TDA7293 datasheet

[Mooly]

I still don't see it tbh 🙂

Are you trying to switch the mains here or the DC side ? How does the cap charge in the right hand diagram 🙂

 

[Kitax]

yeah well i need another swich for the cap to charge... it would take too much swiches actually... :S

 

[Mooly]

Use the nicad battery idea... easy and simple.

 

[Kitax]

ok...

you mean like this, right?

p.s.
the polarity of battery isnt right...

 

[Mooly]

Something like this. The 9 volt nicad starts the relay. When the amp rail takes over, that supply keeps the relay energised.

Choose R1 to give required trickle charge current.
Choose R2 to give 12 volts across the relay.

 

[Kitax]

oh ok... the diodes on the top if ment for the battery not to discharge, right? and the zener, for it to not overcharge right?

 

[Mooly]

That's it. The zener clamps the battery voltage. Set the charge rate low, something like 30/C. Diodes would all be 1N4004 or similar

 

[Kitax]

the problem is that if i use a 12 volt battery... well its pretty expensive for the power switch

 

[Kitax]

http://sharp-world.com/products/device/lineup/data/pdf/datasheet/pr36mf51_e.pdf

can i use this one?

 

[Mooly]

There's a bit of confusion here 🙂

I thought we were keeping it simple and using a normal mechanical relay. A 12 volt relay coil with the relay switching 240 volts mains. Using an opto triac is a whole different thing. The triac would have to control a larger power triac to handle the switch on surge and current requirements.

 

[Kitax]

oh... i just dont want to use a 12 v battery, because of the price...

 

[Mooly]

Use a little PP3 nicad or whatever you can get. Or AA or AAA's.

 

[Kitax]

dont i need 12 volts?

 

[Mooly]

Most 12 volt relays will pull in at far less than 12 volts.

 

[Kitax]

oh... that explains a lot ^^

 

[Mooly]

You could use a 6 volt relay too and 4 AA's. Just adjust the values to suit.

As long as the normal (amp on) relay voltage is arranged to be higher than the battery by a couple of volts then the battery will charge correctly.

 

[Kitax]

you said: "Most 12 volt relays will pull in at far less than 12 volts."
how much less are we talking about?

heavent really delt with relays...

 

[Mooly]

I just tried it for real on a 12 volt relay and it pulls in reliably at 6.7 volts. Every relay will be different but you get the idea.

 

[Kitax]

mmm... so if i take a 6V relay, i could count on about 3-4V?

 

[Mooly]

Yes, a 6 volt relay would pull in with 4 AAA batteries which would give around 5v volts when fully charged. The resistor values would be chosen to give say 6.5 or 7 volts across the relay when the amp was running.