I just purchased a DC-to-DC converter off of eBay; (3A DC-DC Boost Step-up Converter Voltage Regulator 5V-35V to 9V 12V 24V 36V 48V | eBay)
but I have no idea how this thing works. Of course, they give no schematic. I guess it is a switcher of some sort, but the active component's markings are hidden by its heatsink, so no help there. Does anyone have a schematic of one of these things, or something similar? What frequency do they usually operate at? How big of a coil is needed on its output to calm the noise?
but I have no idea how this thing works. Of course, they give no schematic. I guess it is a switcher of some sort, but the active component's markings are hidden by its heatsink, so no help there. Does anyone have a schematic of one of these things, or something similar? What frequency do they usually operate at? How big of a coil is needed on its output to calm the noise?
It is a boost converter (non-isolated). It is likely to be based on an LM2576 (52KHz) or an LM2596 (150KHz), most likely the latter. The circuit diagram is here:
http://www.siongboon.com/projects/2005-08-07_lm2576_dc-dc_converter/lm2576-adj%20circuit.gif
You can eventually increase the size of the output capacitor if you find the ripple to high.
http://www.siongboon.com/projects/2005-08-07_lm2576_dc-dc_converter/lm2576-adj%20circuit.gif
You can eventually increase the size of the output capacitor if you find the ripple to high.
My excuses, that I had overlooked.
Then, I arrive at LM2577 (52KHz): http://www.ti.com/lit/ds/symlink/lm2577.pdf
Alternatively, it may be based on an LM2585 (100KHz): http://www.ti.com/lit/ds/symlink/lm2585.pdf
Figure 19 in the datasheet.
Desolé, FF
It seems to be the LM2577: DC Boost LM2577 Converter Step up Module 3.5 35V to 5 56V 3A MAX with Light -in Voltage Regulators
Then, I arrive at LM2577 (52KHz): http://www.ti.com/lit/ds/symlink/lm2577.pdf
Alternatively, it may be based on an LM2585 (100KHz): http://www.ti.com/lit/ds/symlink/lm2585.pdf
Figure 19 in the datasheet.
Desolé, FF
It seems to be the LM2577: DC Boost LM2577 Converter Step up Module 3.5 35V to 5 56V 3A MAX with Light -in Voltage Regulators
That sure looks like the one I have---THANKS for finding it!! I'm a bit disappointed that the switching frequency (52KHz) is so low.....makes filtering harder (larger-value inductor needed). But I did find two 100 µH, 3 Amp chokes that I think I'll use in series with the output. If my TDA7492 Class-D amp is putting out 20 watts into 4Ω, that's about 2.2 amps of current. Figuring the Class-D at ~ 90% efficient, that's about 2.44 amps, 15 volts, and the chokes should provide ~-20db of attenuation at 50k Hz. I hope that's enough.
the other limit is ripple current. the output cap has only a 400mA rms rating at best, if it is a renowned brand. it's a matter of time but the cap will die. best to replace it with a polymer type like the panasonic os-cap, these have ripple ratings 10x larger. the price may me more than the complete DCDC ...
Yeah, that'd work! Thanks for the suggestion. But I am currently trying to work within the constraints of my existing amp; trying to squeeze the most out of it. It's a little Roland MicroCube with 6xAA cells. So I just need to figure how much peak current I can get from the DC-to-DC converter.
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