help in building TDA7294

[Leglandu]

Originally Posted by Triophile

Quick question re the TDA7294: I see that it has separate pairs of power pins, one pair for the signal stage, the other for the D-MOS output devices. Can I use separate supplies to feed each of these sections, or will this cause oscillation/stability problems?
Many thanks, Jon.

Yes, it seems separation in powering power stage and signal stage make a nice improvement in the sound quality, particularly in the bass.

A simple way to do, although for TDA7293, in french :

Fangorn - comme un arbre dans la ville ... -
(schematic at the middle of the page)

BYW98 permit the small signal stage cap to be charged before power stage cap (x10 bigger). And prevent small cap to discharge in the big one when high current is needed.

The original post :
1er ampli diy : question diverse : Electronique - Page 3 - Cinetson - Hifi et Homecinema
WARNING : the lower BYW98 is wrongly inverted in that schematic !

Edit : oops sorry, didn't realize in time your question was old...

[simple simon]

Originally Posted by yogender

hello

i have also made a amplifier using TDA7293
here is my pcb layout and the circuit

I have just made one of these following yogender's values and am starting to test it. Would the mute/standby capacitors cause my series light bulb on the primary side of the power supply to light up? If so for how long? I have left it on for 3 seconds then bottled out and turned it off.

Without the amp connected the bulb briefly flashes (<0.5 sec)

Thanks,

Simon.

[AndrewT]

the bulb staying on tells you that something id drawing significant current.
Check the voltage from the PSU while the bulb is on. It could be as low as 2% to 5% of the expected operating voltage.

How many amps are being tested?
I think you have already checked the PSU, you said the bulb went off in <0.5s.
Did you check the voltages at the PSU?

Have you connected the amp the right way around? +to+, -to- and 0to0?

[danielwritesbac]

Is it possible to run the input stage of TDA7294 from regulators, right off the same power supply?

[abraxalito]

Originally Posted by danielwritesbac

Is it possible to run the input stage of TDA7294 from regulators, right off the same power supply?

When I first played around with the TDA7294 I also had what I considered to be the very smart idea of separating the power supplies, putting some RC filtering on the input stage power supply pins.

The result was a blown up chip.

Do not go there!

The datasheet does not make this point clear at all - but the tab is connected to pin8, not pin15. Pin8 must remain always the most negative point in the circuit because its the IC substrate. Taking it slightly positive relative to any other pin on the IC will forward bias the isolation which is necessary for the whole thing to function. Put in enough current and the chip goes south.

[danielwritesbac]

Originally Posted by abraxalito

When I first played around with the TDA7294 I also had what I considered to be the very smart idea of separating the power supplies, putting some RC filtering on the input stage power supply pins.

The result was a blown up chip.

Do not go there!

The datasheet does not make this point clear at all - but the tab is connected to pin8, not pin15. Pin8 must remain always the most negative point in the circuit because its the IC substrate. Taking it slightly positive relative to any other pin on the IC will forward bias the isolation which is necessary for the whole thing to function. Put in enough current and the chip goes south.

So, the voltage drop of the BYW98 diode in this illustration Fangorn - comme un arbre dans la ville ... - is actually hazardous?

[abraxalito]

Yes - even though that's a low forward voltage rectifier, when its carrying low currents it doesn't get warm and its forward voltage drop is much higher when cold. So I would not use it between pin8 and pin15 myself. This is assuming that the TDA7293 is basically the same as the 7294, which is something I have not yet checked. I will check this and report back.

[abraxalito]

The TDA7293 samples I have (not guaranteed to be genuine ones as not obtained through a recognised distributor) also have pin8 connected to the substrate. So the same provisos apply as to the TDA7294.