Power supply Linear or Switching

[Williams Audio]

hi,

using a class a amp +/-45v@2amp will be more then 180watts per channel, we have 0.94% trafo efficiency and 1.4volts drop on the rectifiers
90/0.94 + 1.4=97.2volts; 90/97.2= 92.6% total efficiency for the power supply.
THEN WHAY TO USE A SHITCHING POWER SUPPLY?
Did I calculate wrong? What are the benefits of switching power supply when using class a amps?
Best regards

Williams

[Corax]

The following advantages just came to my mind:

- less weight, because less 'iron' is used (at the power transformer);
- if regulated, the output voltage should be stable like a rock;
- less space (volume) necessary, caused by smaller transformer and much smaller bulk capacitor(s);
- slightly higher efficiency possible, because of less copper losses (transformer), rectifier losses (Schottky diodes or even active synchronous rectification with MOSFETs), etc. under full load condition, which would be always the case for class-A.

The ladder case is just an estimation and could be the opposite case if not carefully designed.

[h_a]

Corax already gave already good points; I think less space with regulated rails for free sounds interesting. It's just a pity that these SMPS are not for DIY as even pcb-layout is critical and not as forgiving as audio. Next you need to wind chokes yourself...so interest is limited.

Have fun, Hannes

By the way, did I say SMPS can be a real noise-bomb if not carefully designed?

And use lethal voltages throughout?

[unclejed613]

the efficiency of the transformer is (output current * output voltage)/(input current * input voltage). the difference between input wattage and output wattage is lost as heat. so you should measure the line (mains) voltage and current, and then measure the output voltage and current. these measurements will give you the total efficiency, not just the rectifier efficiency. the rectifiers are probably the MOST efficient part of your power supply. i think the measurements including the power transformer will give you VERY different results.

[infinia]

Originally posted by Williams Audio
hi,

using a class a amp +/-45v@2amp THEN WHAY TO USE A

<SNIP>


SHITCHING POWER SUPPLY?

It's kind of like buying a Rolls Royce and then worrying about the fuel eff. of it.

[unclejed613]

actually, back in 1982 or so there was a design in the works at APT corp, for an APT-2 amplifier, which would have been an improved APT-1 with a switching supply. this was when switching supplies were in ther infancy, and SMPS's had some exciting failure modes back then. one of them was diode failure causing the filter caps to either frag or launch......... it was just about a year after they decided not to build it right away that TI came out with SMPS driver chips with shutdown and protection modes that worked.

[emanuel_hr]

The efficiency of a linear power supply is not that great. The power transformer is rated for a sinusoidal current witch, obviously is not the case with this sort of PS. The pulsed current drawn from it(with short duration and large peak value) reduces both the efficiency and power factor.

[AndrewT]

Originally posted by emanuel_hr
The pulsed current drawn from it (with short duration and large peak value) reduces both the efficiency and power factor.

Hi,
what is different with an SMPS that has it's capacitor charged direct from the mains?

[emanuel_hr]

There is no transformer in between so no I2R(these are the killer most of the time) or magnetising losses. Added to that, a power factor correction circuit can be inserted much easier(in fact it is another switching regulator).

[AndrewT]

Originally posted by emanuel_hr
There is no transformer in between so no I2R(these are the killer most of the time) or magnetising losses. Added to that, a power factor correction circuit can be inserted much easier(in fact it is another switching regulator).

The I2R loss still applies.
The power factor still applies.
It appears that all one has achieved is move the inefficiencies back down the line.