 90% power conversion efficiency.The utility model according to load come adjusting switch frequency, and constantly reduce;In PFM ranks
Section, the lowest point switching characteristic still exists, so as to obtain smooth frequency variation curve.
When loading smaller or unloaded, this practicality is newly in green model(Green Mode)Lower work, is treated to reduce
Machine power consumption and switching loss improve system transfer efficiency.When being operated in green model, switching frequency Fgreen, value is
20KHz or so, and no longer reduce.It is well known that 20KHz is audiorange, by using green model, it is possible to prevente effectively from
The appearance of audio-frequency noise.
As shown in figure 3, the two poles of the earth of AC are coupled with the anode of diode D1, D3 and D2, D4, cathode and the V phases of D1, D2
Even, D3, D4 cathode ground connection.
Resistance R1 one end is connected with Lp, another to terminate to capacitance C1 top crowns and VCC, C1 bottom crown ground connection.
The drain electrode of M1 pipes meets LHL and capacitance CM top crowns, and grid is connected to DRI, and source electrode is connect under CS, R2 and CM
Pole plate, the other end ground connection of R2.
LS one end is connected with diode D anodes, another to terminate to capacitance C bottom crowns and ground, and diode D cathode meet capacitance C
Top crown.
Optocoupler OC mono- terminates FB, other end ground connection.
2nd, using Valley-Switching pattern
As shown in Fig. 2, NP、NSInductance value be respectively LP、LS, LmFor mutual inductance, for energy to be transferred to secondary from primary,
Secondary magnetic flux can not be transferred to by coupling, the ability of storage need to be discharged by other paths.And it is stored in leakage inductance
In energy be switching tube shut-off be generate spike the reason for.
As shown in figure 4, switching tube is in the conduction state at the beginning, primary current, peak value I are formedPP, it is maximum in electric current
When turn off, leakage inductance LPLWith switching tube drain terminal capacitance CMThe resonant tank of composition generates over-pressed spike vibration, forms resonance range one.
In resonance range one, switching tube drain-source voltage peak value can use formula(1)It represents, wherein IPAt the beginning of flowing through transformer
The direct current of grade coil.
After switching tube shut-off, the mutual inductance energy of transformer forms secondary current, peak value I by the rectifying tube D1 of conductingPS,
It charges to filter capacitor C, so as to transfer energy to load.Secondary current continuously decreases in the process, when being close to zero,
Mutual inductance LmWith switching tube drain terminal capacitance CMGenerate resonance range two.There are tri- points of A, B, C, wherein A points in oscillating curve in this section
It is the minimum point of switching tube electrical leakage voltage, and the corresponding drain terminal voltage of C points is higher.
In resonance range two, switching tube drain-source voltage includes formula(2)Represented DC component VDDCAnd formula
(3)Represented harmonic components VDQRTwo parts, wherein RPFor transformer direct current equivalent resistance, VZFor on rectifying tube D1
Pressure drop.
When switching tube turns on again, it can select to turn on when its drain terminal voltage is relatively low, can also select in its drain terminal
It is turned on when voltage is higher.Because drain terminal capacitance CMCurrent spike can be formed during by switching tube discharge, if switching tube is leaked at it
The higher point of terminal voltage is opened, then will generate larger switching noise, forms EMI.
, whereas if in first minimum value A point of switching tube drain terminal voltage(That is the lowest point)So that switching tube is open-minded, then
The current spike of conducting will be minimum, so as to substantially reduce the EMI of entire Switching Power Supply.The conducting of switching tube and deadline can
Formula is used respectively(4)、(5)It represents.
The utility model employs zero current detecting circuit to optimize the open-minded of switching tube, zero detection electricity of switching tube conducting
Line structure optimization is as shown in Figure 5.The circuit provides signal driving switch pipe when its drain terminal voltage difference is relatively low into open-minded, i.e. reality
Existing valley conduction.
As shown in figure 5, the drain electrode of N0 pipes meets the I0 to come from power supply, grid connects the grid of N1 pipes, grid leak short circuit, and source level connects
Ground;
The drain electrode of N1 pipes connects the drain electrode of P0 pipes, the I0 that grid connects the grid of N0 pipes and comes from power supply, source level ground connection;
The drain electrode of N2 pipes connects the drain electrode of P1 pipes and the drain electrode of N4 pipes, and grid connects power supply, and source level connects the drain electrode of N3 pipes and N6 pipes
Grid;
The drain electrode of N3 pipes connects the source level of N2 pipes and the grid of N6 pipes, the I0 that grid connects the grid of N0 pipes and comes from power supply, source
Grade ground connection;
The drain electrode of N4 pipes connects the drain electrode missed with P1 pipes of N2 pipes, and grid connects the grid of N5 pipes, grid leak short circuit, and source level connects
Ground;
The drain electrode of N5 pipes connects the drain electrode of P2 pipes, and grid connects the grid of N4 pipes, source level ground connection;
The drain electrode of N6 pipes connects the drain electrode of P3 pipes and the grid of P4 pipes, source level meet DRI;
The drain electrode of N7 pipes meets drain electrode and the OUT of P4 pipes, and grid connects the I0 come from power supply, source level ground connection;
The source level of P0 pipes connects power supply, and grid connects the grid of P1 pipes, source grid short circuit, and drain electrode connects the drain electrode of N1 pipes;
The source level of P1 pipes connects power supply, and grid connects the grid of P0 pipes, and drain electrode connects the drain electrode of N2 pipes and the drain electrode of N4 pipes;
The source level of P2 pipes connects power supply, and grid connects the grid of P3 pipes, and drain electrode connects the drain electrode of N5 pipes, grid leak short circuit;
The source level of P3 pipes connects power supply, and grid connects the grid of P2 pipes, and drain electrode connects the drain electrode of N6 pipes and the grid of P4 pipes;
The source level of P4 pipes connects power supply, and grid connects the drain electrode of P3 pipes and the drain electrode of N6 pipes, and drain electrode meets drain electrode and the OUT of N7 pipes.
3rd, using converter technique
Due to the influence of inductance, capacitance in switch power supply system, switching power source control circuit can introduce during the work time
Electric current and voltage higher harmonic components with the presence of the noise band that peak value is very high that is, on frequency spectrum, are done so as to generate serious electromagnetism
It disturbs.A kind of effective ways for reducing switching power source control circuit electromagnetic interference are to use " frequency conversion " technology so that switching frequency is not
It is fixed, but changes within the specific limits, so as to which the frequency band of each harmonic of the voltage and current in Switching Power Supply is obtained
To broadening.
If frequency range is △ f, then in switching frequency excursion, broadening is △ f by fundamental wave bandwidth, two
Broadening is 2 △ f by subharmonic bandwidth, and so on, broadening is n △ f by n higher hamonic waves bandwidth.It is constant in noise gross energy
Under the premise of, the amplitude of each harmonic is reduced, and higher hamonic wave amplitude reduction then becomes apparent, so as to effectively inhibit to be
The electromagnetic interference of system.
The utility model employs multi-frequency generator to realize " frequency conversion " technology, structure such as 6 institute of attached drawing of this oscillator
Show.Capacitance C0 is one group of capacitance of different sizes, controls whether it accesses the charge and discharge of oscillator by different control signals respectively
Electrical circuit, these control signals are generated by frequency dividing circuit.Voltage after charging on capacitance C0 is Vc0, and fixed comparison voltage is
Vref, VrefWith Vc0It is compared, so as to form vibration.
It is respectively T to define the charging current of the oscillator and discharge currentch、Tdch, then the charge cycle T of the oscillatorch
With discharge cycle TdchFormula can be used respectively(6)、(7)It represents.
So as to which frequency of oscillation and duty cycle can use formula respectively(8)、(9)It represents.
By changing capacitance, frequency can be adjusted in the case that charging and discharging currents are constant;And by adjusting charging and discharging circuit
On charging and discharging currents, thus it is possible to vary duty cycle.
As shown in fig. 6, the source level of P0 pipes connects power supply, grid connects the source level that Vbh. drain electrodes connect P3 pipes;
The source level of P1 pipes connects power supply, and grid meets Vbh, and drain electrode connects the drain electrode of N1 pipes;
The source level of P2 pipes connects power supply, and grid meets Vbh, and drain electrode connects C0, the upper step of C1 and the "-" interface of BGR;
The source level of P3 pipes connects the drain electrode of P0, and grid connects 1 input of NAND2, and drain electrode connects the drain electrode of N0 pipes and the grid of N1 pipes;
The drain electrode of N0 pipes connects the drain electrode of P3 pipes and the grid of N1 pipes, the grid of N0 pipes connect the leakage of the grid and N3 pipes of N2 pipes
Pole, source level ground connection;
The drain electrode of N1 pipes connects the drain electrode of P1 pipes and 1 input of NAND1, and grid connects the drain electrode of P3 pipes and the drain electrode of N0 pipes, source
Pole connects the drain electrode of N2 pipes;
The drain electrode of N2 pipes connects the source level of N1 pipes, and grid connects the drain electrode of N3 pipes and the grid of N0 pipes, source level ground connection;
The grid for missing N0 pipes and N2 pipes of N3 pipes, grid connect the output of the grid and NAND1 of P3 pipes, and the 1 of NAND2 is defeated
Enter, source level ground connection;
The upper step of C0 connects the drain electrode of P2 pipes and the upper step of C1 and the "-" interface of BGR, bottom crown ground connection;
The upper step of C1 connects the drain electrode of P2 pipes and the upper step of C2 and the "-" interface of BGR, bottom crown ground connection;
1 input of NAND1 connects the drain electrode of P1 pipes and the drain electrode of N1 pipes, and 2 inputs connect the output of NAND2, and output connects NAND2's
1 input and the grid of P3, N3 pipe;
1 input of NAND2 connects the output of NAND1, and 2 inputs connect the output of BGR;Output connects 2 inputs of NAND1.
4th, switching tube current control
In order to reduce electromagnetic interference, while reduce switching loss, improve high conversion efficiency, subtract as far as possible in this utility model
The small cut-off current and load current of switching tube.Specific implementation is to use current sample mode, and passes through and to form feedback, is kept
Electric current is without departing from design specification.
As shown in fig. 7, Ismp and the current in proportion relation for flowing through switch controlled pipe P4.The module operation principle is:
When switch controlled pipe P 4 is opened, P2 and P3 sample output current, and sample rate current generates pressure on the channel resistance of P2
Drop.
When output current increases, the current potential decline of W3 causes the current potential of W2 to decline, since P5 with P6 grid potentials are identical, P6
Source potential(W2)Decline reduces P6 electric currents, and W4 current potentials is caused to decline, and W4 is connected to the grid of P7, increases P7 electric currents, makes
W1 current potentials decline, and P5 electric currents is caused to decline, and N0 is constant-current source, and the grid potential of P5 will be pulled low, i.e. the grid of P6 is pulled low,
P6 electric currents increase, and W4 rises make this feedback control loop reach stable state, so as to limit switch tube current.By to power on
Stream sample circuit causes switching current to be restricted.
Referring to Fig. 7, the source level of P0 pipes connects power supply, grounded-grid, and drain electrode connects the source level of P5 pipes and P7 pipes;
The source level of P1 pipes connects the drain electrode of P2 pipes and the source level of P3 pipes, grounded-grid, and drain electrode connects the source level of P6 pipes;
The source level of P2 pipes connects power supply, grounded-grid, and drain electrode connects the source level of P1 pipes and the source level of P3 pipes;
The source level of P3 pipes connects the drain electrode of P2 pipes and the source level of P1 pipes, grounded-grid, and drain electrode meets drain electrode and the DRI of P4 pipes;
The source level of P4 pipes connects power supply, grounded-grid, and drain electrode meets drain electrode and the DRI of P3 pipes;
The source level of P5 pipes connects the drain electrode of P0 pipes and the source level of P7 pipes, and grid connects the grid of P6 pipes, and drain electrode connects the drain of N0 pipes,
Grid and drain electrode short circuit;
The source level of P6 pipes connects the drain electrode of O1 pipes, and grid connects the grid of P5 pipes, and drain electrode connects the drain of N1 pipes and the grid of P7 pipes;
The source level of P7 pipes connects the drain electrode of P0 pipes and the source level of P5 pipes, and grid connects the drain electrode of P6 pipes and the drain of N1 pipes, drain electrode
Meet Ismp;
The drain of N0 pipes connects the drain electrode of P5 pipes, and grid connects Vb, source electrode ground connection;
The drain of N1 pipes connects the drain electrode of P6 pipes and the grid of P7 pipes, and grid connects Vb, source electrode ground connection.
The above are the preferred embodiments of the utility model, not make limitation in any form to the utility model,
It is every according to the technical essence of the utility model to any simple modification, equivalent change and modification made for any of the above embodiments,
Belong in the range of utility model technical solution.