SMPS for portable audio

[Modelworks]

Originally posted by: Cheesehead


I cannot possibly understand how 5v can possibly power a loud headphone amplifier. An op-amp running on 5v will produce 3.5v RMS at the output, which will result in less than 1/20 of a watt into a 250-ohm load - nowhere near the 1/2 watt I'm looking for.

That is because you are looking at old tech.
There are quite a few opamp type products on the market now that are designed internally to produce high outputs from low input voltages. It isn't that the parts could not have been done before, it is that they were not needed much until the least few years when low power devices like mp3 players came on the market. What a semiconductor company produces depends on what the market needs, so in even the past 6 months there have been a lot of amplifiers that give high outputs from low input voltages.

 

[bobsmith1492]

Originally posted by: Modelworks

Originally posted by: Cheesehead


I cannot possibly understand how 5v can possibly power a loud headphone amplifier. An op-amp running on 5v will produce 3.5v RMS at the output, which will result in less than 1/20 of a watt into a 250-ohm load - nowhere near the 1/2 watt I'm looking for.

That is because you are looking at old tech.
There are quite a few opamp type products on the market now that are designed internally to produce high outputs from low input voltages. It isn't that the parts could not have been done before, it is that they were not needed much until the least few years when low power devices like mp3 players came on the market. What a semiconductor company produces depends on what the market needs, so in even the past 6 months there have been a lot of amplifiers that give high outputs from low input voltages.

You're still not going to get more than +/-5V (with a bridged configuration) from a 5V rail without something to step up the voltage, which limits you to 3.5V RMS and .048W or so peak into a 250 ohm load. You can get rail-to-rail output, but that is required for the above specs.

 

[Modelworks]

Originally posted by: bobsmith1492

Originally posted by: Modelworks

Originally posted by: Cheesehead


I cannot possibly understand how 5v can possibly power a loud headphone amplifier. An op-amp running on 5v will produce 3.5v RMS at the output, which will result in less than 1/20 of a watt into a 250-ohm load - nowhere near the 1/2 watt I'm looking for.

That is because you are looking at old tech.
There are quite a few opamp type products on the market now that are designed internally to produce high outputs from low input voltages. It isn't that the parts could not have been done before, it is that they were not needed much until the least few years when low power devices like mp3 players came on the market. What a semiconductor company produces depends on what the market needs, so in even the past 6 months there have been a lot of amplifiers that give high outputs from low input voltages.

You're still not going to get more than +/-5V (with a bridged configuration) from a 5V rail without something to step up the voltage, which limits you to 3.5V RMS and .048W or so peak into a 250 ohm load. You can get rail-to-rail output, but that is required for the above specs.

The new products have integrated circuits that boost the voltage without the need of doing it externally , lowering the part count. So while the product may say 5v on the input, its actually using much higher voltages internally. Most of these are really new having only been on the market a couple months.

 

[PottedMeat]

Originally posted by: Modelworks

Originally posted by: bobsmith1492

Originally posted by: Modelworks

Originally posted by: Cheesehead


I cannot possibly understand how 5v can possibly power a loud headphone amplifier. An op-amp running on 5v will produce 3.5v RMS at the output, which will result in less than 1/20 of a watt into a 250-ohm load - nowhere near the 1/2 watt I'm looking for.

That is because you are looking at old tech.
There are quite a few opamp type products on the market now that are designed internally to produce high outputs from low input voltages. It isn't that the parts could not have been done before, it is that they were not needed much until the least few years when low power devices like mp3 players came on the market. What a semiconductor company produces depends on what the market needs, so in even the past 6 months there have been a lot of amplifiers that give high outputs from low input voltages.

You're still not going to get more than +/-5V (with a bridged configuration) from a 5V rail without something to step up the voltage, which limits you to 3.5V RMS and .048W or so peak into a 250 ohm load. You can get rail-to-rail output, but that is required for the above specs.

The new products have integrated circuits that boost the voltage without the need of doing it externally , lowering the part count. So while the product may say 5v on the input, its actually using much higher voltages internally. Most of these are really new having only been on the market a couple months.

If its not a bridge - is it a charge pump? Got a datasheet?

 

[bobsmith1492]

Originally posted by: PottedMeat

Originally posted by: Modelworks

Originally posted by: bobsmith1492

Originally posted by: Modelworks

Originally posted by: Cheesehead


I cannot possibly understand how 5v can possibly power a loud headphone amplifier. An op-amp running on 5v will produce 3.5v RMS at the output, which will result in less than 1/20 of a watt into a 250-ohm load - nowhere near the 1/2 watt I'm looking for.

That is because you are looking at old tech.
There are quite a few opamp type products on the market now that are designed internally to produce high outputs from low input voltages. It isn't that the parts could not have been done before, it is that they were not needed much until the least few years when low power devices like mp3 players came on the market. What a semiconductor company produces depends on what the market needs, so in even the past 6 months there have been a lot of amplifiers that give high outputs from low input voltages.

You're still not going to get more than +/-5V (with a bridged configuration) from a 5V rail without something to step up the voltage, which limits you to 3.5V RMS and .048W or so peak into a 250 ohm load. You can get rail-to-rail output, but that is required for the above specs.

The new products have integrated circuits that boost the voltage without the need of doing it externally , lowering the part count. So while the product may say 5v on the input, its actually using much higher voltages internally. Most of these are really new having only been on the market a couple months.

If its not a bridge - is it a charge pump? Got a datasheet?

Interesting idea! Linky please? Who makes them?

 

[cheesehead]

They do sound interesting. I'd be surprised if they work as well as the discrete approach, though.

 

[blahblah99]

Originally posted by: Modelworks

Originally posted by: Cheesehead


I cannot possibly understand how 5v can possibly power a loud headphone amplifier. An op-amp running on 5v will produce 3.5v RMS at the output, which will result in less than 1/20 of a watt into a 250-ohm load - nowhere near the 1/2 watt I'm looking for.

That is because you are looking at old tech.
There are quite a few opamp type products on the market now that are designed internally to produce high outputs from low input voltages. It isn't that the parts could not have been done before, it is that they were not needed much until the least few years when low power devices like mp3 players came on the market. What a semiconductor company produces depends on what the market needs, so in even the past 6 months there have been a lot of amplifiers that give high outputs from low input voltages.

Let's see... 1/2 W @ 250 ohms = 11Vrms = 15.5Vpk. So you need 31Vpp on your supplies. Your op amps aren't going to be swinging rail to rail for audio so you're going to need more voltage than 31V. For simplicity lets just say you require +-18V for your supplies. Most modern op amps can handle 36V between the supply pins.


Taking that route, you need to convert 5V to 18V and 5V to -18V. That's two power supplies, two seperate circuits.

Charge pump circuits aren't going to work as they are used mainly for voltage references and/or circuits that don't require more than a few mA of current. Using charge pumps in an audio circuit as a supply is going to result in high distortion.


I would just drop those ideas altogether and use a single 5V to 36V boost converter that's well regulated and can supply about 100mA @ 36V.

DC bias the output opamp to 18V, add an output capacitor (or a more extravagant method) to block the dc output and viola, you have +-18V swing at the output for your 1/2W power @ 250 ohms.

 

[PottedMeat]

Originally posted by: blahblah99

Originally posted by: Modelworks

Originally posted by: Cheesehead


I cannot possibly understand how 5v can possibly power a loud headphone amplifier. An op-amp running on 5v will produce 3.5v RMS at the output, which will result in less than 1/20 of a watt into a 250-ohm load - nowhere near the 1/2 watt I'm looking for.

That is because you are looking at old tech.
There are quite a few opamp type products on the market now that are designed internally to produce high outputs from low input voltages. It isn't that the parts could not have been done before, it is that they were not needed much until the least few years when low power devices like mp3 players came on the market. What a semiconductor company produces depends on what the market needs, so in even the past 6 months there have been a lot of amplifiers that give high outputs from low input voltages.

Let's see... 1/2 W @ 250 ohms = 11Vrms = 15.5Vpk. So you need 31Vpp on your supplies. Your op amps aren't going to be swinging rail to rail for audio so you're going to need more voltage than 31V. For simplicity lets just say you require +-18V for your supplies. Most modern op amps can handle 36V between the supply pins.


Taking that route, you need to convert 5V to 18V and 5V to -18V. That's two power supplies, two seperate circuits.

Charge pump circuits aren't going to work as they are used mainly for voltage references and/or circuits that don't require more than a few mA of current. Using charge pumps in an audio circuit as a supply is going to result in high distortion.


I would just drop those ideas altogether and use a single 5V to 36V boost converter that's well regulated and can supply about 100mA @ 36V.

DC bias the output opamp to 18V, add an output capacitor (or a more extravagant method) to block the dc output and viola, you have +-18V swing at the output for your 1/2W power @ 250 ohms.

Damn your sensible logic and math. That will probably result in the least amount of space required.

...isn't 1/2W like ear destroying power?

 

[bobsmith1492]

Originally posted by: PottedMeat

Originally posted by: blahblah99

Originally posted by: Modelworks

Originally posted by: Cheesehead


I cannot possibly understand how 5v can possibly power a loud headphone amplifier. An op-amp running on 5v will produce 3.5v RMS at the output, which will result in less than 1/20 of a watt into a 250-ohm load - nowhere near the 1/2 watt I'm looking for.

That is because you are looking at old tech.
There are quite a few opamp type products on the market now that are designed internally to produce high outputs from low input voltages. It isn't that the parts could not have been done before, it is that they were not needed much until the least few years when low power devices like mp3 players came on the market. What a semiconductor company produces depends on what the market needs, so in even the past 6 months there have been a lot of amplifiers that give high outputs from low input voltages.

Let's see... 1/2 W @ 250 ohms = 11Vrms = 15.5Vpk. So you need 31Vpp on your supplies. Your op amps aren't going to be swinging rail to rail for audio so you're going to need more voltage than 31V. For simplicity lets just say you require +-18V for your supplies. Most modern op amps can handle 36V between the supply pins.


Taking that route, you need to convert 5V to 18V and 5V to -18V. That's two power supplies, two seperate circuits.

Charge pump circuits aren't going to work as they are used mainly for voltage references and/or circuits that don't require more than a few mA of current. Using charge pumps in an audio circuit as a supply is going to result in high distortion.


I would just drop those ideas altogether and use a single 5V to 36V boost converter that's well regulated and can supply about 100mA @ 36V.

DC bias the output opamp to 18V, add an output capacitor (or a more extravagant method) to block the dc output and viola, you have +-18V swing at the output for your 1/2W power @ 250 ohms.

Damn your sensible logic and math. That will probably result in the least amount of space required.

...isn't 1/2W like ear destroying power?

I agree 1/2 W is a bit of overkill but remember music has a lot of dynamic range - you don't want a big bass hit distorting because it clips.

Also, if you use a bridged amplifier configuration you can get 11VRMS out of a 16V rail - it effectively doubles your output voltage range. Also, lots of modern op-amps swing rail-to-rail out, though maybe not power amps. Still, 20V with a bridged configuration will easily give you 1/2W into 250 ohms.