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Old 13th March 2013, 08:45 PM   #31
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up to a few hundred mA there are chips for inverting the voltage.

what is Your plan btw ?
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Old 13th March 2013, 09:35 PM   #32
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Quote:
Originally Posted by Arty View Post
up to a few hundred mA there are chips for inverting the voltage.

what is Your plan btw ?
at first my plan it was build a amplifier with tda7297 but with a 12-13 volt power supply i can't have more than 10 watt per channel.
so i decide to use lm 1876 that with a 13/0/-13 power supply give about 10 watt per channel and quality of sound is better.
now i need inverting my 12v power supply with about 400-500 mA in 13 and -13 line.
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Old 13th March 2013, 10:02 PM   #33
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Originally Posted by yoosefheidari View Post
ok
how can i have a 13/0/-13 power supply from a 13v battery?
with 0/5A current in +13 and 0/5A in -13 .
You can't. And you will need more than the 400-500mA that you mention also. The choices are either that you bridge two amplifiers, that you buy a bridged chip like the TA2020 or that you buy a supply boosted chip like the TDA1562 which will give you 40W.
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Old 14th March 2013, 05:38 AM   #34
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ookay.
why is it so important to have it run on a battery?
is it going to be used in a car?

Switchmode Power Supply For Car Audio

this is what you need.
but keep in mind the foot note:
"That it does work if built as described is certain, that you will be able to achieve the same results is not. If you do not have (or at least have access to) an oscilloscope - don't even think about trying to make the supply, as it will not be possible to ensure that the duty cycle of the controller is exactly 50%, or that there is no severe overshoot or ringing at the output."

a nother option is to salvage a car amp with a blown power amp, but working powersupply.
then you can "simply" mesure its output voltage and find a suitable chipamp it can power.

building an SMPS requires .. practice. Chipamps do not like to be powered with rails that can overshoot the absolute maximum supply voltage. they simply die without any warning.
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Old 16th March 2013, 02:45 PM   #35
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Originally Posted by AndrewT View Post
Prove it.
Well, with around 700mV signal (or very little less, sine wave, 30Hz) I had constant 13V output and around 6A power consumption, it was very hot at that power tho.
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Old 16th March 2013, 03:58 PM   #36
AndrewT is offline AndrewT  Scotland
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Thanks for confirming your measurements.
The 13Vac is equivalent to 36.77Vpp
12Vdc and 6Adc input is equivalent ot 72W of input power giving an efficiency at full power into 4r0 of ~57%. Certainly plausible.

What is does confirm is that the amplifier is not operating from a single polarity 12Vdc source. You can't get 36Vpp from 12V supply.
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Old 16th March 2013, 09:06 PM   #37
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Originally Posted by Arvis View Post
TDA1562, I measured nominal power of 41W @ 14V power supply (would probably be a bit less at 12V), just need to use different capacitors than in most circuits on the internet.

would someone care to explain why would that be so impossible?
the chip if i remember is bridged internaly. the "lift" caps can provide 2x supply voltage when needed. (for the "top" part of the sine wave)
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Old 16th March 2013, 10:31 PM   #38
JMFahey is offline JMFahey  Argentina
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Quote:
Originally Posted by AndrewT View Post
Thanks for confirming your measurements.
The 13Vac is equivalent to 36.77Vpp
12Vdc and 6Adc input is equivalent ot 72W of input power giving an efficiency at full power into 4r0 of ~57%. Certainly plausible.

What is does confirm is that the amplifier is not operating from a single polarity 12Vdc source. You can't get 36Vpp from 12V supply.
Dear Andrew, they use a 12V battery but it's not just "a 12V supply " by any means.
The trick is quite clever.
The amp is Class H (or F, don't remember which letter applies here) and for low level signals it is fed straight (probably through a Schottky diode plus a MOS switch or similar) from the 12V supply.
Once output rail approaches 12V, it's switched to the + side of a capacitor, charged to 12V, whose - side gets connected to +12V , so for a brief instant the amplifier is fed from 12+12V=24V.
Since the amp is bridged, it's equivalent to a single amplifier fed from +/-24V with a theorical capability of 48V PP.
We are quite far from that, even if fed from a stiff, high current capability , ripple less car battery, because there are many junctions in the way.
But the idea is real bright.
Problem is it requires a car battery (the intended application) or at least a good, fresh, well charged lead gel battery quite close to the amplifier board or all that switching and pumping is heard as a horrible rhythmic buzzing noise, which some describe.
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