339VDC -> ~15DC - Without TRANSFORMER

[Styx]

did you even read my post?

I quoted word for word that page in the machine book. I even put in bold the bit that say the power is delivered through direct conduction NOT via induction, hence no mutual is needed!!

and Nigel just change the inductor values, I see your point I just chucked some values together in the sim.

CAN WE PLEASE GET BACK ON TOPIC OR KILL THIS TREAD

 

[Nigel Goodwin]

did you even read my post?

I quoted word for word that page in the machine book. I even put in bold the bit that say the power is delivered through direct conduction NOT via induction, hence no mutual is needed!!

and Nigel just change the inductor values, I see your point I just chucked some values together in the sim.

CAN WE PLEASE GET BACK ON TOPIC OR KILL THIS TREAD

I consider it unsafe to leave a thread where it's giving such bad advice, your two inductor idea not only isn't an auto-transformer, but it's potentially dangerous as well!.

The book may or may not be correct (plenty of books are wrong), but there's no context given in the small quote - and it certainly never suggests that two independent inductors can be used as an auto-transformer.

The 'direct conduction' suggest is obviously totally wrong, and easily shown so by simple examples:

1) You have an auto-transformer with 100V input and 10V output, if you are drawing 10A from the 10V output the 100V input will be drawing only 1A from the supply (assuming the impossible 100% efficiency, in practice you may get 90% or so). So the 1A supply current can hardly be suppling the 10A output current by 'direct conduction'.

2) You have an auto-transformer with a 10V input, and a 100V output, in this case 10A input becomes 1A output - but the 10A input doesn't even flow though the output winding - so again, 'direct conduction' doesn't apply.

 

[Roff]

and "Ron H" that 0.1 resistor was placed in to help the simulation - Jacobian loops and all. In practice it would not be put in circuit - it would serve no purpose but to dissipate power. Reran with a 10uOhm resistor (for the simulation to be happy) and reduced the secondary coil downto 10uH and get the same result

Yeah, well, I'd like to see these inductors, totalling 90uH, that have only 10uohm resistance - not to mention the resistance of the mains. I was fully aware that you didn't put in the 0.1 ohm resistor as a discrete part.

The whole point here is you don't want to make an attenuator that draws thousands of amps. Even if you had lossless inductors (which you won't), I'll guarantee you that the power company will bill you for the current. In fact, they will probably penalize you for having such a crappy power factor.
As for being off topic - I think this topic is just as important as the original one.

 

[pebe]

did you even read my post?

Yes, I read your post. But I doubt that you understood my reply.

 

[pebe]

Double entry deleted.

 

[truenoteno]

back onto topic:

how is this 339Vdc generated?

i'm in australia so 240VAC mains = 339VDC, thru bridge rectifier.

So if you've got AC, simply use a small mains transformer! - it can't really get any simpler. If you don't have room for it, you don't have room for anything else either.

there is no room for a small mains transformer that will handle the power that i'm after. SMPS don't use mains transformers, and yet they manage to step down the voltage.

 

[Nigel Goodwin]

there is no room for a small mains transformer that will handle the power that i'm after. SMPS don't use mains transformers, and yet they manage to step down the voltage.

SMPS do use a mains transformer, it's just a smaller high frequency one, but that and the associated components won't really be any smaller than a little mains transformer for a low power application like yours.

What power are you after, you've given the impression that it's only very low?.

 

[Roff]

**broken link removed** has something that might work for you, but I don't know if you can get them in Australia. Digikey sells them, but does not stock them.

 

[truenoteno]

there is no room for a small mains transformer that will handle the power that i'm after. SMPS don't use mains transformers, and yet they manage to step down the voltage.

SMPS do use a mains transformer, it's just a smaller high frequency one, but that and the associated components won't really be any smaller than a little mains transformer for a low power application like yours.

What power are you after, you've given the impression that it's only very low?.

enough power to run a 24 port hub.
probably need around 14 volts at 4 amps max
(just an educated guess)

1 other thing, could i use a tiny transformer to use as the input voltage (rectified first) for a PWM ? < 40v, then use the PWM to step down the 300VDC ?

 

[Nigel Goodwin]

enough power to run a 24 port hub.
probably need around 14 volts at 4 amps max
(just an educated guess)

Your requirements get worse!. Now you're wanting a 56 watt mains power supply that takes next to no room - a 56W PSU by definition is going to be reasonably large.

1 other thing, could i use a tiny transformer to use as the input voltage (rectified first) for a PWM ? < 40v, then use the PWM to step down the 300VDC ?

I don't really understand what you are asking, it doesn't make much sense!. I've got a SMPS transformer in my hand this very second, it's out of a satellite receiver and probably rated at about 50W or so - it's roughly 35x35x35mm. I'm presuming that's too large for your requirements?, plus you need all the rest of the control circuitry as well.

Perhaps you should start right from the beginning, and try telling us what you are wanting to do, why it has to be so small, and why this possible hub doesn't already have a PSU?.

 

[Exo]

1 other thing, could i use a tiny transformer to use as the input voltage (rectified first) for a PWM ? < 40v, then use the PWM to step down the 300VDC ?

I don't really understand what you are asking, it doesn't make much sense!.

I think he wants to use PWM to lower the 300V rectified mains down to the required voltage directly, without the use of a transformer...

wich is ... not realistic eighter

 

[truenoteno]

enough power to run a 24 port hub.
probably need around 14 volts at 4 amps max
(just an educated guess)

Your requirements get worse!. Now you're wanting a 56 watt mains power supply that takes next to no room - a 56W PSU by definition is going to be reasonably large.

1 other thing, could i use a tiny transformer to use as the input voltage (rectified first) for a PWM ? < 40v, then use the PWM to step down the 300VDC ?

I don't really understand what you are asking, it doesn't make much sense!. I've got a SMPS transformer in my hand this very second, it's out of a satellite receiver and probably rated at about 50W or so - it's roughly 35x35x35mm. I'm presuming that's too large for your requirements?, plus you need all the rest of the control circuitry as well.

Perhaps you should start right from the beginning, and try telling us what you are wanting to do, why it has to be so small, and why this possible hub doesn't already have a PSU?.

OK, from scratch ,i need a power supply for my hub. The original inside the hub (no it's not an external psu) has blown up. The size of the orignal psu is about 3inches x 5inches with a height of about 1 inch.
i can't give u exact dimensions as i don't have the unit with me.

The original psu didn't have a step down transformer fed into a bridge rect. The only transformers on the board don't look like they are capable of handling the total power so i'm assuming there is another method for stepping down the high voltages.

 

[Nigel Goodwin]

The original psu didn't have a step down transformer fed into a bridge rect. The only transformers on the board don't look like they are capable of handling the total power so i'm assuming there is another method for stepping down the high voltages.

It's probably just a normal SMPS, the transformers are considerably smaller than 50Hz ones, which is why they are not very big.

Why not try repairing the existing supply?.

 

[truenoteno]

Why not try repairing the existing supply?.

hehe yeah, um, it's been desoldered and scattered amongst the rest of my components