Download Class H Power Amplifier for Power Saving in Fluxgate Current

> REPLACE THIS LINE WITH YOUR PAPER IDENTIFICATION NUMBER (DOUBLE-CLICK HERE TO EDIT) <
1
Class H Power Amplifier for Power Saving in
Fluxgate Current Transducers
Guillermo Velasco-Quesada, Member, IEEE, Manuel Román-Lumbreras, Member, IEEE,
Raúl Pérez-Delgado, and Alfonso Conesa-Roca

Index Terms— AC and DC current measurement, fluxgate
transducer, energy savings, class H amplifier.
electrical power due to its inherent very high efficiency [6].
This work evaluates the energy efficiency improvement
reached in a fluxgate based current transducer when the output
PA is replaced by a class D or by a class H amplifiers. In Section
II, the basic operation of a current transducer based on fluxgate
effect will be introduced. In Section III, the use of different
output PA architectures is evaluated and the potential energy
savings will be analyzed. A practical implementation of a class
H amplifier for this application is described in section IV. The
practical results obtained, in terms of functionality and energy
savings, are presented in section V, when the features of the
designed transducer are tested and different architectures of
output PA are compared.
I. INTRODUCTION
II. FLUXGATE CURRENT TRANSDUCER OPERATION
HE ever-rise energy cost, due to the growing demand for
energy and the emerging shortage of fossil resources, and
the need for greenhouse gas emissions reduction, lead to
increased global awareness of the importance of energy savings
and energy efficiency. Addressing the energy and climate
challenges requires an interdisciplinary approach involving,
among others, technological solutions.
The power electronics engineers are constantly working on
increasing the efficiency of power electronics and power
systems through the use of new and faster switching devices,
new topologies and advanced controls [1]. However, the energy
efficiency is an emerging watchword on issues related to
industrial electronics design [2-3], where the structure of power
amplifiers (PA) is one of the most promising topics, since they
may be the biggest energy consumers in these systems.
The architecture of PA is usually based on a class AB output
stage, which is characterized by features such as low total
harmonic distortion (THD) and low energy efficiency.
There are currently two technologies, referred to as “Green
Amplifiers” [4], which allows energy savings when they are
compared with class AB based designs. Class G and H
amplifiers are based on class AB amplifier with adjustable
power supply voltages, where these values are adapted in
accordance to the amplifier output voltage level [5].
On the other hand, class D amplifiers, also called “switching
amplifiers”, use a different technology because they incorporate
a switched mode amplifier based in pulse width modulation
(PWM) technique. This operating principle saves considerable
The most suitable method for measuring electrical current
depends on both, the current characteristics and the considered
application. In this regard, current transducers based on
fluxgate effect are used for the measurement of DC and AC
currents of high values with a very high accuracy. Furthermore,
in references [7-9] some reviews devoted to the description of
electric current sensors technologies can be found.
Although the basic operation of fluxgate current transducer
is briefly described in this section, more details about this
technology [10-12] and technical advances [13-19] can be
found in the specialized literature, being also possible find this
type of devices in catalogs of sector leading companies [20-21].
The current measurement process in a fluxgate device is
based on the principle of magnetic flux compensation: The flux
(ΦP) produced in a magnetic core by the main current to be
measured (named primary current: IP) is compensated by an
opposite flux (ΦS), created by a current flowing in the
compensation winding, which is wired on the same core (named
secondary current: IS), so that the resulting flux is zero (Fig. 1).
Abstract—This paper presents a new improvement in the design
of a fluxgate-based current transducers in order to reduce the
power consumption of control electronics.
The proposed improvement involves the replacement of the
output linear amplifier of the transducer by a class H amplifier.
The output amplifier is devoted to the magnetic flux compensation
and generates the transducer output current, which is
proportional to the current to be measured. In this way, it is
possible to reduce significantly the power consumption of these
current transducers without affecting their performance in terms
of linearity, accuracy and bandwidth.
T
Fig. 1. Closed loop operation principle of the fluxgate transducer.
> REPLACE THIS LINE WITH YOUR PAPER IDENTIFICATION NUMBER (DOUBLE-CLICK HERE TO EDIT) <
The fluxgate effect and the suitable control electronics are
used to detect the condition of zero resulting flux. In the case of
zero flux, the secondary current (IS) is proportional to the
primary current (IP), according to the number of turns ratio (NP
and NS) of the windings through which these two currents are
flowing. Eq. (1) shows this relationship when NP = 1.
I P  NS  I S
(1)
2
A. Class AB amplifier
The method commonly used to generate the secondary current
(IS) is based on the utilization of a class AB linear amplifier
(Fig. 4). This solution perfectly meets the high performance
required by fluxgate transducers, but has the disadvantage of
poor features associated with its low efficiency. In this case, the
power consumed by electronics (PI), increases linearly with the
value of the secondary current.
III. GENERATION OF CURRENT COMPENSATION
The zero flux condition in the magnetic circuit, in which the
primary and secondary currents are involved, is obtained when
the average value of the fluxgate excitation current generated
by an auxiliary winding (NA) is zero (Fig. 2).
Fig. 4. Structure of class AB amplifier.
Fig. 2. Fluxgate excitation current IA(t) with no flux due to the primary
current. The voltage across the excitation winding is VA(t).
When the primary current is zero (IP = 0), the average value
of the excitation current is zero (<IA> = 0), and the waveform
of this current is as shown Fig. 2. However, when the primary
current is nonzero, or a residual flux exists in the magnetic
circuit, the average value of the fluxgate excitation current is
also nonzero (<IA> ≠ 0), as shown Fig. 3.
The circuit associated with the compensating winding of the
transducer and the measuring resistor is a LR circuit, where R is
the series association of the measuring (or burden) resistor (RB)
and the compensation winding intrinsic resistance (RS), and L is
the inductance of the compensation winding (LS). In this way,
the amplifier output power (PO) matches the power consumed
in this resistance (R).
Input and output power and the efficiency (η) of the PA are
formulated in Eqs. (2).
PI  VCC  I S
PO  R  I S
When the average value of the fluxgate excitation current is
zero with nonzero primary current, means that the flux due to
the primary current (IP) is equal and opposite of the flux due to
the secondary current (IS). In this case, IS is proportional to IP
according to the windings turns ratio (Eq. (1)).
The secondary current (IS) is generated by the control system,
and it is supplied by an output PA with the condition of zero
average value of the excitation current as operation set point.
Given the wide range of operation of these transducers (large
full-scale), and the high accuracy that they can achieve (up to
0.001%), it is mandatory the use of an accurate, linear and free
of interferences output PA. As a consequence, the architecture
used for the implementation of these PA is usually based on a
traditional class AB linear amplifier.
In this context, this work explores the use of high efficiency
architectures for the implementation of this output PA,
specifically the two “green” architectures introduced in the
previous section. The obtained results, in terms of power
consumption, are compared with the use of the class AB PA.
PO R  I S

PI
VCC
(2)
If the R value is selected such that R·IN = VCC, where IN is the
maximum value that the current transducer can measure, and
assuming an ideal class AB amplifier, that can deliver on its
output up to the supply voltage VCC (rail-to-rail operation), then
the PA efficiency can be expressed by Eq. (3).

Fig. 3. Fluxgate excitation current IA(t) with non-zero flow due to a non-zero
primary current. The voltage across the excitation winding is VA(t).

2
IS
IN
(3)
As is known, and as shows Eq. (3), the class AB amplifier
performance is strongly dependent on the supplied current that
in this case is the secondary current (IS).
The difference between the input and the output power (PA)
is dissipated as heat in the PA and this power can be calculated
through Eq. (4).
PA  PI  PO  VCC  I S  R  I S  I S  VCC  R  I S 
2
(4)
The maximum value of the PA dissipated power is reached
accordingly to Eq. (5).
dPA
0 
dI S
IS 
VCC
I
 N
2 R
2
   50 %
(5)
This low power efficiency leads to a high power dissipation
and usually requires the use of heat-sinks for an effective heat
management.
B. Class D amplifier
A class D amplifier is a pulse width modulation (PWM)
> REPLACE THIS LINE WITH YOUR PAPER IDENTIFICATION NUMBER (DOUBLE-CLICK HERE TO EDIT) <
switched mode amplifier. The analog output voltage of class D
PA is related to the average value of the PWM signal used as
control input signal.
Fig. 5 shows the structure of a class D amplifier based on a
half-bridge converter. It is formed by two N channel MOSFETs
(M1 and M2) and one driver circuit. These components are
usually integrated into a single commercial chip when a low and
medium power applications (up to 300 W) are considered, as is
the case of the integrated circuits TAS5624A and TAS5630B
commercialized by Texas Instruments (www.ti.com).
Fig. 5. Structure of the class D amplifier.
As in the case of class AB amplifier, the output magnitude of
the class D PA is the secondary current (IS), and its average
value can be calculated using Eq. (6).
VO VCC  2d  1
(6)

R
R
VO is the output voltage of the class D PA and d is the duty
cycle of the half-bridge inverter operation. It is defined as the
ratio of the M1 transistor conduction time (TON) to the duration
of the switching period (TS). If the conduction time of the
transistor M2 is defined as TOFF, then the switching period can
be expressed as: TS = TON + TOFF, and the duty cycle of the class
D amplifier as: d = TON / TS.
The great advantage of this type of amplifiers is their high
efficiency, which is theoretically equal to 100 % if the losses in
semiconductors M1 and M2 are neglected. In this regard, input
and output powers of class D amplifiers have practically the
same value and can be calculated through Eq. (7).
IS 
PI  PO  R  I S
2
(7)
The small energy consumption of fluxgate current sensors
based on class D amplifiers is highlighted in [13, 22].
But, given that the magnitude of interest is the PA output
current (IS), it is necessary to considerer that there is a ripple in
this current due to the switching process, whose value can be
estimated using Eq. (8).
I S 
2  VCC  TS
 d  1  d 
LS
(8)
The current ripple ΔIS, which does not exist in a class AB PA,
is added to the value of the secondary current and introduces an
error in the measurement of this current (IS + ΔIS). The
maximum value of this error, which can be inadmissible in high
accuracy applications, occurs when d = 0.5 and can be valued
using Eq. (9).
I S max 
VCC  TS
2  LS
(9)
In a commercial fluxgate transducer the value of LS may be
3
of some Henry, and it is determined by the current measuring
range, the characteristics of the magnetic core and the number
of turns of the compensation winding (NS). Therefore, this value
is generally not eligible and it is dependent on the electrical and
physical characteristics of the current transducer.
The value of the switching period (TS) or switching frequency
(fS = 1 / TS) can be set, within certain limits, to control the value
of secondary current ripple (ΔIS), but there are two different
factors to consider:
- The switching losses in the two transistors (M1 and M2)
increase with frequency.
- The switching noise transmission to the secondary current
(IS) due to stray capacitance between windings also
increases with frequency [23].
As a result, the use of class D amplifiers achieves a
considerable energy saving with respect to a linear class AB
amplifiers solution. This saving can be up to 50 % at medium
current values (IP = IN / 2). But, due to the existence of a ripple
in the secondary current, the value of the measurement accuracy
is reduced by one or two orders of magnitude in relation to that
obtained with the use of class AB amplifiers. In this regard, it
is possible to find references to class D amplifiers with low
distortion [24] and distortion-free baseband [25], but these
designs involve the use of DSP (Digital Signal Processor) due
to the high computational complexity required of their control.
Therefore, in applications where high accuracy in current
measurement is required, the utilization of class D amplifier as
output PA of fluxgate current transducers is not applicable in
practice.
C. Class H amplifier
The adjustable power supply amplifiers are based on a class
AB linear amplifier (shown in Fig. 4) but with a not constant
power supply voltage (variable values of ±VCC). The value of
the power supply voltage is adapted in accordance to the value
of the amplifier output voltage (VO).
These amplifiers are widely used in different fields of
industrial electronics (audio frequency amplifiers [26] and arc
welding systems [27]) being in the area of radio frequency (RF)
communications [28-30] and mobile communications [31, 32]
where the largest number of applications are documented.
The value of the power supply voltage can be changed in two
different modes: stepped mode (multi-stage) and continuous
mode (envelope-tracking). But, in any case, the power supply
voltage must be always higher than the output voltage of the
class AB amplifier.
In the first case (multi-stage), and depending on the value of
the amplifier output voltage, the amplifier power supply voltage
switches between two or three different levels, but always
higher than the instantaneous value of the amplifier output
voltage. These amplifiers are referred as class G amplifiers.
Thus, the difference between the supply and output voltage
is reduced in steps, in the same way as power losses in the
amplifier, which are proportional to this voltage difference and
to the secondary current (IS).
In the second case (envelope-tracking), the power supply
voltage of the amplifier follows the output voltage waveform,
> REPLACE THIS LINE WITH YOUR PAPER IDENTIFICATION NUMBER (DOUBLE-CLICK HERE TO EDIT) <
increased by a value (ΔU), as low as possible without causing
distortion in the output signal. These amplifiers are referred as
class H amplifiers or envelope tracking (ET) amplifiers.
The power losses in a class H amplifier are, as in the class
AB amplifier case, directly proportional to the output current
(IS) and to the difference between the power supply voltage and
the amplifier output voltage. But with the advantage that the
voltage difference value is considerably lower in the case of
class H amplifier than in a conventional class AB amplifier.
The input power of the class H amplifier can be evaluated by
Eq. (10).
PI  VO  U  I S  R  I S  U  I S
4
consumption, when the same operating conditions of the current
transducers are considered.
(10)
And its efficiency can be calculated using Eq. (11).
PO
VO  I S
1
(11)


PI VO  U   I S 1  U
VO
In this way, the lower the value ΔU the better the efficiency
and, in the ideal case with ΔU = 0, the efficiency is the unity.
Therefore, the class H amplifier supplying the fluxgate
secondary current has an accuracy similar to the class AB
amplifier, but with similar energy consumption than a class D
amplifier. Consequently, the use of a class H amplifier to supply
the secondary current in a fluxgate current transducer is
proposed in this work. In this way, the following advantages
could be obtained:
- High precision, as in the conventional fluxgate current
transducers based on a linear class AB amplifier.
- Large decreasing of electrical power requirements for the
transducer operation. This power can be reduced up to 50%
when is compared with a conventional fluxgate transducer.
A drawback, related to the use of a class H amplifier, is the
transient response against fast changes in the primary current
(IP). This is due to the lower bandwidth of class H amplifier in
relation to the conventional linear class AB amplifiers.
However, this is not an important disadvantage in this
application since, in a current transducer based on the fluxgate
effect, the transient feature is assumed by the conventional
current transformer effect and not by the fluxgate effect [13].

D. Energy shaving comparison
The input power of the three compared PA is evaluated via
Eqs. (2), (7) and (10) respectively. The parameters involved in
these expressions are the amplifier supply voltage (VCC), the
resistance of the measurement circuit (R), the secondary current
(IS) and the incremental voltage (ΔU) used in the class H
amplifier.
The values of input power of the three compared PA versus
the primary current (IP) are shown in Fig. 6, assuming the
utilization of transducers with the same maximum current
IN = 1000 A, power supply voltage ±VCC = ±15 V and input
power PI(0) = 3 W in not input current conditions (IP = IS = 0).
Also is assumed ΔU = 1 V and NS = 1000.
As discussed above, and as Fig 6. shown, class D and class
H amplifiers show similar features in terms of input power,
while the use of class AB amplifiers lead to a higher power
Fig. 6. Theoretical input power of compared amplifiers
IV. IMPLEMENTATION OF CLASS H AMPLIFIER
A. Structure of power supply
The power supply voltage of a class H amplifier is related to
its own output voltage, and it is determined using the value of
the incremental voltage ΔU. The positive (+VAB) and negative
(-VAB) values of the power supply voltage are can be calculated
accordingly to Eq. (12).
 VAB   VO  U 
(12)
Naturally, the power supply system that provides the power
supply voltages to the class AB amplifier should be high
performance system, as is the case of switched power sources.
The utilized switched source must provide positive and
negative voltages and currents, so it must be able to work in all
four quadrants V/I.
The usual power converter structure that can meet these
demands is a full-bridge converter. But, other options based on
multiple levels buck converter are documented [33, 34].
In this development, two half-bridge converters are used,
because it is necessary that the output signal is referred to a
common point with the electronics devoted to power control.
The structure of the converter used is shown in Fig. 7, where
one half-bridge generates the positive voltage (+VAB) and the
second converter generates the negative voltage (-VAB).
Fig. 7. Structure of class H power amplifier
> REPLACE THIS LINE WITH YOUR PAPER IDENTIFICATION NUMBER (DOUBLE-CLICK HERE TO EDIT) <
B. Control of power supply
The control system of the class AB amplifier power supply
must control the drivers of the two half-bridge converters.
The voltage reference used as set-point of these two half
bridges converters is equal to the output voltage of the class AB
amplifier (VO) plus the constant value of the used incremental
voltage (ΔU), as shown Eq. (12).
A closed loop control is applied to only one of these two
converters (the half-bridge devoted to the positive supply
voltage generation). The duty cycle of this converter (d+) is
obtained by using as reference voltage (V+*) the positive value
of Eq. (12), as shown Eq. (13).
V *  VO  U
(13)
The duty cycle of the second half-bridge converter (d-) will
be the complementary, as stated in Eq. (14).
TON   TOFF   d   1  d 
(14)
As a consequence, the output voltage of both converters has
the same value but opposite in polarity.
Fig. 8 shows a simplified block diagram of the principle
applied to the control of the converter devoted to the positive
supply voltage generation.
5
+VAB
VO
̵ VAB
Fig. 9. Power supply voltages ±VAB (magenta and green traces) and output
voltage VO (blue trace) in class H amplifier.
V. EXPERIMENTAL RESULTS
Fig. 10 presents the final industrial prototype of the designed
transducer, where the main components of the system can be
identified: measuring transformer, printed circuit board (PCB),
and box to contain all transducer elements.
Fig. 10. Designed transducer based on class H output PA.
Fig. 8. Block diagram of inverter control class H
C. Behavior of class H amplifier
The design of the proposed PA (shown in Figs. 7 and 8) was
simulated under different conditions in order to verify its proper
operation before using this amplifier as output stage of a
fluxgate current sensor. Once verified by simulations the
functionality of the designed PA, a laboratory prototype was
built and tested.
Fig. 9 shows the waveforms measured for the output voltage
and power supply voltages of the class H amplifier when 5 V
and 200 Hz sinusoidal voltage is applied as amplifier input
voltage. The voltage tracking difference (ΔU) is set to 1V, 1 Ω
resistor is used as RB and ±VCC are set to ±15 V.
In order to evaluate the performance of this device, some
laboratory tests were conducted. This section presents the
results obtained in these experimental tests. The first test
evaluates the linearity and measurement errors in full-scale DC
current. The second one evaluates the device response for highlevel current transients. Finally, the power consumption was
compared with the consumption of fluxgate transducers based
on class AB and class D PA as output stage, in order to validate
the energy saving achieved.
As is well known, the frequency response (or bandwidth) of
fluxgate current transducers is based on the combination of two
(or even three) different techniques [16]: the fluxgate principle
to operate from DC to low frequencies (few Hz), and the current
transformer principle to operate up to few hundred of kHz. As
a consequence, the upper cutoff frequency of the transducer is
related to the materials and construction parameters of to the
used magnetic components (as are the leakage inductance and
the stray capacitance of the measuring transformer [35]).The
upper cutoff frequency also depends on the value of output
resistor RB but it has no dependence with the electronics
devoted to the fluxgate operation.
Because the fluxgate transducer presented in this paper uses
the same magnetic components presented in [13], it can be
assumed that it also has the same bandwidth (about 170 kHz).
> REPLACE THIS LINE WITH YOUR PAPER IDENTIFICATION NUMBER (DOUBLE-CLICK HERE TO EDIT) <
A. DC current measurement
For this test, the primary current (IP) was generated by a
QPX1200 PowerFlex DC power supply and it was adjusted by
a programmable DC active load. IP was measured by a no
inductive shunt (80 A/150 mV), and this value was used as a
reference. Furthermore, this current was coupled to the fluxgate
transducer through 14 turns. Finally, the output resistor value
utilized for this test was RB = 1 Ω.
Fig. 11 shows the input-to-output current characteristic
measured on the device under test, and Eq. (15) shows the
expression of the linear regression of this characteristic.
I Measured  1.0008  I P  0.0031
(15)
This result indicates good system linearity (1.0008) and low
offset error (around 3 mA).
Fig. 12 shows the relative error in the measurement referred
to the device full-scale. Accordingly with the obtained data, the
relative error is lower than ±0.2 % in the ±700 A range.
VO _ H  I P 1000
6
(16)
In the class AB device NS = 1750 and it uses RB = 2.5 Ω (as
is suggested by manufacturer). This implies that the output
voltage of this transducer is:
VO _ AB  I P 700
(17)
Finally, both devices use the same power supply voltages
(±15 V).
In the first test, a slow slope current ramps (±12 A/ms), with
initial and final values of IP equal to 0 and ±600 A respectively,
are generated. The obtained results for ramps with positive and
negative slopes are shown in Fig. 13. Red and magenta traces
are the evolution of ±VAB, green trace is the output voltage of
the class AB transducer (VO_AB) and blue trace is the output
voltage of the device based in class H PA (VO_H).
+VAB
VO_AB
̵ VAB
VO_H
+VAB
Fig. 11. Experimental input-to-output characteristic of the transducer.
VO_AB
VO_H
̵ VAB
Fig. 13. Response of transducers to current ramps with positive (top) and
negative (bottom) slopes.
Fig. 12. Measured relative output error of the designed transducer.
B. Transient Current Measurement
For these experimental tests, a Danfysik Ultrastab 867-700i
fluxgate transducer has been used as reference instrument for
current measurements. This transducer uses a class AB power
amplifier as output stage.
The experimental setup used for tests is completed by a DC
power supply as generator of the DC primary current (IP) and a
6060B Hewlett Packard DC electronic load. The same IP
current flows through the two fluxgate transducers and their
output voltages are measured and recorded by a DPO3014
Tektronix digital oscilloscope.
In the class H device NS = 1000 and it uses RB = 1 Ω. This
implies that the transducer output voltage is:
In the second test, a pulsating current for testing the dynamic
response of the class H device is generated. The frequency of
the current pulse train is 100 Hz with a 50 % duty cycle, the
slope of the current pulses is ±1200 A/ms and the initial and
final values of IP are 0 and ±600 A respectively.
The obtained results for ramps with positive and negative
slopes are shown in Fig. 14. Red and magenta traces are the
evolution of ±VAB, green trace is VO_AB and blue trace is VO_H.
> REPLACE THIS LINE WITH YOUR PAPER IDENTIFICATION NUMBER (DOUBLE-CLICK HERE TO EDIT) <
+VAB
VO_AB
̵ VAB
VO_H
VO_H
+VAB
VO_AB
̵ VAB
Fig. 14. Response of transducers to current ramps with positive (top) and
negative (bottom) slopes.
Finally, a triangular IP with 150 A of amplitude, 250 A of DC
offset and 1 kHz of frequency was generated. Fig. 15 shows the
transducers response and the evolution of the power supply in
the class H device (same colors are used for traces).
7
In order to appreciate the differences with a linear class AB
amplifier transducer, the same class H amplifier was tested
without the implementation of the output voltage tracking
function, behaving as a simple linear class AB amplifier.
This strategy enables testing three different transducers.
They uses the same magnetic circuit and the same electronics
for implementing the fluxgate measure principle, but using
three variants for the output amplifier implementation: class
AB, D and H amplifiers. The following figure shows the
experimental results obtained in terms of the transducer energy
consumption.
Various measurements of the current transducers energy
consumption have been made on the power supply circuit when
±VCC = ±15 V. Measurements include the self-consumption of
the control electronics and the obtained results are depicted in
Fig. 16. As it shown, the energy consumption characteristic of
the class AB amplifier is proportional to the measured current
(IS), with a non-zero power consumption when no current is
measured due to the self-consumption of the control electronics.
In the case of class D amplifier, as is expected, the evolution
of the energy consumption characteristic is proportional to the
resistance of the compensation circuit (R) and to the square of
the RMS value of the secondary current (IS2).
In conditions of zero primary current, non-zero energy
consumption exists due to the self-consumption of the control
electronics and, in this case, it is slightly higher than in the case
of class AB amplifier.
+VAB
̵ VAB
VO_AB
VO_H
Fig. 15. Response of transducers to a triangular IP waveform.
These results show the concordance between measurements
made using the designed transducer and the linear transducer
used as a reference instrument (in agreement with Eqs. (16) and
(17)). These results also demonstrate the proper operation of the
class H PA used in the designed fluxgate transducer.
C. Power consumption
For these experimental tests, a PREMO fluxgate DCT700A
with IN = 1000 A as maximum current (700 A rated current) has
been used. This transducer includes a class D amplifier for the
generation of the secondary current in the measurement circuit.
Using the same magnetic components, but in substitution of
class D amplifier, a new control electronics with a class H
amplifier has been incorporated.
Fig. 16. Power consumption of the class AB, D and H amplifiers. Ordinate
axis in watts [W] and abscissa axis in amperes [A].
In relation to energy consumption, the class H amplifier
behaves like a class D amplifier, having a similar power
consumption characteristic.
The energy saving of class D and class H amplifiers, in
relation to the class AB amplifier, almost reaches the value of
40 % for some values of measured current (IS) and when the
class H amplifiers is used.
Differences in energy consumption, when they are compared
with the expected values, and the asymmetry observed between
positive and negative currents of class H and D amplifiers
(shown in Fig. 16) can be attributed to the peculiarities of the
control implementation (only the positive supply voltage is
regulated) and to the switching and magnetic losses, since these
effects have been neglected in the analytical description of
current transducers operation.
> REPLACE THIS LINE WITH YOUR PAPER IDENTIFICATION NUMBER (DOUBLE-CLICK HERE TO EDIT) <
VI. CONCLUSIONS
This work presents a new approach in order to reach a
significant improvement, in terms of energy consumption, in
current transducers based on the fluxgate effect.
Since most of the energy consumption is produced in the
output power amplifier that supplies the flux compensation
winding, interest has focused on this output stage which is
present in all fluxgate transducers.
Traditionally, the linear class AB amplifier has been
considered as the optimal solution for its accuracy, linearity,
low-noise and low-distortion in current measurement. As
alternative, and in order to optimize the power consumption of
the control electronics, the use of class D and class H amplifiers
have been analyzed.
Theoretical considerations and experimental results have
shown that both types of amplifiers significantly improve the
energy consumption by almost 40 % in some ranges of the
current transducer operation.
However, the class D amplifier has the disadvantage that it
adds a current ripple to the output current signal, which can be
an inconvenience in cases of high precision applications.
The use of class H amplifiers as output stage of compensation
and current measurement circuit, is the most advantageous
option but with a slightly more complex design.
Experimental results also have shown the good performances
of the designed transduces when it is compared with a
transducer based on a class AB amplifier as output stage.
In summary, the use of class H amplifier has the advantages
of the low power consumption associated with a class D
amplifier, while maintaining all other benefits in terms of
linearity, accuracy, bandwidth, low-noise, etc. which are typical
of a linear class AB amplifier.
REFERENCES
[1]
[2]
[3]
[4]
[5]
[6]
[7]
[8]
[9]
Popović-Gerber, J.; Oliver, J.A.; Cordero, N.; Harder, T.; Cobos, J.A.;
Hayes, M.; O'Mathuna, S.C.; Prem, E., "Power Electronics Enabling
Efficient Energy Usage: Energy Savings Potential and Technological
Challenges", IEEE Transactions on Power Electronics, vol.27, no.5,
pp.2338-2353, May 2012
Consoli, A.; Scelba, G.; Scarcella, G.; Cacciato, M., "An Effective
Energy-Saving Scalar Control for Industrial IPMSM Drives", IEEE
Transactions on Industrial Electronics, vol.60, no.9, pp.3658-3669,
September 2013
Lu Lu; Bin Yao, "Energy-Saving Adaptive Robust Control of a Hydraulic
Manipulator Using Five Cartridge Valves With an Accumulator", IEEE
Transactions on Industrial Electronics, vol.61, no.12, pp.7046-7054,
December 2014
Frink, M., “Green Amps”, Front of House (Magazine), vol.10, no.5,
pp.34-35, February 2012
Guanghai Gong, H. Ertl, J.W. Kolar, "Novel Tracking Power Supply for
Linear Power Amplifiers", IEEE Transactions on Industrial Electronics,
vol. 55, no. 2, pp. 684-698, February 2008
Chang, Joseph S.; Meng-Tong Tan; Zhihong Cheng; Yit-Chow Tong,
"Analysis and design of power efficient class D amplifier output stages",
IEEE Transactions on Circuits and Systems I: Fundamental Theory and
Applications, vol.47, no.6, pp.897-902, June 2000
Ziegler, S.; Woodward, R.C.; Iu, H.H.-C.; Borle, L.J., "Current Sensing
Techniques: A Review", IEEE Sensors Journal, vol.9, no.4, pp.354-376,
April 2009
Ripka, P., “Electric Current Sensors: A Review”, Measurement Science
and Technology, vol.21, no.11, pp.1-23, November 2010
Velasco-Quesada, G. et al. “Technologies for Electric Current Sensors”,
in Novel Advances in Microsystems Technologies and Their Applications,
L.A. Francis and K. Iniewski Eds. FL: CRC Press, 2014, pp.265-292
8
[10] Ripka, P., “Review of fluxgate sensors”, Sensors and Actuators A:
Physical, vol.33, issue 3, pp.129-141, June 1992
[11] Ripka, P.; Janosek, M., "Advances in magnetic sensors," 2008 IEEE
Sensors, pp.1-4, 26-29 Oct. 2008
[12] “Isolated Current and Voltage Transducers: Characteristics-ApplicationsCalculations (3rd Edition),” LEM Components, CH 24101 E/US, 2004
[13] Velasco-Quesada, G.; Román-Lumbreras, M.; Conesa-Roca, A.; Jeréz, F.,
"Design of a Low-Consumption Fluxgate Transducer for High-Current
Measurement Applications," IEEE Sensors Journal, vol.11, no.2,
pp.280,287, Feb. 2011
[14] Xiaoguang Yang; Yuanyuan Li; Wei Guo; Weidong Zheng; Cunfu Xie;
Hongli Yu, "A New Compact Fluxgate Current Sensor for AC and DC
Application", IEEE Transactions on Magnetics, vol.50, no.11, pp.1,4,
Nov. 2014
[15] Xiaoguang Yang; Yuanyuan Li; Weidong Zheng; Wei Guo; Youhua
Wang; Rongge Yan, "Design and Realization of a Novel Compact
Fluxgate Current Sensor", IEEE Transactions on Magnetics, vol.51, no.3,
pp.1,4, March 2015
[16] Michel Ghilardi; Horst Bezold, “Maintaining Precision in Varying
Temperatures”, Bodo’s Power Systems, vol.06-15, pp.16,21, June 2015
[17] Ripka, P.; Draxler, K.; Styblikova, R., "Measurement of DC Currents in
the Power Grid by Current Transformer", IEEE Transactions on
Magnetics, vol.49, no.1, pp.73-76, Jan. 2013
[18] Ripka, P.; Draxler, K.; Styblikova, R., "AC/DC Current Transformer With
Single Winding", IEEE Transactions on Magnetics, vol.50, no.4, pp.1-4,
April 2014
[19] Kui Li; Feng Niu; Yi Wu; Yao Wang; Yihua Dai; Lili Wang; Erping Li,
"Nonlinear Current Detection Based on Magnetic Modulation
Technology”, IEEE Transactions on Magnetics, vol.51, no.11, pp.1-4,
Nov. 2015
[20] PREMO Group, Catalog: DCT 700A Transducers (2014).
[21] LEM International SA, Catalog: High Precision Current Transducers
(2014).
[22] Radivoje Đurić; Milan Ponjavić, “Self-Oscillating Fluxgate Current
Sensor with Pulse Width Modulated Feedback”, ELECTRONICS, vol.14,
no.2, December 2010
[23] W. T. McLyman, “Transformer and Inductor Design Handbook”, 3rd
edition. New York: Marcel Dekker, 2004, p. 532
[24] Stefanazzi, L.; Chierchie, F.; Paolini, E.E.; Oliva, A.R., "Low Distortion
Switching Amplifier With Discrete-Time Click Modulation", IEEE
Transactions on Industrial Electronics, vol.61, no.7, pp.3511-3518, July
2014
[25] Chierchie, F.; Paolini, E.E.; Stefanazzi, L.; Oliva, A.R., "Simple RealTime Digital PWM Implementation for Class-D Amplifiers With
Distortion-Free Baseband", IEEE Transactions on Industrial Electronics,
vol.61, no.10, pp.5472-5479, October 2014
[26] Jingqi Liu; Allasasmeh, Y.; Gregori, S.; Leesti, B.; Snelgrove, M., "An
envelope tracking H-bridged audio amplifier with improved efficiency
and thd less than 0.1%", 25th IEEE Canadian Conference on Electrical &
Computer Engineering (CCECE), pp. 1-4, April 29-May 2 2012
[27] Anderson, K.; Cook, G.E.; Barnett, R.J.; Eassa, E.H., "A class-H amplifier
as a generic power source for arc welding", IEEE Southeastcon '90
Proceedings, vol.3, pp.792-796, 1-4 April 1990
[28] Tafuri, F.F.; Sira, D.; Jensen, O.K.; Larsen, T., "Efficiency enhancement
of an envelope tracking power amplifier combining supply shaping and
dynamic biasing", European Microwave Integrated Circuits Conference
(EuMIC), pp.520-523, 6-8 October 2013
[29] Junghyun Ham, Haeryun Jung, Hyungchul Kim, Wonseob Lim,
Deukhyoun Heo; Youngoo Yang. “A CMOS Envelope Tracking Power
Amplifier for LTE Mobile Applications”, Journal of Semiconductor
Technology and Science, vol.14, no.2, April 2014
[30] Huan Xi; Qian Jin; Xinbo Ruan, "Feed-Forward Scheme Considering
Bandwidth Limitation of Operational Amplifiers for Envelope Tracking
Power Supply Using Series-Connected Composite Configuration", IEEE
Transactions on Industrial Electronics, vol.60, no.9, pp.3915-3926,
September 2013
[31] Jonmei, J.Y.; Kimball, D.; Chin Hsia; Hsuan-yu Pan; Ricketts, S.;
Ghajari, H., "High-efficiency, high-linearity envelope tracking power
amplifier for mobile UHF applications," Military Communications
Conference - MILCOM 2010, pp.1572,1576, Oct. 31 2010-Nov. 3 2010
[32] Young, J.P.; Ripley, D.; Lehtola, P., "Envelope Tracking power amplifier
optimization for mobile applications", IEEE SOI-3D-Subthreshold
Microelectronics Technology Unified Conference (S3S), pp.1-4, 7-10
October 2013
> REPLACE THIS LINE WITH YOUR PAPER IDENTIFICATION NUMBER (DOUBLE-CLICK HERE TO EDIT) <
[33] Rodriguez, M.; Miaja, P. F.; Rodriguez, A.; Sebastian, J.; ”A MultipleInput Digitally-Controlled Buck Converter for Envelope Tracking
Applicationsin Radiofrequency Power Amplifiers”, IEEE Transactions
on Power Electronics, vol.25, no.2, pp.1078-1089, February 2010
[34] V. Yousefzadeh, E. Alarcon, D. Maksimovic, “Three-level buck
converter for envelope tracking applications,” IEEE Transactions on
Power Electronics, vol.21, no.2, pp. 549-552, March 2006
[35] N. Kondrath; M.K. Kazimierczuk, "Bandwidth of Current Transformers",
IEEE Transactions on Instrumentation and Measurement, vol.58, no.6,
pp.2008,2016, June 2009
9