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Part Number: SN6501
I would like to design low noise isolated +/-15V rail from 5V input.
Design Requirement :
Vin : 4.5 - 5.5V
Vout : -15V 90mA / +15V 40mA
Since I can't find any transformer for SN6505 from Mouser, Digikey and Farnell,
I decided to use two SN6501 with two transformers.
Do you see any problem with this design?
Can you recommend any transformer for SN6505 with more than 1:1.7 turns ratio and higher current capacity that I can purchase from Mouser, Digikey or Farnell?
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In reply to EH Lee:
In reply to Abhi Aarey:
Thank you for your patience. I found the following transformer designs with 1:3.5 turns ratios.
You can use these designs/part numbers as examples. Hope this helps!
Also, just the rectifier circuit wouldn't give you voltage doubling, you would need another capacitor in conjunction with the diodes and a slightly different topology for that. However, since you have the right turns ratio, this should now become easier.
Many thanks for transformer recommendations.
Unfortunately the problem is I can't buy recommended 1:3 transformer from anywhere.
Do you have other transformer recommendations form other suppliers which is in mass production?
If not, I would like to stuck with two sn6501 with two transformers since I can buy MIDCOM 1:1.7 transformer everywhere. - one for positive rail, the other for negative rail.
One thing that I would like you to check my schematic once again, I didn't use center tap so output voltage will be 1.7*2*5 = 17V as it is described in the sn6501 datasheet.
You are welcome.
I see, I don't have any other transformer recommendations at the moment, sorry. You can ask your preferred vendor to make a prototype if you like, but that will take a few weeks before you can test and then approve it for production.
Your other option is also OK. It is not the smallest solution, but yes it can be considered. Good point on not using the center-tap - that does make a difference and it gives you the full swing . So you have 2*Vcc swing in the primary windings (D1 to D2 )and the turns ratio is "n", so you will get 2*Vcc *n across the two end points of the secondary windings.
You will get 17V swing in typical case (5V input), but you have to account for Diode drop and LDO drop out voltage before the final output. Also, you will have = 2 * 4.5 * 1.7 = 15.3V worst case swing on the secondary windings when Vin = 4.5V , so we need to be careful here. so it is better to pick a transformer with a higher turns ratio. (maybe closer to 1:2).
Shown below is a list of transformers in the SN6505 datasheet (ok to use with 6501 also). Within this list, I'd recommend using the 750316032 device with a 1:2 turns ratio. This gives you margin to cover for supply variation on the primary side, and also has big V x T product ( = 41V-us) to allow for bigger voltage swing, and also gives you reinforced isolation capabilities.
Hope this helps,
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