MX200 - High Performance Piezo Driver

MX200 Piezo Driver

The MX200 is a complete power supply and high-performance linear amplifier module for driving piezoelectric actuators. The MX200 can drive stack actuators; standard piezoelectric actuators; two wire benders; and three-wire piezoelectric benders requiring a bias voltage. Output currents of up to 1 Amp are developed at frequencies up to 100 kHz with less than 100 uV noise (10Hz to 10kHz).

The MX200 is protected against short-circuit, average current overload, and supply under-voltage. The MX200 can be used as a stand-alone module or mounted to a base with four M3 screws. The PCB mounting version (MX200-PCB) is supplied with headers for direct mounting onto a host motherboard.

Compatible Actuators
Stack Actuators 60V, 100V, 120V, 150V, 200V
Plates and Tubes up to +/-200V
Three Wire Benders 0 to 200V with 200V bias
Three Wire Benders +/-100V with +/-100V bias

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Specifications

Specifications
Power Supply 24 V (18 V to 36 V)
Voltage Range +100 V, +150 V, +200 V
RMS Current 550mA, 330 mA, 220 mA
Peak Current 1 Amp
Power Bandwidth 106 kHz (180 Vp-p)
Signal Bandwidth 200 kHz (100 nF Load)
Slew Rate 60 V/us
Gain 20 V/V
Input Impedance 33 kOhm (In+), 1.6 kOhm (In-)
Input Offset +/- 5 mV
Load Unlimited
Output Noise 100 uV RMS (10 Hz to 10 kHz)
Protection Over-current and under-voltage
Quiescent Current 0.3 A (30 mA in shutdown)
Dimensions 80 x 46 x 40 mm (L x W x H)
Environment -40C to 60C (-40F to 140F)
Weight 95 gram

Connection Diagram

MX200 Connection Diagram

Connection Diagram

Operation

MX200 Block Diagram

MX200 Block Diagram

A boost converter generates the high voltage supply and negative rail. The output voltage range can be set to either +100V, +150V, or +200V. Configuration options are discussed in the following section. The high-voltage amplifier has differential inputs with a gain of 20 and an input voltage range of 10 V. The negative input can be connected to ground or to a differential source. It should not be left floating. The load is connected between the output and ground. The bias voltage output is for three wire bimorph bender actuators.

Configuration

The output voltage range can be set to either +100V, +150V or +200V using the two jumpers LK1 and LK2. Greater output current is available in the lower voltage ranges. Incorrect jumper combinations will damage the amplifier.

Voltage RangePeak CurrentRMS CurrentAverage Current LK1  LK2 
100 V1 Amp550 mA250 mAAOut
150 V1 Amp330 mA150 mABB
200 V1 Amp220 mA100 mAOutA

Table 1. Voltage Range Jumper Settings

Output Current

The maximum continuous RMS current is dependent on the voltage range, as described in Table 1. The average positive output current is also useful for calculating power dissipation and the average supply current. For a sine wave, the average positive output current is equal to $$ I_{av} = \frac{ \sqrt{2} }{ \pi } I_{rms} = \frac{1}{\pi} I_{pk}. $$

The peak current limit for all voltage ranges is +/-1A, which can be supplied for up to 5ms. This is useful in pulse applications where a fast rise-time is required.

Supply Current

The quiescent power for the amplifier and fan is approximately 8 W. Therefore, the quiescent supply current at 24 V is 0.3 A. This can be reduced to 30 mA by pulling the Enable pin low with an open collector output or similar. The supply current is related to the average positive output current by $$ I_s= \frac{1.1 \times V_{out} \times I_{av}+8}{V_s} $$ where \(V_{out}\) is the output voltage range, and \(I_{av}\) is the average output current. Therefore, the maximum supply current is 1.25 A with a 24 V supply at the full rated power (\(I_{av}\)=100 mA).

The power supply must be sufficient for the amplifier, a rating of at least 1.5 Amps is recommended. Note that when power is first applied or when the amplifier is enabled, full current will be required for a brief period to charge the storage capacitors.

Application Circuits

MX200 Application Circuit Diagrams

Bias Output for Piezo Bimorphs

The bias output (Vb) provides a fixed voltage for driving three-wire piezoelectric benders. The bias voltage is approximately 5V above the selected voltage range. The effective capacitance when using bimorph actuators is the sum of both layers.

Actuators that require a symmetrical bias voltage, e.g. +/-100 V can also be driven since this configuration is electrically identical to the unipolar configuration, e.g. 0V to 200V.

Power Bandwidth

The power bandwidth is the highest frequency sine wave that can be produced at full voltage.

Power Bandwidth Calculator

The maximum frequency with no load is limited by the slew-rate of 60 V/us. That is, $$ f_{max}= \frac{60 \times 10^6}{\pi~V_{L(p-p)}} $$ The unloaded power bandwidth for each voltage range is listed below.

Voltage RangePower Bandwidth
100 V190 kHz
150 V127 kHz
200 V95 kHz

Unloaded Power Bandwidth

With a capacitive load, the power bandwidth is limited by the output current. The maximum frequency sine wave is $$ f_{pwr} = \frac{I_{av}}{V_{L(p-p)}~C_L} $$ where \(I_{av}\) is the average current limit (100 mA for the 200V range), \(V_{L(p-p)}\) is the peak-to-peak output voltage, and \(C_L\) is the effective load capacitance. The power bandwidth for a range of load capacitance values is listed below.

LoadVoltage Range
Cap100V150V200V
10 nF190 kHz100 kHz50 kHz
30 nF83 kHz33 kHz16 kHz
100 nF25 kHz10 kHz5.0 kHz
300 nF8.3 kHz3.3 kHz1.6 kHz
1 uF2.5 kHz1.0 kHz500 Hz
3 uF833 Hz333 Hz167 Hz
10 uF250 Hz100 Hz50 Hz
30 uF83 Hz33 Hz16 Hz

Power Bandwidth versus Load Capacitance

In the following figures, the maximum peak-to-peak voltage is plotted against frequency for each voltage range.

MX200 Power Bandwidth

Small Signal Bandwidth

Load Cap.Bandwidth
10 nF180 kHz
30 nF283 kHz
100 nF275 kHz
300 nF160 kHz
1 uF78 kHz
3 uF30 kHz
10 uF8.3 kHz
30 uF3.0 kHz

Small signal bandwidth versus load capacitance (-3dB)

MX200 Small Signal Frequency Response

Small signal frequency response

Noise

The 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. Note that 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 below. The RMS value is 360 uV with a peak-to-peak voltage of 1.8 mV.

MX200 low frequency noise

Low frequency noise from 0.03 Hz to 10 Hz.

The high frequency noise (10 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.HF Noise RMSTotal Noise RMS
10 nF1.5 mV1.5 mV
30 nF2.6 mV2.6 mV
100 nF3.5 mV3.5 mV
300 nF1.2 mV1.2 mV
1 uF306 uV470 uV
3 uF129 uV380 uV
10 uF100 uV370 uV
30 uF120 uV380 uV

High Frequnecy Noise (10 Hz to 1 MHz) and Total Noise (0.03 Hz to 1 MHz)

The majority of high-frequency noise is due to ripple from the boost converter (at 170 kHz). In ultra-low noise applications, the output bandwidth can be restricted to 10 kHz which reduces the noise to less than 100 uV RMS in the 10 Hz to 1 MHz frequency range. This can be achieved with the RLC filter shown below.

Noise Filter

Output Noise Filter

The required inductance and resistance is $$ L = \frac{1}{4 \pi^2 f_c^2 C_L} ~~~~~~\text{and},~~~~~~ R = 1.4 \sqrt{ L/C_L} $$ where \(f_c\) is the cut-off frequency (10 kHz) and \(C_L\) is the load capacitance. The inductor should be rated for at least 1 A with a self-resonance frequency of greater than 1 MHz.

A first-order resistive filter can also be effective, although it must be rated for the expected RMS current. The required value is $$ R = \frac{1}{2 \pi f_c C_L} $$

Overload Protection / Shutdown

The MX200 is protected against short-circuit and average current overload. The module is also disabled when the input supply voltage is less than 12 V. Current overload conditions are signalled by +5 V on the Overload pin.

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 6.2V and should not be driven directly.

Bridge Configuration

The output voltage range can be doubled to +/-200 V by driving the load in a bridged configuration as shown below. In this configuration, the output voltage is $$ V_{out} = 40 \left( V_{in}-5 \right) $$ That is, a 0V to 10V input produces +/-200V at the load. Zero volts across the load occurs when the input voltage is +5V. However, note that the absolute voltage of each terminal is still +100V. The power bandwidth for this configuration can be calculated by considering only one amplifier and doubling the effective capacitance.

MX200 Bridge Configuration

Bridge Configuration for +/-200V

Safety

This device produces hazardous potentials and should be used by suitably qualified personnel. Do not operate the device when there are exposed conductors.Parts of the circuit may store charge so precautions must also be taken when the device is not powered.

Dimensions

The mounting posts accept M3 screws. For the PCB mounting version (MX200-PCB), a schematic and footprint library is available for Altium Designer, contact info@piezodrive.com to receive the file.

MX200 Dimensions

Dimensions (mm)