Environmental Engineering Reference
In-Depth Information
T
Stopped
5ms/div
(5 ms/div)
NORM:200 kS/s
CH2 = 2 V
DC 10:1
T
2
= Trace 2 =
Max
3.360 V
Freq
1.316 kHz
CH2 = 2 V
1ms/div
Sync. Bit
2
1
0
0
0
0
0
0
0
0
1
0
1
FIGURE 4.6
An enlarged diagram of the 12-bit data sent out by the HT12-E encoder.
4.1.2
Energy Storage and the Power Processing Unit
The PPU converts the AC output voltage from the piezoelectric generator
into a DC source through AC-DC full-wave diode bridge rectification. After
this, the capacitor connected across the output of the full-wave bridge rectifier
doubles as a storage device since energy from the piezoelectric generator is
finite and occurs for only a short pulse as well as a filter, which helps to
smooth the voltage ripples in the rectified DC voltage. Hence, by choosing
a capacitor with a higher capacitance value, the rectified DC voltage can be
stepped down to a lower level effectively by the capacitor; at the same time,
the capacitor can better smooth the DC voltage and also provide more energy
storage for the harvested energy. Thereafter, the capacitor output voltage, the
unregulated DC voltage, is further regulated by a voltage regulator circuit
into regulated DC voltage.
Due to several design constraints imposed on the impact-based VEH sys-
tem like miniature size, simple design, and low-cost requirements, a simple
voltage regulator is used. According to Dewan et al. [112], if the voltage differ-
ence between the input and output of the linear voltage regulator is kept to a
minimum, then the linear regulator's efficiency is maximized. This is because
a small amount of voltage is dropped across the voltage regulator; hence, lit-
tle energy is wasted. A switched-mode voltage regulator, on the other hand,
suffers from ripples in the output voltage due to its switching rates and has a
very high quiescent current compared to a linear voltage regulator, especially
 
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