# TD250 6-Channel 250V Amplifier for Driving Piezo Tubes

The TD250 is an ultra-low noise, six-channel voltage amplifier with a bipolar 250V output range. The six channels can be driven independently, or configured as three channels with non-inverting and inverting outputs, which are ideal for driving piezoelectric tube scanners. The three-channel configuration can also be used to obtain +/-500V with a bridged load.

The TD250 can drive unlimited capacitive loads such as piezoelectric tubes, stack actuators, standard piezoelectric actuators, and bender actuators. Applications include, nanopositioning, microscopy, electro-optics, vibration control, and piezoelectric motors.

The output connector is an industry standard 9-Pin D-Sub connector. The amplifier is supplied with a 75cm output cable and breakout PCB. A breakout box is also available which provides BNC connectors for each output and a plug-in screw-terminal connector. OEM and customized versions are also available.

### Specifications

 Electrical Specifications Output Voltage +/-250V RMS Current 22mA per channel Peak Current 50mA per channel Gain 25 V/V Slew Rate 30 V/us Signal Bandwidth 50 kHz Power Bandwidth 20 kHz (400 Vp-p) Max Power 25 W Load Stable with any load Noise <70 uV RMS (100 nF load) Protection Over-current protection Input Impedance 100 kOhm Input Connector BNC Output Connector 9 Pin D-Sub Power Supply 90 Vac to 250 Vac
 Mechanical Specifications Environment 0 – 40 C (32-104 F), Non-condensing humidity Dimensions 275 x 141 x 64 mm (10.8 x 5.5 x 2.5 in) Weight 1 kg (2.2 lb)

### Channel Configuration

The standard configuration for the TD250 is three non-inverting and inverting pairs for driving piezoelectric tubes and bridged loads, the order code for this configuration is TD250-INV. As illustrated below, the outputs can also be configured as six independent non-inverting channels, which has the order code TD250-SGL.

TD250 channel configuration

The front panel output connector is an industry standard 9-Pin Female D-Sub Connector (TE 3-1634584-2). Any Male 9-Pin D-Sub connector is compatible. The connector pinout is shown below.

Output connector pinout

 Signal Pin Output 1 5 Output 2 9 Output 3 4 Output 4 8 Output 5 3 Output 6 7 Ground 1,2,6

### Driving Piezoelectric Tube Scanners

The voltage range, noise, and bandwidth of the TD250 have been optimized for driving piezoelectric tube scanners, for example the TB6009. Although many configurations are possible, the driven internal electrode configuration shown below is simple and provides the maximum X, Y and Z travel range. This configuration requires a tube with a continuous internal electrode and four external electrodes.

In the driven internal electrode configuration, the X and Y electrodes are driven in the standard way with equal and opposite voltages. By applying the full-scale negative voltage to the internal electrode, a contraction equal to half the vertical scan range is obtained. This method exploits the higher positive electric field strength of the piezoelectric material, which is usually five times the negative electric field strength. Care must be taken not to apply positive voltages to the internal electrode, since this can risk depolarization if the tube voltage limit is less than ±500V, which is commonly true for tubes less than 1.2mm thick.

Driving Piezoelectric Tubes with the TD250-INV

Another common electrode configuration uses a separate circumferential electrode for the Z axis. This electrode is driven by a single channel with the full bipolar range.

In larger piezoelectric tubes, it is possible to quarter the external and internal electrodes. The internal electrodes can be either grounded or driven in the bridged configuration. Since the bridged configuration doubles the voltage difference across the piezo material, the thickness can also be doubled which significantly improves the resonance frequency. The disadvantages of this method include increased wiring and fabrication difficulty.

To obtain an output voltage range of +/-500V, the TD250-INV can used with a bridged load, as illustrated below.

Bridged configuration using TD250-INV

In the bridged configuration, the power bandwidth can be assessed by using the full peak-to-peak load voltage in the calculator, or by doubling the effective capacitance.

### Power Bandwidth

The calculator below plots the maximum peak-to-peak output voltage versus frequency and capacitive load.

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. However, the TD250 is protected by both peak and average current limits. Since the average current limit of the TD250 is $I_{av+}=10$ mA, the maximum frequency sine-wave is $$f = \frac{0.01}{V_{pp} C}.$$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
$$I_{av+} = \frac{\sqrt{2}}{\pi} I_{rms} .$$

### Small Signal Bandwidth

Small signal frequency response

 Load Cap. Bandwidth No Load 100 kHz 3 nF 39 kHz 10 nF 14 kHz 30 nF 5.1 kHz 100 nF 1.5 kHz 300 nF 520 Hz 1 uF 150 Hz

Small signal bandwidth versus load capacitance (-3dB)

### 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 in the 20 Hz to 100 kHz range, 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 measured to be 50 uV RMS with a peak-to-peak voltage of 300 uV. This noise level is less than the resolution of a state-of-the-art 24-bit digital-to-analog converter.

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

$$\sigma = \sqrt{ \sigma_{LF}^2 + \sigma_{HF}^2 } .$$

 Load Cap. Bandwidth HF Noise RMS Total Noise RMS No Load 100 kHz 130 uV 139 uV 3 nF 39 kHz 80 uV 94 uV 10 nF 14 kHz 50 uV 71 uV 30 nF 5.1 kHz 30 uV 58 uV 100 nF 1.5 kHz 40 uV 64 uV 300 nF 520 Hz 50 uV 71 uV 1 uF 150 Hz 70 uV 86 uV

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

Each channel is independently protected against average and peak current overload. Exceeding these limits will result in signal distortion.

The front-panel overload indicator will illuminate when the total power supplied to all channels is greater than 25W. This can occur when all channels are simultaneously operated at full power or when there is a failure of one or more channels. During a maximum power overload, the power supply is temporarily disabled and will reset once the power drops below 25W.

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

### Breakout PCB

The included breakout PCB connects to the included D-sub cable and provides screw-terminal access to the output signals. The screw terminal block can be exhanged with wires or any other connector with a pitch of 2.54 mm.

The breakout PCB also includes a location for a series resistor and parallel capacitor. This is useful for reducing the bandwidth when using small load capacitances (< 30nF). For suitable capacitance values, refer to the table “RMS Noise Versus Load Capacitance”. Note that capacitances should be a film type rated for 500 Vdc, e.g. EPCOS B32671P5104K.

Supplied Breakout PCB

### Breakout Box

The breakout box provides BNC connectors for each output and a plug-in screw-terminal connector (Amphenol 20020004-D081B01LF). The breakout box connects to the amplifier via an included 75cm male-male 9-Pin D-Sub cable.

Order Code: TD250-Breakout

TD250 Breakout box

Plug-in screw terminal connector

### Output Cables

A number of 300 V D-Sub cables are available for the amplifier. All are supplied with at least one 9-Pin D-Sub connector for connecting to the amplifier. The second connector is either a D-Sub connector for connecting to the breakout box, or free wires. A DSUB9-MM-75cm cable is supplied with the amplifier.

 Connector 2 Length Order Code 9 Pin Male 75 cm DSUB9-MM-75cm 9 Pin Male 150 cm DSUB9-MM-150cm Free Wires 75 cm DSUB9-MW-75cm Free Wires 150 cm DSUB9-MW-150cm

9 Pin D-Sub Cables

9 Pin male-male D-Sub cable

 Signal Colour Out 1 Yellow Out 2 Grey Out 3 Orange Out 4 Purple Out 5 Red Out 6 Blue Ground Brown, Green Black

Cable Wire Color

### Enclosure

The TD250 enclosure has a side air intake and rear exhaust. These vents should not be obstructed.

### 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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