Using a transformer with higher frequency AC - Page 1
Forum section: electronics / projects

author: TheGoyNextDoor
author_rank: Newbie
timestamp: April 26, 2018, 09:50:09 pm
content: To power a TDA7498E class-D audio amplifier IC for use in my car which outputs 14.4V from the alternator. This IC requires a 36 VDC for the VCC, according to the datasheet, so an inverter would be needed to supply this voltage. If the amplifier is lowpassed at a cutoff frequency of 80Hz, I'm thinking I could run the inverter at a frequency above the cutoff so that I don't hear a hum through the speaker. Will the transformer operate safely at higher frequencies without any problems?

author: NiHaoMike
author_rank: Super Contributor
timestamp: April 27, 2018, 12:34:37 am
content: A boost converter will work nicely for that conversion ratio.

author: german77
author_rank: Regular Contributor
timestamp: April 27, 2018, 12:55:25 am
content: Quote from: NiHaoMike on April 27, 2018, 12:34:37 amIt agree with that. but I will put spike protection and noise reduction. Cars tends to have very shitty DC voltage that would easily burn your boost converter.Running an transformer at higher frequencies will create more eddy currents and increase the skin effect. Basically it will work at a lower efficiency and have less current handling .

author: Zero999
author_rank: Super Contributor
timestamp: April 27, 2018, 08:55:18 am
content: Quote from: german77 on April 27, 2018, 12:55:25 amWell a transformer will need to be run off an inverter, which would be just as vulnerable to spikes, as a boost converter.The TDA7498E will work down to 14V, just with less power output, but would still need a boost converter to work reliably, as the voltage can drop below that.

author: Kleinstein
author_rank: Super Contributor
timestamp: April 27, 2018, 09:05:06 am
content: Boost converter tend to need a rather large storage inductor and quite some input capacitors / fitlering at higher power. The advantage is that they allow regulation over quite some range.As the supply voltage likely does not need to be tightly regulated, there should be not problem using a forward converter and thus a higher frequency transformer. Regular iron based transformers get extra losses at higher frequency, though something like 1 kHz is usually not that bad. For higher frequency one usually used different core materials, like ferrites or special (e.g. amorphous, nano-crystalline) alloys. With the higher frequency the transformer can also get considerably smaller.The usual way with high supply for high power car audio is a forward converter somewhere in the 20-50 kHz range. From the EMI side a boost converter tends to be more difficult.

author: JS
author_rank: Frequent Contributor
timestamp: April 28, 2018, 04:59:55 am
content: Depending on the frequency a transformer could work fine, at higher frequencies than designed, s more a problem going to lower frequencies. At higher frequencies it could handle higher voltages but always the same current as that would be limited by the cooper size. So, with all this, if you can build a transformer with a specified minimum freq in mind you can do it even more efficient than a 50Hz one running on say, at 200Hz. This will result in a smaller transformer for the same power level.If you go to a much much higher freq, over few kHz, eddy currents and later skin effect start to become a problem, that's why SMPS use specific transformers, much smaller than the mains ones rated for the same power and usually with ferrite or special cores.If you have to use a transformer at a lower level than designed, as a rule of thumb you can use it a a constant V/f. While in theory does work the other way (increasing voltage with increasing freq) can be done but doesn't keep up for long. For reference, same motor rated for 50Hz and 60Hz will have not only higher rotational speed but also higher power rating at 60Hz than at 50Hz. (sometimes they even rate for higher currents as they have better cooling at higher speeds)JS