PDu150CL V5
Ultra-low Noise 150V Piezo Driverwith Strain Gauge Feedback

Specifications
Power Supply+24V, Ground

Output Voltage-30V to +150V

Peak Current

300 mARMS Current

235 mA

Power Bandwidth

80 kHz (150 Vp-p)

Signal Bandwidth

180 kHz

Slew Rate

38 V/usGain

20 V/V

Input Impedance

The PDu150CL combines a miniature high-voltage
power supply, precision strain conditioning circuit,feedback controller, and ultra-low noise amplifier ina package the size of a credit card. It provides all of
the necessary functions for high-resolution openloop or closed-loop control of piezoelectric
actuators with integrated resistive strain sensors.

Input Offset
Load
Output Noise

The PDu150CL produces up to 300mA of output
current at frequencies up to 80 kHz withexceptionally low noise and is protected against
short-circuit, average current overload, andexcessive temperature. Passive cooling is available
for low power applications or the integrated fan canbe used for power dissipations above 5W. The
PDu150CL can be mounted on a base structure withfour M2.5 screws or directly onto a hostmotherboard (PDu150CL-PCB).

10 𝑘Ω (Closed loop mode)
3.05 𝑘Ω (Open loop mode)±5 mV
Unlimited
26 uV RMS,
1uF Load, 0.03Hz to 1MHz

Protection

Short-circuit, average current,
and under-voltage protection

Quiescent Current

100 mA (10 mA in Shutdown)

Connectors

Screw terminals (AWG 20-30)

Dimensions

40 x 89 x 44 mm

Environment

0 to 60C (32 to 140F)
Non-condensing humidity

Weight

80 g

B+
−𝜈𝜀
24V Supply

Input
Strain

VS
G
G
EN
IN
SNS

S0VS+BB+
G
HVHV+
G

S-

+𝜀

S+

0V -

+

−𝜈𝜀

+𝜀

B-

G
EN

GroundEnableFigure 1. Basic Connection diagram

PDu150CL V5 Datasheet

1

Modified 21/01/2021

Operation

Power Bandwidth

As shown in Figure 2, PDu150CL can be used in either
open-loop or closed-loop modes. In the open-loop
mode, the input signal is connected directly to the power
amplifier. Note that the power amplifier uses a novel
low-noise differential architecture that cannot be
connected to ground.

The maximum slew-rate is 38 V/us. Therefore, themaximum frequency sine-wave is
𝑓𝑚𝑎𝑥 =The power bandwidth for a 150 Vp-p sine-wave is
80 kHz.

In the closed-loop mode, the input signal acts as acommand signal for the feedback loop. The strain signal
is derived from a resistive strain gauge attached to thepiezo or structure.

+24V
SupplyWith a capacitive load, the power bandwidth is limitedby the output current. The maximum frequency sinewave is
𝑓𝑝𝑤𝑟 =

Bridge Sensor Sensor
Balance Gain Offset

EnableStrain Signal

Load
(uF)
0.03
0.1
0.3
1
3
10
30

SNS

Feedback Gain

IntegralControl

Input

ClosedLoop
HV+ Piezo+

20
HVOpenLoop

𝜋𝑉𝐿(𝑝−𝑝) 𝐶𝐿

Voltage Range
50 V
100 V
150 V
64000
32000
21000
19000
9600
6400
6400
3200
2100
1900
960
640
640
320
210
190
96
64
64
32
21

Table 1. Power bandwidth (in Hz) with a capacitive load

Figure 2. PDu150CL Block Diagram

The maximum peak-to-peak voltage is plotted below
versus load capacitance.

Output Current

180

The peak output current is 300mA. In addition, themaximum average current is 105mA. The average
current is useful for calculating the power dissipation
and average supply current. For a sine wave, the average
positive output current is equal to

160

3uF

10uF

300nF 100nF

1uF

30nF

Peak to Peak Voltage (V)

140

1
√2
𝐼𝑎𝑣 =
𝐼𝑟𝑚𝑠 = 𝐼𝑝𝑘 .
𝜋
𝜋

120
100
80
60

Supply Current

40

The quiescent power for the amplifier is approximately
2 W or 85 mA. This can be reduced to <10 mA by pulling
the Enable pin low with an open collector circuit. If the
fan is used, the quiescent power is increased by 0.5W,

20
0

2

10

The supply current is related to the total average output
current by
𝐼𝑠 =

𝐼 𝑝𝑘

where 𝐼𝑝𝑘 is the peak current limit, 𝑉𝐿(𝑝−𝑝) is the peakto-peak output voltage, and 𝐶𝐿 is the effective load
capacitance. The power bandwidth for a range of load
capacitance values is listed in Table 1.

S0VS+BB+

Strain Sensor
Conditioning

Boost
Converter

38 × 106
𝜋𝑉𝐿(𝑝−𝑝)310Frequency (Hz)

4

10

5

10

Figure 3. Power Bandwidth

200 × (𝐼𝑎𝑣 + 0.010).
24

where 𝐼𝑎𝑣 is the total average output current. The
maximum supply current is 0.9 A at full power.
PDu150CL V5 Datasheet

2

Modified 21/01/2021

Signal Bandwidth
The small-signal bandwidth for a range of capacitive
loads is listed in Table 2. The small-signal frequency
responses are plotted in Figure 4.
Load
Capacitance
No Load
30 nF
100 nF
300 nF
1 uF
3 uF
10 uF
30 uF

SignalBandwidth
180 kHz120 kHz34 kHz
11 kHz3.2 kHz980 Hz190 Hz73 Hz

Figure 5. Low frequency output noise (0.03 Hz to 10 Hz)

The high frequency noise (10 Hz to 1 MHz) is listed in thetable below versus load capacitance. The total noisefrom 0.03 Hz to 1 MHz is found by summing the RMS
22values, that is 𝜎 = √𝜎𝐿𝐹
+ 𝜎𝐻𝐹.

Table 2. Small signal bandwidth (-3 dB)

Load
Capacitance
10 nF
30 nF
100 nF
300 nF
1 uF
3 uF
10 uF
30 uF

Magnitude (dB)

40
30

30n

10u

1u

100n

300n

30n

20
10
0

2

10

Phase (deg.)

3u

3

10

4

10

5

10

0

HF
Noise
450 uV
170 uV
60 uV
34 uV
21 uV
16 uV
16 uV
18 uV

Total
Noise
450 uV
170 uV
62 uV
37 uV
26 uV
23 uV
22 uV
23 uV

Table 3. HF Noise (10 Hz to 1 MHz) and total noise-50

Strain Sensor Specifications

-100
-150

2

10

3

4

10
10
Frequency (Hz)Strain Sensor Specifications

5

10

Figure 4. Small signal frequency response

Power Amplifier NoiseThe output noise contains a low frequency component(0.03 Hz to 10 Hz) that is independent of the load
capacitance; and a high frequency component (10 Hz to
1 MHz) that is inversely related to the load capacitance.
The noise is measured with an SR560 low-noise amplifier(Gain = 1000), oscilloscope, and an Agilent 34461A
Voltmeter. The low-frequency noise is plotted in Figure
5. The RMS value is 15 uV with a peak-to-peak voltage of
100 uV.

PDu150CL V5 Datasheet

Bridge Excitation

5V (Differential)

Sensor Resistance350 𝛀 to 1000 𝛀

Sensor Configuration

Single, Half or Full Bridge

Bridge Balance Range+/- 6 mV

Gain Range

200 to 3000

Offset Range+/- 6 mV

Bandwidth

10 kHzInput Noise Voltage

3 uV RMS (0.1Hz to 100Hz)

Table 4. Strain Sensor Specifications

3

Modified 21/01/2021

Sensor Connection

Full Bridge Strain Sensor
A full-bridge arrangement constructed from two 90
degree rosette sensors provides good immunity totemperature variation, the best linearity, and twice theresolution of a half bridge; however, this configuration
also requires more wiring. Actuators with full-bridgestrain sensors are available from www.piezodrive.com

The PDu150CL is compatible with single element strain
sensors, half-bridges,
andfull-bridge
sensorarrangements. The advantages of these different
arrangements and the recommended methods ofconnection are described in the following. Suitable strain
sensors are available from many suppliers, including
www.omega.com.

B+

Single Element Strain Gauge−𝜈𝜀Single element strain sensors can be useful inapplications where the temperature is stable orsimplicity is a priority. As shown below, therecommended configuration requires three dummy
resistors (R) equal in resistance to the strain gauge. The
best temperature stability is achieved when the dummy
resistors have the same temperature coefficient as thestrain gauge and are thermally connected to the strain
gauge.

S-−𝜈𝜀The strain elements aligned with the direction of piezo
expansion are denoted by +𝜀 and the 90 degree
elements are denoted – 𝜈ε. This convention is adopted
since a positive strain in the piezo +𝜀 causes a negative
resistance change in the 90 degree element due toPoisson’s ratio (𝜈). Note that the mounting of the tworosette sensors are opposite.

S+

R

+𝜀

B-

R

S-

S+

0V -

B+
R

+𝜀

+𝜀

Sensor Noise and Resolution

B-

Since the sensor noise is filtered by the complementarysensitivity function of the control loop, the bandwidth ofinterest is typically 0.1Hz to 100Hz. The upper frequency
limit has little effect since the majority of noise in thisbandwidth is due to low-frequency noise from the onboard references and primary gain stage. With a bridge
resistance of 350 Ohms, the total input referred noisevoltage is plotted below, the RMS value is 3uV with apeak-to-peak voltage of 20uV.

Half Bridge Strain Sensor
A half bridge arrangement with a 90 degree rosette
sensor provides good immunity to temperature variation
and approximately 30% better resolution than a single
element. The recommended configuration requires twodummy resistors (R) that are equal in value to the strain
gauge resistance.
B+
−𝜈𝜀

S-

Noise (uV)

R
S+

R

+𝜀
B-

The strain element aligned to the piezo expansion isdenoted by +𝜀 and the 90 degree element is denoted– 𝜈ε. This convention is adopted since a positive strain in
the piezo +𝜀 causes a negative resistance change in the
90 degree element due to Poisson’s ratio (𝜈).

PDu150CL V5 Datasheet

Figure 6. Total noise with a 350 Ohm Bridge (0.1Hz to 100Hz)

The sensor noise can be used to estimate the sensor
resolution. The induced voltage for a two-varying
element full bridge is [1, 2]

4Modified 21/01/2021

1
𝑉 𝐺𝐹 𝜀 (1 + 𝜈)
2 𝑒Where 𝑉𝑒 is the excitation voltage (5V), GF is the gauge
factor (typically ~2), 𝜀 is the strain, and 𝜈 is the Poisson’s
ratio (0.34 for PZT5H). For a full-scale strain of 0.1%, theexpected bridge voltage is 6.7 mV. Therefore, theexpected RMS resolution isrequires an input of -1.5V to +7.5V during calibration,rather than 0V to +7.5V.

𝑉𝑠 =Resolution =For stack actuators with different voltage ratings, thecalibration input signal should be chosen accordingly. For
example, a suitable calibration input for a piezo with avoltage rating -20V to +100V would be -1V to +5V.

3 uV
= 0.045% of Full Scale
6.7 mV

Closed-Loop Operation
Once the sensor is calibrated, the PDu150CL can beplaced in closed-loop mode. The structure of the closedloop system is illustrated below.

Sensor Calibration Procedure
The following procedures are required to calibrate thebridge conditioning circuit and should be performed withthe sensor and piezo connected to the PDu150CL.

Input

Balance the Bridge
Small mismatches in the bridge resistances can be
accounted for by the “Bridge Balance” pot. This step
optimizes the temperature sensitivity of the bridge
circuit.
1) Place the PDu150CL in “Open-Loop” mode and apply
0V or a short-circuit to the input terminals.
2) Connect a voltmeter between the S- and S+
terminals (without disconnecting the bridge).
3) Tune the “Bridge Balance” pot until the measured
voltage is zero.

Controller

Amp

Piezo

Sensor

𝛼
𝑠

20

𝐺(𝑠)

𝐹(𝑠)

StrainFigure 7. Feedback structure of the PDu150CL

The closed-loop sensitivity is defined by the sensitivity ofthe strain sensor. For example, if the piezo has a fullscale range (FSR) of 20 um and the strain sensor iscalibrated for 0V to 10V, the closed loop sensitivity is
Sensitivity =FSR= 2 𝜇m/V
10V

Set the Sensitivity and Offset
This step calibrates the sensor so that a 0V to 150V signal
applied to the piezo produces a 0V to 10V strain signal.
1) Turn the “Sensor Gain” pot fully anti-clockwise, (10turns).
2) Ensure the PDu150CL is in “Open-Loop” mode andapply 0V or a short-circuit to the input terminals.
3) Monitor the SNS terminal and tune the “Sensor
Offset” pot until the voltage is zero.
4) Apply 7.5V to the input terminal to generate 150V
across the piezo.
5) Monitor the SNS terminal and tune the “Sensor
Gain” pot until the voltage is +10V.

Calibrating the Feedback Gain
The feedback gain defines the closed-loop bandwidthand settling time of the system. It is usuallyadvantageous to choose the lowest satisfactory
feedback gain to avoid unnecessary sensor noise. A
simple calibration procedure is described in thefollowing:1) Turn the “Feedback Gain” pot fully anti-clockwise (10turns).
2) Place the PDu150CL in closed-loop mode and apply a
1Vp-p triangle wave with a 5V offset to the input
terminal. If the sensor was calibrated with a full scale
range other than 10V, use an offset voltage equal to
mid-range.
3) Monitor the input signal and SNS terminal with an
oscilloscope and increase the feedback gain until the
point where overshoot begins to occur.

Variations
Many variations of the above procedure are possible.
Some useful options are listed below.
The offset and gain can be tuned simultaneously byapplying a 5-Hz sine wave to the input terminals with arange of 0V to 7.5V, which results in 0V to 150V acrossthe piezo. Monitor the SNS terminal with an oscilloscope
and tune the “Sensor Offset” and “Sensor Gain” pots
until the measured sine-wave is between 0V and 10V.

For applications that do not require high-speed tracking,the above procedure is not required. The minimum
feedback gain is suitable.
To achieve a specific -3dB bandwidth, replace thetriangle wave with a sine-wave and tune the feedback
gain until the amplitude of the SNS signal is 0.7Vp-p.

Rather than calibrating the sensor to +10V at full scale,
another voltage such as +5V may be more desirable.
If negative voltages across the piezo are acceptable, it isconvenient to calibrate the full piezo voltage range, e.g.
-30V to +150V, to a SNS voltage of 0V to +10V. This
PDu150CL V5 Datasheet

5

Modified 21/01/2021

Headroom

20

When the full-scale range of the sensor is calibrated to
the full-scale range of the piezo, some consideration for‘headroom’ is required. To allow the control loop tocompensate for effects such as thermal drift and creep,
the input signal is typically restricted to a range of 10%
to 90% so that the control-loop can utilize the remaining
10% at the lower and upper extremes. For example, asystem with a full-scale range of 0V to 10V, would havea practical closed-loop input range of 1V to 9V.

Input
Sensor

Displacement (um)

15

10

5

An alternative to the above approach is to account forheadroom during calibration. For example, rather thanusing the full scale range for calibration, e.g. -30V to+150V, a smaller range can be chosen, e.g. -15V to+130V. By using this method, the resulting closed-loop
input range will be 0V to 10V, which may be moredesirable than 1V to 9V.

0
0.02

0.04

0.06

0.08

0.1
t (s)

0.12

0.14

0.16

0.18

0.2

Figure 9. 10-Hz Full-Range Tracking Performance

20

Example Application
In this example, an SCL050518 stack actuator with fullbridge strain sensor is operated in closed-loop. The
actuator develops a displacement of 20um at 150V andutilizes a full-bridge strain sensor constructed from two
90 degree rosettes.

Displacement (um)15

The PDu150CL was calibrated so that an applied voltage
of 0V to 150V corresponds to a strain signal of 0V to 10V.
The feedback gain was then chosen to achieve goodtracking performance with a 10-Hz full-range triangle
wave, as shown in Figure 9.

105Open Loop
Closed Loop00

The open- and closed-loop responses to a full-range
1-Hz sine-wave input are plotted in Figure 10. Excellent
compensation of hysteresis can be observed.

2

4
6
Input Signal (V)810Figure 10. Open- and Closed-Loop response (1-Hz Sinusoid)

Before evaluating the total positioning noise, thefeedback gain is adjusted to provide a closed-loop
bandwidth of precisely 20 Hz by applying a 20-Hz sinewave and varying the feedback gain until the amplitude
response is -3dB. This allows a direct comparison toother methods with an identical bandwidth.

The total positioning noise due to the amplifier, sensor,
and feedback controller can then be quantified bymeasuring the differential output voltage of the power
amplifier with a zero volt input [3].
The differential output voltage was measured using an
SR560 low-noise amplifier with a gain of 10 and apassband of 0.03 Hz to 1 MHz. The resulting voltage wasscaled by the sensitivity of the piezo (20um/150V) and isplotted in Figure 11. The RMS value is 8.8 nm with apeak-to-peak value of 60 nm over 50 seconds. This
represents an RMS resolution of
Resolution =8.8 nm
= 0.044% of Full Scale
20 um

This value agrees with the predicted resolution in“Sensor Noise and Resolution”.

Figure 8. SCL050518 Actuator

PDu150CL V5 Datasheet

6

Modified 21/01/2021

Figure 11. Closed-loop positioning noise (0.03Hz to 1MHz)

Overload Protection / Shutdown
The PDu150CL is protected against short-circuit andaverage current overload.
Figure 12. Dimensions (mm)The amplifier can be shutdown manually by pulling the
Enable pin low with an open-collector, or open-drain
circuit. The Enable pin normally floats at 5V and should
not be driven directly.

Contact / Support
info@piezodrive.com

Heat Dissipation

References

The heat dissipation is approximately[1] A Review of Nanometer Resolution Position Sensors:
Operation and Performance; A. J. Fleming; Sensors andActuators A: Physical; 2013, 190, 106-126

𝑃𝑑 = 200 × (𝐼𝑎𝑣 + 0.010).
For example, with a sinusoidal output, the power is
𝑃𝑑 = 200 × (𝑉𝐿(𝑝−𝑝) 𝐶𝐿 𝑓 + 0.010).

[2] Design, Modeling and Control of Nanopositioning
Systems; A. J. Fleming & K. K. Leang; Springer, 2014

For low-current applications that dissipate less than
5W, the heatsink fan may be removed. If the power
dissipation is above 5W, forced air or the included fan isrequired.

[3] Measuring and Predicting Resolution in
Nanopositioning Systems; A. J. Fleming; Mechatronics;
2014, 24, 605-618

SafetyRevision History

This device produces hazardous potentials and should be
used by suitably qualified personnel. Do not operate thedevice when there are exposed conductors.

Date
16/01/21

Rev By Changes
R2 KB Temp range updated

Parts of the circuit may store charge
so precautions must also be taken
when the device is not powered.

Dimensions
The mounting posts accept M2.5 screws. The PCB
mounting version (PDu150CL-PCB) is supplied with pins
rather than screw terminals and is designed to be
mounted directly onto a host motherboard. A schematicand footprint library are available for Altium Designer.
Contact info@piezodrive.com to receive the file.

PDu150CL V5 Datasheet

7

Modified 21/01/2021