PX200 – 140 Watt Voltage Amplifier

The PX200 is a low-noise voltage amplifier designed to drive capacitive and other loads from DC to hundreds of kHz. The output voltage range can be unipolar, bipolar, or asymmetric with a peak-to-peak value of between 50V and 200V. Two amplifiers can be connected in bridge-mode to provide ±200V or +400V. The amplifier will deliver up to 4 Amps peak with a sinusoidal output, or up to 8 Amps peak for pulse applications.

The PX200 is compact, lightweight, and can be powered from any mains supply. The output connectors include LEMO 00, LEMO 0B, BNC (adaptor included), and plug-in screw terminals, so many commercially available piezoelectric actuators can be directly connected. The PX200 is suited to a wide range of applications including: electro-optics, ultrasonics, vibration control, nanopositioning, and piezoelectric motors.

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Specifications

Electrical Specifications
Output Voltage Ranges 100 Vp-p 150 Vp-p 200 Vp-p
RMS Current 3.1 A 2.0 A 1.5 A
Peak Current 8.0 A 8.0 A 8.0 A
Power Bandwidth 110 kHz 93 kHz 55 kHz
Gain 20 V/V
Slew Rate 35 V/us
Signal Bandwidth 390 kHz
Max Power 140 W Dissipation
Load Stable with any load
Noise 150 uV RMS (10 uF Load, 0.03 Hz to 1 MHz)
Protection Continuous short-circuit, thermal
Voltage Monitor 1/20 V/V (BNC)
Current Monitor 1 V/A (BNC)
Analog Input Signal input (BNC, Zin = 48.7k)
Output Connectors LEMO 0B, LEMO 00, Screw Terminals, BNC
Power Supply 90 Vac to 250 Vac
Mechanical Specifications
Environment 0 – 40 C (32-104 F), Non-condensing humidity
Dimensions 212 x 304.8 x 88 mm (8.35 x 12 x 3.46 in)
Weight 2 kg (4.4 lb)

Output Voltage Range

The desired output voltage range is specified when ordering. The default output range is 0V to +200V (PX200-V0,200). The available voltage ranges and associated current limits are listed below.

Voltage Range RMS Current Peak Current Order Code
0 to +200 1.5 A 2.0 A PX200-V0,200
0 to +150 2.0 A 4.0 A PX200-V0,150
0 to +100 3.1 A 4.0 A PX200-V0,100
0 to +50 3.1 A 8.0 A PX200-V0,50
-50 to +50 3.1 A 4.0 A PX200-V50,50
-50 to +100 2.0 A 4.0 A PX200-V50,100
-50 to +150 1.5 A 2.0 A PX200-V50,150
-100 to +50 2.0 A 4.0 A PX200-V100,50
100 to +100 1.5 A 2.0 A PX200-V100,100
-100 to 0 3.1 A 4.0 A PX200-V100,0
-150 to 0 2.0 A 4.0 A PX200-V150,0
-200 to 0 1.5 A 2.0 A PX200-V200,0

Table 1. Voltage Range Configurations

Output Current

The PX200 has a peak and average current limits as described in Table 1. The RMS current limit defines the maximum frequency that is achievable with a capacitive load. This topic is discussed in “Power Bandwidth”.

During short-circuit the output current is limited to the rated maximum. The peak current can be drawn for up to five milliseconds before the output is disabled for three seconds. The average current limit has a time-constant of ten milliseconds and is reset 50 milliseconds after a previous current pulse. This behaviour is described in “Overload and Shutdown”.

Pulse Current Option

For applications that require a high peak current, the peak current limit can be increased to 8 Amps by appending the order code with “-PULSE”, e.g. “PX200-V0,200-PULSE”. In this configuration, the average current limit remains the same; however, the peak current limit is increased to 8 Amps and the maximum pulse duration is reduced to the time listed in Table 2. The voltage span is the peak-to-peak output voltage range, e.g. the voltage span for the -50V to +150V range is 200V .

Voltage Span Pulse Current Pulse Time
200 V 8 A 150 us
150 V 8 A 200 us
100 V 8 A 300 us
50 V 8 A 300 us

Table 2. Maximum peak current duration in the pulse configuration

For a current pulse that is less than the peak current limit, the maximum pulse duration is described in Figure 1.

Figure 1. Maximum pulse duration versus peak current and voltage span

Power Bandwidth

With a capacitive load, the RMS current for a sine-wave is$$I_{rms} =  \frac{V_{pp}C\pi f}{\sqrt{2}}$$where  \(V_{pp}\) is the peak-to-peak output voltage,  \(C\) is the load capacitance and \(f\)  is the frequency. Therefore, the maximum frequency for a given RMS current limit \(I_{rms}\), capacitance, and voltage is$$f_{max} = \frac{I_{rms}\sqrt{2}}{V_{pp}C\pi}$$ The above equation is also true for any periodic waveform, including triangle waves and square waves. This property arises since the amplifier detects average current, which not affected by the waveform shape.

The ‘power bandwidth’ is the maximum frequency at full output voltage. When the amplifier output is open-circuit, the power bandwidth is limited by the slew-rate; however, with a capacitive load, the maximum frequency is limited by the RMS current and load capacitance. The power bandwidth for a range of capacitive loads is listed below.

Load Capacitance 50V Range 100V Range 150V Range 200V Range
10 nF 222 kHz* 111 kHz* 74 kHz* 55 kHz*
30 nF 222 kHz* 111 kHz* 74 kHz* 55 kHz*
100 nF 222 kHz* 111 kHz* 62 kHz 35 kHz
300 nF 93 kHz 46 kHz 20 kHz 11 kHz
1 uF 28 kHz 14 kHz 6.2 kHz 3.5 kHz
3 uF 9.3 kHz 4.6 kHz 2.0 kHz 1.1 kHz
10 uF 2.8 kHz 1.4 kHz 60 Hz 350 Hz
30 uF 930 Hz 460 Hz 200 Hz 117 Hz

Table 3. Power bandwidth versus load capacitance and output voltage span

In the above table, the frequencies limited by slew-rate are marked with an asterisk. The slew-rate is approximately 35 V/uS which implies a maximum frequency of $$f^{max} =  \frac{35 \times 10^{6}}{\pi V_{pp}}$$

Small Signal Bandwidth

The small-signal frequency response and -3 dB bandwidth is described in Figure 3 and Table 4.

Figure 3. Small signal frequency response for a range of load capacitances.

 

Load Capacitance Bandwidth
10 nF 393 kHz
30 nF 431 kHz
100 nF 367 kHz
300 nF 208 kHz
1 uF 88 kHz
3 uF 30 kHz
10 uF 9.3 kHz
30 uF 3.7 kHz
110 uF 1.3 kHz

Table 4. Small signal bandwidth versus load capacitance (-3dB)

Noise

The output voltage noise contains a low frequency component (0.03 Hz to 20 Hz) that is independent of the load capacitance; and a high frequency (20 Hz to 1 MHz) component that is approximately inversely proportional to the load capacitance.

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 4. The RMS value is 120 uV with a peak-to-peak voltage of 600 uV.

Figure 4. Low frequency noise from 0.03 Hz to 20 Hz

The high frequency noise (20 Hz to 1 MHz) is listed in the table below versus load capacitance. The total RMS noise from 0.03 Hz to 1 MHz is found by summing the RMS values, that is \( \sigma = \sqrt{\sigma^{2}_{LF} + \sigma^{2}_{HF}}\). For a load capacitance of less than 1 uF, the noise is primarily broadband thermal noise; however, for a capacitance of greater than 1 uF, the noise is primarily due to low-frequency noise.

Load Cap. Bandwidth HF Noise RMS Total Noise RMS
10 nF 393 kHz 530 uV 543 uV
30 nF 431 kHz 586 uV 598 uV
100 nF 367 kHz 689 uV 699 uV
300 nF 208 kHz 452 uV 468 uV
1 uF 88 kHz 261 uV 287 uV
3 uF 30 kHz 106 uV 160 uV
10 uF 9.3 kHz 56 uV 132 uV
30 uF 3.7 kHz 52 uV 131 uV
100 uF 1.3 kHz 47 uV 129 uV

Table 5. RMS noise versus load capacitance (0.03 Hz to 1 MHz)

Front Panel

Control Type Function
Power Power On/Off
Offset Adds a DC offset to the input signal
Input Input Input signal ( +/-15V max)
Voltage Monitor Output The measured output voltage, scaled by 1/20
Current Monitor Output The measured output current, 1 A/V
Input+ Input Internally connected to the centre pin of the Input BNC connector
Input- Input Internally connected to the shield of the Input BNC connector
Volt Mon Output Internally connected to the Voltage Monitor BNC Output
Current Mon Output Internally connected to the Voltage Monitor BNC Output
Shutdown Input A voltage from +2V to +24V (relative to Input-) disables the amplifier
Overload Out Output +5V output when the amplifier is disabled or in overload state
Voltage Limits Limits the maximum negative and positive output voltage
Overload RED when the amplifier is disabled or in an overload state
Power GREEN when the power is on
HV- Output Connected to the negative high-voltage power supply rail
HV+ Output Connected to the positive high-voltage power supply rail
Output- Output High-voltage output signal return (used to measure current)
Output+ Output High-voltage output signal
LEMO 00 Output Output High-voltage output connector, suits LEMO FFA.00.250 cable plug
LEMO 0B Output Output High-voltage output connector, suits LEMO FGG.0B.302 cable plug
DC Output Volt. Display showing average output voltage

Amplifier Configuration

The amplifier can be configured with an inverting, or non-inverting input, and a gain of either 20 or 10.

Amplifier Configuration Order Code Notes
Non-inverting (default)
Inverting -INV
Gain = 20 (default)
Gain = 10 -Gain10

Table 6. Amplifier configuration

The DC offset control is configurable with a positive or bipolar range. The maximum achievable DC offset is limited by the output voltage range of the amplifier. In general, the positive DC offset range is recommended as this allows direct selection of zero offset; however, the bipolar range may be preferable for amplifiers configured with a negative output range.

The front panel potentiometer can be disabled by enabling a PCB mounted trim-pot. The PCB trim-pot can be set to a required fixed value prior to shipping.

Offset Configuration Order Code Notes
Positive Offset Range (default) Max +200V
Bipolar Offset Range -OR2  Max +/-200V
Front panel source (default)
PCB trim-pot source -OS2 Disables front panel adjustment

Table 7. Offset configuration

Bridged Mode

In bridged mode, two amplifiers are connected in series to double the output voltage range and power.

For example, Figure 5 shows the configuration to obtain \(\pm\)200V across the load. A \(\pm\)5V signal applied to both inputs produces \(\pm\)200V across the load. In bridged mode, only the Output+ terminal from each amplifier is used, the negative output terminal is not connected. Since there is no current returning through the negative terminal, the current monitor is disabled; however, the overload and protection features are unaffected. Common bridged-mode configurations are listed in Table 7.

Figure 5. Bridge mode configuration for obtaining 200V

Load Voltage RMS Current Positive Amp Negative Amp
200V 1.5 A PX200-V100,100 PX200-V100,100-INV
100V 3.1 A PX200-V50,50 PX200-V50,50-INV
0V to 200V 3.1 A PX200-V0,100 PX200-V100,0-INV
0V to 300V 2.0A PX200-V0,150 PX200-V150,0-INV
0V to 400V 1.5A PX200-V0,200 PX200-V200,0-INV

Table 8. Common bridge-mode configurations

Overload Protection

The amplifier is protected against short-circuit, over-current, and excessive temperature. During these conditions, the front panel overload indicator will illuminate and the Overload Out signal is +5V.

During an overload or shutdown state, the output is partially disabled and may float at approximately 50% of the voltage range.

When the amplifier is switched on, the overload protection circuit is engaged by default and clears after three seconds.

The amplifier can be shut down by an external source by applying a voltage of between +2V and +24V to the Shutdown input (relative to Input-). The impedance of the shutdown input is approximately 5 kΩ.

Enclosure

The PX200 has a side air intake and rear exhaust, which can not be obstructed. If sufficient airflow is not available, the amplifier will enter a thermal overload state as discussed in “Overload and Shutdown”.

The PX200 can be installed in a 19-inch x 2U rack space using the PX200-Rack1 kit. Two amplifiers can also be installed in a side-by-side configuration using the PX200-Rack2 kit.

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.

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