truenoteno
New Member
1st thing that comes to mind is a step down SMPS, but my pulse width modulator (LM3524) can' t handle 339v input voltage. I have the TL494 if that's a better chip
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truenoteno said:1st thing that comes to mind is a step down SMPS, but my pulse width modulator (LM3524) can' t handle 339v input voltage. I have the TL494 if that's a better chip
Nigel Goodwin said:truenoteno said:1st thing that comes to mind is a step down SMPS, but my pulse width modulator (LM3524) can' t handle 339v input voltage. I have the TL494 if that's a better chip
For a start you don't give any indication of the current you require, if it's low you could use a simple dropper resistor - a large one!.
Assuming you need more than that, as you say an SMPS would do the job. 339V is pretty well what you get from recified mains, so there are LOTS of suitable designs already available, as used in TV's etc. Try searching for TDA4605 or UC3842, both are commonly used in TV SMPS's.
Neither of the two chips you mention seem to used much in domestic equipment, although the TL494 is used in PC PSU's quite a lot.
Styx said:err "auto-transformer" !!!!!
check it out it is yr solution - see above post
Nigel Goodwin said:Styx said:err "auto-transformer" !!!!!
check it out it is yr solution - see above post
You appear to have missed the original specification? - the supply it needs to work from is DC!.
Also, two inductors don't make an auto-transformer, it's just a 'proper' transformer without isolated windings.
Styx said:and 2 inductors DO make an autotrasformer. An autotransformer is an unisolated transformer.
Nigel Goodwin said:Styx said:and 2 inductors DO make an autotrasformer. An autotransformer is an unisolated transformer.
Yes, it's a transformer, and works by transformer action between the two windings - two inductors won't do that, unless they are wound on the same core - in which case it's a transformer, and not two inductors.
You can't just connect two inductors together and create an auto-transformer - but feel free to try it?.
It *cannot* work. There must be mutual inductance between the two windings...... It does work with just inductors ONLY to step-down, they tend to be wastful because of teh flux-leakage is high, but the point is it works!...
pebe said:It *cannot* work. There must be mutual inductance between the two windings...... It does work with just inductors ONLY to step-down, they tend to be wastful because of teh flux-leakage is high, but the point is it works!...
Styx said:and as I stated it is acting MORE like a voltage divider rather than a "true" autotrasfomer
can we get back on topic or drop this
Nigel Goodwin said:Styx said:and as I stated it is acting MORE like a voltage divider rather than a "true" autotrasfomer
NO! - it acts solely as a potential divider, not at all like an autotransformer, as such the inductors will dissipate just as much heat as a resistive divider.
can we get back on topic or drop this
We're still waiting for a response about the source of the 339V DC, which I agree would probably be useful to know!.
Styx said:Nigel Goodwin said:back onto topic:
how is this 339Vdc generated?
i'm in australia so 240VAC mains = 339VDC, thru bridge rectifier.
truenoteno said:Styx said:Nigel Goodwin said: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.
Styx said: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
The section of the article you have quoted refers to an autotransformer or a transformer. In both those cases the primary and secondary windings have mutual inductance because the windings are on the same bobbin.Dont believe me? get out the book I have quoted above and check it out. The creation of a single phase coreless autotrasformer is a crude hack that is aeospace approved.
Also your comparrison of this "inductive divider" just like a resistive divider is completly wrong. If you were to connect a resistor straight across the AC no matter what frequecy is chosen current will flow based on V = I*R.
However, connect an inductor across an AC supply and increase its frequency then the current (and thus power trasfer) will decrease - standard inductor theory. No extra power is lossed, the inductor will just "oppose" the flow of current. It is this effect that this crude autotrasformer works on.
If resistors were used you would have conduction loss based on the current flowing, the only loss in this autotransformer arrangement is due to the equivent-series-resistance of the inductors.