EMRFD Message Archive 14469

Message	Date	From	Subject
14469	2017-12-29 16:36:09	Ravi Miranda	Sizing of WV of capacitors for an LPF
Hi, How does one size the Working Voltage of a capacitor for an LPF, is this different for SSB/AM/FM? Say, Vcc is 13.8V and the output is 35Watts (approx). Any suggestions? Have a great weekend. Ravi -- I'm here to add more value to the world than I'm using up.
14470	2017-12-29 17:13:14	Tayloe, Dan (Noki...	Re: Sizing of WV of capacitors for an LPF
P = Vpeak*Vpeak/(2*R)   For 35w and 50 ohms and re-arranging terms, Vpeak = sqrt(2*50*35) or 59.1v.  I would go with 100v rated parts.   Dan, N7VE
14471	2017-12-31 12:50:50	arfghans	Re: Sizing of WV of capacitors for an LPF
There may be a bit more to consider, if you want to be thorough. The main thing is a mismatch condition, especially an open circuit, where the voltage will be higher. Also, some filter topologies with higher section Q will produce un-obvious increases in voltage (and current) in some filter elements. Try simulating your filter (and amplifier) in Spice. Apply various loads and see what voltages and currents arise in the filter elements.  I went thru this process in the design of high-power bandpass filters, and it was a real eye-opener. With 1500W into mismatches (3:1 SWR), some capacitors saw 4 kV rms and circulating currents reached 27A... No wonder the high-power filters from 403A and VA3AM are huge, expensive, and get hot when run at full power. Gary NA6O