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Old 22nd September 2004, 04:12 PM   #11
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Quote:
Originally posted by djQUAN
from my point of view, I think non regulated SMPS's are cheaper and simpler to build. a reason cheap amps use them. I have heard that non regulated ones tend to be more efficient. I have not proven it though.

a regulated PSU is a bit more complex or very complex depending on the design, and it needs additional filtering on the output of the PSU. but the rails would be stiffer.
Efficiency ? There's no reason that efficiency would be any different. The additional components are a pair of sensijng resistors and a photo-coupler.
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Old 26th September 2004, 07:31 AM   #12
djQUAN is offline djQUAN  Philippines
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I have read (again) from my mag, about 2 years ago an article about car amps written by a car amp designer.


Quote:
The additional components are a pair of sensijng resistors and a photo-coupler.
it may sound simple. this is what the guy said.....

regulated PSU's need high quality low ESR caps, output chokes and optically isolated feedback for regulation. unregulated supplies are less expensive because they do not need output chokes and feedback circuitry and since unregulated designs have 50-50%duty cycle all the time, there is much less ripple current and cheaper caps can be used.

for the pros and cons of regulated and unregulated supplies, I think I have to quote this directly.

"Some designers try to keep their supplies regulated down to battery voltages as low as 9.5 volts. the supply compensates by increasing current. the current increases dramatically at the lower voltages. because of the higher currents at lower voltages, the supply efficiency drops further, requiring even more current. at higher voltages, the pulse width reduces, causing increased ripple current. this high current creates heat in the filter capacitors and can destroy the capacitor's electrolyte. some manufacturers do not use capacitors of sufficient quality for this range of of regulation. these amplifiers may not perform up to specification just one year after installation. also, the extra current at low voltages is extra hard on a battery that is already suffering. so we recommend that amplifiers stay in regulation down to about 11-11.5 volts.any properly working charging system can easily keep the battery voltage well above this."

-robert zeff, car audio and electronics january 2002.
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Old 26th September 2004, 12:13 PM   #13
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most of the losses take place in the power diode and the power transistor (switch), followed by the snubber, capacitor ESR and thermal and other losses in the magnetics -- i believe that most of the transistor switching losses occur during the transition period.

the graphs of efficency which I have seen show efficiency somewhat like a parabola -- low at low currents, rising to some optimal level, then falling at high currents -- these graphs can be found on both the Nat Semi and Linear Tech websites (I haven't checked TI).

if you don't regulate (i.e. maintain a constant duty cycle) the output voltage will track the input voltage -- it would be interesting to put a data-logger on the cigarette lighter output jack to see how this varies during the course of a trip !

one thing which we don't have to do as DIYr's is conform our project ot some linear programming optimization model -- we don't have to be particularly "green" if we feel that Class-A is best.
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Old 26th September 2004, 02:02 PM   #14
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Quote:
it would be interesting to put a data-logger on the cigarette lighter output jack to see how this varies during the course of a trip !
interesting? I have a digital voltmeter always plugged in into the cigarette lighter socket. my charging system varies from 12.8V to 14.2V. I know some causes of the varying voltage, the other times when it varies, I have no idea.
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