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Design Ideas

Two Transistor Circuit Replaces IC (177k pdf)
EDN 2/02 - Bi-directional IIC buffer is enhanced to add an enable pin accommodating hot-swappable operation. Replaced LTC4300.

Analog Circuit is Accurate Battery Fuel Gauge (55k pdf)
Unpublished 10/98 - Circuit acts as a fuel monitor for a rechargable battery, typically NiCd or NiMH chemistries. Analog type needle output meter appears like an automobile gas gauge.

Simple Circuit Safely Deep-Discharges NiCd Battery (88k pdf)
EDN 4/99 - Circuit is powered by the battery being discharged, LED flashes near end-of-charge. Ultra-low current drain won't harm battery if left connected.

Power OK LED for PC (9k pdf)
Electronic Design 1/14/98 - Simple, low cost three transistor circuit lights LED only if all four PC power supply voltages (+/-5V, +/-12V) are present.

RTD Calculator
Unpublished 10/97 - Javascript program converts 100 ohm platinum resistance into temperature.

Pi Filter has Sharp Notch (19k pdf)
Electronic Design 10/1/97 - Simple filter network makes a great low-pass filter having a sharp notch just outside passband. Can be implemented as active filter using GIC circuit. Use this component calculator to determine resistor and capacitor values. Voted best of issue!

Bi-Color LED Indicates Power/Fault (13k pdf)
EDN 12/5/96 - Single LED indicates both power on and blown-fuse conditions.

Bi-Directional Level Translator (22k pdf)
EDN 11/7/96 - Novel two transistor connection converts 5V logic signals to 3V logic signals without latchup. This flexible architecture works for 1V to 12V conversions as well. Voted best of issue!

Variable Low Pass Filter (20k gif)
Unpublished 1995 - A second order variable bandwidth low pass filter is formed using one IC and some passive components. This low cost circuit is good out to 2.5MHz.

Base Current Compensated High Voltage Amplifier (11k gif)
Unpublished 1995 - The base current of a single transistor high voltage amplifier varies from unit to unit and over temperature and current. To compensate, this opamp circuit measures the base current and adds an equal but opposite current to the input.

Model NTC Thermistor in SPICE (25k pdf)
Electronic Design 3/14/91 - SPICE subcircuit accurately models NTC thermistor. Model uses the .TNOM statement to set temperature. This allows circuits with transistors and diodes to be analyzed over temperature.

Variable Length 22AWG Twisted Pair Transmission Line SPICE Model (2k txt)
Unpublished 00/91 - Very good working four port subcircuit model of a transmission line. Can be adapted to CAT5 and others. Length of line defined by 1ft = 1V.

Improved Vbe Doubler (212k pdf)
Unpublished 00/90 - Circuit is a compensated Vbe doubler which operates over a wide current range.

Fan Speed Controller (130k pdf)
Unpublished 07/85 - Simple circuit for fan speed control based on thermal feedback. To reduce product noise. Design idea was rejected! Years later companies are making millions from such circuits.