Encyclopedia of Electronic Circuits Examples

Note: These examples require a special schematic viewer---click here for download instructions.

These examples are reproduced with the permission of McGraw-Hill, Inc., as well as the indicated originators.

Example #1---LOGARITHMIC AMPLIFIER
Unusual frequency compensation gives this logarithmic converter a 100 us time constant from 1 mA down to 100 uA, increasing from 200 us to 200 ms from 10 nA to 10 pA. Optional bias current compensation can give 10 pA resolution from -55 degree C to 100 degree C. (Reprinted with the permission of National Semiconductor Corp. Data Conversion/Acquisition Databook, 1980, p. 3-107.)

Example#2---MINI-STEREO
This circuit is built around two chips: the MC1458 dual op amp, configured as a preamplifier, and the LM378 dual 4-watt amplifier. The gain of the preamp is given by R3/R1 for one side and R4/R2 for the other side, which is about 100. That gain can be varied by increasing the ratios. The left and right channel inputs are applied to pin 2 and 6. The left and right outputs of U1 at pins 7 and 2 are coupled through C5/R10 and C3/R6, respectively, to U2 to drive the two 8-ohm loudspeakers. (Hands-On Electronics, 5/87, p. 96.)

Example#3---80-M AMATEUR RADIO TRANSMITTER
This transmitter consists of a keyed crystal oscillator/driver and a high efficiency final, each with a TMOS Power FET as the active element. The total parts cost less than $20, and no special construction skills or circuit boards are required.

The Pierce oscillator is unique because the high Crss of the final amplifier power FET, 700-1200 pF, is used as part of the capacitive feedback network. In fact, the oscillator will not work without Q2 installed. The MPF910 is a good choice for this circuit because the transistor is capable of driving the final amplifier in a switching mode, while still retaining enough gain for oscillation. To minimize cost, a readily-available color burst TV crystal is used as the frequency-determining element for Q1.

An unusual 84% output efficiency is possible with this transmitter. Such high efficiency is achieved because of the TMOS power FET's characteristics along with modification of the usual algorithm for determining output matching. (Motorola, TMOS Power FET Design Ideas, 1985, p. 44.)

Example#4---ONE-WAY VOICE-ACTIVATED INTERCOM
An omnidirectional electret microphone can be used to pick up the sound and convert it into an electric signal. The output of the microphone is fed along two paths. In the first path, the signal is send to the inverting input at pin 6. In the second path, the microphone signal is fed to the non-inverting input of U2, where it is amplified and output to the speaker, SPKR1. (Reprinted with permission from Popular Electronics, 4/92, p. 67. Copyright Gernsback Publications, Inc., 1992.)

Example#5---ALTERNATING LED FLASHER
The alternating LED flasher is simply a two-transistor oscillator with LEDs connected to the collector of each transistor, so that they light in time with the circuit’s oscillations. (Popular Electronics, 9/89, p.23.)

Example#6---FUNCTION GENERATOR (COUNTER MODULE)
This is the first of three circuits which make up an audio frequency function generator. Each circuit can be used individually for custom applications

The Counter Module (MOD1) has a 0.35-inch high, six-digit liquid crystal display. Pulses at 1-second intervals are derived from the AC power line which has a typical accuracy of 99.99%.

Example#7---FUNCTION GENERATOR (CMOS TIMER)
A DUAL CMOS TIMER'S (IC5) output triggers another timer's input. Once Q2 starts IC5-a on initial power-up, the circuit continues to oscillate.

Example#8---FUNCTION GENERATOR (FUNCTION GENERATOR CHIP)
AN XR 2206 FUNCTION GENERATOR CHIP provides a triangle output at pin 2 when S1-a is open.