# Calculating the current needed in amplifier.

Discussion in 'General Electronics Chat' started by hindiikawayos, Jun 17, 2011.

1. ### hindiikawayos Thread Starter Member

Jun 8, 2011
40
0
Hello!
I would like to ask anybody on how to calculate the current needed to supply a power amplifier? thank you!

2. ### jegues Well-Known Member

Sep 13, 2010
735
45
Can you provide us with a schematic or be more specific as to what you are implementing?

3. ### Audioguru Expert

Dec 20, 2007
10,504
1,168
1) You need to know if the amplifier is 55% efficient class-AB or 90% efficient class D.
2) You need to know the power supply voltage for the amplifier.
3) You need to know the output power of the amplifier and its load impedance.
4) You need to know if the amplifier is blasting at full power all the time or if it is playing music where only the peaks are at full power.

If you know all this then calculating the power supply current is easy.

4. ### hindiikawayos Thread Starter Member

Jun 8, 2011
40
0
how can you determine if an amplifier is a class AB or a class D? tnx!

5. ### Audioguru Expert

Dec 20, 2007
10,504
1,168
You simply learn about amplifier circuits and see which class it is by looking at its schematic, or by looking at the datasheet of its amplifier IC.

A class-AB amplifier has its output transistors continuously driving current into the speaker so it is not efficient and it gets hot.
A class-D amplifier has its output transistors switching on and off with pulse-width-modulation at a high frequency so it is very efficient.

6. ### hindiikawayos Thread Starter Member

Jun 8, 2011
40
0
I get it. But in your own opinion which is more preferably class AB or class D? Thanks...

7. ### Audioguru Expert

Dec 20, 2007
10,504
1,168
A class-AB amplifier is simple and inexpensive. But it wastes power by getting hot.
A class-D amplifier circuit is very complicated but it is efficient.

8. ### hindiikawayos Thread Starter Member

Jun 8, 2011
40
0
Thank you Mr Audioguru! I'll try to learn more about class-D amplifier.

9. ### Audioguru Expert

Dec 20, 2007
10,504
1,168
The Philips (called NXP Semiconductors today) TDA8920 is a modern class-D amplifier IC but Texas instruments also have some.
It is a stereo amplifier with an output of 69W per channel into 4 ohm speakers at low distortion or it can be bridged as a single amplifier producing 138W into 8 ohms at low distortion.
It costs only \$6.95 at Digikey today.

Look at its datasheet.

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10. ### hindiikawayos Thread Starter Member

Jun 8, 2011
40
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Thanks a lot Mr Auodioguru!