Negative supplies are better for monster power valves (tubes) who's anode (plate) is a dirty great block of copper that has to be bolted to something and/or water cooled.Negative power supplies are not "better" than positive power supplies. They are merely tools, necessary to achieve certain goals. Their, "advantage" is that, if you need a negative voltage, a negative power supply can do that better than a positive power supply.
But that doesn't necessarily characterize a supply as positive or negative.You might characterize power supplies as to if the regulation is done along the positive rail or the negative rail.
My 1983 book about telephones says the, "wait" voltage is negative compared to the planet, but the telephone wires reverse polarity when the call is connected. There is a FWB inside the handset, so it doesn't seem to matter (to the telephone) which polarity arrives. This seems to lend credence to your idea.There's also a question of corrosion. Why do all the Telephone Exchanges have a -48 volt bus?
Yes that is part of what I was referring to.. in the first part and remembered the discussion about batteries too being involved in that due to the lead content.What I've learnt ago is that back in the days of Telegraphy, the "Posts" that carried the wires were -ve to the "ground" to avoid or reduce "electrolytic" corrosion" of the posts. Same with the wires and cables. The "Earth" return rods were also protected the same way. And it caught on and continues.
The positive terminal on 48VDC power systems originally was connected to earth to reduce galvanic corrosion due to leakage currents on buried lead-sheathed outside plant cables and other metallic pipes (water,gas) and components buried in the ground. Although lead is no longer used to sheath outside plant cables, the practice continues to minimize corrosion on existing lead-sheathed cables and other buried metallic components.
I routinely work with -48VDC and 800+ Amps... thats far from "lower current"I wanted to ask which are benefits of Negative voltage.
I think that systems which use negative voltage are working with a lower current, and it is easier to achieve faster switching speed of power MOSFETs used in SMPS systems.
I don't know have I right about that, and I wanted know are there more advantages of using Negative voltage.
Luckily, The DC-DC step down power supply for the logic chips have their negative side connected to GND ( I mean in an Ericsson AXE Exchange). Just cannot imagine how to trouble-shoot the circuit boards, if all the Vcc and Vdd are connected to GND.From what I've heard.. The telecom system chose -48VDC because they believe it reduced potential corrosion and buildup on battery plates thus extending their lifespan compared to positive voltage systems.
Virtually all telecom equipment runs on -48VDC.. (for now) with some +24VDC systems for microwave,etc... Utilities may utilize +130VDC
I completely fail to see the purpose of this circuit:Sorry guys for wrong schematic....and thanks for the answers....
now I think that I have made a good circuits. The main problem was that I didn't know is there positive or negative voltage in circuit.
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