how much curent i need for 250w mosfet amplifier

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milad-k800

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Joined 2008
#1
Hi,I have made a power amplifier for car with this details: 2 amplifier-100W bridged.it has good sound.
now I have a schematic mosfet power amplifier design with supply voltage +/-70V rated at 270W and I want build this amplifier for car.I have no problem with car SMPS circuit.
but I have several question about this amp...

1-I dont know this amp how much current need per rail for full power(270W)

2-Can I connect 2 of this amp with +/-70V-270W in bridge mode? this bridged amplifiers how much need current for per rail and deliver what power to the output?

3-How can with -/+70V for higher output power raise up the current for per rail? ex:-/+70V__-/+5A.if this possible what power will deliver to the output?(for single amplifier)

please help me about this secrets of the amplifiers....Thanks.
 
#2
this can be calulated

Pout = 270 Watt
U = 12 Volt (battery)
I = X Ampere
Eff = 0.80 (=80%)
we want to know also the efficiency of SMPS + Amplifier
as these will have some % losses of power
say your system has got an efficiency of 80%
(when 100 watt input from battery, you get 80 Watt output to speakers)

Pin = Pout/Eff
we do the math:
Pin = 270/0.80 = 337.5 Watt

Pin = U x I
we do the math:
337.5 = 12 x I
I = 337.5/12 = 28.125 Ampere
------------------------------------------

We check if result is correct:
Pin = 12 V x 28.125 A (watt)
Pout = 0.80 x Pin (watt)

Pout = 0.80 x 12 x 28.125 = 270 Watt
=======================================


Now, in order to estimate this we of course have to know good values.
We must have, speaking computing, good indata in order to get good outdata.

To get average drawn current, we need the average RMS Watt power output
and
the average efficiency of your SMPS + Amplifier
as well as the
correct Voltage of your Battery, when under this heavy loading
( almost 30 Ampere )
 
#3
note:

if you put out stereo 270 watt
you have to double the current value
as my example is only for one channel

a good guess would be 2 x 28 Ampere
which makes ~ 60 Ampere
if you use one battery to supply both channels

the protection fuses should be accordingly
~ 30-40 Ampere fuse for each channel
I think
 
#4
Hi

Note that this is for sine, not music, current for that would be lower, and if AB class amp, maybe you can get 80% eff. overall

And 30-40A fuse for each amp will be far too much, I have 80A and over 1.2kw only on sub, then is there 4ch amp too which add 100-200w...

you will probably need only 30-40A for both channels
 
#5
hi,i want only know that this 270w amplifier need how much current for +/-70v per rail?
not smps power supply-with 50-60HZ power supply.

1-I dont know this amp how much current need per rail for full power(270W)with 50-60HZ power supply

2-Can I connect 2 of this amp with +/-70V-270W in bridge mode? this bridged amplifiers how much need current for per rail and deliver what power to the output?with 50-60HZ power supply

3-How can with -/+70V for higher output power raise up the current for per rail? ex:-/+70V__-/+5A.if this possible what power will deliver to the output?(for single amplifier)with 50-60HZ power supply

thanks for the replies😉
 
#6
Hi

I already told you how to get this...

1. depends on load
2.Yes. same current as for one, just now 2x because of second channel
3.?? raise current? raise output power, decrease impedance of load,...

Why do you need to know the current?As you should know it anyway...
 
#9
to be able to ask a sensible question, one needs to understand what it is that is being asked. If one has no brief then it becomes impossible to formulate the question.

eg,
let's suppose we give an answer, What would one do with it?
If we were to give the (deliberately) wrong answer would one be able to check whether it made any sense in the context of the original brief?
 
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