Celltower Power Supply - Page 1
Forum section: electronics / beginners

author: LaserTazerPhaser
author_rank: Regular Contributor
timestamp: September 06, 2019, 06:02:03 pm
content: Whats the typical working voltage of power amp stages in typical urban celltowers along with the type of supply used for turning mains into DC?

author: ArthurDent
author_rank: Super Contributor
timestamp: September 07, 2019, 07:23:23 pm
content: I'm at a total loss as to why just anyone would need, or want, to know that information. Perhaps giving us a little more information of what you are trying to do might help.

author: MagicSmoker
author_rank: Super Contributor
timestamp: September 07, 2019, 07:34:46 pm
content: Many cell sites use -48V, same as POTS (Plain Old Telephone Service). This is both because the MOSFETs in many RF PAs (power amplifiers) are designed for 48V operation, and telephone ESS (electronic switching systems) have traditionally been designed for 48V as well.

author: TheHolyHorse
author_rank: Regular Contributor
timestamp: September 08, 2019, 10:29:39 am
content: Quote from: ArthurDent on September 07, 2019, 07:23:23 pmMaybe he's building his own cell tower, because why not

author: LaserTazerPhaser
author_rank: Regular Contributor
timestamp: September 13, 2019, 05:33:47 am
content: Was considering they might have used swiching regulators to step down the voltage or cap droppers to power the amps.Are the amps cooled with forced convection or do they simply run the power semis well below their derating values?

author: MagicSmoker
author_rank: Super Contributor
timestamp: September 13, 2019, 04:33:06 pm
content: Transformerless (aka "capacitive dropper") power supplies are never used to supply more than a few watts of power, and even then they rarely cost less (or take up less volume) than a competently designed flyback.Telecom power supplies are designed for very high reliability and efficiency, with upfront cost almost not even a consideration. The most common topology I've seen is a boost PFC front end either feeding a phase-shifted full bridge (for >500W) or an LLC half-bridge (<600W, yes, some overlap there). Cooling depends on the power level, obviously, but typically forced convection is used starting at relatively low power levels (say, 300W) because telecom supplies are often crammed together in a 19" rack so don't have a lot of means of shedding heat via radiation or natural convection.

author: dmills
author_rank: Super Contributor
timestamp: September 14, 2019, 02:00:49 am
content: Also, telecom companies are WELL aware of what heat does to system reliability...Power is actually one of the major operating expenses for a cell network so they quite regularly upgrade their supplies to score an extra point or two on the efficiency of the mains supplies, which is nice because it means a steady stream of really excellent quality 48V power supplies hit the surplus market for basically no money.The Ham radio LDMOS fraternity thanks them for this (ADSL interference on SW, not so much)!

author: MagicSmoker
author_rank: Super Contributor
timestamp: September 14, 2019, 04:44:11 pm
content: LDMOS FETs, mainly because they are far more rugged (read: tolerant of load mismatch) than BJTs; almost as rugged as vacuum tubes, actually. Good linearity and much easier impedance matching (can often be done with just transmission line transformers rather than complex - and narrowband - conjugate matching networks) are also huge advantages. In fact, I haven't seen a commercial BJT-based RF PA in decades...