In this paper, a current-balancing converter is proposed herein and applied to driving LED strings paralleled, so as to make the required current shared among LED string. There are two stages of the proposed current-balancing converter. The first stage is one buck converter under constant current control and transfers DC current to AC current, whereas the second stage is passive AC-DC rectifiers with front-end current-balancing transformers. Some experimental results, together with a simple mathematical derivation, are provided to verify the proposed scheme.

A Simple Current-Balancing Converter for LED Lighting

The development of high-power light emitting diode (LED) for street lighting is growing continuously owing to its greater energy efficiency, long operating life and light control. Users of street lighting are compelled to adopt this technology over traditional light sources. An alternative solution based on a novel 9LEDM (9-LED module) and adaptive driver is shown. The design of the 9LEDM is derived from the thermal, photometric, power electronics techniques to meet the application of street lighting. The 9LEDM performances with a price less than 1$/Watt (W) and luminous flux higher than 110 Lumens (Lm)/W compared with traditional ones. Furthermore, several restrictions of driving the solid-state lighting loads are overcome by an adaptive street lighting driver with an AC/DC converter of a quasi-resonant operation flyback topology and with Soft Startup, Full ON, Half ON functions by sensing the ambient light and working temperature. Finally, a high performance/cost 50 W pole head as a design example is conducted to illustrate the complete design process, and the results from the demonstration projection with two pole heads of 50 W for a 12 m pole show a luminous intensity range from 38 to 19 lux with a heat sink temperature of 58degC and an energy saving more by 72% compared with conventional street lighting after three months of running.

Development of street lighting system-based novel high-brightness LED modules

Piezoelectric transformers (PTs) are solid-state devices that transform electrical energy into electrical energy by means of a mechanical vibration. These devices are manufactured using piezoelectric materials that are driven at resonance. With appropriate design and circuitry, it is possible to step up and step down the voltages between the input and output sections of the piezoelectric transformer, without making use of magnetic materials and obtaining excellent conversion efficiencies. The initial concept of a piezoelectric ceramic transformer was proposed by Charles A. Rosen in 1954. Since then, the evolution of piezoelectric transformers through history has been linked to the relevant work of some excellent researchers as well as to the evolution in materials, manufacturing processes, and driving circuit techniques. This paper summarizes the historical evolution of the technology.

https://www.mdpi.com/2076-0825/5/2/12/pdf

Piezoelectric Transformers: An Historical Review

This paper demonstrates power electronic drivers for white LED lamps. Due to some obvious features such as high luminous efficiency, low-loss energy, long life, safety, green, and so on, it's expected to replace conventional lamps including incandescent, halogen and fluorescent lamps at least in some general illumination application within the near future. It's always used in automotive fields. Innovative design in driver circuits of white LED lamps with respect of functionality, efficiency, cost, size and reliability enables the successful introduction of new LED based lighting products. First of all, it describes LED's characteristics briefly which include electrical character, driver requirement, luminous characteristic, thermal performance and package structure. In the second part, a series connection of single LED cells is presented in detail. For efficiency reasons, white LED lamps can not be droved via series resistor, but need PWM models with current control. In the third part, different standard DC-DC converter topologies are discussed which can be adapted to feed a constant current into a LED load. Hence, roughly, it consists of two general types which named non-isolated driver and isolated driver separately. This paper will introduce more detailed classifications. It's convenient to choose proper driver circuit and suited components through the comparison between the topologies of this paper. In addition, PFC(Power Factor Correction) circuit is also involved in high power factor. Finally, some hot spots in white LED lamps fields are focused on.

The topologies of white LED lamps' power drivers

This paper presents a steady-state analysis of the isolated class-E $^2$ converter outside nominal operation. By transforming the isolated class-E $^2$ converter into the typical topology of the class-E inverter, the switching patterns can be comprehended on the parameter spaces easily. The output power and the power-conversion efficiency can be expressed as functions of circuit parameters such as coupling coefficient of the transformer, load resistance, and operating frequency. The class-E $^2$ wireless power transfer (WPT) system was designed and implemented in this paper for verifying the analytical expressions. The analytical predictions of system performance against coupling-coefficient and load-resistance variations agreed with PSpice simulation and experimental results quantitatively, which showed the validity of the analytical expressions. Comparisons between the class-E $^2$ and class-D-E WPT systems are shown along with their discussions. Additionally, two application examples of the analytical expressions are introduced in this paper, which shows the usefulness of the analytical equations.

Steady-State Analysis of Isolated Class-E$^2$ Converter Outside Nominal Operation

An up to 5 Watts wide range power supply LED driver demonstrator with a piezoelectric transformer (PT) has been built to show the static and dynamic behavior as an off-line power supply The target of the power converter controller using a PT, with 23 mm thickness and 17 mm diameter at frequency of 155-175 kHz, designed in a resonant circuit of class-E topology, is to maintain a constant output current of 290 mA/DC with variable output voltage drop at wide input voltage range of 85-250 V/AC Also, the ZVS (zero-voltage-switching) condition is achieved over the full operation range The used 1200 V fieldstop IGBT (1A-Type) shows losses around 200 mW over the full operating range for constant output current The paper shows the regulation method for off-line power supplies using PT in class-E topology in constant current mode regulation (CCMR) The regulation algorithm has been programmed in C language operated by a 32-bit DSP (TMS320F2812) Besides, in the class-E application, the duty cycle of the switching frequency needs to be controlled in order to achieve the ZVS during the operation at different load and input condition This goal is achievable only by phase locked loop (PLL) feedback in a satisfying way To solve this problem, the idea of PT with an auxiliary tap has been applied The application is suited for low size LED line adapters, to be integrated in bulb sockets The results are applicable for any controller design of resonant PT step-down topologies The several suited optimum control concept is investigated in this paper, considering the circuit expense being minimized

A Line Power-Supply for LED Lighting using Piezoelectric Transformers in Class-E Topology

The target of a power converter controller using a piezoelectric transformer (PT) designed as a resonant circuit, as in half-bridge or class-E topology is to maintain constant output voltage or current and to achieve the ZVS (zero-voltage-switching) condition over the operation range In the presented class-E application, the design of the closed-loop feedback is achieved for 0-3 Watts at 6 V/DC output with a varied output load between 12 Omega-12 kOmega, at input voltage range of 85-260 V/AC using different PT samples, at switching frequency range of 145 to 180 kHz, with the concept of PI control The transient responses of the controller are presented with the jump of load and input voltage In addition, the transfer function of class-E from original 4th order transfer function is linearized to be 1st order linear function as a function of the output current from the switching frequency and the varied input voltage The Laplace transformation of the class-E converter with feed back PI control is analyzed using a linear model method The stability condition of the closed loop control is analyzed with the Routh-Hurwitz stability criterion method

Dynamic behaviour of PI controlled class-E resonant converter for step-down applications using piezoelectric transformers

An array of solutions to handle the losses in switching mode power supplies such as zero-voltage-switching (ZVS), or as zero-current-switching (ZCS), have been developed and applied. There is still a limitation to eliminate the losses in the switching devices to be near to zero. The loss characteristics of a switching IGBT, such as turn-off switching loss due to the tail current under either ZVS or ZCS condition is defined as an important factor that limits the efficiency of the converter, especially in small size power supplies used at high operation switching frequency. In this work the dissipative energy of a resonant converter using PT is not reduced only by ZVS condition, but also by non-switched intervals during the operation, called burst mode. The system is classified to represent two cases of output load, called full load and light load. In the light load situation, the converter can optimize the transferred energy without losing the constant output regulation behaviour, which is done by burst mode control. Different burst mode classification methods between full load and light load have been investigated for different control techniques. The frequency based burst mode classification was evaluated to be most advantageous over phase-angle or switch current time interval observation, perspectively independent of the resonant converter topology. An active burst mode technique has been derived for output voltage feed-back. The work has been proved for a class-E topology, fulfilling the "code of conduct on efficiency of external power supplies" in a 3 Watts off-line power supply application.

High efficiency control methods for class-E resonant converter for step-down applications using Piezoelectric Transformers (PT)

A 1 to 5 Watts wide-range power supply demonstrator with a transoner-type piezoelectric transformer (PT) has been built in class-E topology to show and to model the dynamical functionality of an off-line power supply. While modelling the feedback closed-loop control, the ZVS or near-ZVS behaviour during transient response, was achieved by maintaining a sufficient transistor on-time, being constant. The dynamical modelling was applied for 0-3 Watts and 6 V output at input voltages between 85 and 260 V AC, using different PT sample parameter sets. The PT samples were all 2.3 mm thick, and had a diameter of 17 mm. The used fieldstop-IGBT 1 A-type showed always losses less than 700 mW over the full operating range at frequencies between 145 and 180 kHz. The application is suited for smart-card format power supplies below 5 mm thickness. Compared to the half-bridge, the class E concept, as a current fed topology, promises a larger control bandwidth at the same frequency, tracking the duty-cycle with the frequency instantaneously. Modelling the transient responses, the output voltage in the high frequency model was considered as a constant voltage source for the low frequency pass of the output network. The poles and zeros of the state-space matrices deliver the stability criteria after the used vectors of boundary conditions do not change in average any more. The measurements had been in good agreement with the partially applied differential equations analysis, and the SPICE simulation, as well. The control loop stability is given with proportional/integrating regulator up to integrating time constants of less than 20% of the switching period, while the regulation against line voltage by frequency modulation was completely achieved. The method provided a complete analytical dynamical design and modelling of the class-E DC-DC-converter, including the low frequency part, as the output rectification and charging capacitor, and the feedback loop, respectively

S. Nittayarumphong

Papers

A Line Power-Supply for LED Lighting using Piezoelectric Transformers in Class-E Topology

Dynamic behaviour of PI controlled class-E resonant converter for step-down applications using piezoelectric transformers

High efficiency control methods for class-E resonant converter for step-down applications using Piezoelectric Transformers (PT)

Dynamical Modelling of Class-E Resonant Converter for Step-Down Applications Using Piezoelectric Transformers