Analog circuit enforces slow servo response

Posted on Feb 6, 2014

The all-analog circuit presented controls the rateat which a miniature turbojet engine can be throttled. Increasing or decreasing the throttle too quickly on a miniature turbojet engine, or any jet engine, can lead to quick failure in flight, causing expensive repairs and potential safety problems due to flameouts. This circuit can be used as an analog

Analog circuit enforces slow servo response
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backup circuit in a microcomputer-based throttle controller, or as the primary throttle-rate controller. The response rate, servo direction, clockwise (CW) and counterclockwise (CCW) gain (end points) and servo-centering parameters are adjustable. This circuit, Figure 1, takes a received radio-control, incoming positive-going pulse which varies from 1 to 2 ms (the standard for most aircraft radio-control systems), at a fixed frame rate of 20 ms, integrates it over time. It uses the output of the integrator to control the output pulse width of a 555 IC monostable multivibrator. The rate of pulse-width change is determined by the effective integrator time constant, R24 and VR1 in series, C1, and the duty cycle of the incoming pulse stream. Q1 is switched on for the duration of the positive-going pulse, applying +5 V to the integrator-input resistor, R24 and VR1 in series. The circuit is designed such that a point will be reached where the effective charge rate-based on the input pulse width-and the reset/discharge rate of integration capacitor C1 by R1, balances for each positive-pulse duration, causing the output of integrator U3 to stabilize at a DC value as a function of the received-pulse width. An LTC2054 zero-drift op amp is used for the integrator. This op amp has an ultralow input bias current, ±1 pA (typical) and ±150 pA (maximum), offset voltage of 3 V and a drift spec of 30 nV/ °C (maximum>. The open-loop gain of...

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