Hi everyone!
My goal is to build an integrated stereo amp based on the LM3886, that will include a soft switch (that activates a relay witch connects the main transformer to the mains) , and a DC protection circuit with a turn on delay.
I relized that i can't use the same 12VDC power rail for the soft switch and the speaker protection together, because the soft switch transformer will have to be always on, and the DC protection circuit will have to be switched on when the main transformer is switched on, for the turn on delay to occur.
so how can i combine those two circuits together? do i need to use separate transformers or maybe use a voltage regulator to lower the voltage from the main transformer (about 30VDC for the LM3886) to 12V for the protection circuit? wouldn't it be wasteful?
I always wondered how does it designed in commercial amps?
tnks for the helpers
My goal is to build an integrated stereo amp based on the LM3886, that will include a soft switch (that activates a relay witch connects the main transformer to the mains) , and a DC protection circuit with a turn on delay.
I relized that i can't use the same 12VDC power rail for the soft switch and the speaker protection together, because the soft switch transformer will have to be always on, and the DC protection circuit will have to be switched on when the main transformer is switched on, for the turn on delay to occur.
so how can i combine those two circuits together? do i need to use separate transformers or maybe use a voltage regulator to lower the voltage from the main transformer (about 30VDC for the LM3886) to 12V for the protection circuit? wouldn't it be wasteful?
I always wondered how does it designed in commercial amps?
tnks for the helpers
A separate small transformer to power the start up control circuits.
You can run the delay trigger from either the main transformer, or from a tapping on the soft start trigger output.
The delay circuit itself can be powered by either transformer. It's the trigger signals that need to be sequenced.
You can run the delay trigger from either the main transformer, or from a tapping on the soft start trigger output.
The delay circuit itself can be powered by either transformer. It's the trigger signals that need to be sequenced.
Hi Andrew! I think i understood your second option, you ment that the softstart output will activate 2 relays, something like this:
I didn't understand your first option though, the main voltage is 30V and the DC protection circuit voltage is 12V
An externally hosted image should be here but it was not working when we last tested it.
I didn't understand your first option though, the main voltage is 30V and the DC protection circuit voltage is 12V
Guys a little help please?
I need to know how this is supposed to be done, i don't really want to use the LM7812 becuse 30V is it's limit.
if you can refer me to a project where a similar thing has been done, it will also help.
tnks again
You can also use a LM7824 as a pre-regulator (use it first and send its output to the input of the LM7812). The LM7824 has an input voltage limit of 40V.
-Charlie
tnks for your answers! i read that linear regulators are very inefficient, is it the best option i have?
Based on what you say, if i'll open my old yamaha AV reciever i should find a regulator for this purpose?
i am very confused, i searched the web for weeks to find how this thing works and i just can't find anything.
i was also counting on using the "after turn on" 12V rail for a sound control (some little opamp's), and i always hoped it will run from a pure 12V rail.
if you say this is the method manufacurers use, i will go for it.
Based on what you say, if i'll open my old yamaha AV reciever i should find a regulator for this purpose?
i am very confused, i searched the web for weeks to find how this thing works and i just can't find anything.
i was also counting on using the "after turn on" 12V rail for a sound control (some little opamp's), and i always hoped it will run from a pure 12V rail.
if you say this is the method manufacurers use, i will go for it.
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