Reverse-Phase Dimmer ICs Eliminate RFI

Four reverse-phase dimmers eliminate the RFI generated by triac-based light dimmers that can interfere with nearby electronics. The LS7636, LS7636FO, LS7637, and LS7637FO reverse-phase dimmer ICs turn on drive transistors at the zero-crossover point of each half cycle, enabling a slow current rise. Current is terminated later during the half-cycle, depending on the desired dimming level. RFI generation is minimized because power to the load is not turned on abruptly as with leading-edge (triac-based) dimmers, and therefore the reverse-phase ICs do not require the need for external filtering. In addition, these dimmer ICs can drive any electronic transformer. The LS7636 automatically reverses direction when reaching maximum or minimum intensity, while the LS7637 stops dimming when reaching maximum or minimum intensity. The LS7636FO and LS7637FO versions power up to full-on intensity when AC power is first applied. All of these ICs have three selectable operating modes. These modes allow the load to be turned on to maximum intensity or to a previous set memory level in response to a short pushbutton application and to continue dimming in the same direction or reverse with each new long pushbutton application. All ICs are available in 8-pin DIP and SOIC packages. Pricing for the LS7636 and LS7637 in 10k-piece quantities is $0.40. Pricing for the LS7636FO and LS7637FO in 10k-piece quantities is $0.45. LSI COMPUTER SYSTEMS INC., Melville, NY. 631 271-0400.