CN110572019A

CN110572019A - wide-range, high-reliability and low-EMI flyback switching power supply

Info

Publication number: CN110572019A
Application number: CN201810597326.5A
Authority: CN
Inventors: 王清金; 仝建; 侯荣立
Original assignee: Qingdao Topscomm Communication Co Ltd
Current assignee: Qingdao Topscomm Communication Co Ltd
Priority date: 2018-06-06
Filing date: 2018-06-06
Publication date: 2019-12-13

Abstract

The invention belongs to the field of design of flyback switching power supplies of PWM control circuits, and the power supplies realize triple lightning surge protection of wide-range input of the power supplies by using enhanced piezoresistors, secondary voltage-sensitive clamping voltage reduction and high-voltage MOS voltage division circuits. And the flyback power supply outputs a signal, the signal is fed back and regulated by the optocoupler and is transmitted to the PWM control IN circuit, so that the PWM duty ratio is controlled to drive the MOSFET power tube, the output of the flyback transformer is controlled to complete closed-loop control, and meanwhile, the flyback transformer supplies power to the control IC. The power supply can improve electromagnetic interference (EMI) in a wide range of high and low frequency bands by utilizing the fusion of a capacitance pi-type filter (CLC) and a jitter frequency technology in operation, can disperse prominent harmonic components of switching frequency, effectively reduces the EMI and output ripple noise, and meets the requirement of stable and reliable operation of the flyback power supply in severe environment.

Description

Wide-range, high-reliability and low-EMI flyback switching power supply

Technical Field

The invention relates to a technology for effectively improving the input range and the surge protection capability and reducing EMI (electro-magnetic interference) in a switching power supply circuit, in particular to the technology for designing triple surge protection to realize lightning surge above 20KA, removing an electrolytic capacitor behind a bridge, applying cascade MOS (metal oxide semiconductor) and applying a jitter frequency technology, and is a novel power supply protection design method.

Background

The lightning surge is surge voltage and surge current formed by induction of an object by natural lightning or exceeding of normal working voltage and current peak value generated by switching transient state and fault of a power system. The power supply is used as a core component of the power supply and is directly connected with a power grid, and the power supply is subjected to external interference or lightning surge without time. The traditional power supply only adopts a voltage dependent resistor for absorption, and the surge residual voltage is enough to damage a rear-stage element and fail; the electrolytic capacitor is used behind the rectifier bridge, so that the service life is short, the high withstand voltage electrolysis cost is high, and the input voltage range of a power supply is limited.

The equipment products that operate in the electric wire netting are various, and the good or bad degree of electric wire netting quality directly influences the efficiency, the loss of consumer, leads to its life-span to reduce when serious, and electric protection component malfunction etc.. The drive of the flyback switching power supply is a PWM working mode with fixed frequency, and high-frequency harmonic waves of a power grid are inevitably introduced to generate electromagnetic interference (EMI) so as to reduce the quality of the power grid. The three elements of electromagnetic interference are the source of the interference, the propagation path and the sensitive equipment. The means for reducing EMI are to suppress interference sources, switch propagation paths, and improve the immunity of the device. The traditional flyback switching power supply has poor interference source suppression effect through an RCD buffer absorption circuit, and can also influence secondary output and product performance.

Disclosure of Invention

Compared with the traditional surge protection circuit, the design idea of the invention is that a triple lightning surge protection circuit is formed by a primary three-enhancement type pressure-sensitive absorption clamping thermal-sensitive current-limiting, secondary pressure-sensitive clamping residual voltage and a tertiary high-voltage MOS voltage division protection circuit by utilizing the characteristics of different pressure-sensitive clamping voltages and thermistor current-limiting, so that the energy is absorbed step by step, the instant overvoltage surge is reduced, the impact of high-strength lightning surge above 20KA can be sufficiently borne, and the surge resistance of a power supply is effectively improved.

According to the traditional switching power supply, high-voltage electrolysis energy storage filtering is used behind a rectifier bridge, the high-voltage electrolysis can be eliminated by the circuit designed by the invention, voltage reduction is realized through strong surge absorption capacity, and a safety capacitor is used behind the rectifier bridge, so that the problems of short electrolysis service life and high cost are solved, and the operation reliability of the power supply is enhanced.

The input range of the traditional switching power supply is 220Vac +/-20%, wherein the MOS withstand voltage is generally 1000V, the invention forms two MOS cascade circuits by a designed triple surge protection medium-high voltage MOS voltage division protection circuit, the input high voltage of the switching power supply is widened to 220Vac + 100%, and the input range of the power supply is greatly enlarged.

Compared with the traditional EMI suppression method, the input end of the flyback power supply adopts capacitance pi type low-frequency filtering, PWM works and adopts dithering technology high-frequency filtering, and the capacitance pi type low-frequency filtering and the PWM work are combined to suppress an interference source, so that not only is the EMI reduced within the bandwidth of 150 KHz-30 MHz, but also the fixed frequency of the PWM is dispersed within the range of +/-5% frequency offset, the reliable work of the power supply is ensured, the prominent harmonic component is dispersed, and the EMI is effectively reduced.

The winding sequence of the flyback switching transformer is from bottom to top in sequence: primary Np/2, insulating tape, shielding winding, insulating tape, secondary winding, insulating tape, shielding winding, insulating tape, primary Np/2, auxiliary winding and insulating tape. The shielding layer cuts off an interference propagation path, and then the ripple noise is reduced through the secondary output capacitor pi-type filter circuit, so that the power supply stability is improved.

Fig. 5 is a schematic diagram of a flyback switching power supply circuit controlled by 3842 general PWM, which is driven by a constant switching frequency of 60KHz and cannot effectively prevent surge impact and suppress EMI.

Drawings

FIG. 1 is a block diagram of the circuit configuration of the present invention;

Fig. 2 is a winding structure diagram of the flyback switching transformer of the present invention;

Fig. 3 is a schematic winding diagram of the flyback switching transformer of the present invention;

FIG. 4 is a schematic diagram of the triple protection against lightning surge according to the present invention, which is mainly composed of an enhanced voltage-sensitive absorption circuit, a secondary voltage-sensitive clamping circuit and a high-voltage MOS voltage-dividing protection circuit;

FIG. 5 is a circuit diagram of the PWM control IC switch conversion rectification output circuit of the present invention;

Fig. 6 is a high frequency filtering circuit diagram of the jitter frequency technique of the present invention.

Detailed Description

The invention will be further illustrated by the following examples in conjunction with the accompanying drawings:

As shown in the attached figure 1, the wide-range, high-reliability and low-EMI flyback switching power supply circuit comprises an enhanced pressure-sensitive, capacitance pi-type low-frequency filter circuit, an input rectifier circuit, a secondary clamping pressure-sensitive circuit, a high-voltage MOS voltage division protection circuit, a switch conversion and secondary rectifier circuit and a jitter frequency technology high-frequency filter circuit which are sequentially connected, wherein an N1 winding of a flyback switching transformer is connected with a 3 pin of a high-voltage MOS, an N2 winding is connected with the secondary rectifier circuit, a pi filter output VOUT of a secondary capacitor is connected with a feedback circuit, the feedback circuit is connected with a PWM control IC circuit, a drive MOSFET is connected with a transformer, the PWM duty ratio is adjusted according to a feedback signal, the output change of. The flyback transformer T1 is characterized in that a primary winding of a transformer T1 comprises an N1 winding, an N5 winding and an N6 winding which are the same in phase, a secondary winding comprises an N3 winding opposite to the primary winding, and shielding layer windings N2 and N4 which are opposite in phase are respectively wound between the N1 winding and the N3 winding and between the N3 winding and the N5 winding.

Referring to fig. 2 and 3, the winding sequence of the flyback switching transformer is from bottom to top in sequence: primary Np/2(N1), insulating tape, shielding winding N2, insulating tape, secondary winding N3, insulating tape, shielding winding N4, insulating tape, primary Np/2(N5), auxiliary winding N6 and insulating tape. With the sandwich winding, the N1 and N5 windings are 38 turns, the shield windings N2 and N4 are 20 turns in opposite phase, the secondary winding N3 is 11 turns in opposite phase to the primary, and the auxiliary winding is 12 turns. The insulating adhesive tapes 3 between the shielding layer windings N2 and N4 and the secondary winding N3 keep a distance from the magnetic core, and the insulating adhesive tapes 2 between the shielding layer windings N1 and N2 and between the shielding layer windings N5 and N4 and N6 increase the insulating strength of the primary winding, the primary winding and the magnetic core, effectively cut off an electromagnetic interference path through the shielding layer, reduce EMI, and improve the load carrying capacity of the secondary winding due to the close coupling of the primary winding and the secondary winding.

As shown in fig. 4, a lightning surge input by a power supply firstly passes through a first-stage surge absorption circuit composed of an enhanced pressure-sensitive RV1 pressure-sensitive and an RT1 heat-sensitive circuit to absorb the surge, and a capacitor pi-type filter common-mode inductor smoothes the surge current; after full-bridge rectification is performed by the diodes VD1, VD2, VD3 and VD4, a second-stage clamping circuit absorbs clamping residual voltage formed by C5 and a voltage-sensitive RV 2; when the surge residual voltage exceeds 700V, the voltage stabilizing tube VD3 conducts and clamps the voltage of 600V, and drives the high-voltage MOS tube VT1 to be turned off for voltage division protection.

the high-frequency filtering circuit of the jitter frequency technology consists of N2, R21, R22, R23, R24, R25, C20 and C21. The RC signal charges and discharges the C20 through R21, the signal is compared with the parallel voltage division of R23 and R24 and then output, the output voltage signal is overturned, the fixed frequency of the RC signal is further changed, a frequency jittering circuit is formed, the switching frequency is enabled to work within the range of 60KHz +/-5%, and the EMI is reduced.

In summary, the invention mainly adopts the following technologies and measures to solve the problems of low lightning surge protection capability, narrow power input range and poor electromagnetic interference elimination effect of the traditional flyback power supply.

1. According to the pressure-sensitive, thermosensitive and MOS working characteristics, a triple lightning surge protection circuit is designed to absorb surge and clamp residual voltage step by step and protect a rear-stage circuit to work normally, so that the rear electrolytic replacement of a rectifier bridge is replaced by a safety capacitor, the lightning surge problem of a power grid is solved, the cost is reduced, and the service life of a power supply is prolonged.

2. by adopting the design of a cascade circuit with 2 MOS, the problem of insufficient extreme withstand voltage of the common MOS is solved, and the input voltage range of the power supply is greatly widened.

3. According to an EMI reduction means, a low-frequency capacitor pi-type filtering absorption and high-frequency jitter technology filtering method is designed, an interference source is restrained, a transmission path is switched by a flyback transformer shielding layer, and EMI is reduced.

The above description is only an embodiment of the present invention, and not intended to limit the scope of the present invention, and all modifications of equivalent structures and equivalent processes performed by the present specification and drawings, or directly or indirectly applied to other related technical fields, are included in the scope of the present invention.

Claims

1. a wide-range, high-reliability and low-EMI flyback switching power supply comprises an enhanced voltage-sensitive and capacitance pi-type low-frequency filter circuit, an input rectification circuit, a secondary clamping voltage-sensitive circuit, a high-voltage MOS voltage division protection circuit, a switching conversion and secondary rectification circuit and a jitter frequency technology high-frequency filter circuit which are sequentially connected, and a triple surge protection circuit is formed, an EMI circuit is reduced, and the switching conversion circuit is guaranteed to operate reliably. The flyback transformer T1 is characterized in that a primary winding of a transformer T1 comprises an N1 winding, an N5 winding and an N6 winding which are the same in phase, a secondary winding comprises an N3 winding opposite to the primary winding, and shielding layer windings N2 and N4 which are opposite in phase are respectively wound between the N1 winding and the N3 winding and between the N3 winding and the N5 winding.

2. The wide-range, high-reliability, low-EMI flyback switching power supply of claim 1, wherein the flyback switching transformer is wound in a sequence from bottom to top as follows: primary Np/2, insulating tape, shielding winding, insulating tape, secondary winding, insulating tape, shielding winding, insulating tape, primary Np/2, auxiliary winding and insulating tape.

3. The wide range, high reliability, low EMI flyback switching power supply of claim 1, wherein the enhanced voltage-sensitive circuit comprises a first stage surge absorption circuit that is voltage-sensitive with RV1 and temperature-sensitive with RT 1.

4. The wide range, high reliability, low EMI flyback switching power supply of claim 1, wherein the pi-type low frequency filter circuit comprises a C3 ballast capacitor, an LX1 common mode inductor, and a C4 ballast capacitor.

5. The wide range, high reliability, low EMI flyback switching power supply of claim 1, wherein the input rectification circuit is a full bridge rectification circuit consisting of high withstand voltage 2KV diodes VD1, VD2, VD3, VD 4.

6. The wide range, high reliability, low EMI flyback switching power supply of claim 1, wherein the secondary clamp circuit is surge absorbing and clamped by a C5 ballast capacitor and a voltage-dependent RV 2.

7. The wide-range high-reliability low-EMI flyback switching power supply as claimed in claim 1, wherein the high-voltage MOS voltage-dividing protection circuit is formed by connecting R1, R2 and a voltage-regulator tube VD3 in series, connecting C1 in parallel with R1, connecting C2 in parallel with R2, connecting R3 with R4, connecting VT1 between R3 and R4 with 1 pin of high-voltage MOS, connecting voltage-regulator tube VD7 in parallel between 1 pin and 3 pins of VT1, connecting capacitors C6 with C1, C2 and 3 pins of VT1 respectively, and connecting C7 capacitor with 3 pins of VT1 and PGND. The 2-pin of VT1 is connected to rectified VDAC.

8. The wide range, high reliability, low EMI flyback switching power supply of claim 7, wherein VD3 is a high voltage regulator and VT1 is a high voltage MOS.

9. The wide range, high reliability, low EMI flyback switching power supply of claim 1, wherein the switching converter circuit employs a PWM control IC to drive the flyback transformer to operate at a constant frequency, with a secondary rectifier capacitor with pi-type filtering output.

10. The wide range, high reliability, low EMI flyback switching power supply of claim 1, wherein the dither technique high frequency filter circuit is comprised of N2, R21, R22, R23, R24, R25, C20, and C21. The RC signal charges and discharges the C20 through the R21, the signal is compared with the R23 and the R24 in parallel to divide voltage and then output, the output voltage signal is inverted, the fixed frequency of the RC signal is changed, and a frequency jittering circuit is formed.

11. The wide range, high reliability, low EMI flyback switching power supply of claim 10, wherein the chip N2 is an operational amplifier.