I want to propose a new way of designing a power supply for class D amps which I believe will extend the high efficiency of the class D to the power-supply although in an unorthodox way and mixing old and new in it .
The old power-supply was and is transformer based , be it a toroidal transformer or not , followed by a rectifier and filter caps of high values .Disadvantages are sagging voltage as current rises , hum on the lines and a lot of weight ,but it can deliver a higher current than its specification for short periods of time if one can live with the resulting lower voltage during these moments . And , if , not shorted or badly overloaded extremely rugged , they last for ages.
The new power-supply is an SMPS , is stabilized up to its maximum specified output and is lot smaller and lighter than the old ones , but very sensitive to voltage-spikes on the power-lines and damages to itself due to heat and vibration of its inductive components .
Music on the other hand is a live thing with constant variations and a ratio between average power to peak power generally at least 1 to 3 and up to 1 to 10 .
Let us stay with the ratio 1 to 3 for the sake of calulations , the least favourable in this example . What this means is that an amplifier with an output of 300 watts max and an effiency of 90% and higher will need a power-supply of 330 watts peak but only 110 wats average . So for the average you can feed it with a transformer rated for 125 wats aprox. but that will be totally insufficient for the peak-power, and the power-supply voltage will fluctuate quite a lot which is a bad thing for class-D amps.
Now let us assume we use a transformer with a 200 watt rating . It will be somewhat better but still totally insufficient for peak-reproduction , even when using extremely large capacitors .
But what happens when we use a transformer rated for only 160 watts which has an output voltage around 75 to 80 % of the rail- voltage the class-D needs for its max output and then boost that voltage to the exact value needed? We get our exact rail-voltage . The booster will maintain that as long as the voltage at its input is within its range so it does not matter if the input dips down, or carries hum superimposed. Since the transformer can supply higher current for short periods it will maintain the output even when asked to deliver 300 watts momentarily as it averages out. Their efficiency is 85% and up so take that into acount as the transformer will have to supply this loss.
The class-D will be happy as it gets its specified rail voltage . The booster will compensate for fluctuating input-voltage from the toroid and , as long as you use 10000uf capacitor or more if you like at the input of the booster you will have a very stable rail for your amp.
The chinese make very cheap booster modules with ratings of 600 , 1200 and even 1800 watts , the latter for about 12 euros plus shipping , see:
Modulo de alimentacion de corriente continua de alta corriente, potenciador de potencia electrico, 1800W, 35 40A, 30A, DC DC, nuevo|power module|constant currentdc dc - AliExpress
These can handle up to 30 amps input and a lesser amount out , depending on the ratio IN/OUT voltages. The good thing about using them is that any new or old transformer whose voltage and power ratings are within acceptable limits will do , so that one can even buy some old amp just to scrap it retaining only the transformer .
I have done it and it works . Added advantage is one can current-limit these boosters as well if needed or wanted . And if they were to fail you would be safeguarded from your amp getting too high voltages because you stabilize UP not DOWN.
Plesa comment and contribute your opinions and ideas on this . Michael
The old power-supply was and is transformer based , be it a toroidal transformer or not , followed by a rectifier and filter caps of high values .Disadvantages are sagging voltage as current rises , hum on the lines and a lot of weight ,but it can deliver a higher current than its specification for short periods of time if one can live with the resulting lower voltage during these moments . And , if , not shorted or badly overloaded extremely rugged , they last for ages.
The new power-supply is an SMPS , is stabilized up to its maximum specified output and is lot smaller and lighter than the old ones , but very sensitive to voltage-spikes on the power-lines and damages to itself due to heat and vibration of its inductive components .
Music on the other hand is a live thing with constant variations and a ratio between average power to peak power generally at least 1 to 3 and up to 1 to 10 .
Let us stay with the ratio 1 to 3 for the sake of calulations , the least favourable in this example . What this means is that an amplifier with an output of 300 watts max and an effiency of 90% and higher will need a power-supply of 330 watts peak but only 110 wats average . So for the average you can feed it with a transformer rated for 125 wats aprox. but that will be totally insufficient for the peak-power, and the power-supply voltage will fluctuate quite a lot which is a bad thing for class-D amps.
Now let us assume we use a transformer with a 200 watt rating . It will be somewhat better but still totally insufficient for peak-reproduction , even when using extremely large capacitors .
But what happens when we use a transformer rated for only 160 watts which has an output voltage around 75 to 80 % of the rail- voltage the class-D needs for its max output and then boost that voltage to the exact value needed? We get our exact rail-voltage . The booster will maintain that as long as the voltage at its input is within its range so it does not matter if the input dips down, or carries hum superimposed. Since the transformer can supply higher current for short periods it will maintain the output even when asked to deliver 300 watts momentarily as it averages out. Their efficiency is 85% and up so take that into acount as the transformer will have to supply this loss.
The class-D will be happy as it gets its specified rail voltage . The booster will compensate for fluctuating input-voltage from the toroid and , as long as you use 10000uf capacitor or more if you like at the input of the booster you will have a very stable rail for your amp.
The chinese make very cheap booster modules with ratings of 600 , 1200 and even 1800 watts , the latter for about 12 euros plus shipping , see:
Modulo de alimentacion de corriente continua de alta corriente, potenciador de potencia electrico, 1800W, 35 40A, 30A, DC DC, nuevo|power module|constant currentdc dc - AliExpress
These can handle up to 30 amps input and a lesser amount out , depending on the ratio IN/OUT voltages. The good thing about using them is that any new or old transformer whose voltage and power ratings are within acceptable limits will do , so that one can even buy some old amp just to scrap it retaining only the transformer .
I have done it and it works . Added advantage is one can current-limit these boosters as well if needed or wanted . And if they were to fail you would be safeguarded from your amp getting too high voltages because you stabilize UP not DOWN.
Plesa comment and contribute your opinions and ideas on this . Michael
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