I am currently designing a low voltage class D amplifier circuit. I am using a class D amplifier IC (TS4962, http://www.st.com/web/en/resource/technical/document/datasheet/CD00045973.pdf) and a boost converter (TPS61222-EP, http://www.ti.com/lit/ds/symlink/tps61222-ep.pdf) for battery operation. The switch current of the boost converter is typically 400 mA while the maximum supply current for the class D amp is 3.3 mA and the internal resistance from standby to GND is typically 300k ohms. My question is should I use a current limiting resistor from the output of the boost converter to the supply of the amplifier IC? Or should the built-in protection of the amplifier IC be able to handle the current coming out of the boost converter?
The amp chip should be designed to work off of a voltage supply. So that means the current capability of the source is irreleavant, as long as it's more than what's required by the chip. A curent limiting resistor will just cause the supply to dip, possibly resulting in more distortion. Or in extreme cases, cause the UVLO(under voltage lockout) of the chip to trip and make a huge dropout in your music.
What is the battery voltage?
What voltage are you stepping it up to?
What speaker impedance are you using?
How much power do you expect?
What voltage are you stepping it up to?
What speaker impedance are you using?
How much power do you expect?
I'm using two cells for a total of 3 volts and i'm stepping it up to 5 volts. I currently have an 8 ohm speaker that I was going to connect it to but I might go for a 4 ohm to get the extra wattage. In your opinoin, DUG, for a battery powered application what would be the best? Also, I would like an adjustable volume on the amplifier so should I use a pre amplifier for that or just adjust the amplifier resistance inputs?
Look at the data sheet for the amplifier.
Look for output power at 8ohm load with a 5V supply. (chart)
Look at chart for efficiency of the amplifier with 5V supply vs output power.
Use these numbers to calculate how much power you need at 5V. ( it will be more than output power)
Calculate current required from a 5V supply for that power. ( I = P / V )
Look at the data sheet for the boost converter and see if it can deliver the current you need with 3V input and 5V output. (twice as much for stereo)
If you don't want to use the source to control volume then a stereo potentiometer will be needed. (logarithmic or audio taper)
A preamp will be needed if you don't have enough signal out of your music source...IMHO don't put it in if you don't need it.
🙂
Look for output power at 8ohm load with a 5V supply. (chart)
Look at chart for efficiency of the amplifier with 5V supply vs output power.
Use these numbers to calculate how much power you need at 5V. ( it will be more than output power)
Calculate current required from a 5V supply for that power. ( I = P / V )
Look at the data sheet for the boost converter and see if it can deliver the current you need with 3V input and 5V output. (twice as much for stereo)
If you don't want to use the source to control volume then a stereo potentiometer will be needed. (logarithmic or audio taper)
A preamp will be needed if you don't have enough signal out of your music source...IMHO don't put it in if you don't need it.
🙂
Thank you all for all your help! DUG, I'll do my calculations and confirm the requirements. If I have any more questions I'll be sure to post.
I have a few more questions. First, what would be the best way to control the volume for this type of circuit? I know you can use the source or the gain on the amplifier but I'm thinking about going with the source control and programming the gain of the amplifier to it's max. What's the schematic for the best source volume control? What is the best potentiometer to use? Also, what's the typical output voltage of an electret microphone and what would be a good gain to set the amplifier to for a 4 ohm speaker output?
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