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Kitax 14th January 2013 02:53 PM

TDA7293 datasheet
here is the datasheet

i have 3 things that i want to know
1) what does symbol mean at quick reference data
2) are the 120v the maximum supply voltage? and if i get it right, the norman supply voltage is 50V dc
3) if i want to convert 220ac to dc, do i have to first transfer it to 72vac? if i am right, then after diode bridge and caps, it should be about 50v dc, am i right?

Mooly 14th January 2013 03:23 PM

Maximum supply voltages are absolute max ratings with no signal. Less is better for normal use :)

Somewhere around -/+ 40 volts DC would be ideal. That means you need a 25-0-25 volt AC transformer. The 25 volts AC will be a little higher than that at light loading, say nearer 27 volts. That will give around 38 volts DC per winding after rectifying and smoothing. So that gives a total of 76 volts.

(You have to look and consider what the max power dissipation in the chip will be when driving your speakers. Thats why lower supply voltages are used in practice. Reliablity improves dramatically too)

Kitax 14th January 2013 04:49 PM

25-0-25 volt transformer? umm what does the 25-0-25 stand for?

what do you mean rectifying?

Mooly 14th January 2013 05:07 PM

You've alot of reading to do :)

The 25-0-25 denotes a transformer with a "centre tap" between its two 25 volt windings. In other words its like a 50 volt winding with a connection in the middle. That point becomes the amplifiers "zero" or ground point.

Rectifing means using diodes to change the AC voltage from a transformer into DC voltage.
Rectifier - Wikipedia, the free encyclopedia

Kitax 14th January 2013 08:52 PM

oh... im just not quite that fammiliar with english terms, as i am learning in whole another language...
so i guess i would need to use only one of the windings? couse 38V sounds like the closest i can get to 40...

Kitax 14th January 2013 08:53 PM

oh also... in the typical schematic... could you explain the function of boot loader?

Mooly 15th January 2013 07:31 AM

"Boot loader" seems to be some odd term they use. I've never come across that before in amp design. What it refers to is the "Bootstrap" part of the circuit (within the chip) that allows the output voltage to add to the supply voltage and so allow (internally in the chip) a higher voltage to be ued for the output driver stages. Its just for efficiency and to squeeze the most voltage swing out of the design. Its an old technique and uses those small electrolyitics to work.

You have to understand the power supplies...

The amp normally runs on a split or dual supply. That means an equal DC voltage ABOVE and an equal voltage BELOW a zero point.

A 38 volt winding, thats 38 volts AC and would give 38* root 2 which is 53 volts DC. That is just ONE rail. All you could do with that is make the "single rail" version of an amp which is AC coupled (big cap to couple the speaker to the amp). Its to high to double up on and make a dual supply.

For dual rail you need the 25-0-25 type transformer like this


Kitax 15th January 2013 06:06 PM

oh... tnx for the info...

actually didnt know what the +/- at the supply voltage ment... and i think it would be better if i used 30-0-30 transformerr? on the other hand... the min voltage is +/- 12 volts... if i use 2x24v (2.08 amp) transformers... i would not be able to run 2 of the chips in parallel, because of the amp limit... i would need to get 2 transformers, for each chip, right?

Mooly 15th January 2013 06:19 PM

You are better setting out what the design goals are first.

What is the max power you want to aim for and into what impedance ?

For example 80 watts RMS into 6 ohm or 100 watts RMS into 8 ohm and so on. From that you can calculate the supply voltages needed and then move on to decide what transformer to use :)

Kitax 15th January 2013 07:29 PM

well i wanted a 100w RMS (if i understand RMS) amp into 4ohm speakers. i wanted to use the chip amp mentioned earlier, but now im having socond thoughts... oh and i want to make it legit, so i can turn it all the way up, and not worry about overheating, and stuff like that.

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