Optimized synchronous rectification stage for low output voltage (3.3 V) DC/DC conversion

2013 IEEE Energy Conversion Congress and Exposition

Fernández

Rodriguez

et al. 2013

Abstract.-The Asymmetrical Half Bridge converter (AHBC) has proven to be a promising candidate for LED lighting applications. It provides high efficiency, galvanic isolation and it can be easily built without electrolytic capacitor. On the other hand, its main drawback is its poor attainable bandwidth. In any two-stage ac-dc LED driver based on the AHBC, the first stage is a Power Factor Corrector (PFC) converter which has to be also implemented without electrolytic capacitor. As a consequence, its output voltage (input voltage of the AHBC) presents a low-frequency ripple. Due to the poor bandwidth of the AHBC, this voltage ripple will be transferred to the converter output voltage, leading to flickering. Due to the complex and non-linear transfer function of the AHBC, any analog feedforward loop has to be tuned for a given operating point, leading to a poor performance when the AHBC moves away from that point. In this paper, a digital feedforward loop is proposed in order to solve this problem. The digital implementation allows the feedforward loop to perfectly cancel the ripple under any condition (e.g., output voltage variation due to dimming). Besides, this digital feedforward loop has been designed and simplified considering the specific purpose of cancelling flickering in the emitted light. In this way, it can be easily implemented in small-size microcontrollers. Experimental results with a 40-W prototype prove the usefulness of the proposed feedforward loop.

Section: Resultsmentioning

confidence: 99%

“…A deep analysis can be easily found in literature [23]- [25], [29]- [31]. The main issue regarding the AHBC (see Fig.…”

Section: Loopmentioning

confidence: 99%

See 1 more Smart Citation

Digital implementation of the feedforward loop of the asymmetrical half-bridge converter for LED lighting applications

2013 IEEE Energy Conversion Congress and Exposition

Fernández

Rodriguez

et al. 2013

“…Due to the control scheme of this topology and the limited output-voltage range required in LED drivers, its output filter can be very small. The voltage across the transformer secondary side, due to the aforementioned control scheme, also makes self-driven synchronous rectification easy to be implemented, leading to high efficiency in low-output-voltage applications [28], [29]. Its transformer, apart from providing galvanic isolation, leads to high step-up or -down conversion ratios without loss of efficiency.…”

Section: Introductionmentioning

confidence: 99%

Optimized Design of a High Input-Voltage-Ripple-Rejection Converter for LED Lighting

IEEE Trans. Power Electron.

Castro

Lamar

et al. 2018

-The Asymmetrical Half Bridge (AHB) converter has been deeply analysed as second stage in acdc LED drivers. Galvanic isolation, high reliability and high efficiency are their main advantages while a limited duty cycle range (i.e., 0-0.5) and a poor dynamic behaviour are their main disadvantages. As second stage of an LED driver, the most demanding requirement for its control loop is cancelling the low-frequency ripple introduced by the first stage. According to its limited maximum attainable bandwidth, this is normally achieved by implementing a feedforward loop. Nonetheless, the static gain of the standard AHB converter presents a non-linear relation between the output voltage and the duty cycle. As a consequence, the effectiveness of this feedforward loop is limited. In this paper, the use of the Zeta Asymmetrical Half Bridge (ZAHB) converter as second stage of an LED driver is analysed and an optimized design is proposed. Regarding its advantages, it presents an extended duty cycle range (theoretically, 0-1.0). Besides, it presents a linear relation between the output voltage and the duty cycle. Therefore, although its dynamic behaviour is still limited, it can perfectly cancel the low-frequency ripple introduced by the first stage of the LED driver by means of a straightforward feedforward loop. The optimized design proposed in this paper is focused on minimizing the losses in the magnetic components (transformer and inductor) by wisely choosing the value of the two turns ratios of the transformer.

“…Due to its many advantages, the use of the Asymmetrical Half Bridge (AHBC) [1], [2] has expanded over many fields of application, such as lighting [3], [4], PC power supplies [5], Power Factor Correction [6], [7], telecommunication and computer server applications [8], [9] and, in general, low-to-medium power applications [10]. One of its advantages is that the voltage withstood by the primary switches is limited to the input voltage.…”

Section: Introductionmentioning

confidence: 99%

Small-Signal and Large-Signal Analysis of the Two-Transformer Asymmetrical Half-Bridge Converter Operating in Continuous Conduction Mode

IEEE Trans. Power Electron.

Díaz

Lamar

et al. 2014

Abstract.-The Asymmetrical Half-Bridge converter (AHBC) has many advantages over other PWM converters. The possibility of soft switching in primary switches and reduced switching losses in the secondary ones implies that the AHBC is a suitable topology for many high-performance applications. Besides, the lack of dead times, except those needed for achieving soft switching, is a very interesting feature to implement self-driven synchronous rectification. Moreover, the small size of its output filter is also a remarkable advantage in some fields (e.g., LED lighting). On the other hand, it also has some disadvantages. One of them is the short range of the duty cycle (lower than 0.5) and the other one is the difficult regulation due to a complex transfer function. The Two-Transformer AHBC (TTAHBC) solves the first problem as it enlarges the duty cycle range making its top limit higher than 0.5. Nevertheless, the regulation of this converter is still very complex and, besides, the transfer functions of the standard AHBC are not valid for the TTAHBC. As a consequence, the small-and large-signal models have yet to be studied. In this paper, the complete small-signal and largesignal analysis of the TTAHBC operating in Continuous Conduction Mode is provided. The large-signal and smallsignal models are developed taking into account the main parasitic components that affect the transient response of this converter. The validation of the resulting model is carried out by means of both, simulation and experimental results. The prototype is a 60-W TTAHBC designed for an input voltage of 400 V and an output voltage of 48 V.