Boost converter
It is a class of switched-mode power supply (SMPS) containing at least two semiconductors, a diode and a transistor, and at least one energy storage element: a capacitor, inductor, or the two in combination.
For high efficiency, the switched-mode power supply (SMPS) switch must turn on and off quickly and have low losses.
The advent of a commercial semiconductor switch in the 1950s represented a major milestone that made SMPSs such as the boost converter possible.
The new model led to insightful design equations which helped the growth of SMPS.
Battery power systems often stack cells in series to achieve higher voltage.
However, sufficient stacking of cells is not possible in many high voltage applications due to lack of space.
Boost converters can increase the voltage and reduce the number of cells.
Two battery-powered applications that use boost converters are used in hybrid electric vehicles (HEV) and lighting systems.
A white LED typically requires 3.3 V to emit light, and a boost converter can step up the voltage from a single 1.5 V alkaline cell to power the lamp.
An unregulated boost converter is used as the voltage increase mechanism in the circuit known as the "Joule thief", based on blocking oscillator concepts.
This energy would otherwise be wasted since the low voltage of a nearly depleted battery makes it unusable for a normal load.
This energy would otherwise remain untapped because many applications do not allow enough current to flow through a load when voltage decreases.
The special kind of boost-converters called voltage-lift type boost converters are used in solar photovoltaic (PV) systems.
These power converters add up the passive components (diode, inductor and capacitor) of a traditional boost-converter to improve the power quality and increase the performance of complete PV system.
Also, while the switch is opened, the capacitor, in parallel with the load, is charged to this combined voltage.
The basic principle of a boost converter consists of 2 distinct states (see Figure 2):
When a boost converter operates in continuous mode, the current through the inductor (
If we consider zero voltage drop in the diode and a capacitor large enough for its voltage to remain constant, the evolution of IL is: Therefore, the variation of IL during the Off-period is: As we consider that the converter operates in steady state conditions, the amount of energy stored in each of its components has to be the same at the beginning and at the end of a commutation cycle.
In this case, the current through the inductor falls to zero during part of the period (see waveforms in Figure 4).
Although the difference is slight, it has a strong effect on the output voltage equation.
The voltage gain can be calculated as follows: As the inductor current at the beginning of the cycle is zero, its maximum value
Furthermore, in discontinuous operation, the output voltage gain not only depends on the duty cycle (D), but also on the inductor value (L), the input voltage (Vi), the commutation period (T) and the output current (Io).
