Lateral MOSFET power supply and RMS output power.

[tallerseverino]

I also read that toroidals from 300VA needs an specific circuit, some kind of low-turning-on.

I think my english is bad, it should be slow-turning-on. Sorry.

 

[washburn_it]

It is called "soft-start" and it is needed if the transformer is rated > 300VA.
Are you going to build the low power or high power version of the P101?

 

[AndrewT]

I allege that all transformers need such a "soft start" device to allow a close rated fuse to be used.

required power = VA
close rated fuse = VA / Vac

If one chooses not to use a close rated fuse, then the fuse required to prevent nuisance blowing is likely to be around:
fuse = 3 * VA / Vac

 

[tallerseverino]

To washburn: I read your repply on how the high power p101 will stress less the mosfets, and I think I will go with it.
I will need 8 mosfets, but well, if well built and not stressed they should live longer, warm-up less quickly and the lower the temperature, the better for solid state devices..

I will take this road as soon as I figure it all out, the DC rails for the high power, the PT ratings,( I wish I had found this forum sooner) I mean, use the 4 mosfets but not drive them to it's full potential, lower power but.. 2 units of them in stereo.

Also I think the high power biasing method is more accurate.

Have you mounted the high power p101?

To Andrew: Yes, I agree, if the idea of "soft start" is good for a toroidal it should be good to any toroidal. An enginner would say that we could ignore the fact and assuming that's not noticeable until 300VA. I'm thinking about use these circuits for each channel whatever the trafo ratings, precautions and good design (consideration of all parts when "glued" together) are key.

What about speaker protection? Will it be redundant with the "soft start" or they could go along well? Popped in my mind speaker protection is for not let DC go to speakers, and that soft start helps but...

The output DC could come up even using soft start?

Should I go with speaker protection? Another history altogether.

Thanks and regards.

 

[AndrewT]

Soft start and speaker protection are completely different and quite separate topics.

 

[washburn_it]

Soft-start is only for the transformer to limit the inrush current at power up, DC protection is only for the speakers: both "systems" are independent from each other.
There are a lot of DC prot. around the net but, if you like Rod's projects, you can find a DC protection project on his website.

I've just completed 2 P101 modules (high power version) but I didn't test them yet.
I will use them for hifi purpose anyway.

 

[tallerseverino]

Washburn, which heatsinks have you used for each p101?
Did you use +/-70vDC rails as Rod recommends?
I've been checking the rod website and found very much information about the two topics, soft start and speaker protection. Still too much in my head for a saturday afternoon.
regards.

 

[washburn_it]

I will use a 0.4 °C/W 300x40x120 mm heatsink and the supply voltage is +/- 56V with 7x4700 uF per rail (65800 uF total).

 

[tallerseverino]

Well, I have the old heatsink, it's alluminium (gray) and the size is around the same, about 30cm, 12 cm but the height is about 2cm. I remember I had difficulties finding it then, and I'm not sure if it's 0,3ºC/W or 0,6ºC/W, I have to check, I think It maybe is ok for one p101 alone.

How much power are you expecting from your p101 high power with this configuraton? (maybe a dumb question, but sunday morning not my best time in the week).

 

[washburn_it]

Around at 200 Watt @ 4 ohm but even if it were 180 Watt it would be enough if they are "clean" and not distorted.