Greetings everyone.
I'm on a project with the LM3886, I want to get 60 watts out of 4 ohms, I'm having trouble designing the power supply, reading the datasheet, page 22, I found some equations to find (Voutpeak) and (Iopeak) and I have found these values:
Voutpeak: 21.90
Ioutpeak: 5.47
Max. Supplies ≊ ± 31.71
Already on page 23 looking at the example, I noticed that I need ± 25 to power my amplifier, and that this power supply should supply 5.47 amperes.
Looking at another example of equation (attached image) I found different values, in the equation I used the value of 85mA of resting current and got 91.38 watts of power needed to power the amplifier, using the law of ohm watts / voltage. I found: 91.38 / 50 = 1.82 amps.
Could someone help me with this?
I'm on a project with the LM3886, I want to get 60 watts out of 4 ohms, I'm having trouble designing the power supply, reading the datasheet, page 22, I found some equations to find (Voutpeak) and (Iopeak) and I have found these values:
Voutpeak: 21.90
Ioutpeak: 5.47
Max. Supplies ≊ ± 31.71
Already on page 23 looking at the example, I noticed that I need ± 25 to power my amplifier, and that this power supply should supply 5.47 amperes.
Looking at another example of equation (attached image) I found different values, in the equation I used the value of 85mA of resting current and got 91.38 watts of power needed to power the amplifier, using the law of ohm watts / voltage. I found: 91.38 / 50 = 1.82 amps.
Could someone help me with this?
Attachments
I've got a few RingNot power supply boards & assembled PSUs left. They work just fine with LM3886's, in fact they're designed to drive a pair of LM3886's. ±28V output, peak current enormous thanks to the huge filter capacitors. Steady state current 3.6 amps RMS from each supply, limited by the 200VA transformer. Members have used them to drive a pair of "Modulus86" chipamp boards and report being happy with the result.
I recommend the Antek AS-2222 toroidal transformer to go with it.
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I recommend the Antek AS-2222 toroidal transformer to go with it.
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5.5A is the peak. This will happen once per cycle.
Peaks are carried by your large filter caps.
2A is the average. This is what the power supply must have to keep the filter caps filled.
Or another way: 50V at 5.5A is 275 Watts! This seems excessive for one 60 Watt amplifier. 50V at 2A is 100W (1.82A is 91W) which seems reasonable for a transistor amp at 60%-70% efficiency. Yes, in stereo nearer 3.6A total.
Or another way: if Mark likes it, it's good.
Thank you PRR!
In these 3.6 amps to supply a stereo amplifier, I can round to 4 amps, which results in 50 * 4 = 200 watts of supply, to choose the transformer, I heard that I must multiply the power consumed in the amplifier by 1.5 to get the (VA) of the transformer. 200 * 1.5 = 300VA.
To get the correct supply from my amplifier should I use an 18v + 18V ~ 300VA transformer?
PRR has estimated the power needs to just below 200W.
Then, you suggest a 1.5 factor I am not sure where you get from?
It may be from the relation-ship between what ideally leaves a class AB amplifier and what the amplifier actually draws from the power supply. PRR has taken than into account.
Alternatively, it is a kind of subjective de-rating factor aiming at lowering the temperature of the transformer. Is this case, it is not mandatory unless it is a pure class A amplifier. It is not.
The music "crest-factor" will mean you never use the full power when playing music.
Use a 200VA transformer or above you can find at a good price.
Then, you suggest a 1.5 factor I am not sure where you get from?
It may be from the relation-ship between what ideally leaves a class AB amplifier and what the amplifier actually draws from the power supply. PRR has taken than into account.
Alternatively, it is a kind of subjective de-rating factor aiming at lowering the temperature of the transformer. Is this case, it is not mandatory unless it is a pure class A amplifier. It is not.
The music "crest-factor" will mean you never use the full power when playing music.
Use a 200VA transformer or above you can find at a good price.
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ISOBRUNOBARBATO is in Brazil, and has no practical access to Antek or any US supplier on account of excessive Courier cost + heavy Brazilian Tariff, his realistic option is to find a suitable one in Brazil or have one custom wound ... locally of course.
Oi amigo, tudo bem?
I think you want to build a *mono* 60W into 4 ohm amplifier.
If datasheet recommends +/-25V rails, so be it, they know.
For that you need a 18Vx18V transformer, we are talking AC (tensao alterna) of course.
For normal Musical use, rating it at 150% the RMS power is fine, 200% if you want to play it extra safe, cool, etc.
So for a single amplifier, you will need 90VA to 120VA , or 18+18VAC 2.5A to 3.5A .
If you are near Sao Paulo , in the first street parallel to Santa Ifigenia you have "A Casa do Transformador" who has lots of them ready made or can custom wind one for you.
For a stereo amplifier: same voltage but double current.
PS: your equation is fine, but don´t worry about idle current, it can be ignored compared to main current consumption when amplifier is LOUD.
Oi amigo, tudo bem?
I think you want to build a *mono* 60W into 4 ohm amplifier.
If datasheet recommends +/-25V rails, so be it, they know.
For that you need a 18Vx18V transformer, we are talking AC (tensao alterna) of course.
For normal Musical use, rating it at 150% the RMS power is fine, 200% if you want to play it extra safe, cool, etc.
So for a single amplifier, you will need 90VA to 120VA , or 18+18VAC 2.5A to 3.5A .
If you are near Sao Paulo , in the first street parallel to Santa Ifigenia you have "A Casa do Transformador" who has lots of them ready made or can custom wind one for you.
For a stereo amplifier: same voltage but double current.
PS: your equation is fine, but don´t worry about idle current, it can be ignored compared to main current consumption when amplifier is LOUD.
LM3886 chip power amplifier power supply design. see the table at the bottom of that link. It depends on your application but a 120va transformer might be enough even for a stereo amp.
Edit: besides Tom good article above, Dan Fraser makes good points here: What should be the transformer rating in respect to wattage of a power amplifier,
Edit: besides Tom good article above, Dan Fraser makes good points here: What should be the transformer rating in respect to wattage of a power amplifier,
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Hi JMFahey, great, thank you. I intend to build a stereo amplifier. That is, two channels of 60 watts in 4 ohms.
The transformer will be toroid, I will do in the industry, in Brazil there is an excellent one.
I want the amplifier to be able to reproduce at a crest factor of 3dB, that is, a pure sine wave at 60 watts RMS, I believe I will use 300VA to power the stereo amplifier. It is a little more than necessary. Better that there is a power supply with more energy to spare, this brings a smoother work to the transformer.
The factor of 1.5 that I used above, I found on Tom's website
LM3886 chip power amplifier power supply design.
For AC to DC conversion on cap-input filter, the factor is 1.6 to 1.8, depending on whether sag or heat is limiting.
Speech/music NEVER runs FULL power ALL the time. Hi-Fi should "never clip". A 200VA transformer will reasonably power 2*60W audio with comfort. If you want to go bigger, it is "only" cost and weight. I've used 100VA for a mono 20W amp. (The iron was cheap.) Stage-amp duty is tougher, but you rarely find VA more than twice Audio Watts.
Speech/music NEVER runs FULL power ALL the time. Hi-Fi should "never clip". A 200VA transformer will reasonably power 2*60W audio with comfort. If you want to go bigger, it is "only" cost and weight. I've used 100VA for a mono 20W amp. (The iron was cheap.) Stage-amp duty is tougher, but you rarely find VA more than twice Audio Watts.
Here in the US where a gigantic variety of transformers are easily purchased, and shipping is cheap, and taxes/customs are negligible,
sure, hobbyists routinely buy transformers that are bigger than necessary. This means we don't need to include Thermal CutOuts in our circuits, and we don't need to perform intimidating calculations, and we don't need to worry about what happens if somebody connects a lower-than-expected-impedance loudspeaker.
In other locales, perhaps the proletarian wisdom of penchpenny tightwads like JM Fahey might be worth paying attention to. Every unnecessary VA that you don't buy, is money back in your pocket. Maybe a significant amount of money.
sure, hobbyists routinely buy transformers that are bigger than necessary. This means we don't need to include Thermal CutOuts in our circuits, and we don't need to perform intimidating calculations, and we don't need to worry about what happens if somebody connects a lower-than-expected-impedance loudspeaker.
In other locales, perhaps the proletarian wisdom of penchpenny tightwads like JM Fahey might be worth paying attention to. Every unnecessary VA that you don't buy, is money back in your pocket. Maybe a significant amount of money.
JM Fahey is very generous, at more than 1VA per audio watt. I wouldn't call that penny pinching. 2/3 of a VA per watt is suggested per Dan Fraser for AB amps and 1/2 for class D amps. That's BTW in line with Hypex suggesting a 160va transformer for a stereo ucd180.
Edit: but if indeed the goal is to reproduce sinewaves forever, then the rules change.
Edit: but if indeed the goal is to reproduce sinewaves forever, then the rules change.
I just realized that some members may not know, Antek now sells to individuals through an eBay storefront. (And to businesses through their website). Everything is "Buy It Now" and at least for me, in the US, it's free shipping.
I buy regularly Transformers from Toroidy, either directly for special version (very nice) or from TME ( Transfer Multisort Elektronik - Composants electroniques ) and shipment prices are very reasonable 
Marc
Marc
I buy regularly Transformers from Toroidy, either directly for special version (very nice) or from TME ( Transfer Multisort Elektronik - Composants electroniques ) and shipment prices are very reasonable
Marc
You are indeed right about TME, more reasonable shipping costs. I also appreciate prices in EUR and not Zloty. For long I only knew of Conrad and RS-online.
For me it is not possible to buy things outside of Brazil, the transformer freight of 200VA for example, would cost me $ 69.50 and when I arrive in Brazil, I have to pay 60% of the value of it in taxes.
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