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A Single Supply Bootstrapped Boost Regulatorfor Energy Harvesting Applications
Zachary Nosker1 Yasunori Kobori1 Haruo Kobayashi1 Kiichi Niitsu2 Nobukazu Takai1Tetsuji Yamaguchi2 Eiji Shikata2 Tsuyoshi Kaneko3 Kimio Ueda4
1Division of Electronics and Informatics, Gunma Univ, 1–5–1 Tenjin-cho Kiryu, Gunma 376-8515 Japan2Department of EECS, Nagoya Univ, Furo-cho, Chikusa-ku, Nagoya, Aichi 464-8603 Japan3AKM Technology Corporation, 1-9-1 Ichibancho, Aoba-ku, Sendai, Miyagi 980-0811 Japan
4Asahi Kasei Microdevices, 1-105 Kanda Jinbocho, Chiyoda-ku, Tokyo 101-8101 JapanIntroduction
1. Energy harvesting systems capture powerfrom ambient sourcesI Examples: solar, vibrational, thermal transducers
2. Our approach targets real-world applicationsI Operates from a single input voltageI Only requires 3 external components (CI, CO, L)I Efficiency and load range maximizedI Starts up with very low input voltageI Target→ low-power Micro-Controller system
Energy Harvesting Block Diagram
Energy Harvester Thermal Solar
Vibra6onal RF Harves6ng
Etc.
Boost Converter / Ba>ery Management System Power
MCU
Wireless Interface ZigBee, etc
Energy Storage
I The proposed circuit does not require anenergy storage device (battery)
Proposed Circuit – Design Specifications
1. Bootstrapped boost regulatorI Can startup from input voltage below Vt(NMOS)
I Works down to VIN = 240mV2. Efficiency > 95%
I Low IQ (≈ 15µA)I Low conduction/switching losses
3. Output Load > 5mW
Overall System Block Diagram
IO MN
MP L
CO
VI
VO
Charge Pump
Startup Oscillator
Mode Logic and
Driver
+ VREF One-shot
Comparator
VCP
VO VCP
VI
V1shot
R1
R2
VSO
VDRVn
VDRVp
CI
State Logic
-
+
en
Rhys
Startup Charge Pump Schematic
VCP VCP-OSC
Buffer
VI
en
Charge Pump Osc.
VI
C1
C2
C1
C2
C1
C2
1. Native NMOS, C1 = 5pF, C2 = 40pF2. Values optimized to startup main switches
Charge Pump Startup Simulation
.250 .500 .750 1.0 1.25time (us)
3 5 0
1 5 0
−50.0 (
mV
) (
mV
)
4 0 0
3 0 0
2 0 0
1 0 0
(m
V)
(m
V)
V_{CP−OSC}
V_{CP}
time (us)
Steady State Simulation
11.34 11.35 11.36 11.37 11.38time (ms)
1.05
1.03
1.01
.99
V (V
)V
(V)
5 04 03 02 01 0
I (m
A)
I (m
A)
1 .25
.75
.25Y2 (V
)Y2
(V)
V_{OUT}
I_L
V_{DRVn}
time (ms)
Circuit Calculations
vO
iL
t0 t1 t2
ton toff
IP
ΔvO
I Inductor current equation
iL(t) =
VI
Lt, t0 < t ≤ t1
IP −VO − VI
L(t− t1) , t1 < t ≤ t2
I Output voltage ripple
∆vO =1
CO
∫iL(t) dt =
I2PL
2CO(VO − VI)
∆vO = t2onV2
I
2LCO(VO − VI)
I Maximum load current
IO(max) = tonV2
I
2LVO
I Smaller inductor→ larger peak currentI Larger inductor current→ more lossesI Optimum inductor value selected
Circuit Efficiency
90 91 92 93 94 95 96 97 98 99
100
0 1 2 3 4 5 6 7
Eff
icie
ncy
(%)
Output Load (mW)
Efficiency Comparison
40
50
60
70
80
90
100
0 1 2 3 4 5 6 7
Max
imum
Effi
cien
cy (%
)
Maximum Load (mW)
Conventional
This Work
Charge Pump Test Chip
Chip photomicrographLab bench setup
Test Chip Data
!"
#!!"
$!!!"
$#!!"
%!!!"
$#!" %!!" %#!" &!!" &#!" '!!" '#!" #!!"
!"#$%&'!(
!)*%&'!(
+,-./0%12'3%$045%+,63%7-5-
()"*)+,"
$!!-."*)+,"
Conclusion
1. Introduced bootstrapped boost for EHapplications
2. Better performance than previous worksI Higher efficiencyI Extended load range
3. Only requires 3 external componentsI Input capacitor, output capacitor, inductorI No external energy storage components
Zachary NOSKER (Gunma University) www.el.gunma-u.ac.jp/˜kobaweb/ [email protected]
