Primary-side sensing for a flyback converter in both continuous and discontinuous conduction mode

Abstract

-Primary-side sensing is an observer-based approach to estimate the output voltage of flyback converters from a primary winding (or an auxiliary winding). Various observer-laws have been recently developed for flyback converters operating in discontinuous conduction mode (DCM). The extension to continuous conduction mode (CCM), however, has not been considered due to the difficulties in compensating for the voltage drop in the secondary winding. From the possibility to predict the winding voltage drop using the magnetizing current and the transformer model, this paper presents a new observer method that can work accurately and smoothly in both CCM and DCM. The methodology can be combined with any controller to provide either output voltage regulation or output current regulation. The proposed sensing technique is verified by simulation.Keywords -Primary side sensing, flyback converter, continuous conduction mode, discontinuous conduction mode. I IntroductionConventional flyback converters make use of a transformer and an opto-coupler to achieve a galvanic isolation in the power transmission and feedback path, respectively. Though an opto-coupler offers a direct and easy way to capture the output voltage, its transfer function is highly nonlinear and dependent on both time and ambient temperature. This drawback imposes an upper constraint on the converter operating temperature, efficiency and size [1]. Therefore, a non-opto-coupler solution is expected to bring a significant improvement for both system performance and production cost.To eliminate the opto-coupler from the converter circuit, Nalepa et al.[1] suggested using an observer to extract the output voltage from the primary winding voltage. This primary-side sensing idea was then extended to work with an auxiliary winding in [2][3][4][5][6][7][8]. Since Nalepa's approach can be equally applied to either the primary or auxiliary winding, we will concern ourselves with the auxiliary winding, as illustrated in Fig. 1. Where and V o are the converter input and output voltage, respectively. For simplicity, the flyback transformer is exemplified by an ideal model with L m

Bulletin of the Polish Academy of Sciences: Technical Sciences

“…The averaged value The additional term in Eqns. ( 18) and ( 19), proportional to the square root of the load conductance, is the result of introducing the "correction factor" in [6] proposed for DCM in [19].…”

“…Flyback DC-DC switch-mode converter is a very popular power with many applications because of its unique features such as the galvanic isolation between input and output, the wide range of possible voltage transfer function and the possibility to supply many isolated loads. The elementary descriptions of flyback converters can be found in textbooks, as for example [1][2][3], and many aspects of their properties, applications and control methods are presented in many sources, for example in [4][5][6][7][8][9][10][11][12][13].…”

Current estimation circuit for discontinuous conduction mode flyback pulse‐width modulation controller

“…1, usually the controller detects the primary-side current by R CS and detects the output voltage by the auxiliary winding. Owing to the compensation difficulty caused by right half plane zero in continuous conduction mode, DCM is used widely for its good output adjustment [19][20][21][22][23]. The waveforms of the converter operating in DCM are shown in Fig.…”

Influence of element’s parameters on the output characteristics of the voltage multiplier when powered from the inverter in resonance conditions

“…The large-signal and small-signal models of transformer-less converters are most frequently presented in the literature. The number of the descriptions of the flyback averaged models is not so high and the examples may be found in papers [8][9][10][11][12][13][14][15][16][17][18][19][20].…”

“…Some averaged model descriptions of a flyback converter are universal [8][9][10][11][12][13], and others are addressed to converters with a selected control loop [14][15][16][17][18][19][20]. The averaged models of a flyback presented in the literature are usually the models of ideal converters (without parasitic resistances) [9,11,16,18] or converters with parasitic effects only partially included [12][13][14][15]17,19]. The complete set of parasitic resistances is included only in the models presented in [8] and [10].…”