Telephone Ring Generator using 60hz Power Transformer -  This ring generator will ring a telephone once every 10 seconds. The interval between rings can be lengthened or shortened by varying the value of the 1 Meg resistor. The 70 volt/ 30 Hz ring voltage is produced from the 120 volt side of a small 12. 6 VAC power transformer. . .  [Design by Bill Bowden]

Tester 4-20ma Current Loop -  This circuit injects an adjustable current through a wire loop. Using a digital current meter, the current can be adjusted from near zero to over 24 milliamps . . . [Hobby Circuit designed by David Johnson P.E.,  05/01/12]

Three-Terminal Adjustable Regulators -  The unregulated DC supply is a very common type and the simple regulator shown in fig. 1 may be added for projects that require a stable voltage. . . .  [designed by Charles Wenzel]

Transformer Buys Lower Shutdown Current -  11/23/94 EDN Design Idea   The step-up DC/DC converter in Fig 1 trades a slight loss in efficiency and a transformer in place of a less expensive inductor for two important advantagesThe inductor offers low shutdown current because the transformer elimin. . .  [by Tian Jin-gin, Taiyuan Semiconductor Factory, Taiyuan, Shanxi, China]

Transformer Coupled Splitter -  Active amplified transformer isolated signal splitter that enables hum-free connection of1-guitar to more than1-amp as well as having a direct output. . .  [Guitar Effect by RC Keen]

Transformer driver controls bidirectional switch -  07/17/97 EDN Design Idea   You can use a transformer-driver IC to simply control a MOSFET on/off switch. . .  [by Gerald Grady, Maxim Integrated Products, Sunnyvale, CA]

Transformerless Power Supply -  I have received a few emails asking for a transformerless power supply. Here is such a supply. This supply uses no heavy step down transformer and has an extremely low parts count. The circuit can be built very small and can supply small currents for small projects. The major downfall of this supply is that it is not isolated from the AC line and can only supply small currents. . .  [Design by Aaron Cake]

Transformerless Power Supply -  Circuit designed by Ron J . . .  [Andy Collison's website]

Transformerless Power Supply -  This circuit will supply up to about 20ma at 12 volts. It uses capacitive reactance instead of resistance - so it doesn't generate very much heat. The circuit was designed to provide a cheap, compact power supply for Cmos logic circuits that require only a few milliamps. The logic circuits were then used to control mains equipment, using an optically-isolated triac. . . .  [Electronic design by Ron J.]

Transformerless Power Supply (jose pino) -  Simple, low cost and easy to build power supply. Ideal for applications that doesn't requiere too much power. (5/28/2006) . . .  [Jose Pino]