Abstract
This paper shows the modelling of linear–assisted or hybrid (linear & switching) DC/DC voltage regulators. In this kind of regulators, an auxiliary linear regulator is used, which objective is to cancel the ripple at the output voltage and provide fast responses for load variations. On the other hand, a switching DC/DC converter, connected in parallel with the linear regulator, allows to supply almost the whole output current demanded by the load. The objective of this topology is to take advantage of the suitable regulation characteristics that series linear voltage regulators have, but almost achieving the high efficiency that switching DC/DC converters provide. Linear-assisted DC/DC regulators are feedback systems with potential instability. Therefore, their modelling is mandatory in order to obtain design guidelines and assure stability of the implemented power supply system.
Highlights
Series linear regulators have been structures widely used in power supply systems for decades, providing supplies with low or moderate currents and consume [1,2]
This kind of voltage regulators has several advantages that lead their use. In spite of these advantages, linear regulators suffer from some serious drawbacks
The most important are the values of the output capacitance CL, its equivalent series resistance, the load resistor RL and the inductor L1
Summary
Series linear regulators have been structures widely used in power supply systems for decades, providing supplies with low or moderate currents and consume [1,2]. Taking into account expression (1) and that the load current is constant (equal to Vout/RL), ireg(t) will tend to decrease linearly (Fig. 2), just reaching a value below Iγ In this moment, the comparator changes its output from high to low level, cutting Q1 and forcing IL to decrease. Some capacitance can be suitable in order to eliminate possible transitory peaks in the output voltage when the regulator supplies variable loads (that is, high slew–rate in the output current) This output capacitor improves the response of the converter appreciably. The most important are the values of the output capacitance CL, its equivalent series resistance, the load resistor RL and the inductor L1 All these points make necessary to analyze the regulator in order to obtain design approaches that guarantees its stability. It is observed that the system can be stable or unstable with different values of the load resistor, the inductance L1, the load capacitance CL and its ESR
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