Tapping 12v from a NAP140 clone PCB board

[BIA]

Hi , i have a problem i need help with im planning on assembling a NAP140 clone amp with a 12v DC speaker protection circuit board , can anyone help me with a solution on providing 12 VDC to the speaker protection board form the amplifier board voltage rail . Rather than having a seperate 12 VDC voltage source .





this is the schematic of the Amp

 

[Mark Johnson]

Here is one way to get +12VDC from a +40VDC supply.

 

[BIA]

Is that safe though ?
i was hoping to tap into one of the exsiting transistors that are on the amp boards and get 12VDC that way

 

[JMFahey]

Is that safe though ?
i was hoping to tap into one of the exsiting transistors that are on the amp boards and get 12VDC that way

Yes, do it like transistormarkj says.
You can't "tap voltage" from the power amp but from the PSU; in this case from a +40V rail.
Post the PSU schematic just in case there's another possibility but so far this one is good.

 

[BIA]

Hi , i dont have the PSU it takes a few weeks to come from China , but here is an image ,



i notice there are LED's and resistors on the board so may be possible to power a Speaker Protection Relay from it .

 

[JMFahey]

Don't you already have the schematic?
Anyway, the solution posted above turns raw +40V into regulated +12V , fine.

 

[BIA]

Hello thanks for your replies much appreciated .

Just one thing about the LM7812 and the speaker relays im getting are 5A will there be enough current from the lm7812 to power the relay ?



OMRON 5A Relay X2

 

[JMFahey]

Sorry but you are mixing 2 unrelated ratings.
I think 5A is the relay *contact* rating but what what we need to know is the relay *coil* current.
Please post exact relay model and google its datasheet or search it in, say, Mouser or Digikey.

 

[BIA]

omron relay spec

Coil Current:11.5mACoil Resistance:4.17kohmCoil TypeC, MonostableCoil Voltage VAC Nom:48VCoil Voltage VDC Nom:48VContact ConfigurationPCOContact Current Max:5AContact Voltage AC Nom:250VContact Voltage DC Nom:30VExternal Depth:25.5mmExternal Height:29mmExternal Width:13mmNom Operating Power:530mWRelay Mounting:Through HoleRelay TypeowerApproval Bodies:CSA / SEMKO / SEV / ULCoil Operating Lower Percent Limit:70%Coil Operating Upper Percent Limit:110%Contact Current AC Max:5AContact Current DC Max:5AContact Voltage AC Max:240VContact Voltage DC Max:30VDC Coil Power:530mWExternal Length / Height:29mmMounting TypeCBNo. of Poles:2Operating Temperature Max:70°COperating Temperature Min:-40°COperating Time:15msRelease Time:15msSeries:G2RSwitch Current Max:5ASwitching Current Max:5A

 

[BIA]

Here the relay spec again

So can i power this with the lm7812 schematic posted at the start of this thread ?

 

[BIA]

I just noticed that this PCB requires 24VAC , weird ! i will have to take the relays off and design somthing a bit simpler

 

[JMFahey]

Not *this* one, you posted data for a 48V DC coil relay, yet your protection circuit runs on 12V
Continue searching fo the proper 12V DC part.
Anyway the current for the 48V one is only 11.5 mA ; the 12VDC one will need around 4X that or 45/50mA (check it anyway).
Including the rest of the circuit I doubt it needs more than 100 mA .
Piece of cake.

 

[JMFahey]

I just noticed that this PCB requires 24VAC , weird ! i will have to take the relays off and design somthing a bit simpler

Well, you might start by posting its circuits.
Otherwise we hear you mumble , but don't know what you are mumbling about