cupoftea
Advanced Member level 6
Hi,
We are doing an SMPS for a person at the moment….unconnected with that, but necessary as an add-on for his job, is that we must also produce a “high frequency SMPS” (10MHz +) for driving LEDs.
I apologise in advance, but the spec for the HF SMPS is very open, ….all we have to do is in some way demonstrate the cost and efficiency and size advantages of a high frequency SMPS….by making some kind of HF SMPS that drives LEDs.
Anyway, I take it offline LED drivers are out of the question at these frequencies?....since ferrite is impossible due to core losses, and an air core transformer, with 3500VAC isolation is going to be spewing RF all over the place?
As discussed, the spec is very open…..but the customer has mentioned that he likes the following advantages of HF SMPS…..
1…..Use of PCB printed coils instead of “normal” inductors.
2…The use of much smaller energy storage components, ie inductors and capacitors.
3….The use of GaN transistors, for high switching frequency.
4…Customer thinks some of his products don’t need a radiated emissions EMC test pass anyway…..so if there are extra RF emissions, then “so what”.
5…customer thinks there can be cost savings. (eg due to not needing “bought” inductors., but just PCB inductors)
..Anyway, I am thinking that skin effect issues could well make any solution bigger and more expensive? Also, the only capacitors possible are ceramics or “air dielectric” ones, but even ceramics have SRF of eg 5MHz for a typical 1uF, 0805, X7R.
I have read multiple web articles, but all are gushingly over-worshipping of 10MHz plus SMPS’s, without detailing any of the drawbacks.
I am suspicious that there are pretty good reasons why 10MHz+ SMPS can never realistically be cheaper than todays 50-1MHz SMPS?
Also, there is the situation of ferrite-core-less SMPS’s suffering issues of coupling if they are placed near conductive objects?
Also, there is the issue of the tolerance on ceramic capacitors which make up resonant SMPS elements?
Also, many modern RF Amplifiers use switching techniques anyway (Class E?)…they are almost an SMPS in their nature, and these are not known for their cheapness….so why is it that their application in SMPS is going to be cheap? (cheaper than what exists now)
Also, a 10MHz+ SMPS must surely be resonant, and these inevitably have high circulating currents....and if a wide vin and/or vout range is required, then the circulating current tends to be higher still.
Also, resonant SMPS tend to have higher no_load losses, (due to circulating currents still flowing at no_load)
Also, as discussed, the new High frequency radio transmitters, are essentially SMPS (of a kind) anyway...and they are neither cheap, nor small, so surely this technology for SMPS is wayward and far-out?...then again, if all you need to do is stuff some current through some LEDs....
So can you think of a good example HF LED driver SMPS that we can put forward for this?
We are doing an SMPS for a person at the moment….unconnected with that, but necessary as an add-on for his job, is that we must also produce a “high frequency SMPS” (10MHz +) for driving LEDs.
I apologise in advance, but the spec for the HF SMPS is very open, ….all we have to do is in some way demonstrate the cost and efficiency and size advantages of a high frequency SMPS….by making some kind of HF SMPS that drives LEDs.
Anyway, I take it offline LED drivers are out of the question at these frequencies?....since ferrite is impossible due to core losses, and an air core transformer, with 3500VAC isolation is going to be spewing RF all over the place?
As discussed, the spec is very open…..but the customer has mentioned that he likes the following advantages of HF SMPS…..
1…..Use of PCB printed coils instead of “normal” inductors.
2…The use of much smaller energy storage components, ie inductors and capacitors.
3….The use of GaN transistors, for high switching frequency.
4…Customer thinks some of his products don’t need a radiated emissions EMC test pass anyway…..so if there are extra RF emissions, then “so what”.
5…customer thinks there can be cost savings. (eg due to not needing “bought” inductors., but just PCB inductors)
..Anyway, I am thinking that skin effect issues could well make any solution bigger and more expensive? Also, the only capacitors possible are ceramics or “air dielectric” ones, but even ceramics have SRF of eg 5MHz for a typical 1uF, 0805, X7R.
I have read multiple web articles, but all are gushingly over-worshipping of 10MHz plus SMPS’s, without detailing any of the drawbacks.
I am suspicious that there are pretty good reasons why 10MHz+ SMPS can never realistically be cheaper than todays 50-1MHz SMPS?
Also, there is the situation of ferrite-core-less SMPS’s suffering issues of coupling if they are placed near conductive objects?
Also, there is the issue of the tolerance on ceramic capacitors which make up resonant SMPS elements?
Also, many modern RF Amplifiers use switching techniques anyway (Class E?)…they are almost an SMPS in their nature, and these are not known for their cheapness….so why is it that their application in SMPS is going to be cheap? (cheaper than what exists now)
Also, a 10MHz+ SMPS must surely be resonant, and these inevitably have high circulating currents....and if a wide vin and/or vout range is required, then the circulating current tends to be higher still.
Also, resonant SMPS tend to have higher no_load losses, (due to circulating currents still flowing at no_load)
Also, as discussed, the new High frequency radio transmitters, are essentially SMPS (of a kind) anyway...and they are neither cheap, nor small, so surely this technology for SMPS is wayward and far-out?...then again, if all you need to do is stuff some current through some LEDs....
So can you think of a good example HF LED driver SMPS that we can put forward for this?
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