Tech Directions - December 2007 - (Page 14)

Is This Op-Amp Any Good? Lab-Built Checker Removes All Doubt! By Charles Harman Charman@pdq.net E LECTRONICS students— and instructors—experience having the means to check an op-amp (operational amplifier) at the proto-board stage as a real blessing. Most students lack the experience or knowledge that it takes to recognize whether an op-amp is operating normally or not. With this handy opamp checker, you can simply remove the component in question Charles Harman taught electronics at ITT Technical Institute in both Houston and Garland, TX, before retiring. He is currently a proctor for the Electronics Technician Association. from the proto-board, insert it into the op-amp checker, and see whether or not the checker’s LEDs (light-emitting diodes) are toggling. It’s that simple. modate most single, commonly used op-amp types.) When the user presses the PTT, the inserted op-amp becomes the How It Works An op-amp is an active device that has high gain, a differential input, and an output. When the user inserts an op-amp into the opamp checker’s 8-pin DIP socket and pushes the press-to-test (PTT) button, the op-amp is activated. (An 8-pin DIP socket is used to accom- +V R3 220 K +V BATT 1 9V COM 9V .1 μF C1 3 + 4 2 — A1 R1 2.2 K 7 6 R4 220 Ω Photo 1—Op-amp checker built on a proto-board active element of a RC-type relaxation oscillator powered by two 9 V batteries. A bipolar square wave output from the op-amp drives two parallel opposing LEDs. The peak– peak amplitude of the output square wave swings from +Vsat to –Vsat (about 16 Vpp). The toggle rate of the LEDs is a function of the oscillator’s RC time constant and the op-amp’s slew rate. The faster the toggle rate, the greater the slew rate. The slew rate is a measure of how fast a signal can be processed by the op-amp. For LED1 R2 22 K LED2 BATT 2 —V —V When an op-amp is inserted, circuit will oscillate if the op-amp is good. Fig. 1—Schematic PTT 14 techdirections ◆ DECEMBER 2007

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Tech Directions - December 2007 Technically Speaking Contents Direct from Washington The News Report Technology Today Technology's Past Mastering Computers Is This Op-Amp Any Good? Lab-Built Checker Removes All Doubt Here Comes the Sun! Residential Solar Systems Add Up to Savings Pinhole Cameras—For Science, Art, and Fun! Poster Project Maps Out Design Process Gifts for Geeks E-gallery More than Fun

Tech Directions - December 2007

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