A boost converter circuit such as TPS61022
is shown in Figure 1-1. With alternate turning on and off of the two integrated MOSFET, the inductor stores
energy and then released to VOUT which is higher than the input voltage. The average
value of VOUT is set by the FB pin and R1, R2 resistors.
Figure 1-1 Simplified Schematic of TPS61022
The ideal operating waveform at heavy
loading condition are shown in Figure 1-2. In the image:
- IL is the inductor
- IOUT is the output
current of the boost converter.
- ID is the current
through the synchronous rectification MOSFET.
- SW is voltage waveform in SW
- ΔVOUT is output
The output voltage drops when the inductor is storing energy, and increases when
the inductor energy is released. This behavior results in output voltage ripple
defined by Equation 1
. This formula is commonly found in boost converter data sheet. The ΔVOUT
is typically lower than 1% of the average output voltage if the boost converter is
Figure 1-2 Ideal Operating Waveform of a
In this equation:
- COUT is the effective output capacitance.
- fSW is the switching
frequency of the boost.
However, one may observe much larger
output voltage ripple than the calculation result in real circuits. This application
details the root cause of the observation and proposes solution to solve the