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Author Topic: 3843 boot converter frequency  (Read 1188 times)
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satya
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« on: February 25, 2010, 09:49:35 09:49 »

hi

3843 boost converter consists  RT=3.3K and Ct 22nF

how calculate frequency.


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oldvan
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« Reply #1 on: February 25, 2010, 12:21:03 12:21 »

Interesting power spply IC.

http://www.microsemi.com/datasheets/UC184xA.pdf
Quote
The UC184xA family of control ICs provides all the necessary features to implement off-line
fixed-frequency, current-mode switching power supplies with a minimum of external components.

Page 5 chart Figure 1, 2.2 nF 3.3K is prox 200 KHz
Formula indicates freq is inversely proportional to capacitence,

For RT > 5k:
f = 1.72 / (RT CT)

so 22 nF 3.3K should give prox 20 KHz.

Formula predicts F at 23.7 KHz, but may not be correct because R < 5k.

If you change R to over 5K and adjust C accordingly, you can calculate directly from the formula.
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« Reply #2 on: February 25, 2010, 02:42:17 14:42 »

Thanks old rusty van, That made me think back 20 odd years, (now I feel old). I read a book a about that time called "don't fumble with formula" by who I forget?.
but it true with most C/R timers if you keep the R and shift the decimal point right on the cap. then the freq is lowerd by one decimal point left. 2.2uf to 22uf & 200kh to 20kh
this trick also works with pic chip R/C timers too.
« Last Edit: February 25, 2010, 02:45:30 14:45 by pickit2 » Logged

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