# Picking battery for power amplifier

I have bunch of TDA2003 (class AB) amp ICs and I would like to make some amplifiers with them. One would be stationary bridged 20w version and one portable version. However I'am a beginner and I never had expierence with batteries.

1. Is this IC efficient for working on battery?
2. I'am planning on buying 5ah battery, how long would such battery last for me? Maybe 5ah is an overkill? 4-6h of constant work is what I need. (NOTE: I'am not going to blast it on full power all the time. I guess 50% of power ussualy)

Battery charge time, size, weight doesn't matter for me at all. Price and efficiency what matters

• No class-AB amp is particularly efficient. Your second question depends entirely on the operating voltage of the battery, the quiescent current of the amp, and the required output level. – Nick Johnson Jul 17 '15 at 10:47
• If I found correctly on datasheet Quiescent drain current (pin 5) is 44 mA. if I buy this battery Capacity: 4000mAh. Output voltage: 10.8~12.6 D C Output current:1-2A. And running it so it outputs 10w power. I just need formula or something so I can calculate myself – user3718568 Jul 17 '15 at 10:56

If you have a 12 volt, 5 ampere-hour battery and you want 10 watts out of it, then since:

$$P = IE,$$

we can rearrange to solve for the current required from it like this:

$$I = \frac{P}{E} = \frac{10W}{12V} = 0.833 \text{ ampere}$$

Then, since the battery has a capacity of 5 ampere-hours, you can take 0.833 amperes from it for:

$$t =\frac{C}{I} = \frac{5Ah}{0.833A} = 6\text{ hours}$$

This isn't strictly true, however, because battery capacity is usually specified based on a certain rate of discharge, usually C/10 or C/20, and you'll pay a small penalty (in this case) for exceeding that rate. Check your battery's data sheet to find out how much of a hit you'll take.

Here are some guidelines. Look at the data sheet to determine: -

• The battery voltage needed to achieve 20 watts bridged output
• The speaker impedance to achieve that power out
• The peak current that can be expected at this power
• Quiescent current when not driving sound to the speakers

Then, start to narrow down your choice of battery - battery voltage should become apparent and peak handing current for the battery also. You also need to decide the duty cycle of producing power to the quiescent time (when the amp is only consuming low current) to determine the ampere-hours of the battery over a typical period of time between re-charges. Get this number and double it (playing safe)

This dictates the capacity of the battery.

Regards efficiency - it's a class AB amp and the data sheet should tell you the efficiency.