What class D amplifier to build? Single 55V input voltage. - Page 1
Forum section: electronics / projects

author: Yansi
author_rank: Super Contributor
timestamp: January 05, 2025, 01:00:38 pm
content: Hello,what class D audio amp topology would you suggest building for a single (unipolar) 55V supply? Just need a mono block amp, not interested in stereo. Looking for easier solutions, rather than stellar performance.Normally, I would pick whatever integrated circuit from Texas and be done with it, unfortunately, nothing available for such high input voltage. Why so high voltage? Well, I have a "16 ohm" load, and if I manage to find a better power supply module, I would happily go even higher, say 70 V.So probably only building discrete ones is what I ma left with. With a single supply, it of course must be a BTL output configuration. Whether AD or BD modulation, that probably does not matter much, guessing AD would lead to a simpler design (output legs always opposite state - so only a 2 state modulation).Could you suggest please any well known easy to implement topologies for the modulator?Not really looking for a ready made module (doubt could find one fitting into the mechanical constraints) or a diy assemble yourself kit (same - need to customize it mechanically to fit).The only integrated class D modulator I know of that can handle up to 200V is IRS2092, I have some design experience with it, but I doubt it would help me here to much (single ended output, need balanced supply). But I kind of guessing, I could utilize the same second order integration topology, and just drive a bridge with it, and take differential voltage input for the integration.

author: Yansi
author_rank: Super Contributor
timestamp: January 05, 2025, 01:46:29 pm
content: One of my ideas would be to use more or less the topology ofIRAUDAMP1and modify it for bridge output. The 2nd order integrator would not be fed directly from the switching output, but the switching outputs would go first into differential amplifier, then fed into the integrator.I kind of think it should work. But I usually think wrong, so better have my dumb ideas checked.Thank you,Y

author: langwadt
author_rank: Super Contributor
timestamp: January 05, 2025, 02:57:39 pm
content: https://www.digikey.dk/da/products/detail/stmicroelectronics/STA516BETR/5402878?

author: Yansi
author_rank: Super Contributor
timestamp: January 05, 2025, 03:57:35 pm
content: That is afaik only a power stage - already stumbled upon that one. Quad half-bridge brick. No modulator, no analog. I admit, the price ain't bad, but IRS20957 and a pair of beefy MOSFETs will achieve much more robust and scalable solution for about the same price. In such a case, I will go with more robust output stage, that would allow me to use more, that 60V.//EDIT: I know, that ST has also a matching modulator ICs for this power stage, but I just don't want to fuck around with anything programmable. Please not this time.

author: jmelson
author_rank: Super Contributor
timestamp: January 05, 2025, 04:36:16 pm
content: Check out the datasheet for the Harris HIP4080. I tried to build a servo amp using this chip, but was trying to go for a higher voltage. But, it should work fine at 55 V DC. It uses external FETs. The HIP4080 is still available. Don't be fooled by their 80 V rating on the data sheet, I talked with their tech reps many years ago, and they ADMITTED it was a lie!Jon

author: Yansi
author_rank: Super Contributor
timestamp: January 05, 2025, 04:53:04 pm
content: What is a lie? Can it not survive even declared 80V?Note: Am not looking for a FET driver. Pleeenty of those available. Need either ideally whole integrated class D mono amp that could run from 55V+, or find any suitable modulator topology, that is well behaved and easy to implement. So far I could think of only the second order integration modulator from IRAUDAMP1.

author: MathWizard
author_rank: Super Contributor
timestamp: January 06, 2025, 11:10:39 pm
content: Some day soon, I need to make a basic class-D amp, and see how good/bad my cheap MOSFET's are at audio. A simple 2N304 or BC547 driving a speaker doesn't sound that bad, so I wonder what MOSFET's or JFET's for low current drives, are like.

author: BrianHG
author_rank: Super Contributor
timestamp: January 07, 2025, 12:31:30 am
content: All in one IC solution:https://www.ti.com/product/TPA3255Though, you will need to drop your supply voltage by 2v, should be easy enough...If you want pure class D, IE: digital in, the above one has analog in, this guy will work up to 58v:(This one is basically mosfets with a logic level driver input.)https://www.ti.com/product/TAS5634They both can operate in balanced bridged mode and for higher quality, parallel the chips outputs into a single output for that extra low Rds on, high current output.

author: BrianHG
author_rank: Super Contributor
timestamp: January 07, 2025, 01:58:02 am
content: Now to find a fanless 600watt 48v switcher.MeanWell has them and they be adjusted up to ~53v out, however, they have a fan, not great for audio.Need a nice switcher with a huge heatsink instead.

author: Andy Chee
author_rank: Super Contributor
timestamp: January 07, 2025, 08:53:53 am
content: If I were to scratch build a class-D design I might consider trying out SICAM topology, which has been studied by Michael A.E Andersen, and has published several papers on the topic.In a nutshell, it combines the DC-DC (or AC-DC) power conversion stage with the PWM audio modulation stage.

author: Yansi
author_rank: Super Contributor
timestamp: January 07, 2025, 09:26:36 pm
content: Quote from: BrianHG on January 07, 2025, 01:58:02 amWhy would I need a 600W switcher? 150W-200W is likely more then enough. Remember, that I will be driving a 16 ohm load. Easy to find a fan-less module, and as the average output power will be low (audio and rather limited at the low end - no need to feed speaker cabinet what it can't play), the power supply demand will be rather low. Plan to use a Meanwell LOP-200-54. Would gladly use something with even more voltage, but those power supplys are quite rare. I guess something like 70V would be optimal.62V rated IC, I don't know, there is zero to none reserve with the voltage I plan to run it at. Although, there will be rather low load current, I still do not feel safe doing so. I come from the power industry, where there is always a healthy reserve being designed for the switching transistors, to safely contain spikes from the parasitic inductances. Or do you think, that it is safe and wise to run an IC with such low supply voltage reserve?//EDIT: Sh!t, the TAS5634 is again only a power stage. Still need a modulator. And then i could easily make a robust foolproof 100+V rated power stage from discrete, as will have to build the modulator myself anyway.

author: Yansi
author_rank: Super Contributor
timestamp: January 07, 2025, 09:36:01 pm
content: Searched for SICAM, first paper that I have opened, some matrix converter popped out on me. With due respect, lets leave such theoretical topologies for theoretical researches.Meanwhile, I got a silly idea (or maybe not so silly?)Would it be possible, to use the IRS2092, or, in fact any other even low power class D fully integrated chip with external feedback, and use its outputs to drive external power stage? By connecting the floating bootstrapped section permanently to same supply voltage source, as the low side driver, I could simply get two digital output signals to feed an external gate driver.With the IRS2092 it should be easy, as the feedback to the modulator is external and can be simply connected after the second power stage. What do you think about that idea?It would certainly spare me building the complete modulator and startup circuitry on my own.

author: langwadt
author_rank: Super Contributor
timestamp: January 07, 2025, 09:41:39 pm
content: is using a low power class-d amp as modulator doable?

author: BrianHG
author_rank: Super Contributor
timestamp: January 07, 2025, 10:13:59 pm
content: If I get the time this summer, I'm thinking of making a stereo peak 300w/channel amp using the TPA3255.My goal is to achieve very low distortion driving a 4 ohm load to 100wrms with 300w headroom.To do this, I'll probably use 2x TPA3255 for the lower impedance output and to spread out the heat as I like running frequencies down to 15hz through my sound system.I might use a third one in stereo with an opamp based electronic bandpass filter to drive the woofer and mid/tweeters separately.

author: BrianHG
author_rank: Super Contributor
timestamp: January 07, 2025, 10:17:24 pm
content: Quote from: langwadt on January 07, 2025, 09:41:39 pmThe TPA3255 and TAS5634 derive their feedback from their output pins internally to compensate their modulators.You would want a class D amp with a separate feedback pin where you can also design your own loop filter.

author: langwadt
author_rank: Super Contributor
timestamp: January 07, 2025, 10:49:40 pm
content: Quote from: BrianHG on January 07, 2025, 10:17:24 pmsomething like the TPA3111? the block diagram doesn't show any feedback path (though that doesn't mean there isn't any)