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Browse Prior Art Database

Variable Speed Control For a DC Fan

IP.com Disclosure Number: IPCOM000100139D
Original Publication Date: 1990-Mar-01
Included in the Prior Art Database: 2005-Mar-15
Document File: 1 page(s) / 28K

Publishing Venue

IBM

Related People

Celenza, N: AUTHOR

Abstract

The circuit in the figure provides 15 V to the fan of a cash register when the printer is not running (low power dissipation), and 10 V when the printer is not running (low power dissipation). Also, the change in fan speed is not perceived by the customer.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 100% of the total text.

Variable Speed Control For a DC Fan

       The circuit in the figure provides 15 V to the fan of
a cash register when the printer is not running (low power
dissipation), and 10 V when the printer is not running (low power
dissipation).  Also, the change in fan speed is not perceived by the
customer.

      Switching the fan voltage from 15 V to 10 V could not be used
since it would cause a perceivable noise change from the fan speed
change.  Using a thermistor in series with the fan would not cause
the 5 V change required for the 15oC temperature change.  Linear
regulator LR1 provides a reference voltage of 1.25 V from pin 2 to
pin 1, thus forcing a constant current through R2 varied only by a
resistance change in thermistor Rth1.
           Vf = Vref/(R2+Rth1)*(1+R1)

      From the above equation one can see that the change in Vf (fan
voltage) per change in temperature can be any desired value just by
choosing the proper values for R1 and R2.

      Also, Vfmin, the low temperature value for Vf is:
           Vfmin = Vin-VCR1+Vref

      Vfmin can be any desired value by choosing the proper zener
voltage for CR1.