Page 1 of 1


PostPosted: Sat May 03, 2003 6:12 pm
by Todd WD4NGG
This is a schematic copy of a 200 watt PDM Class-S Modulator I built back in 1996. It has several novel features. The Power Switch Mosfet is a single TO-220 P-Channel device rated at 200 volts Source-to-Drain. Level-shifting to the Mosfet gate is done using a 74OL6001 High-Speed Optoisolator and an Elantec EL7104 High-Speed Gate Driver Chip. The Gate-Driver chip is referenced to the IRF9640 Source B+ and uses an isolated floating power supply. All components are mounted inside an aluminum box for RFI shielding and all power leads go through feedthru caps and RFI chokes to keep all the RFI inside the box. I can place a sensitive AM portable radio right next to the box and just barely hear a trace of RFI. Since the Mosfet dissipates so little power a single TO-220 device is entirely adequate to fully modulate a 200 watt AM carrier. The unit has been running for 13 years now so it is very reliable. 73 Todd WD4NGG.Image