Electronic transformers for halogen lamps are very compact and lightweight. An equivalent power (60W) iron-core version weighs over 1500 grams versus 50 g of the electronic one. Size is much smaller and operation generates less noise and heat. These devices are produced massively which makes them very economical. By adding a few external components we can easily make a powerful DC power supply with any desired voltage and even multiple voltages at once.
Step 1: Electronic Transformer
Weight is around 50g for a 60W unit. Size is less than 3" x 1.5". You can find the description of a typical circuit in this link: Transformer .
Step 2: Block Diagram of Halogen Lamp Transformer
Step 3: Adding an External Ferrite Core Transformer
By adding an externalferrite core transformer (toroidal or EE) we guarantee total & safe isolation from the AC mains voltage, Primary winding carries only 12 turns. Secondary winding/s require only around 1 turn X volt output. In this way we can choose the output voltage we need by only adding or removing few turns. Step-down, step-up,and multiple outputs for full-wave or split supplies. Use 1mm2 insulated electrical wire. The core material should be ferrite and not iron powder.
Step 4: Output Configuration Examples
Step 5: Transformer
Transformer core can be Toroidal or EE type.Material should be ferrite. Output frequency is around 40KHz (varies with load). For a DC supply, add a full-wave rectifier stage / filter / and constant voltage or constant current regulator if needed. Use ultra-fast recovery diodes. 1N4000 series are not suitable for 40KHz switching. Use UF4000 series for 1 Amp or UF5400 series for up to 3 Amps.
Step 6: Dummy Load
Electronic transformers need a minimum load to operate correctly, else output will not be stable or even null. If your application load is insufficient, add a dummy load. Use a resistor or a small incandescent lamp.
Step 7: Some Waveforms (AC Output)
Step 8: DC to 20w Halogen Bulb & LED
Step 9: Caution
Extreme caution when connecting to AC mains. Never open the transformer when connected !