Series-resonant direct-current/direct-current converter
Technical field
The present invention relates to the DC power supply converter technique, relate in particular to a kind of based on 3525 series-resonant direct-current/direct-current converter control circuit.
The LLC series-resonant direct-current/direct-current converter is to cause that industry is paid attention to and the circuit of research recent years again, and its maximum characteristics are to have adopted the resonant transformation technology.The benefit that this technology is brought mainly contains: (1) because resonant element is operated in the sinusoidal resonance state, and the voltage natural zero-crossing on the switching tube can both realize that in variable-frequency scope the ZVS of metal-oxide-semiconductor opens and turn-offs, the loss of power is very little; (2) because loss is very little, and the ratio that operating frequency can be done is higher, can effectively alleviate the volume and the cost of converter, improve power density; (3) the secondary diode turn-offs naturally, has eliminated the due to voltage spikes of secondary, has reduced turn-off power loss; (4) primary current is approximately sinusoidal wave, and conduction and radiation are smaller, EMC and EMI excellent performance.
But also there is a difficult point problem in series-resonant direct-current/direct-current converter, and output voltage is difficult to stablize under underloading and idle condition exactly.Because for the LLC series resonant converter, following relation is arranged between its output voltage gain M and the switching tube operating frequency f:
Wherein, Uin is the converter input direct voltage; Uo is the converter output dc voltage; Lr is the resonant inductance value; Cr is the resonant capacitance value, and Lp is a main transformer magnetizing inductance value, and N is the former secondary turn ratio of main transformer; F is the converter operating frequency,
Po be the converter power output.
Following formula is the result show, the relation of being inversely proportional between series resonant converter output voltage gain M and the switching tube operating frequency f: operating frequency is high more, and M is more little, and output voltage is low more; Operating frequency is low more, and M is big more, and output voltage is high more.Therefore, when unloaded and underloading, for regulated output voltage, it is very high that operating frequency need rise.So at least, brought two problems: (1) operating frequency is too high, causes magnetic device to be difficult to optimize, and may influence the stability of circuit; (2) operating frequency raises, the also corresponding quick rising of circuit loss, and efficient reduces.Adding dead load at output can to a certain degree solve the underloading problem, but can increase no-load loss, reduces the converter operating efficiency.
Document one " control method of series-resonant direct-current/direct-current converter and device " (one Chinese patent application number 03140448.0) has disclosed a kind of control method and device of series-resonant direct-current/direct-current converter.This device comprises drive circuit, series resonant circuit, pi regulator, discriminator, pulse-width modulation circuit and frequency conversion control circuit.The subject matter that this method exists is: (1) FREQUENCY CONTROL and regulating circuit are by realizations such as integrated circuit CD4046, circuit more complicated; (2) during unloaded and underloading, the converter operating frequency is than higher, and circuit loss is bigger.
Summary of the invention
The object of the present invention is to provide a kind of series-resonant direct-current/direct-current converter, with solve existing series-resonant direct-current/direct-current converter output unloaded with the underloading condition under the magnetic device that exists be difficult to optimize, circuit loss is excessive and export the problem that voltage regulation performance can not meet the demands.
In order to realize above-mentioned functions, the present invention provides following technical scheme:
A kind of based on 3525 series-resonant direct-current/direct-current converter; Comprise load, control circuit, drive circuit and series resonant circuit based on 3525; After isolating amplification, the driving pulse that said drive circuit sends control circuit gives series resonant circuit; Series resonant circuit offers load with the direct current energy after the conversion under the effect of drive signal, it is characterized in that, said control circuit comprises:
Sample circuit: from feedback signals such as load circuit sampling and outputting voltage and load currents;
Voltage pi regulator and comparator: the output pulse frequency that the output of voltage pi regulator is delivered to 3525 chips through resistance is provided with circuit; Comparator is compared the output of voltage pi regulator with reference value, comparative result is delivered to the error amplifier in-phase input end of 3525 chips;
Current PI adjuster and comparator: the output pulse frequency that the output of current PI adjuster is delivered to 3525 chips through diode is provided with circuit; Comparator is compared above-mentioned adjuster output with reference value, comparative result is delivered to 3525 chip error amplifier in-phase input ends;
The output voltage comparator: output voltage sampled value and reference value are compared, and comparative result is delivered to the error amplifier in-phase input end of 3525 chips;
Pulse frequency and pulse width modulation chip 3525: regulate output pulse frequency and duty ratio according to the output of voltage pi regulator, current PI adjuster and the output of three comparators, the output pulse is amplified the rear drive switching tube through isolating.
A kind of electric current and voltage control method based on 3525 series-resonant direct-current/direct-current converter; Converter output voltage and load current are sampled; And sampled signal carried out PI computing and comparison; By control and drive circuit series resonant converter is controlled again, is made the converter output voltage keep stable (voltage stabilizing state) or load current to keep stable (limited current state), it is characterized in that may further comprise the steps:
1) from load circuit unscented transformation device output voltage and load current signal;
2) above-mentioned output voltage signal and voltage given value are carried out the proportional integral computing, regulate output pulse frequency according to the result of proportional integral computing; Simultaneously operation result is delivered to voltage comparator and reference voltage signal comparison, output judges whether converter is operated in unloaded or light condition according to comparator;
3) above-mentioned load current signal and current limliting set-point are carried out the proportional integral computing, judge whether to be in limited current state, and regulate output pulse frequency according to the result of proportional integral computing; Simultaneously operation result is delivered to voltage comparator and reference current signal comparison, output judges that it still is the severe limited current state that converter is operated in slight limited current state according to comparator;
4) if converter is operated in unloaded or light condition; 3525 chip output frequencies change, the duty ratio intermittence be zero (all the other constantly duty ratios be maximum 50%; Be the distinctive intermittent work mode of this patent) drive signal as the driving pulse of said drive circuit; Thereby guarantee converter voltage stabilizing work, reduce the power MOS pipe switching loss; When being operated in heavy condition, the control circuit output frequency changes, duty ratio constant be 50% pulse signal as driving pulse, converter is operated in the VFC state;
5) after load current surpassed the current limliting set-point, the control circuit of converter automatically switched to the current limliting operating state.
Aforesaid electric current and voltage control method based on 3525 series-resonant direct-current/direct-current converter is characterized in that: in said step 2) and 3) in, said reference voltage signal and reference current signal are confirmed according to the electrical characteristic of said load.
Aforesaid electric current and voltage control method based on 3525 series-resonant direct-current/direct-current converter is characterized in that: in said step 5),
During slight current limliting, the control circuit output frequency changes, duty ratio constant be 50% pulse signal as driving pulse, converter is operated in the VFC state, it is constant that output current keeps;
During the severe current limliting, the control circuit output frequency changes, duty ratio intermittence be zero drive signal of (all the other duty ratios be maximum 50%) constantly is as driving pulse, thereby guarantees that the converter output current keeps constant.
The present invention has the following advantages:
1, utilizes distinctive intermittent work mode, make converter voltage stabilizing work when unloaded and underloading.When having solved existing series resonance DC/DC converter and only adopting the pulse frequency modulated mode, the magnetic device that when unloaded and underloading, exists is difficult to optimize the problem excessive with circuit loss, and converter loss when unloaded stand-by operation is extremely low;
2, the pulse frequency modulated and the pulse width modulation that utilize 3525 common pulse width modulation chips and small number of peripheral circuit to realize converter; And converter operating frequency maximum and minimum value can be provided with respectively, conveniently carry out magnetic device design and optimization;
3, voltage stabilizing and limited current state automatically switch according to the load current size.Load current is operated in the voltage stabilizing state during less than the current limliting set-point; Load current surpasses cut-off current to be given regularly, is automatically brought to limited current state, and cut-off current can be set arbitrarily.This function may be used in the battery charging plant;
4, converter has the short circuit current limitation defencive function, and cut-off current can pass through relative parameters setting;
5, control circuit of the present invention is simply effective, and the distortion topology of series resonances such as full-bridge LC, half-bridge LC and LLC all is suitable for, and stronger engineering significance is arranged.
Description of drawings
Fig. 1 is series resonant circuit schematic diagram (is example with the half-bridge);
Fig. 2 is the theory diagram of DC to DC converter of the present invention;
Fig. 3 is the theory diagram of converter control circuit of the present invention;
Fig. 4 is the circuit theory diagrams of converter control circuit of the present invention;
Fig. 5 is converter of the present invention output pulse frequency and duty cycle adjustment process sketch map from start to steady operation (voltage stabilizing) process;
Fig. 6 is converter of the present invention duty cycle adjustment sketch map from start to steady operation (voltage stabilizing, current limliting) process;
Fig. 7 is provided with schematic diagram for the low-limit frequency of converter control circuit 3525 output pulses of the present invention;
Fig. 8 is provided with schematic diagram for the highest frequency of converter control circuit 3525 output pulses of the present invention;
Fig. 9 is the drive waveforms sketch map during for converter 50% duty ratio of the present invention.
Embodiment
The method that the present invention adopts pulse frequency modulated (PFM) and two kinds of modulation systems of pulse width modulation (PWM) to combine is controlled series resonant circuit, the problem that frequency rises too high and circuit loss is excessive in the time of can solving the existing underloading of simple employing pulse frequency modulated mode with zero load.Key of the present invention is; Sample circuit carries out after PI regulates and handle output voltage and load current signal; Delivering to IC chip 3525 output pulse frequencies is provided with pin on the one hand; Deliver to 3525 operational amplifier in-phase input ends through comparator after relatively on the other hand, thereby produce the driving pulse of frequency and EDM Generator of Adjustable Duty Ratio, make converter be operated in voltage stabilizing or limited current state.Among the present invention 3525 comprises SG3525 or UC3525, is commonly referred to as 3525.
Fig. 2 is the theory diagram of DC to DC converter of the present invention.This converter mainly comprises series resonant circuit, drive circuit, output voltage and load current sample circuit, output voltage and load current PI adjusting and comparison circuit, 3525 output pulse frequencies and control circuit of duty ratio etc.
Fig. 3 is the theory diagram of control circuit of the present invention.Directly delivering to 3525 output pulse frequencies through resistance and diode is provided with circuit on the one hand in the output of voltage pi regulator 1 and current PI adjuster 2, delivers to 3525 error amplifier in-phase input ends again after handling through three voltage comparators on the other hand.The above-mentioned signal that 3525 bases receive produces the driving pulse of frequency and duty ratio real-time regulated and delivers to drive circuit, and converter is exported stable voltage (voltage stabilizing state) or constant electric current (limited current state) under the effect of drive circuit.
Fig. 4 is the typical implementation of Fig. 3.Wherein, pi regulator amplifier U1 and U2 can realize that comparator U3~U5 can realize that output pulse frequency and pulse width regulating circuit are realized through integrated circuit 3525 through LM393 through operational amplifier LF353.VCC and VEE are the positive and negative operating voltages of operational amplifier, generally desirable ± 12V~± 15V, VDD is generally desirable+5V.Reference voltage Ur1~Ur3 is and is not less than zero a certain numerical value, and its big I is confirmed according to the electrical characteristic of load.Below the main scheme of Fig. 4 that combines describe.
Consult shown in Figure 4; 3525 principles: in case certain reason (increasing such as load) causes the converter output voltage to reduce through pulse frequency modulated (PFM) realization output voltage stabilizing; Then the output voltage V pid1 of voltage pi regulator 1 can raise; Flowing into the electric current that 3525 output pulse frequencies are provided with pin resistance R 16 and R17 through resistance R 8 and R20 can increase, the corresponding reduction of 3525 output pulse frequencies, the converter output voltage since the operating frequency reduction raise.Like this, just realized the voltage stabilizing work of converter.Current stabilization adjustment process during current limliting work also can be done similar analysis.
Fig. 5 provided based on the series resonant converter of controlling schemes of the present invention startup, zero load and underloading voltage stabilizing regulate and heavily loaded voltage stabilizing adjustment process in the change procedure of 3525 output pulse duty factor D and operating frequency f.In the voltage stabilizing adjustment process, 3525 output pulse frequencies and duty ratio change with load variations, and it is stable that output voltage keeps.Because load current is less than the current limliting set-point, current PI adjuster 2 is in positive saturation condition, is output as high level (being approximately VCC), and diode D1 is in cut-off state owing to bearing back-pressure.
This process can be divided into the following time period:
It is zero that the output voltage initial value is established in [0, T1], and converter begins to start (unloaded or underloading) during t=0, and output voltage rises gradually.Because less than the current limliting set-point, the voltage and current pi regulator is just saturated, is output as high level (being approximately VCC) less than voltage given value and load current for output voltage, corresponding output pulse frequency is minimum value f
MinOutput voltage sampled value Uof is less than output short circuit protection level Ur2 (corresponding output voltage is Uo1) in this time period; Comparator U4 output low level; Comparator U3 and U5 output high level; Vpid4 ≈ VDD*R6/ (R6+R15), the output pulse duty factor that this voltage is corresponding is D0, output voltage rises gradually.Here R6 can not be zero, otherwise can make and cause converter to start by D0=0;
[T1, T2] T1 converter output voltage sampled value Uof constantly rises greater than output short circuit protection level Ur2 and continuation, and comparator U3, U4 and U5 all export high level.Because resistance R 15 is smaller, Vpid4 ≈ VDD is arranged, and the VDD level is higher than 3525 inner triangular carrier maximum levels, therefore 3525 export pulse V
OUTADuty ratio is maximum D=0.5.Because the voltage and current pi regulator still all is in the forward saturation condition, output pulse frequency still is minimum value f
Min, output voltage quickens to rise;
Along with the converter output voltage meets and exceeds (overshoot) rated output voltage, the voltage pi regulator withdraws from saturation condition and output voltage V pid1 reduces gradually [T2, T10], and output pulse frequency f raises gradually.T2 voltage pi regulator output constantly Vpid1<Ur1, comparator U3 output low level, 3525 output pulse V
OUTADuty ratio D=0, the output pulse disappears, and output voltage reduces gradually.Because the effect of voltage pi regulator, T2 is after the moment, and Vpid1 rises again after can continuing to be reduced to certain value gradually, and T3 is Vpid1>Ur1 constantly, and comparator U3~U5 exports high level, output pulse V
OUTADuty ratio D=0.5,3525 export pulse again, and the converter output voltage rises rapidly; Vpid1 descends again after can continuing to rise to certain value gradually; Up to T4 (analyzing same T2) constantly Vpid1<Ur1 make D=0,3525 output pulses disappear, the converter output voltage begins again to descend.The converter voltage stabilizing adjustment process in the moment such as T2~T10 can be made similar analysis, and corresponding during this period of time is the voltage stabilizing adjustment process of unloaded or underloading;
[T10 ...] establish T10 constantly, the converter load becomes heavy duty but load current is no more than the current limliting set-point.Vpid1>Ur1 is arranged in this process always, and comparator U3~U5 exports high level, and the output pulse duty factor is D=0.5 always, and converter is in pulse frequency modulated and voltage stabilizing state always.
Fig. 6 has provided the change procedure based on the series resonant converter of controlling schemes of the present invention 3525 output pulse duty factor D and operating frequency f in startup, idle voltage stabilizing work, slight current limliting and the severe current limliting course of work.Wherein, 0~T4 is the voltage stabilizing course of work, here no longer explanation., to establish T4 shock load constantly and make load current surpass the current limliting set-point, converter is in the current limliting operating state, and job analysis is following:
Because load current surpasses the current limliting set-point, the Vpid2 level reduces [T4, T5], and diode D1 causes the converter output pulse frequency to raise by by transferring conducting state to automatically, and output voltage reduces, and voltage pi regulator 1 is in positive saturation condition.Because Vpid2>Ur3, comparator U3~U5 exports high level, and the output pulse duty factor is D=0.5 always, and converter is in pulse frequency modulated and current stabilization state, metal-oxide-semiconductor ZVT always;
[T5 ...] establish T5 constantly, load continues to increase (load resistance reduces); Vpid2 level intermittence is lower than Ur3, and converter is in the intermittent work state, and the duty ratio intermittence is zero; Converter still is operated in the current stabilization state, and detailed process and preceding text are similar, here no longer narration.
During the converter output short-circuit; Output voltage sampled value Uof is less than output short circuit protection level Ur2, comparator U4 output low level, comparator U3 and U5 output high level; Exporting pulse duty factor this moment is smaller certain value (can change through the resistance of regulating resistance R 6); Converter still is in the current limliting operating state, and it is constant that output current keeps, and realizes short-circuit protection function.
Fig. 7 has provided the lowest operating frequency method to set up.When lowest operating frequency mainly appeared in the start-up course or heavily loaded voltage stabilizing is worked, 1 output of voltage pi regulator and 2 outputs of current PI adjuster were positive saturation condition.Analysis can know that the main components and parts and the parameter of decision highest frequency have R8, R20, R16, R17, C10 and VCC level, change the value that above-mentioned component parameter and level can change low-limit frequency.
Fig. 8 has provided the maximum operating frequency method to set up.Maximum operating frequency mainly occurs in current limliting adjusting and the short circuit adjustment process, and voltage pi regulator 1 is output as positive saturation condition, and current PI adjuster 2 is output as negative saturation condition.Analysis can know that the main components and parts and the parameter of decision low-limit frequency have R20, R16, R17, C10, D1 saturation voltage drop and VEE level, change the value that above-mentioned component parameter and level can change highest frequency.
Below disclose the present invention with preferred embodiment, so it is not in order to restriction the present invention, and all employings are equal to replacement or the technical scheme that obtained of equivalent transformation mode, all drop within protection scope of the present invention.