Jim Keith is a senior engineer with Bell-Mark. He received an ASEE from the Wentworth Institute of Technology, Boston, Mass., and a BS in missionary radio technology from the Moody Bible Institute, Chicago, Ill. Email address: jkeith@bell-mark.com
3 results found for Jim Keith, displaying items 1 - 3
November 16, 2009[Ideas For Design] Adjustment-Free Fan Controller For Under $1
No frills here—just inexpensive functionality. This circuit activates a cooling fan when the temperature of a target high-power-dissipation device, such as a processor chip, exceeds a predetermined limit. The key element in the design is the Epcos PTC Temperature Limit Sensor (see the datasheet at www.epcos.com/inf/55/db/ptc_03/01900191.pdf), which cost about $0.50....
June 11, 2009[Ideas For Design] Charge-Pump VCO Increases Parts Count But Saves On Cost
This charge-pump voltagecontrolled oscillator (VCO) has a number of neat features: single positive power-supply operation, positive VCO reference voltage, fast response, high linearity, temperature compensation, and open collector output. Seldom are all of these features present simultaneously. Though the component count is relatively high compared to commercially available devices, cost is low because all components are garden variety. Central...
March 17, 2005[Ideas For Design] Confidently Calculate Rectifier Input Capacitors
A rectifier input capacitor's size is often considered nebulous. Therefore, common practice is to pick a large size, and if the ripple voltage is low enough, all is okay (see the figure, a). If not, it can be increased in size. Other attempts sometimes calculate percent ripple, which I consider a largely useless term because we tend to visualize the waveform as an oscilloscope sees it—a sawtooth waveform with the limit being the...
