Dear TI people or other very nice helping guys,
For a 1-10V fluorescent lamp dimmer I've selected this device make a flyback converter to power a simple MCU and a few other components. Besides minimal no load power, small size is an important design parameter as well.
I would like to refer to the latest datasheet of this part: "SLUSBE8A –MAY 2013–REVISED JANUARY 2014"
It would be nice (if you intent to help me) that I do get my questions answered, because now I'm stuck on THESE THINGS and not other things.
THESE THINGS are the situations when you see a question mark while READING this message. Sorry I have to say this but I experience so often useless responses.
I would like to make the circuit that is shown in the DESIGN PROCEDURE section of the datasheet, and adjust the component values tailored for my application. I'll show here as well:
So I attempt to work out the full design procedure. Everything fine until I get to the transformer (coupled inductors for flyback) part on page 20.
tR = 2u, fMax = 74 kHz, DMAGCC = 0.425
So DMAX = 0.501
VINMIN = 230V -15% = 230 * 0.85 = 195.5
VBULKMIN = VINMIN * sqrt(2) * 0.8 = 221.2 V, the 0.8 is for 20% ripple on bulk capacitor.
VOCV = 5V
VF = 310 mV
VOCBC = 0, I don't use this
Nps(max) = 49.1, that is pretty large
I was thinking about this one from Pulse Electronics
So my Nps = 17.2
Rather than continuing with the selection of RCS value I realized I already also defined the primary inductance with the selection of this transformer.
Lp = 544 uH
This is a significant lower inductance compared to to one I get with the equations.
I use the equation below to calculate the peak primary current.
= 0.9, they said it was a good approximation
IPP(max) = 242 mA
So for my very small output power it is fine to use a lower inductance on the primary and allow the peak current to be higher, is it?
VCST(max) = 735 mV
RCS = 3.0 ohm, standard e24
I'm not completely certain about the verification of the minimum on time, should the calculated value be higher OR lower than the 300 ns specification? And what do I need to use for VCST(min) the min, typ or max specification? And VCST(max)?
For both typical I get:
VIN(max) = 230 + 15% = 230 * 1.15 = 264.5
tON(min) = 85.7 ns
Also for the next check. Does the calculated value for tDMAG(min) be higher OR lower than the 1.2 us specification? And which tON value do I need to use in the equation.
I hope I can get answers to there questions. So I have a better change it works when i make it.