Post on 24-Jan-2016
description
Battery-Powered Driver for Fundamental-Mode Orthogonal Fluxgates
Prepared by: Anton PlotkinSupervisor: Professor Shmuel Ben-Yakov
Department of Electrical and Computer Engineering Ben-Gurion University of the Negev, P.O. Box 653, Beer-Sheva 84105, Israel
28.06.06
The Aim
Provide the maximum battery life of the driver for fundamental-mode orthogonal fluxgates.
Contents
1. Orthogonal fluxgate.
2. Fundamental-mode operation.
3. Current source.
4. Current source with transformer.
5. Full-bridge driver.
6. Comparison.
7. Conclusions.
1. Orthogonal fluxgate
15 mm
1 m
m
20 mmAmorphous wire
Sensing coil
Crimp connectors
iex
Printed circuit board
Advantages:
• Good resolution.
• Simplicity and small size compared to parallel fluxgates.
Construction:
• Core: Co-based amorphous wire, 120-m diameter.
iex
vout
From: Macintyre S.A., Magnetic Field Measurement.
2. Fundamental-mode operation
i ex
, mA
0 2.5 5.0
0
80
-80
4.90.1 2.4
Time, ms
Positive excitation
Negative excitation
2.6
Vdc=3.5-4.5 V RL=2…3 iex=±80 mA
PL=5…10 mW
3. Current source
Advantages:
• Simplicity.
Disadvantages:
• Requires a bipolar supply voltage to obtain a bipolar iex.
• Requires a gain of 10 (Rs ≈ 0.1 RL) to reduce the losses of Rs, which yields a relatively high amplifier supply current.
• The output current of the op-amp is iex.
• The efficiency of the output stage is low (10 %).
D/A
Rs
vex iex
RL
4. Current source with transformer
D/A
Rs
vex
Advantages:
• The maximum efficiency of the output stage is 75%.
• Lower amplifier output current.
• Lower amplifier supply current: Rs = 0.1 RL n2 results in a gain of 2 for n=3.
Disadvantages:
• The duty cycle of iex should be 50%.
• Transformer: core and copper losses, large size, EMI.
iex/n
iex
RL
4. Current source with transformer
D/A
Rs
vex
Dynamic stability:
=Rs/(Rs+n2RL||jLm+jLlk)
• vout/vex=1, <0
• vout/vex=jLm/Rs, 0<<1
• vout/vex=(Rs+n2RL)/Rs, 1<<2
• vout/vex=AOL, >2
n2RLLmLlk
AOL
Lm
Llk
Llk
Lm
vout
5. Full-bridge driver
iex
VDD
RLL
Advantages:
• Any duty cycle of iex with a single VDD.
Disadvantages:
• Triangle-wave current instead of sine-wave one.
• The control requires current measurements.
• The dependence of frequency on L and VDD.
• Inductor: core and copper losses, large size, EMI.
iex
t
5. Full-bridge driver: control
L5
{L*n*n}
1
2
R15400k
0
R14
1k
D4
1N4678
12 L3
{L*n*n}
1
2
Vdd
Vdd
U4A
74HC14
1 2
714
U4B
74HC14
3 4
714
U6SD103A
01
12
PARAMETERS:VDD = 4.2VImax = 0.09Imin = 0.004Rload = 3n = 100L = 10uH
R6200k
R161k
C6
1nD31N4678
12
R17
1k
Vdd
L1
0.5mH
1 2D
pre
Vdd
U10SD103A
01
12
U2SI1539DL
Dn
Gn
Sn
Dp
Gp
Sp
6
21
3
54
C31n
E1
V(%IN+, %IN-)EVALUE
OUT+OUT-
IN+IN-
L2 {L}12
pre
L4 {L}12
R5230k
R240k
0
0
D2
1N4678
12
U3A
TLV2352I/3_1/TI3
2
84
1
+
-
V+V-
OUT
R221k
Vdd
R420k
K K2
COUPLING = 0.99K_Linear
L1 = L4L2 = L5
Vdd
D
U3B
TLV2352I/3_1/TI5
6
84
7
+
-
V+V-
OUT
E2
V(%IN+, %IN-)EVALUE
OUT+OUT-
IN+IN-
U5A
74HC74
3
1
2
4
5
147
6CLK
CLR
D PRE
QVCC
GND Q
U1SI1539DL
Dn
Gn
Sn
Dp
Gp
Sp
6
2 1
3
5 4
U15SD103A
01
12
U9SD103A
0 112
C10.1n
0
K K1
COUPLING = 0.99K_Linear
L1 = L2L2 = L3
U7SD103A
0 112
R340k
R121k
V1{VDD}
R1 {Rload}
6. Comparison: efficiencyCurrent source with transformer: 30 % efficiency
(Irms=50 mA)
• Output stage efficiency: (3.6/4.2) x 75 % = 65 %
• Transformer: Pcopper=6 mW
• Op-amp: Pqs=5 mW
• P(Rs)=1 mW
Full bridge: 40 % efficiency (Irms=60 mA)
• P(RDS on)=9 mW
• Inductor: Pcopper=4 mW, Pcore=1.4 mW
• P(Rc)=1.5 mW
6. Comparison: sizeCurrent source with transformer:
• Transformer: toroid, D=4.83 mm, H=2.54 mm (w/o winding)
Full bridge:
• Inductor: pot, D=7.24 mm, 2B=4.16 mm
• Current transformers: toroid, D=2.54 mm, H=1.27 mm (w/o winding)
6. Comparison: cost ($)Current source with transformer:
• Transformer: 20
• D/A (DAC8830, TI): 7
Full bridge:
• Inductor: 15
• Current transformers: 2×10
7. Conclusions• The maximum efficiency of the driver is 40 %
(the minimum losses are 16 mW).
• The main factors limiting the efficiency of the current source are the supply of the op-amp and the transformer copper losses.
• The main factors limiting the efficiency of the full bridge are the switching losses (either RDSon or gate driving) and the inductor copper losses.
• Both the transformers and inductor should be carefully shielded to reduce the EMI.