V20W Mide Technology Corporation, V20W Datasheet - Page 19

• Manufacturer Part Number: V20W
• Description: PIEZOELECTRIC ENERGY HARVESTER
• Manufacturer: Mide Technology Corporation
• Series: Volture™r

Specifications of V20W

• Sensor Type: Acceleration
• Sensing Range: 75Hz ~ 175Hz
• Output Type: Analog
• Operating Temperature: -40°C ~ 90°C
• Features: Piezoelectric Vibration Energy Harvesting, Hermetically Sealed
• Package / Case: Cantilever Piezo Film (Wafer)
• Mounting Type: Through Hole
• Termination: PC Pins
• Lead Free Status / RoHS Status: Lead free by exemption / RoHS compliant by exemption

APPLICATIONS INFORMATION -
deplete C1 until its voltage drops below the hysteresis
band, at which point the converter is disabled and the
cycle repeats. Thus C1 is maintained at approximately
V
pulses ideally suited to charging a battery or capacitor,
or directly powering an intermittently-operating sensor.
Since the voltage at C1 is held approximately constant,
the effective load seen by the piezo is not significantly
affected by activation of U2 or changes to the actual
load. Additionally, the voltage maintained on C1
ensures charge is drawn from the piezo beam only
when its voltage exceeds C1’s voltage by one diode
drop, which occurs only when the beam approaches its
maximum deflection. Thus a limited amount of charge
is drawn on each cycle of the piezo beam, timed to
coincide with the maximum deflection of the beam.
This combination of factors helps prevent excessive
mechanical damping of the beam, allowing usable
output voltages to be output at lower vibration
amplitudes while the piezo beam is driven near its
mechanical resonance.
U2 provides a regulated output voltage determined by
the ratio of R7 and R8. The power output per G of
vibration will remain relatively constant across G-levels
and loads, provided the load is capable of drawing at
X1
X2
Piezo Bimorph
oc
Figure 2: Simple high-efficiency voltage conversion and load-isolation circuit for piezo energy harvesting applications. The C1
/2. The typical output is a train of voltage-regulated
voltage setpoint in this example is fixed, but could be made adaptive using additional circuitry.
D1
BAV199
BAV199
D2
VCC
GND
+ C1
100uF
REVISION N0. 001
V REF
100K
10nF
R4
C2
R5
2.2M
1
3
5
6
LTC154 0CMS8
LOAD ISOLATION EXAMPLE
+IN
HYS
REF
-IN
15M (Optional)
R3
OUT
V+
V-
REVISION DATE: 06-03-2010
8
7
2
least as much power as is being supplied (Figure 5).
The converter duty cycle is approximated by the ratio
of input power (G-level) vs. output power (voltage *
current * time), less any small conversion losses and
leakage. When the input power exceeds the output and
losses, duty cycle will be 100%, and excess voltage at
C1 is safely disposed of through D5.
R6 sets the peak current through inductor L1, and can
be specified according to the equation:
where I
the load. Generally, the peak inductor current should be
set to maximum to improve efficiency with smaller
(<300uH) inductors in space-limited applications;
refer to the LT1474 datasheet for more thoughtful
trade-offs between peak current and inductor size.
Battery-charging applications requiring a (pulsed)
constant-current charge phase, or where both the
charge circuit and the load are directly connected
across the battery pack, may require a lower I
setting to reduce voltage ripple caused by the charge
pulses.
MAX
VCC
1
R6
RUN
is the maximum desired output current to
7
6
3
8
R
BAT43W
U2
LTC1474CMS8
VIN
SENSE
LBI
RUN
SENSE
D6
GND
LBO
VFB
SW
1
2
5
4
SW
0.067
I
MAX
VOUT
+
VFB
1uF
C3
0.25
V4
12pF
D8
BAT43W
PEAK
VOUT
GND
19