May 22, 1997

Transformerless supply fits CATV applications

Michael Ellis, Antec Technology Center, Norcross, GA

Coaxial CATV systems derive their power from a 60-Hz square wave that shares the center conductor with the television channels. You often need to place active devices along the distribution path. If the dc-power requirements for these devices are small, you can use a transformerless power supply to provide power to the active devices. The circuit in Figure 1 provides current as high as 10 mA at 5V dc. You can modify the component values for any desired output voltage and current. The design equations for selecting the components are the input parameters,

Minimum ac square-wave input voltage=V_IN(min);

Maximum ac square-wave input voltage=V_IN(max);

Desired dc output voltage=V_OUT;

Maximum desired dc output current=I_OUT;

For a complete derivation of the design equations and the Spice-simulation results, send a self-addressed envelope to Michael Ellis, ARRIS, 11450 Technology Circle, Duluth, GA 30097.