Hello to all.
I need to make an smps that will powered from a car's 12v battery.
The secondary must have +/- 12v & +/- 5v about 1A each output.
From what i read in this forum i assume that primary must have the same windings with the 12v secondary and almost double from 5v secondary.
But how many must be the first winding.
I want to use sg3525 because i have many of those.
My purpose is to power up a dvd player for my car since i have only an in-dash lcd with tv and scart input.
Maybe i can use the dvd player's original power supply by changing the etd type transformer.
Pls advise
Thank you in advance
I need to make an smps that will powered from a car's 12v battery.
The secondary must have +/- 12v & +/- 5v about 1A each output.
From what i read in this forum i assume that primary must have the same windings with the 12v secondary and almost double from 5v secondary.
But how many must be the first winding.
I want to use sg3525 because i have many of those.
My purpose is to power up a dvd player for my car since i have only an in-dash lcd with tv and scart input.
Maybe i can use the dvd player's original power supply by changing the etd type transformer.
Pls advise
Thank you in advance
By the way my players original smps uses TEA1523 chipset.
The transformer has 2 windings of primary coil. One for the oscillation and one for powering the TEA chip.
All i wabt to know is how to make another transformer.
I am thinking that if i make one with for example 10 turns primary it will draw too much current from my car.
The dvd players car supply secondary is only maximum 1A.
Pls suggest me something.
I am willing to make a new smps but i am afraid that i will fail in the transformer.
Thank you in advance
The transformer has 2 windings of primary coil. One for the oscillation and one for powering the TEA chip.
All i wabt to know is how to make another transformer.
I am thinking that if i make one with for example 10 turns primary it will draw too much current from my car.
The dvd players car supply secondary is only maximum 1A.
Pls suggest me something.
I am willing to make a new smps but i am afraid that i will fail in the transformer.
Thank you in advance
I attached a pcb i made using sg3525. I took it from http://sound.westhost.com/project89.htm
I plan to use small fets cause i want only 3A output.
What do you think?
Thank you
I plan to use small fets cause i want only 3A output.
What do you think?
Thank you
Johnny-
Assuming you are running the '3525's oscillator at 72kHz for a switching frequency of 36kHz (common frequency for almost all car amps with DC-DC converters, AT & ATX power supplies), and your transformer core is a high-permeability ferrite, you should wind your core as follows:
4T + 4T primary
2T + 2T for the +/-5V secondaries
6T + 6T for the +/-12V secondaries.
If you're using regulation with an optoisolator, you will need some powdered-iorn cores for the secondary side filtering, as well.
Amidon Associates has a great datasheet for all their powdered-iron and ferrite cores. The cores I have used are the FT-114-77 (Ferrite Toroid, 1.14" O.D., #77 material). At 20kHz, it can handle about 60W. Extrapolating up to 36kHz, you should easily be able to get 100W through it.
A number of good reference books are available for calculating transformer turns, ratios and the like. The book I refer to the most is Geo. Chryssis' book "High Frequency Switching Power Supplies". The transformer section has all the theory you could ever need/use, but it also has some good, real-world design examples, too. I have taken his design procedure, and boiled it down to a 8-11 (depending on the number of secondaries) step cut-n-dried process to design any double-ended SMPS transformer.
I did an SMPS similar to this about 10yrs ago, using the SG3525, two IRF510s (later IRF540s), a smaller FT-82-77 core and four Schottky rectifiers for the +/-15V secondaries. I got about +/-500mA out of it to power an active crossover for the car. I scrapped the X-over, and cannibalized it's parts out for other projects over the years. It worked out pretty well, too. Sorry no pics of it.
Hope this helps.
Steve
Assuming you are running the '3525's oscillator at 72kHz for a switching frequency of 36kHz (common frequency for almost all car amps with DC-DC converters, AT & ATX power supplies), and your transformer core is a high-permeability ferrite, you should wind your core as follows:
4T + 4T primary
2T + 2T for the +/-5V secondaries
6T + 6T for the +/-12V secondaries.
If you're using regulation with an optoisolator, you will need some powdered-iorn cores for the secondary side filtering, as well.
Amidon Associates has a great datasheet for all their powdered-iron and ferrite cores. The cores I have used are the FT-114-77 (Ferrite Toroid, 1.14" O.D., #77 material). At 20kHz, it can handle about 60W. Extrapolating up to 36kHz, you should easily be able to get 100W through it.
A number of good reference books are available for calculating transformer turns, ratios and the like. The book I refer to the most is Geo. Chryssis' book "High Frequency Switching Power Supplies". The transformer section has all the theory you could ever need/use, but it also has some good, real-world design examples, too. I have taken his design procedure, and boiled it down to a 8-11 (depending on the number of secondaries) step cut-n-dried process to design any double-ended SMPS transformer.
I did an SMPS similar to this about 10yrs ago, using the SG3525, two IRF510s (later IRF540s), a smaller FT-82-77 core and four Schottky rectifiers for the +/-15V secondaries. I got about +/-500mA out of it to power an active crossover for the car. I scrapped the X-over, and cannibalized it's parts out for other projects over the years. It worked out pretty well, too. Sorry no pics of it.
Hope this helps.
Steve
Mobile supply power conditioning & filtering
FYI: for some interesting tips and designs you might check out this extensive thread as well: http://www.diyaudio.com/forums/showthread.php?s=&threadid=81178
FYI: for some interesting tips and designs you might check out this extensive thread as well: http://www.diyaudio.com/forums/showthread.php?s=&threadid=81178
Thank you all for replying but my question is this.
If i use only 4t primary then the circuit must draw a lot of current form my car.
because the primary will have zero resistant. and only the fets will prevent a short circuit.
Where am i thinking wrong?
Also i plan to use a ferrite ring of an old pc supply used there as ac filter. Is it good?
Thank you
If i use only 4t primary then the circuit must draw a lot of current form my car.
because the primary will have zero resistant. and only the fets will prevent a short circuit.
Where am i thinking wrong?
Also i plan to use a ferrite ring of an old pc supply used there as ac filter. Is it good?
Thank you
I would NOT use the ferrite from the AC Filter for your trannsformer. Instead, and I can't think of why I didn't mention this in ly last ranting er- posting: Why not just use a modified version of your pc supply? It already puts out +/-5V and +/-12v, so why not? Instead of running it of the AC mains, replace everything on the primary side with components suitable for runing on a +12V supply, and re-wind the main trtansformer's primary fior the 4T + 4T.
That brings me to my other point: you asked why only 4T + 4T for the primary, wouldn't the FETs see a dead short to ground?
The short version to that answer is, no, they will not. At 60Hz, this would almost be a dead short, but as switching frequency goes up, so does impedance. At ~36kHz, the AC impedance of the windings is rather high, lending itself to small size, and rather high efficiency.
There is a thread somewhere in this Forum on modding an old AT or ATX box to run on 12V while keeping the output section intact. Do a search for it.
That brings me to my other point: you asked why only 4T + 4T for the primary, wouldn't the FETs see a dead short to ground?
The short version to that answer is, no, they will not. At 60Hz, this would almost be a dead short, but as switching frequency goes up, so does impedance. At ~36kHz, the AC impedance of the windings is rather high, lending itself to small size, and rather high efficiency.
There is a thread somewhere in this Forum on modding an old AT or ATX box to run on 12V while keeping the output section intact. Do a search for it.
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