PDm200 Miniature High Voltage Amplifier

The PDm200 is a complete high-performance power supply and linear amplifier module for driving piezoelectric actuators. The output voltage range can be switched between bipolar or unipolar modes with a range of 100V, 150V, or 200V. Up to +/-400V can be achieved in the bridged configuration. In the unipolar mode, the negative output range is fixed at -30V for use with stack actuators.

The PDm200 can drive stack actuators; standard piezoelectric actuators; two wire benders; and three-wire piezoelectric benders requiring a 200V bias voltage.

PDm200 Miniature High Voltage Amplifier
Compatible Actuators
Stack Actuators 60V, 100V, 120V, 150V, 200V
Plates and Tubes up to +/-200V
Two Wire Benders Up to +/-200V
Three Wire Benders 0 to 200V with 200V bias

The PDm200 is suited to a wide range of applications including: Electro-optics, ultrasound, vibration control, nanopositioning systems, and piezoelectric motors.

The PDm200 is protected against current overload and excessive temperature. The PDm200 can be used as a stand-alone module or mounted to a base with four M2.5 threaded spacers. The PCB mounting version (PDm200-PCB) is supplied with headers for direct mounting onto a host motherboard.

Specifications

Power Supply +/-12 V to +34 V
Max Unipolar Output -30V to 200 V
Max Bipolar Output +/-200 V (+/-400 V bridge mode)
Peak Output Current 300 mA
RMS Output Current 100 mA (+/-100 V Output)
Power Bandwidth 63 kHz (3.9 nF load, 100 Vp-p)
Signal Bandwidth 200 kHz
Slew Rate 20 V/us
Dimensions 71 x 38mm
Weight 50 g
Gain 20 V/V
Input Impedance 200 kOhm
Input Offset +/-10 mV
Load Any
Overload Protection Thermal and current
Noise 1 mV RMS (1uF Load)
Environment -40 to 60C (-40 to 140F)
Quiescent Current 100 mA (7.5mA in Shutdown)

Connection Diagram

pdm200 condiag 408w

Operation

A power converter generates a unipolar or bipolar supply. The output voltage range is controlled by the voltage selector jumpers. The amplifier has a gain of 20 and an input voltage range of +/-10 V. The load is connected directly to the high-speed output (V1) or through a filter (V2) which reduces the noise and bandwidth. In most applications, the V2 output is recommended.

When the amplifier is configured for 200V operation, a 200V bias supply is enabled for bimorph bender applications.

pdm200 blockdiagram 377w

Example Applications

Configuration

The PDm200 is configurable to suit a wide range of power supply and output voltage ranges. The output voltage range is selected by two jumpers marked L1 and L2, each of which has four possible positions marked by the letters a to d and e to h.

In unipolar output mode, the negative output range is fixed at -30 V and the jumper L2 is always in the “E” position. The correct position for the L1 jumper is listed below for different power supply voltages.

Output Voltage Power Supply Voltage
Max Min +/-12V to +/-14V +/-15V to +/-17V +24V* to 30V +30V* to 34V
200 V -30 V D D
150 V -30 V D C D C
120 V -30 V C B C B
100 V -30 V B A B A

Unipolar Jumper Configuration

*With a single supply, the negative output voltage range is reduced from -30 V to -20 V.

In bipolar output mode, the correct positions for the L1 and L2 jumpers are listed in below. In the +/-200 V mode, a 220 O resistor is recommended in series with the output. See “Stability” for more details.

Output Voltage Power Supply Voltage
Max Min +/-12V to +/-14V +/-15V to +/-17V +24V* to 30V +30V* to 34V
200 V -200 V D,H D,H
150 V -150 V D,H C,G D,H C,G
100 V -100 V B,F A,F B,F A,F

Bipolar Jumper Configuration

The PDm200 can also be used in lower voltage applications; however, the output current may be reduced. The corresponding low-voltage jumper positions are listed below

Output Voltage Power Supply Voltage
Max Min +/-12V to +/-14V +12V to +15V
80 V -30 V A,E
80 V 0 V D,E
60 V -60 V D,H

Low Voltage Jumper Configuration

Output Current

The peak output current is approximately 300 mA and the maximum average DC output current is approximately

$$I_{av}=\frac{0.375 V_S}{V_{out}} -0.01 ,$$ where \(V_S\) is the differential supply voltage e.g. 30V, and \(V_{out}\) is the differential output voltage range e.g. 400V.

The average DC current is the average current flowing in either the positive or negative direction. For a sine wave, the average DC current is related to the RMS current by

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

Calculate Output Current

The PDm200 calculator can be used to estimate the maximum input and output current for a given supply voltage and output voltage range. Some common values are tabulated below.

Output Voltage RMS Current Average Current
Max Min
150 V -30 V 118 mA 53 mA
200 V -30 V 87 mA 39 mA
100 V -100 V 102 mA 46 mA
200 V -200 V 40 mA 18 mA

RMS and Average Output Current for a +/-15 V Supply

Supply Current

The maximum supply current is 0.5 A at full load. For a partial load, the supply current is

$$I_{in}=\frac{P_{in}}{V_S} ,$$ where the required input power is

$$ P_{in} = 1.33 V_{out} (0.01+I_{av} ) ,$$ where \( V_{out} \) is the differential output voltage range and \(I_{av}\) is the average output current.

Power Bandwidth

The PDm200 calculator can be used to estimate the maximum frequency for a given output voltage and capacitance.

Calculate Power Bandwidth

With a capacitive load, the power bandwidth is limited by the average output current. The maximum frequency sine wave is

$$f_{pwr}=\frac{I_{av}}{ V_{L(p-p)} \left( C_L + 3.9nF \right)} $$. The power bandwidth for a range of load capacitance values is listed below.

Load Peak to Peak Voltage
uF 100 V 200 V 300 V 400 V
0.01 55395 14029 6715 3237
0.03 22714 5752 2753 1327
0.1 7411 1877 898 433
0.3 2534 642 307 148
1 767 194 93 45
3 257 65 31 15
10 77 19.5 9.3 4.5
30 25.7 6.5 3.1 1.5

Power Bandwidth with Capacitive Load

In the following figures, the maximum peak-to-peak voltage is plotted against frequency for a range of capacitive loads.

The power bandwidth is primarily related to the average current limit as described above. However, when operating at full range, e.g. +/-200 V, with the minimum supply voltage, e.g. +/-15 V, the power supply droop can distort the top of a signal. This effect can be reduced by increasing the supply voltage. If this is not possible, the full-range power bandwidth should be de-rated by 50%.

Signal Bandwidth

With a load capacitance greater than 100 nF, the small signal bandwidth is
$$ f_{bw} = \frac{1}{63 C_L} .$$ With a load capacitance less than 100 nF, the small signal bandwidth is approximately 200 kHz.

The bandwidth of the low noise output (V2) is approximately one quarter of the high speed output, that is,
$$ f_{bw} = \frac{1}{233 C_L} .$$ The small signal bandwidth for a range of capacitive loads is listed in the table below.

Load Capacitance High Speed Bandwidth Low Noise Bandwidth
10 nF 200 kHz 200 kHz
30 nF 200 kHz 140 kHz
100 nF 158 kHz 42 kHz
300 nF 52 kHz 14 kHz
1 uF 15 kHz 4.2 kHz
3 uF 5.2 kHz 1.4 kHz
10 uF 1.5 kHz 430 Hz
30 uF 530 Hz 140 Hz

Small signal bandwidth

Noise

The output of the PDm200 contains a small amount of switching noise from the boost converter and random noise from the high-voltage amplifier. With a +/-15 V supply and +/-100 V output range, the RMS noise is listed below.

Load Capacitance High Speed Output Low Noise Output
10 nF 4.1 mV* 4.1 mV*
100 nF 1.3 mV* 1.3 mV*
1 uF 1.3 mV 0.72 mV
10 uF 0.42 mV 0.30 mV

RMS Noise versus load capacitance

For applications requiring extremely low noise, a larger resistance can be used to reduce the effective bandwidth, which is approximately

$$ f_{bw} = \frac{1}{2 \pi R C_L} .$$ where \( C_L \) is the load capacitance. The recommended bandwidth in low-noise applications is 100 Hz.

The noise measurements were performed with the input shorted. The noise may increase when significant current is drawn from the output due to ripple from the boost converter.

*For load capacitances of 100nF or smaller, a 220 Ohm resistor is recommended in series with the load.

Application Notes

The amplifier input \( V_{in} \) should not be left floating as it will drift towards a supply rail. However, the input can be left floating if a 1 kOhm resistor is connected from \(V_{in}\) to ground. This input impedance is now 1 kOhm.

Heat Dissipation

With a capacitive load, the majority of input power is dissipated as by the amplifier. The worst-case power dissipation is approximately 15 W. The quiescent heat dissipation can be calculated from the equation for \( P_{in} \) in “Supply Current”. Note that when using the +/-200V output range, the quiescent power dissipation is always >5 W so forced air cooling is always required, as discussed below.

The thermal impedance of the PDm200 from junction to ambient is approximately 10 C/W in still conditions. An air-flow of 100 LFM or greater is required when more than 5 W is dissipated continuously. The PDm200 will shut down when the heat-sink reaches 70 C.

Stability

In the +/-200 V range, oscillation can occur with some load capacitances when the output voltage is very close to the negative rail ( -190V). This problem can be eliminated by placing a 220 Ohm resistor in series with the load capacitance as shown in the example applications. Alternatively, a 330pF 25V 0603 capacitor can be soldered on top of R14 which reduces the bandwidth to approximately 3 kHz and will avoid oscillation. This capacitor can be installed before delivery if necessary.

Note that PDm200 modules produced before July 2014 required a minimum load capacitance of 3.9 nF for stability. After July, 2014, this load capacitance was included on the PCB (C33). However, it can be removed in applications that require maximum performance with load capacitances in the 5 nF to 30 nF range. If the capacitor is removed, the cable length and inductance should be minimized to avoid oscillation.

Bias Output

The bias output (Vb) provides a fixed +200 V output for driving 200 V three-wire actuators like benders that require a bias voltage. Actuators that require a +/-100 V bias can also be driven in this configuration as this is electrically identical.

The bias output can sink or source an average current of 10 mA. However, there is no protection so care must be taken not to exceed the current limit. If more than 10 mA is required, the primary output of a second PDm200 can be used to generate the bias.

Enable / Shutdown

The Enable pin is a high impedance signal that floats 5V above the negative supply rail. It can be pulled to the negative supply rail to disable the amplifier. The voltage on this pin can also be monitored to check the status of the amplifier. Any monitoring circuit should have an input impedance of greater than 200 kOhm. A high level voltage on the enable pin indicates a normal status while a low level indicates a thermal shutdown.

The recommended enable circuits for unipolar and bipolar supplies are shown below. Any small signal transistors are suitable, e.g. BC817 and BC807.

Enable circuit for unipolar supply

PDm200 Enable circuit for unipolar supply

Enable circuit for bipolar supply

Overload Protection

The PDm200 is protected against over-current and thermal overload. If the PCB temperature exceeds 70 degrees C the amplifier will be disabled until the temperature reduces.

Bridge Configuration

The output voltage range can be doubled by driving the load in a bridged configuration as shown below. Both amplifiers should be configured for +/-200 V operation.

Enable circuit for bipolar supply

Overload Protection

The PDm200 is protected against over-current and thermal overload. If the PCB temperature exceeds 70 degrees C the amplifier will be disabled until the temperature reduces.

Bridge Configuration

The output voltage range can be doubled by driving the load in a bridged configuration as shown below. Both amplifiers should be configured for +/-200 V operation.

pdm200 dimensions 400w

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