PD200 – 60 Watt Voltage Amplifier

The PD200 is a high bandwidth, low-noise linear amplifier for driving piezoelectric actuators. The output voltage range can be switched between bipolar or unipolar modes with a range of 200V, -50V to +150V, or +/-100V. Up to +/-200V can be achieved in the bridged configuration.

The PD200 can drive unlimited capacitive loads such as stack actuators; standard piezoelectric actuators; two wire benders; and three-wire piezoelectric benders requiring a 200V bias voltage. The PD200 is highly user configurable with jumpers for options such as the voltage range, polarity, and gain control. Two potentiometers are also provided to limit the positive and negative voltages to any arbitrary value between zero and full range. Due to the extensive configuration options, the PD200 is suited to a wide range of applications including electro-optics, ultrasound, vibration control, nanopositioning systems, and piezoelectric motors.

There are four output connectors including Lemo 00, Lemo 0B, BNC, and screw terminals that allow the direct connection to almost any commercially available piezoelectric actuator, including those from PI, Piezomechanic, PiezoSystems, etc.

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Compatible Actuators

Specifications

Output Voltage Range

The desired voltage range should be identified when ordering. The following voltage ranges can be obtained with the correct combination of installed jumpers. Note that incorrect jumper settings may destroy the amplifier.

The standard output voltage range is 0V to 200V. However, the amplifier can be supplied with any voltage range by appending the order code with the voltage range code, for example, the standard configuration is PD200-V200. The voltage range jumper locations are labelled with the LP, LG, and LN prefixes on the PCB.

The jumper settings can be modified by disconnecting the amplifier from mains power then removing the top panel to access the PCB board. Either the front or back panel can be removed by unscrewing the retaining screws then gently lifting the panel free. By placing the panel slightly below the level of the enclosure, the top panel can be slid free to expose the PCB. This procedure is reversed to reassemble the amplifier.

Voltage Limits

The output voltage range can be restricted to an arbitrary positive and negative value. There are two potentiometers that can be accessed from a pair of holes on the bottom panel. By gently turning the potentiometers fully clockwise with a 2-mm flat-head screwdriver, the full voltage range becomes available. The voltage range is reduced by turning the potentiometers anti-clockwise. The hole closest to the front panel controls the negative voltage range while the rear hole controls the positive range.

Output Current Range

The standard peak output current is +/-2 Amps; however, for applications that require very fast step changes in voltage, the amplifier can be configured in pulse mode with a 10 Amp current limit. The maximum pulse time for each mode is plotted below.

The output current range can be configured by disconnecting the amplifier from mains power then removing the front and top panel. The amplifier can be supplied preconfigured to any current range by appending the order code with the current range code, for example, the standard configuration is PD200-C2.

Maximum pulse time versus current

Power Bandwidth

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With a capacitive load, the peak load current for a sine-wave is

$$ I_{pk}=\pm V_{pp} \pi C f ,$$

where \(V_{pp}\) is the peak-to-peak output voltage, \(C\) is the load capacitance and \(f\) is the frequency. Given a peak current limit \(I_{pk}\), the maximum frequency is therefore \(f=I_{pk}/V_{pp} \pi C\). However, the PD200 is protected by both peak and average current limits. The average current \(I_{av+}\) is defined as the average positive or negative current. For example, for a sine-wave

$$I_{av+} = \frac{1}{2\pi} \int_{0}^{\pi} I_{pk} \sin(\theta) d\theta = \frac{I_{pk}}{2\pi} \left[-\cos\right]_0^\pi = \frac{I_{pk}}{\pi} .$$

Therefore, for a sine-wave \(I_{av+}=I_{pk}/\pi\). Since the average current limit of the PD200 is fixed at \(I_{av+}=0.26\), the maximum frequency sine-wave, or power bandwidth of the PD200, is equal to

$$ f = \frac{0.26}{V_{pp} C}.$$

The above result is true for any periodic waveform such as triangular signals. The RMS current for a sine-wave can also be related to the average current,

$$ I_{av+} = \frac{\sqrt{2}}{\pi} I_{rms} .$$

The power bandwidths for a range of load capacitance values are listed below.

In the following figure, the maximum frequency periodic signal is plotted against the peak-to-peak voltage.

Noise

The output noise contains a low frequency component (0.03 Hz to 20 Hz) that is independent of the load capacitance; and a high frequency component (20 Hz to 1 MHz) that is inversely related to the load capacitance. Many manufacturers quote only the AC noise measured by a multimeter (20 Hz to 100 kHz) which is usually a gross underestimate.

The noise is measured with an SR560 low-noise amplifier (Gain = 1000), oscilloscope, and Agilent 34461A Voltmeter. The low-frequency noise is plotted in Figure 5. The RMS value is 650 uV with a peak-to-peak voltage of 4.3 mV. The noise level is approximately equal to the least significant bit of a 16-bit digital-to-analog converter.

Low frequency noise from 0.03 Hz to 20 Hz. The RMS value is 650 uV, or 4.3 mVp-p

The high frequency noise (20 Hz to 1 MHz) is listed in the table below versus load capacitance. The total noise from 0.03 Hz to 1 MHz can be found by square summing the RMS values, that is
$$ \sigma = \sqrt{ \sigma_{LF}^2 + \sigma_{HF}^2 } .$$

Input and Offset Configuration

The input stage is normally non-inverting; however, it can be configured as inverting by changing LK14 and LK15 to their “B” position. The default jumper position is “A” which is marked with a white bar on PCB overlay. The amplifier can be supplied with an inverting input by appending the order code with -INV.

The input offset source is also configurable. When LK21 is in the “B” position, the offset is derived from the on-board trim-pot R12, which is adjustable from zero to full-scale. The default configuration for LK21 is in the “A” position where the offset voltage is derived from the front-panel potentiometer.

The standard offset voltage range is from zero volts to full-scale; however, for applications that require negative offset voltages, LK13 can be moved from the “A” to “B” position. In the “B” position, the offset range is from -100V to full-scale.

Bridged Mode

In bridged mode, two amplifiers are connected in series to double the output voltage range and power. To obtain +/-200V at the load, the amplifiers are configured as illustrated below. Both amplifiers are configured in the +/-100V range and the lower amplifier is also inverting. A +/-5V signal applied to both inputs will develop +/-200V at the output.

Bridged configuration for obtaining +/-200V

Overload Protection

The Shutdown indicator will illuminate during a shutdown caused by an average current overload. During shutdown, the amplifier output current is limited to a few mA and may float to the high or low voltage rail if the load impedance is high or capacitive.

When the amplifier is turned on, the overload protection circuit is engaged by default and will take approximately three seconds to reset.

Output Connections

An actuator can be connected to the amplifier by either screw terminals or the LEMO 00, LEMO 0B, or BNC connectors. The recommended connectors are listed below. The full connector part number will depend on the diameter of the cable and desired strain relief.

The LEMO 0B connector is recommended in high power applications. Preassembled LEMO cable assemblies are available from here.

The plug-in screw terminal has contacts for the output voltage, ground, and the positive and negative high-voltage supply rails, which are useful when driving piezoelectric bender actuators.

PD200 Screw terminal connections

Bender actuators can be driven with a single bias voltage, for example 200 V, or bipolar bias voltages, for example +/-100 V. The 200 V unipolar configuration is illustrated below.

Piezoelectric bender actuator connection to the PD200

Enclosure

The PD200 enclosure has a side air intake and rear exhaust. These vents should not be obstructed.

The PD200 amplifiers can be rack-mounted in a three channel arrangement as shown below. The rack panel (19-inch X 2U) is supplied separately and requires some user assembly to mount between one and three channels. The rack order code is PD200-RackPanel.

Warranty

PiezoDrive amplifiers are guaranteed for a period of 3 months. The warranty does not cover damage due to misuse or incorrect user configuration of the amplifier.