US EuroTek, Inc.

4. Selection guide for amplifiers/supply electronics

US EuroTek, Inc. offers a wide range of supply electronics to obtain the optimum solution for different applications of Piezoelectric actuated systems.
For specifying dynamically operated actuator/amplifier systems the power/current requirements are determined by the actuator's capacitance. Note that the actuator's capacitance can vary up to 50% (e.g. see section 3.2.) leading to correspondingly elevated power/current ratings.
The supply electronics and actuators from US EuroTek, Inc. are set to positive polarity for both high voltage and low voltage components, so that widest compatibility is achieved e.g. for power efficient arrangements according sec. 2.5.
On request US EuroTek, Inc. supplies piezocomponents for negative operating polarity.

4.1. SQV amplifiers
The range of SQV amplifiers comprises the 3 main voltage ranges, where Piezoelectric actuators are offered namely 150 V (+200 V), 500 V and 1000 V. The output power is a few watts, which is sufficient for most applications. Smaller volume actuators can be operated even with higher dynamic/frequencies. SQV amplifiers show low noise and are therefore best suited for positioning tasks with highest positioning sensitivity.
SQV amplifiers are available as 3-channel versions e.g. for optornechanical xyz adjusters.

4.2. LE amplifiers
LE amplifiers are used, when the power/current requirements cannot be covered by the SQV amplifiers. The LE series includes current boosters for optimum system power efficiency, when e.g. a high frequency sinoidal oscillation has to be excited, or to get short rise/fall-times for a rectangular signal.
The LE amplifiers are available for power levels up to hundreds of watts.
Due to these elevated power levels, selfheating of actuators according sec. 3.2. should be considered.

4.3. RCV recharging amplifiers
The RCV switched amplifiers are designed for driving large volume/large capacitance Piezoelectric actuators with high currents and powers up to the kilowatt range beyond the levels of the LE analog amplifiers. This situation occurs for example with the active excitation and cancellation of vibrations in heavy mechanical structures e.g. vehicles, airplanes etc.
Because the design of RCV amplifiers has to be adapted to some extent to the operated load, there are no standardized devices. In principle, RCV amplifiers can also be designed for lower power ratings. Please contact us for details.

4.4. Bipolar amplifiers
Usually Piezoelectric actuators such as stacks are operated unipolar or asymmetrically bipolar to get maximum displacement. Some applications exist, where Piezoelectric elements are operated symmetrically bipolar, but to avoid depolarization of the PZT ceramic, the electrical field strength and thereby actuator's efficiency has to be held sufficiently low.
Reasons for bipolar operation include simple electrical driving conditions e.g. of piezobenders (bimorphs), shearmode actuators or enhancement of stack actuators lifetime e.g. within feedback control loopd for position stabilization. In this case, the middle position is defined by 0 V, no offset is required for symmetric positioning range. This leads to long term low electrical fields preventing materials degradation by charge carrier diffusion.
Nevertheless, bipolar amplifiers can also generate unipolar or asymmetric output by applying a proper signal.

4.5. BMT, AGV antagonistic amplifiers
The AGV/BMT amplifiers are designed to drive push-pull (antagonistic) stack arrangements or piezobenders ("Bimorphs ) described in section 3.1. By electrical preloading, the full operating range of the ceramics can be used without the risk of depolarization which may happen during simple bipolar operation. The modulation of the antagonistic Piezoelectric elements is done by a single driving signal, complementary action is achieved by different static offsets shown in fig. 9a, b, c. This strategy ensures forced synchronization of motion of the 2 elements even under high dynamic driving conditions.
For an antagonistic setup, the actuators have to show potential free design, meaning that the operating ground of the Piezoelectric elements has to be separated from general ground of the arrangement.

Fig. 9a: Push-pull-stack arrangement with schematic electronic supply configuration

Fig. 9b:Operation of a parallel-bimorph with electrical preloading

fig9c.jpg (20960 bytes)
Fig. 9c: Equivalent circuit to Piezoelectric actuator arrangements 9a, 9b

4.6. HVP high voltage switches for pulse operation
HV-pulse generators are used when currents beyond the level of common amplifiers are necessary and where a steady movement of an actuator is not required, but only defined levels should be set within short times or where mechanical shocks have to be produced.
The HVP high voltage pulse generators from US EuroTek, Inc. show some interesting features enabling the user to drive Piezoelectric actuators in a more sophisticated way than the simple "high , "low procedure with common switches. Beside the levels "charging = high , "discharging = low there exist a third level "neutral , where the output is set to high resistance, so that the charge content (= position) of the actuator is kept constant. Thus the system can be set and held in intermediate positions. This is achieved by applying signal pulses with width less the time constant RC of the system, leading to only a partial charging of the actuator's capacitance corresponding an intermediate position. A general approach for pulsed actuator operation is not to oversize current specs for a distinct application, because too powerful pulses may cause unnecessary mechanical and electrical stress to the system. On the other hand the mechanical reaction time cannot be infinitely improved by increasing the pulsepower (see sec. 2.8.).

4.7. Computer interfaces
For computer control of Piezoelectric actuators a lot of designs and arrangements for interfacing exist. The selection of the proper interface for a distinct application depends on the basic hardware/software the user can provide, and the flexibility he wants to achieve with his setup.
Computer with internal D/A converter: computer output is an analog signal
The supplies low voltage analog signal output (e.g. 0 V to +10 V) is applied directly to the analog amplifiers etc. from US EuroTek, Inc..
HV-PC-card: The computer output is an analog signal. This card is inserted in the computer and produces immediately an analog-HV-signal for voltages up to +150 V or +500 V also in multichannel configuration. The power range is similar to the SQV or lower power LE amplifiers. This signal is directly applicable to the Piezoelectric actuator. Space saving configuration.
External D/A Converters: The computer output is digital data.
In this case, the digital data has to be transferred via a serial or parallel interface similar to any other peripheric device for a computer e.g. a printer.
The data is then converted by a D/A stage into an analog signal with subsequent amplification by usual analog amplifiers.
The low voltage D/A converting unit can be a stand-alone device, or can be integrated to the amplifiers cabinet. In all these cases, the analog functions of the amplifiers remain active e.g. a manual setting of an "offset voltage is possible, which is useful for adjusting setups before starting computer control. Multichannel systems are available.

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US EuroTek, Inc.
23561 Ridge Route, Suite U, Laguna Hills, CA 92653
Toll Free: (800) 991-1420
Tel. (949) 770-9911 ~ Fax (949) 770-2492

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