75℃_CRYSTAL_OVEN

Published:2009/7/8 2:59:00 Author:May | From:SeekIC

Proportional temperature controller using National LM3911 IC holds crystal oven temperature constant within 0.1℃ of 75 ℃, to improve stability of oscillator used in frequency synthesizers and digital counters.Duty cycle of square-wave output of IC (ratio of OFF to ON time) varies with temperature of sensol in IC and with voltage at inverting input ter-minal. Duty cycle change makes average heater current change as required to bring temperature back to desired value. Square-wave frequency is determined by R4 and C1. 4N30 optocoupler drives power transistor having oven heater in collector circuit. During ON intervals of square wave, power transistor is driven to saturation, and during OFF intervals is cut off.-F. Schmidt, Precision Temperature Control for Crystal Ovens, Ham Radio, Feb. 1978, p 34-37.



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