Electronics > Beginners
sourcing small power transformers
brybot:
Hello all, I'm new to the forums, but I've been watching Dave's videos for quite some time.
Anyway, I have an LED aquarium light fixture that I am modifying to add a dimming fixture. It draws 20W and uses two transformers capable of passing that power to the LEDs. The first transformer is 120VAC to 120VAC, which I assume is for isolation, but I'd love to know more if anyone has ideas. The voltage is rectified and fed into a constant current LED driver that generates it's own low voltage power rail, and switches the rectified voltage through an additional transformer with a feedback coil to power the LEDs.
Both of these transformers are capable of passing at least 20VA through them. And they are both tiny, on the order of 2-3 CM^3 in volume.
I've searched and searched, but I cannot find anything similar on Digi-Key, Mouser, or other suppliers. The power transformers I find there are all 500g, and 10CM^3 or larger for that kind of power. Does anyone know where I can find a small transformer off the shelf? Thanks!
Giaime:
I might be mistaken, but from your description it seems that you have a switching power supply and you're trying to think in terms of 50Hz transformers.
Could you post a picture of the electronics of this light fixture?
brybot:
I'm on 60 Hz here ;). Anyway, the first transformer is definitely 120 Vac, 60 Hz and 1:1. The second transformer is similar in size, however I am not sure of it's turn ratio. I believe it's operating at a switching frequency in the many hundreds of kHz or low single MHz, but I'll have to check the datasheet again. I'll post the circuit and a picture soon.
langwadt:
--- Quote from: brybot on October 30, 2018, 10:59:05 pm ---I'm on 60 Hz here ;). Anyway, the first transformer is definitely 120 Vac, 60 Hz and 1:1. The second transformer is similar in size, however I am not sure of it's turn ratio. I believe it's operating at a switching frequency in the many hundreds of kHz or low single MHz, but I'll have to check the datasheet again. I'll post the circuit and a picture soon.
--- End quote ---
there is no way a 20W 60Hz transformers is that small, as you have noticed they are all similar and much bigger, that is just physics. It is either switchmode or just a filter
brybot:
Ah, yes you're right. The first "transformer" is a line filter, probably for EMC since there is a switcher on the other side. The second is a SMPS transformer, and indeed is operating at greater than 60 Hz.
Thanks! That's what I needed to know.
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