Design and Implementation of high frequency transformer for SMPS Based flyback DC-DC converter

Transcription

1 Design and Imlementation of high frequency transformer for SMPS Based flyback DC-DC converter * Hameed Miyan; # C.M.Tavade; * L.M.Deshande; ## Prashanth R.S. *Research Scholar Deartment of Electrical science, VTU Belgaum (K.S.), India #Professor and Head,deartment of E & CE, BKIT,Bhalki-58538, India ##Deartment of E & CE BKIT, Bhalki-58538, India hameedmiyan@gmail.com Abstract - In switch mode ower sulies (SMPS), flyback converters are very oular because of, design simlicity, low cost, multile isolated oututs, high outut voltages and high efficiency. They are referred esecially for low ower alications. In this aer we have resented the design of transformer for variable DC inut (18V to 60V) to 1V DC outut. And observed the wave form across the switch, rimary & secondary of the transformer. Keywords: SMPS isolated DC-DC converters, flyback converters, transformer design. I INTRODUCTION According to efficiency and ower density, SMPSs are more oular than linear ower sulies [1]. Most of the advanced communications and comuter systems require SMPSs which have high ower density, high efficiency and constant oeration frequency []. At the last decade, a lot of converter toology has been roosed for switch mode ower sulies. Among the currently existing transformer couled switching mode DC-DC converter, Flyback converters are the simlest isolated DC-DC converter toology because of absence of inductor at the outut filter, only one semiconductor switch and only one magnetic comonent (transformer or couled inductor). Besides, obtaining u to 5000V outut voltage and having multile oututs are the sueriorities [5-6]. Because of these advantages, flyback converters become the most referred DC-DC converter toology for switch mode ower sulies [3]. Flyback converters are oular for its, simle in design for low ower alications, Low cost because of less comonent requirement, Blocking voltage not occurred on the outut diode, thus diode cost reduced, There is no additional inductor at the outut circuit This simlifies the usage of multile oututs, Transient resonse is fast because of outut inductor absence. Flyback converters are referred mostly for low ower alications for low outut ower alications where the outut voltage needs to be isolated from the inut main suly. The outut ower of flyback tye SMPS circuits may vary from few watts to less than 100 watts. The overall circuit toology of this converter is considerably simler than other SMPS circuits [8]. Inut to the circuit is generally unregulated dc voltage obtained by rectifying the utility ac voltage followed by a simle caacitor filter. The circuit can offer single or multile isolated outut voltages & can oerate over wide range of inut voltage variation. In resect of energyefficiency, flyback ower sulies are inferior to many other SMPS circuits but it s simle toology & low cost makes it oular in low outut ower range [5]. Flyback converters are widely used in Low ower SMPS alications: Cell hone charge unit, comuter ower sources (< 50W), To roduce high voltage source for CRTs, To roduce high voltage for Xenon flash lams, lasers, hotocoies, Isolated driver circuits. The commonly used flyback converter requires a single controllable switch like MOSFET & the usual switching frequency is in the range of 100 KHz. A two-switch exists that offer better energy efficiency & less voltage stress across the switches but cost more & the circuit comlexity also increases slightly [9,10].. In this aer, we resent, Basic flyback converter oeration in art-ii, Proosed flyback converter oeration, Ste By Ste Design Procedure. Result & Discussion, in art-iii, IV & V resectively. II. FLYBACK CONVERTER Converters can be classified as isolated and non-isolated. Flyback converter is one of the simle toology in isolated converters. Fig.1.1 shows the tyical toology of flyback converters. ISSN : Vol 4 No 6 Dec 01-Jan

2 Figure 1.1: Basic flyback Toology. Dot-ends of the inductors determine the oeration of converter. Polarity of rimary winding (L) and secondary(ls) are not same. Oeration of the converter is very simle; when the switch is turned-on, energy absorbed into the rimary winding, then stored energy transferred to the secondary winding after switch turnedoff [4,10]. This means there is no transformator action and L-Ls are only couled- inductors. When switch Q is turned on, Vdc alied to rimary winding. Because of constant Vdc, rimary current I rise to eak value linearly [6]. At this interval, secondary winding is oositely olarized to the rimary inductor and consequently diode, D. Load current is sulied by caacitor, C. When switch Q is turned-off, stored energy at the air ga and magnetic core are transferred to secondary winding and load is fed by inductor Ls. Is discharge linearly over resistive load. Stored energy at the air ga can be obtained from rimary inductance and rimary current by (1). Figure 1.. Shows the waveforms of flyback converter toology. (1). Figure : Waveforms of flyback converter toology. III PROPOSED FLYBACK CONVERTER OPERATION: The roosed circuit diagram of SMPS based flyback DC to DC converter is shown in figure3. This circuit takes the advantage to reduce cost & ower suly size & to imrove efficiency. The design delivers 30W at 1V. A nominal efficiency of 80% at full load is achieved using this toology. ISSN : Vol 4 No 6 Dec 01-Jan

3 Figure 3: Proosed flyback converter circuit. The current limit is externally set by resistors R1 and R to a value just above the low line oerating eak DRAIN current of aroximately 70% of the default current limit. This allows use of a smaller transformer core size and/or higher transformer rimary inductance for a given outut ower, reducing MOSFET switch ower dissiation, while at the same time avoiding transformer core saturation during startu and outut transient conditions. The resistors R1 & R rovide a signal that reduces the current limit with increasing line voltage, which in turn limits the maximum overload ower at high inut line voltage. This function in combination with the built-in soft-start feature of MOSFET IC, allows the use of a low cost RCD clam (R3, C3 and D1) with a higher reflected voltage, by safely limiting the MOSFET drain voltage, with adequate margin under worst case conditions. Resistor R4 rovides line sensing, setting UV at 100 VDC and OV at 450 VDC. The extended maximum duty cycle and the higher reflected voltage ossible with the RCD clam also ermit the use of a higher rimary to secondary turns ratio for T1 which reduces the eak reverse voltage exerienced by the secondary rectifier D8. As a result a 60 V Schottky rectifier can be used for u to 15 V oututs, which greatly imroves ower suly efficiency. Outut regulation is achieved by using a simle Zener sense circuit for low cost. The outut voltage is determined by the Zener diode (VR) voltage and the voltage dros across the otocouler (U) LED and resistor R6. Resistor R8 rovides bias current to Zener VR for tyical regulation of +/- 5% at the 1 V outut level, over line and load and comonent variations. IV STEP BY STEP DESIGN PROCEDURE The detailed system configuration of a flyback converter with otically isolated feedback loo is drawn in figure3. The circuit structure, analysis and design of transformer for the converter are described below. Ste 4.1. Determine system requirements: V ACMAX 65V AC V ACMIN 85V AC f L 50Hz f S 13 KHz V O 1V DC P O 1W 80%0.8 Loss allocation factor Z0.5. Ste 4.. Determine maximum duty cycle at low line D MAX using V OR and V MIN : Once the V OR and V MIN are known, it is easy to calculate the D MAX : D MAX V OR + V OR ( V V ) Ste 4.3. Determine rimary waveform arameters I AVG, I P, I R and I RMS : The average DC current I AVG at low line is simly the inut ower divided by V MIN, where the inut ower is equal to the outut ower divided by the efficiency. MIN DS ISSN : Vol 4 No 6 Dec 01-Jan

4 I AVG P0 ηx V With K RP 0.4 and D MAX already determined, the shae of the current waveform is known. Due to the simle geometry of the waveform, the Primary eak current I P, rile current I R and RMS current I RMS can be easily derived as a function of I AVG : IAVG IP K RP 1 x DMAX I RMS I I R P x K MIN RP K RP IP X DMAX X KRP Ste 4.4 Determine rimary inductance L P : Because the energy transferred from rimary to secondary each switching cycle is simly the difference between 1/ x L P x I P and 1/ x L P x (I P - I R ). The rimary inductance LP can be exressed as a function of I P, Dmax, and Vmin: L P Dmax V I f After reviewing the core sizing information rovided by the core manufacturer it was decided to use an EE core of size about 0mm. A Siemens N67 magnetic material is used, which corresonds to a Philis 3C85 or TDK PC40 material. The manufacturer recommends for that magnetic core a maximum oerating flux density of: Bmax0.T The cross-sectional area of the EE0 core is: Ac 33.5mm Ste 4.5. Calculate number of rimary turn s n P and secondary turns n s : The oerating flux density is given by: LI B max n Ac From the above equation one can obtain the equation for the number of turns of the rimary winding: LI n B x A The A L factor (defines how many turns needed for a given inductance) is determined by: L L ( Bmax Ac ) ( Bmax Ac ) P A L n L I L I max ( ) min c ( ) From the manufacturer catalogue recommendation, the core with an A L of 100nHis selected. The desired number of turns of the rimary winding is: L n A The number of turns needed by the +1V secondary is (assuming an ultrafast rectifier is used); ( V0 + Vfwd )( 1 Dmax ) n ns Dmax Vmin outut ower at minimum inut line voltage, while meeting all secifications. Minor adjustments may be necessary to centre the outut voltage. L ISSN : Vol 4 No 6 Dec 01-Jan

5 V RESULTS AND DISCUSSION The DC outut voltage is noted for different DC inut voltages and it is found to 1V DC voltage &.5A current for each case. The inut & the flyback outut relationshi is shown in table 5.1. And DC outut waveform is shown in figure 5.1. Figure 5.1: DC outut waveform for different in voltage of flyback converter. Table5.1. Inut Vs flyback outut Relationshi. Inut DC Voltage (V) Flyback DC outut Voltage(V) The voltage across the rimary winding of a transformer is shown in figure5.. The voltage value measured for 4V DC inut and it is found to be 4V with almost no sikes. This is due to the roer selection of RCD clam circuit. The frequency of a waveform is about 13 khz. Figure5.: waveform at the rimary winding if the transformer. The voltage across the secondary winding of a transformer is shown in figure5.3. The voltage value measured for 4V DC inut and it is found to be 1V. ISSN : Vol 4 No 6 Dec 01-Jan

6 Figure5.3: Waveform across the secondary winding of a transformer. The voltage across switch is also measured and it is found to be 48V for the 4V inut. The voltage V DS is two times that of the inut voltage. The switch is oerating at a frequency of 13 khz and is shown in figure5.4. Figure5.4: Voltage waveform across the switch (V DS ). VI CONCLUSION In this aer, analyze, design of transformer and imlementation for flyback converters with desired arameters which is used in low ower switch mode ower sulies achieved. Imlementation results are closely-matching with those obtained from the mathematical calculations. The results resent that; roosed flyback converter is an excellent candidate for high-frequency, isolated DC-DC converters with low ower alications. Acknowledgment One of the authors (hameed miyan) gratefully acknowledges to Dr. V.Satyanagakumar rofessor & chairman EEE deartment UVCE Bangalore for their valuable suggestions. Authors were grateful thanks to Dr.B.B.Lal rincial BKIT Bhalki and Er.Ishwar Khandre chairman BKIT Bhalki for their encourage ment and suort. References [1] Chung H., Hui S.Y.R., Wang W.H., "An Isolated Fully Soft-Switched Flyback Converter with Low Voltage Stress", Power Electronics Secialists Conference, PESC '97 Record., 8th Annual IEEE Volume, -7 June 1997 Page(s): [] Henry S.H. Chung, Wai-leung Cheung, Kam-shing Tang, A ZCS Bidirectional Flyback Converter, Power Electronics Secialists Conference, 004. PESC 04. IEEE 35th Annual Volume, 0-5 June 004 Page(s): [3] Prieto, R., Cobos, J.A., Garcia, O., Asensi, R., Uceda, J., Otimizing the winding strategy of the transformer in a flyback converter Power Electronics Secialists Conference, PESC '96 Record., 7th Annual IEEE Volume, 3-7 June 1996 Page(s): [4] Salem, T.E.; Titon, C.W.; Porschet, D., Fabrication and Practical Considerations of a Flyback Transformer for Use in High Pulsed- Power Alications, SSST '06. Proceeding of the Thirty-Eighth Southeastern Symosium on 5-7 March 006 Page(s): [5] Chen, T.H., Lin, W.L., Liaw, C.M., Dynamic modeling and controller design of flyback converter, IEEE Transactions on Volume 35, Issue 4, Oct Page(s): [6] Pressman A.I., "Switching Power Suly Design", Second Ed. McGraw-Hill, 1998, [7] Billings K. "Switch Mode Power Suly Handbook", McGraw-Hill, [8] Czarkowski, D, & Kazimierczuk, M.K. (199) Linear circuit models of PWM flyback & buck/boost converters IEEE Transactions on circuits & system-i: Fundamental Theory & Alications,39,8 (Aug.199), [9] Barbosa, P.M., Barbi, I. A single-switch flyback-current-fed DC-DC converter, IEEE Transactions on Power Electronics- May 1998 Volume: 13, Issue: 3,Page(s): [10] Inaba, C.Y. Konishi, Y. ; Tanimatsu, H. ; Hirachi, K. ; Nakaoka, M. Soft switching PWM DC-DC flyback converter with transformer - assisted ulse current regenerative assive resonant snubbers Power Electronics and Drive Systems, 003. PEDS 003. The Fifth International Conference on 17-0 Nov ISSN : Vol 4 No 6 Dec 01-Jan