Specification
Project Overview
- Status: Draft; feasibility and architecture not approved.
- Design a high-voltage amplifier and its power supply for a microscope scanning-probe stage using the PiezoDrive SA050520 actuator.
- No schematic or PCB has been built.
Intended Use
- Laboratory microscope scanning stage.
- Single actuator channel is the initial scope.
- Continuous operation at 0–100 V, 10 kHz is required; burst-only current ratings are not acceptable.
What the Device Should Do
- Produce a sinusoidal voltage across the actuator: V(t) = 50 V + 50 V sin(2π × 10,000 Hz × t).
- Target range: 0–100 V, frequency: 10 kHz.
- Source and sink capacitive current without oscillation, clipping, or unsafe startup/shutdown excursions.
- Provisional prototype goals: residual output noise ≤5 mV RMS integrated over 0.1 Hz–100 kHz, excluding the commanded sinusoid and deterministic harmonics; carrier ripple ≤20 mVpp at the actuator terminals with a 20 MHz measurement bandwidth. These are engineering targets, not validated microscope-resolution requirements or achieved results.
- A separate provisional sinusoidal tracking/distortion goal is ≤0.1% THD at the intended load; gain/phase calibration and endpoint behavior remain to be qualified.
Main Features
- High-voltage output and included power supply.
- Current limiting, thermal protection, controlled startup/shutdown, and actuator discharge are required design features, not yet implemented.
Mechanical System Architecture
- Actuator is an off-board stack mounted in the user's stage.
- Mechanical flow: stack → stage flexure/moving mass → scanning probe.
- Mounted-stage resonance, moving mass, preload, cooling, and amplifier packaging are not yet specified.
- Manufacturer lists 74 kHz actuator resonance; this is not a guarantee of the assembled stage bandwidth or safe continuous full-amplitude operation.
Electrical System Architecture
- Functional flow: waveform command → protected high-voltage source/sink amplifier → actuator.
- Power flow: external source → included power supply → amplifier rails.
- User selected an energy-recovering switching amplifier. Development direction: synchronous regenerative half-bridge, multistage damped output filter, signed-current feedback/protection, and actuator-terminal voltage feedback.
- Include an isolated external low-voltage source, boost bus supply, bulk energy buffer, bus overvoltage dump, and fail-safe actuator discharge. Returned energy must not rely on an ordinary boost regulator being able to sink current.
- Architecture review gives conditional development approval only: filter/control stability, PWM timing, continuous losses and fault energy paths must be qualified before a complete schematic is claimed.
Hardware Subsystems
- Amplifier: stable with effective piezo capacitance and wiring parasitics; bidirectional output current required.
- Power supply: rail voltages, input source, power rating, and returned-energy handling to be determined from selected amplifier topology.
- Protection: output current limit, temperature sensing, safe discharge, and output-voltage limits.
- Actuator: exact SA050520; do not substitute on the assumption that it is a 1 µF load.
Interfaces and Connections
- Waveform-command input amplitude/source and connector are unresolved.
- Default prototype command interface: external 0–5 V analog input mapped to 0–100 V output, with startup ramp and default-disabled enable. This is an agent-selected assumption, not a user-provided interface specification.
- Piezo output wiring and grounding are unresolved.
- Power-source interface is unresolved; prefer a certified isolated external low-voltage supply over a custom mains front end for the first prototype, subject to power feasibility.
Power and Runtime Expectations
- The user authorizes inclusion of a power supply.
- Continuous 10 kHz, 100 Vpp operation is confirmed.
- No runtime, efficiency, or cooling target is approved yet.
- Use a certified isolated external 48 V supply as the prototype input direction; its exact rating is pending the completed loss budget. Nominal high-voltage bus near 120 V is provisional and may change to satisfy headroom and PWM timing.
Power Tree and Power Budget
- No supply rails are selected; the following is load-current sizing, not a DC supply power budget.
- Ideal capacitive current: i = C dV/dt; I_peak = 2π f C V_peak.
- At 10 kHz and 50 V peak with the originally stated 1 µF: 3.14 A peak, 2.22 A RMS.
- At the manufacturer's 1.8 µF small-signal nominal value: 5.65 A peak, 4.00 A RMS.
- A 3.6 µF effective-capacitance scenario requires 11.31 A peak, 8.00 A RMS. This is a preliminary sizing scenario, not a measured value at this drive and not a guaranteed worst case.
- A 4.32 µF scenario (1.8 µF × 1.20 tolerance factor × 2 effective-capacitance factor) requires 13.57 A peak, 9.60 A RMS. This does not include all temperature growth and is not a guaranteed worst case.
- A provisional amplifier capability target is approximately 20 A peak, 14 A RMS for continuous repetitive operation; this remains subject to load characterization, thermal protection, and topology review, not just absolute-maximum or pulse ratings.
- Required sine-wave voltage slew rate: 3.14 V/µs; design needs margin.
- Reactive load current is not equal to real DC input power. Driver losses, dielectric losses, returned-energy handling, and mechanical loading must be evaluated separately.
Manufacturing and Assembly Expectations
- Prototype first; PCB stackup, assembly vendor, footprints, and manufacturing files are not selected.
- Provide voltage/current/temperature test access once the circuit is selected.
Firmware-Relevant Hardware Requirements
- No embedded controller or firmware is required by the user so far; waveform-generation source remains open.
Physical Design Expectations
- High-voltage insulation, guarded terminals, heat sinking, and safe handling are required.
- Board envelope and enclosure remain open pending thermal design.
Important Design Decisions
- Use 0–100 V unipolar operation rather than ±50 V.
- Include a power supply in the design.
- Correct the load assumption using the named actuator's published capacitance before selecting current capability.
- Use continuous RMS and thermal ratings, rather than pulse-current specifications, to qualify the output stage.
Source Findings
- PiezoDrive product page lists SA050520 capacitance as 1.8 µF and voltage range as −30 to +150 V; 0–100 V is within the published voltage range.
- PiezoDrive SA-series specification page lists capacitance tolerance ±20% and actuator resonance 74 kHz. It explains that the listed capacitance is small-signal and effective capacitance increases with drive amplitude and temperature, reaching approximately twice small-signal capacitance at full range. Full range is not the same as this 100 Vpp requirement.
- These are manufacturer website specifications, not a separately verified PDF datasheet. No separate SA050520 PDF datasheet was identified.
- Mounted-stage resonance and allowable continuous operation at this drive remain unverified.
- Architecture check requires including the 1.44 µF low-tolerance case in ripple and stability verification, plus 1.8, 3.6, and 4.32 µF, open load, and extended-capacitance faults.
Assumptions
- Single-channel voltage drive; no closed-loop position control specified.
- Values calculated above assume a purely capacitive load below relevant mechanical resonances; actual impedance must be measured on the mounted actuator.
- Continuous operation is a user-confirmed requirement, not an assumption.
- User has no noise specification or intended imaging resolution; the provisional electrical noise targets above enable prototype development without claiming imaging performance.
- Provisional piezo-temperature trip is 70°C with sensor open/short detection and a latched fault; this is below the published 85°C ceiling but is not a validated internal-temperature or mechanical safety envelope.
Change Notes
- User clarified 100 V means peak-to-peak and the waveform is sinusoidal.
- User approved a 0–100 V swing, identified SA050520, and authorized a power supply.
- Manufacturer lookup changed nominal capacitance from the initial 1 µF assumption to 1.8 µF; final current rating remains open pending effective-capacitance and temperature assessment.
- User confirmed continuous operation and authorized the manufacturer's capacitance as the design basis.
- Architecture feasibility calculations and candidate-screening evidence are saved separately in Continuous Drive Feasibility.
- User chose the switching architecture and confirmed no noise/resolution specification is available; provisional electrical goals and the architecture-review caveats were recorded before prototype capture.