A kind of magnetic flux offsets formula high-efficiency flyback dc-dc
Technical field
The present invention relates to a kind of dc-dc, particularly relate to a kind of a kind of magnetic flux utilizing the element such as inductance and electric capacity to complete voltage conversion function as energy-storage travelling wave tube and offset formula high-efficiency flyback dc-dc.
Background technology
Dc-dc minimum system by only having a switch, a transformer, a diode and two electric capacity (one input port and second at output port) composition.The transducer of low output voltage, the conduction loss of rectifier diode forward voltage drop becomes to take loss as the leading factor, is thisly lost in the total-power loss that can reach 50% in some cases; The technology of existing inverse-excitation type dc-dc is: replace synchronous rectification diode with the MOSFET with low conducting resistance, and can control by anti-phase primary control signal the normal running being used as synchronous rectification MOSFET flyback converter; Fig. 1 is the general principle figure of known inverse-excitation type dc-dc, an input voltage source provides transformer and a main switch S1 of two armature windings be connected in series 1, the control signal Vc(S1 of main switch S1) there is a variable duty ratio cycle, to guarantee that stable output voltage is constant frequency control signal, concerning output circuit, an alternating polarity voltage is provided by main transformer 2 secondary winding 3, in the shutoff cycle of the switch of main switch S1, synchronous rectifier S2 coupling output circuit comprises a load R0 and filtering capacitor C0; Synchronous rectifier S2 receives the control signal Vc(S2 by an inverter 4).Its shortcoming is: under this inverse-excitation type dc-dc is operated in CCM, DCM or critical conduction mode, all unavoidably there is the loss that in power loss in main switch S1 and synchronous rectifier S2 cross-conduction process or synchronous rectifier S2, diode reverse recovery causes.
The patent of invention zero-voltage switch flyback conversion equipment of Zhejiang University's application, comprise a circuit of reversed excitation, circuit of reversed excitation is provided with a clamp circuit, clamp circuit comprises an auxiliary switch, an electric capacity and a booster diode, auxiliary switch auxiliary switch in parallel with booster diode and capacitances in series form auxiliary branch, auxiliary branch is connected in parallel on the transformer primary side winding two ends of circuit of reversed excitation or is connected in parallel on former limit switch ends, former limit switch and auxiliary switch are not complementary duty, auxiliary switch is conducting a period of time before the switch conduction of former limit only, when former limit switch conduction, the voltage that former limit switch bears is close to zero.This invention has certain limitation, mainly reduces the loss of power of main switch, can not realize reducing MOSFET diode closed, disconnect time loss, therefore its inverse-excitation type dc-dc is only under the condition of unloaded or underloading, could realize high efficiency output.
Summary of the invention
The object of the invention is for above-mentioned deficiency, and a kind of of proposition can eliminate the loss caused by cross-conduction and Reverse recovery, improve the high-efficiency flyback dc-dc of dc-dc efficiency.
Technical solution of the present invention is: inverse-excitation type dc-dc comprises main transformer, be connected to the main switch S1 be connected in series in main transformer armature winding loop and input voltage source, be connected to the synchronous rectifier S2 in main transformer secondary winding loop and output loading R0 and the electric capacity C0 for output circuit filtering, it is characterized in that: be provided with an auxiliary secondary winding in the secondary side of main transformer, between an input and an output of auxiliary secondary winding of synchronous rectifier S2, be connected with a drive circuit.
Drive circuit described in technical solution of the present invention comprises a control transformer, the control secondary winding of this control transformer is connected with the output of main transformer auxiliary secondary winding by a totem pole configuration circuit, control the input of another termination synchronous rectifier S2 of secondary winding, the control armature winding of control transformer is connected with a RC differential circuit.
Totem pole configuration circuit described in technical solution of the present invention is connected in series by two triodes and forms.
Control armature winding described in technical solution of the present invention and control secondary winding are wrapped on the outer magnetic flux path of E+I type core assembly of control transformer respectively, and the main winding of control transformer is wrapped in control transformer center leg.
The present invention adopts a control transformer to separate from main transformer, on control transformer again access control armature winding and control secondary winding; In this way, as long as control armature winding and control secondary winding, under driving magnetic field is not strong situation too, the primary magnetic field that driving magnetic field can not disturb main transformer to produce, result be control secondary winding electric current only and control the current related of armature winding; The present invention can not only realize eliminating or the basic loss eliminated cross-conduction and cause, and drive circuit of the present invention is simple, and cost is low.
Accompanying drawing explanation
Fig. 1 is the electrical schematic diagram of prior art.
Fig. 2 is electrical schematic diagram of the present invention.
Embodiment
As shown in Figure 2, the armature winding 1 of main transformer 2 is connected with input power Vin by main switch S1, the output of main transformer 2 secondary winding 3 is coupled with a load R0 and filtering capacitor C 0 parallel circuits by synchronous rectifier S2, be provided with an auxiliary secondary winding 14 in the secondary side of main transformer 2, between an input and an output of auxiliary secondary winding 14 of synchronous rectifier S2, be connected with a drive circuit, this drive circuit is the control transformer separated from main transformer 2, and this control transformer can be that a discrete transformer or a flat surface transformer embed on a printed circuit, the control secondary winding 16 of this control transformer is connected with the output of main transformer 2 auxiliary secondary winding 14 by a totem pole configuration circuit, totem pole configuration circuit is by two triodes 11 be connected in series, 12 are formed, triode 11 is NPN transistor, triode 12 is PNP transistor, by totem pole configuration circuit for synchronous rectifier S2 provides control signal, two triodes 11, the base stage of 12 connects one end that control transformer controls secondary winding 16, control transformer controls the input of another termination synchronous rectifier S2 of secondary winding 16, the DC offset voltage of this totem pole configuration circuit is provided by the auxiliary winding 14 that main transformer 2 secondary side increases, this auxiliary winding 14 is connected with the collector electrode of triode 11 by rectifier diode 13, the grounded collector of triode 12.By this type of drive, the opening and closing being carried out control synchronization rectifier S2 by main switch S1 control signal can be ensured, thus eliminate or substantially eliminate the loss caused by main switch S1 and synchronous rectifier S2 cross-conduction, improve dc-dc efficiency; The signal source 17 of main switch S1 control signal in main transformer 2 primary return, is connected on the armature winding 15 of control transformer by a RC differential circuit.
The control armature winding 15 of the control transformer in the present invention is wrapped in the outer magnetic flux path 5 of E+I shaped iron core, on 7, the main winding 8 of control transformer is wrapped in the center leg 6 of control transformer, the control secondary winding 16 of control transformer is wrapped in E+I type core assembly 9 equally, the outer magnetic flux path 5 of 10, on 7.Control secondary winding 16 and be wound onto outer magnetic flux path 5,7, make magnetic flux be delivered to outside magnetic flux path from central leg 6, thus basic no current on control secondary winding 16 is flow through; In Fig. 2, control armature winding 15 to be wound around in an identical manner, make magnetic flux path 5 outside, the magnetic flux that 7 magnetic fluxs produced and center leg 6 produce is cancelled out each other, in this way, as long as the driving magnetic field controlling armature winding 15 and control secondary winding 16 is not too strong, the primary magnetic field that driving magnetic field can not disturb control transformer to produce, result be control secondary winding 16 electric current only and control armature winding 15 current related; Control secondary winding 16 and produce the input of output signal as a totem pole configuration circuit, and provide control signal to synchronous rectifier S2.