2012 IEEE International Conference on Power Electronics, Drives and Energy Systems December16-19, 2012, Bengaluru, India Study of Rectifier Diode Loss Model of the Flyback Converter T.Halder Assistant Professor Kalyani Government Engineering College, PIN -741235 Kalyani, West Bengal, India Abstract—This paper advocates an inclusive power loss modeling efficiency. Reinstating the normal power diode with a and simulation of rectifier diode of the Flyback power converter synchronous rectification (SR) with a MOSFET or Schottky working under continuous conduction mode (CCM) and diodes significantly reduces the massive conduction losses discontinuous conduction mode (DCM). The small signal model which exemplify how designers are able to renovate a standard which takes into considerations all active and passive components diode-rectified isolated Flyback switch mode power supply of the Flyback converter is implemented by means of MATLAB / PSIM software for computing constructive loss model of Flyback (SMPS) into a self-driven-synchronous-Flyback circuit. A diode. The simple model and computer simulations are well suited Flyback diode with high conduction losses and reduced diode for hypothetical, lucid investigations and simulation model of the reverse-recovery problems are not much predictable [1-15] for converter. Lastly, a loss of rectifier diode is studied for DCM and power circuit’s efficiency of the converter. The proposed CCM for the Flyback converter using synchronous rectification Flyback Schottkey diode can cut the conduction losses and and Schottkey diode. Spurious over voltage and over current may perk up the diode reverse-recovery problems by using a self be caused by a diode switching at the divergent points in the driven auxiliary switch and some additional componenents circuit bringing into play the different type of power diodes and incorporate to output circuit of the converter to achieve zero its rating . Voltage and current waveforms focuses along with current turn-off of the output diode and the reverse-recovery transient switching functions of different rating of diodes. Switching action of the diode is together with various energy currents of the diode is slowed down to reduce the diode losses for each operating cycle. This may give rise conspicuously reverse-recovery losses. All inductive components are realized evaluations of the huge power losses in the diode at high switching on a single magnetic core by utilizing a small series inductance frequency and load of the Flyback converter. in addition to the leakage inductance of the coupled inductor. Furthermore, for the use of this topology in the practical Keywords—Flyback converter; Rectifier diode, CCM, DCM, Loss design, the PWM current mode control is employed for the Model, Simulation and Result proposed Flyback converter. A detailed analysis and a simple are presented. Experimental results for 40W prototype are also I. INTRODUCTION discussed to demonstrate the performance of the proposed ow-a-days there are various customs used to make better Flyback converter under DCM or CCM of circuit operation Ninclusive loss models of the rectifier diode of the Flyback power supply topology. In a conventional diode-rectified Flyback converter, the output diode rectifier is a substantial power loss contributor. The average current in the output diode is equal to the DC output current, and the peak current can be more than a few times higher, depending on the duty cycle. The forward-voltage drop of the diode is characteristically 0.5V for Schottky diodes and 0.75V for standard junction diodes. This large forward voltage drop leads to relatively high conduction losses in the diode and a substantial power limit in Fig. 1 Flyback converter using RCD snubber converter The Fig. 1 shows the basic Flyback converter circuit using common resistance capacitor and diode (RCD) snubber which Manuscript prepared October 9, 2011) This work was supported in part by the is used to dissipate the leakage energy and protect from the Jadavpur University, Kolkata-32 , India and Kalyani Government Engineering atypical surge voltage coming from leakage inductance and its college , Nadia , West Bengal , India. T.Halder is with Government College, Engineering & Textile Technology Berhampore, Murshidabad, (GCETTB) detrimental leakage energy. West Bengal, India e-mail: [email protected]. 978-1-4673-4508-8/12/$31.00 ©2012 IEEE II. BASIC FEATURES OF DCM proportional to the power transistor on-time (ton) for the discontinuous case. • I t does not necessitate a larger core volume than the • CCM, for the same output power requirements. Output rectifiers are operating at zero current just prior to becoming reverse biased. Therefore, reverse recovery • Small inductor size of the Flyback converter. requirements are not critical for these rectifiers. • Easy control characteristics and hardware unit. • Similarly, the power transistor turns on to a current level this is initially zero, so its turn-on time is not critical. • Flux gets reset to zero, so there does not exist a DC flux and flux swing. • Transistor turn-on to zero current also results in low radio • frequency interference (RFI) & electromagnetic The peak current ratings of power devices are higher than interference (EMI) interference generation. those operated in CCM of operation. • • High values of ripple current make output capacitor ESR Natural commutation of the output diode, minimizing requirements quite stringent. In most practical switching loss and secondary noise discontinuous of the Flyback circuits, capacitance values • Low-noise turn-on of the primary power switch. must be increased in order to achieve an adequate ESR. Transient response is correspondingly slower. • Opportunity of a quasi-resonant mode of operation to lower noise even further, the shortcoming of the DCM III. BASIC FEATURES OF CCM operations that the currents in the circuit are higher than for CCM operation The fundamental features of the DCM compared to CCM are focused and curtly explained with consequent point • No RHPZ (Right Half Pole Zero) in the low frequency wise. portion, higher cross over frequency achievable. • Low AC ripple, smaller conduction losses compared to • Simple low-cost secondary diode does not suffer from trr DCM. (reverse recovery time of diode) losses • Low hysteresis losses due to operation on B-H minor • No turn losses on the MOSFET, Id=0 (Drain Current) at loops. the time of turn on (not considering capacitive losses). • It necessitates larger core volume than the complete • Valley switching is possible in a quasi-resonant mode. energy transfer mode (DCM) for the same output power requirements and load. • It is easier to implement synchronous rectification on the secondary side of the Flyback converter • Here, the flux does not get reset to zero, hence there exists • a DC flux and flux swing. Evidently, in this mode, the flux It is not focus to sub-harmonics oscillations in current does not utilize the whole top half of the hysteresis curve. mode control • Low ripples on the output or load side of the converter. • Large AC ripple, together with conduction losses on the MOSFET and resistive paths like ESRs (equivalent series • trr (reverse recovery time) related losses on the both resistances) of copper wires. secondary side diode and the primary side (MOSFET). • It is not focus to sub-harmonics oscillations in current • Requires ultra fast recovery (UFR) diode or schottky diode mode control. to circumvent excessive losses. • It is complete energy transfer mode, whereas inductor • Turn-on losses on the MOSFET Id ≠ 0 at time of turn-on current would be zero at a particular interval of time. overlap of vds (t) and i(t) where vds(t) and i(t) is the drain to source voltage and drain current respectively. • It is easier to implement synchronous rectification on the secondary side of the Flyback Converter. • Requires a heavy compensation ramp in peak current- mode control when duty cycle is above 50% • Bigger hysteresis losses on the magnetic core (ferrite core) • • It is more multifarious to become stable in voltage mode A small transformer can be used because the average operation or control energy storage is low. Use of fewer turns also translates into reduced I2R losses. • RHPZ ((Right Half Pole Zero) hampers the accessible bandwidth. • Stability is easier to achieve because at frequencies less than one half the switching frequency there is no net • Despite similar energy storage, the inductance amplifies inductance reflected to the transformer secondary and in CCM and so the transformer dimension will be larger hence no second pole in the input-to-output transfer than that of DCM function. Also, no right half-plane (RHP) zero appears • since energy delivered to the output each cycle is directly It is incomplete energy transfer mode whereas Inductor current would never be zero at any instant. • Peak current of rectifier and switch is half that of the value recovery period if the reverse current falls too stridently, (low of discontinuous mode of operation. value of (S), stray circuit inductance may cause unsafe over voltage (V ) across the device. It may be required to safeguard • Low output ripple rr the diode using an RCD snubber. During the period t5 large • Recovery time rectifier losses are pronounced current and voltage be present all together in the device. At • high switching frequency this may affect in substantial Feedback loop complicated to stabilize due to two poles enhance in the total power loss. Significant parameters and right half plane zero. defining the turn off characteristics are, peak reverse recovery current (Irr), reverse recovery time (trr), reverse recovery charge IV. DESIGN SPECIFICATION OF THE FLYBACK CONVERTER (Qrr) and the snappiness factor S. Of these parameters, the Input Voltage Vs = 190V-250V (DC) snappiness factor S depends mainly on the construction of the Output Voltage, V0=48V (DC) diode (e.g. drift region width, doping lever, carrier life time Load current, I0= 3A etc.). Other parameters are interrelated and also rely on snappy Magnetizing inductance, Lm= 0.15 mH factor S.