• VARIABLE ISOLATED AC VOLTAGE SPANS 0VAC TO 280VAC
  I designed and built this circuit about 25 years ago. It came in handy for many projects that were powered from 120 VAC, 240 VAC and 277 VAC. It provides complete isolation from the power line. It uses two 1:1 isolation transformers that are wired in parallel for the140vac range and in series for the 280vac range. The selector switch also diverts power to the appropriate output socket to avoid mishaps in sending the wrong voltage to the load. My home-built unit also included an AC volt and amp meter to monitor the output. However, this circuit only indicates the AC power connections.

Method Sets Voltage in Multipleoutput Converters:  02/01/01 EDN-Design Ideas / (added 05/03)

Parasitic Capacitance Effects in Step-Up Transformer Design:  AN39 - Linear Technology - This note explores the causes of the large resonating current spikes on the leading edge of the switch current waveform. These anomalies are exacerbated in very high voltage designs. (app note added 7/06)

Power Supplies and Regulators:  new low power discrete switcher (Electronic circuit added 7/03)

Power Supplies and Transformers:  Basic structures of power supplies (Electronic Schematic / circuit added 4/02)

Signal transformer application:  Coilcraft - Power Magnetics Application Note - (Circuit / schematic design added 6/06)

Step Down Rectifier Makes a Simple DC Power Supply:  04/09/98 EDN-Design Ideas / (Electronic Schematic / circuit added 04/02)   -- A simple and useful nonisolated rectifier features voltage step-down operation, acceptable Class A line-current harmonics, inherent short-circuit protection, and, optionally, a regulated output

Telephone Ring Generator using 60hz Power Transformer:  (added 8/03)

Theory and Construction of MIC Splitters:  5 page booklet in PDF format (Electronic Schematic / circuit added 4/02)

Transformer Buys Lower Shutdown Current:  11/23/94 EDN-Design Ideas / (Electronic Circuit diagram added 03/03) 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 advantages: The inductor offers low shutdown current because the transformer eliminates a leakage path. The circuit stays in regulation, even if the input voltage rises above its nominal figure. Note that in Fig 1, the input voltage is negative with respect to the output's ground. Transistor Q1 shifts the output voltage's level down to a level compatible with IC1's feedback pin...  

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 (Electronic circuit added 5/02)

Transformer Driver Controlsbidirectional Switch:  07/17/97 EDN-Design Ideas / (Electronic Circuit diagram added 03/03)   -- You can use a transformer-driver IC to simply control a MOSFET on/off switch

Transformerless Power Supply:  (Circuit / schematic design added 6/06)

Use Amplifier Phono Input as Line Level Input: Inverse RIAA Filter:  The circuit does two functions: signal level attenuation and inverse RIAA filtering. The signal attenuation is needed to convert the 500 mV signal to 2.5 mV signal. The inverse-RIAA filtering is needed to make the frequency response of the system flat (same equalization that is used when music is transferred to vinyl in the studio). The picture blow shows the frequency response of the ideal inverse-RIAA filter (Schematic / circuit added 10/05)