Teletext power supply

teletext power supply elektor february 1982 — 2-21 teletext power supply The series on the Teletext decoder failed to describe a suitable power supply. This particular supply can not only be used to power the decoder, but will also serve other low power applications requiring voltages of +60 V, +5 V and +12 V. Thanks to the modern stabiliser ICs, DC voltages are no longer a problem. Here the 7805 and the 7812 regulate the +5 V and +12 V voltages. The two ICs can endure a maximum output cur- rent of 1 A, which is more than enough as far as the complete Teletext decoder is concerned, since this only requires 600 mA at 5 V and 400 mA at 12 V. Choosing the right transformer is a little more complicated, since the circuit has to provide three different voltages. Things become even more complicated when one of the voltages is 5... 10 times higher than the others. The stab- ility of the Teletext tuning voltage (60 V) is of minor importance, as the tuner stabilises it and reduces it to ...