## 2 Working Principle of the TIBuck DC/DC Converter
### Advantages over the Buck DC/DC Converter  
As introduced in [21], the TIBuck DC/DC converter outperforms the traditional Buck DC/DC converter in terms of lower harmonic switching components, higher resolution to track the output voltage and lower switching losses. 1. Lower switching harmonic components. The lower the amplitude of the switching node voltage, \(\mathrm{v_{sw}(t)}\), the lower the switching harmonic components. These harmonic components result in undesirable output voltage noise and must be attenuated by the output filter. Reducing the harmonic components of \(\mathrm{v_{sw}(t)}\) simplifies the design of the output filter compared to the equivalent in a traditional Buck DC/DC converter, allowing either the reduction in filter order (reducing hardware complexity and number of elements) or increased cut-off frequency (increasing the bandwidth of the converter) [19]. Figure 6 depicts the filtering process, illustrating the separation between frequencies stated by Equation (7). Figure 6: Spectral representation of the comparison between the Buck and TIBuck DC/DC converters in regards to filtering action of the output voltage. 2. Lower switching losses. The switching losses mostly depend on the switching frequency, characteristics of the switches and voltage stress [25]. According to Equation (7), for a given bandwidth, the switching frequency must be kept high enough for the correct operation of the DC/DC converter as a VLC driver. Increasing the switching frequency of the DC/DC converter leads to a significant increase in switching losses. To track communication signals into the bandwidth of HB-LEDs, the switching frequency of the VLC driver would need to be in the range of 10-15 MHz. The characteristics of the switches depend on the technology available, and it is assumed that the best possible switch could always be used. At this point, only the voltage stress of the switches can be modified to reduce the switching losses In a TIBuck DC/DC converter, the voltage stress of the switch is \(\mathrm{V_{1}}-\mathrm{V_{2}}\), which is lower than the regular Buck DC/DC converter case (i.e., \(\mathrm{V_{1}}\)). This reduction in the voltage stress is also an advantage in switch selection, because the lower the voltage rated, the better the characteristics and performance at high-switching-frequency operation. 3. Higher duty-cycle resolution. Increased switching frequency has a negative effect on the duty-cycle resolution (i.e., number of discrete values of the duty cycle, \(\mathrm{C_{sw}}\), using a digital control). From Equation (5), for a fixed clock frequency \(\mathrm{f_{clk}}\), if \(\mathrm{f_{sw}}\) increases, then the resolution of the duty cycle decreases (i.e., by the \(\mathrm{C_{sw}}\) decrease). On top of this decrease in the duty-cycle resolution in high-frequency converters, the behaviour of the HB-LED as a load imposes a further decrease in the resolution, which is the case in designing VLC drivers. As depicted previously in Figure 1, only the useful voltage range between \(\mathrm{V_{th}}\)(T) and \(\mathrm{V_{max}}\)(T) can be used for HB-LED as a load, to avoid distortions in the safe operating range (in this initial approach, temperature dependency is ignored). This means that only the values of the duty cycle that generate voltage levels in this range are useful. Figure 7 represents the useful duty-cycle range of a Buck DC/DC converter and a TIBuck DC/DC converter (optimized for this task) using a string of n HB-LEDs as a load (for the sake of simplification, sinusoidal waveforms are used as communication signals). The duty-cycle range of a Buck DC/DC converter can be easily obtained from Equation (8) just by making \(\mathrm{V_{2}}=0\) V. Its output voltage range goes from 0 V to \(\mathrm{V_{1}}=\mathrm{nV_{max}}\)(T) by maximizing the communications signal (i.e., \(\mathrm{V_{\Omega}}=\mathrm{V_{pp}}\)).