DER 263 based 42V/700mA PWM Dimming
Hi.
we have designed a pwm dimming led driver using the circuit idea as per the DER263 Document,
the changed specs would be i/p:90-265VAC, o/p: 42V/700mA
the problem with our circuit is with dimming portion,
my query whether the components in PWM dimming portion of this circuit does change for the new specs, or can we go with the same circuit,
please help in this regards,
further, can we vary the Duty Cycle of the comparator with out using the 0-10V Control, i,e by varying the R-c Network of the comparator can it be done,
and what about the active load components changes to be incorporated
please help in this regards
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thank you
since my output is 42V i will be able to connect 12leds but the dimming is happening only at 14Leds not on 12 leds is it okay,
further under full dimming i.e., leds off condition, the lnkph switch just keepsm on/off condition but there is no led dimming at this condition , is this condition normal
please help in this regards,
i dont exactly get get what you mean....
Btw, DER263 works in dimming by controlling the IFB which is dependent on the PWM duty cycle. voltage on C6 varies with PWM duty cycle, if you dont get any dimming, check voltage on c6 whether its changing with the PWM duty.If not, you may need to trim R11 so that at full dimming or minimum light output, voltage at this pin is around 3V (Vfb + 0.6V).
The circuit is the same but you need to tweak the values to satisfy the new LED load. Pls follow the description on page 9-11 of the report. Please also note that there is a mistake on Fig 7, r11 should be in series with U2b collector. Please refer to the main schematic Fig 3 for the correct connection. We will update the report.
If you dont want a 0-10V control. Another method you can do is to use a potentiometer in place of R26 (plus a series resistor) that will be used to vary the duty cycle. This effectively varies the dc level at pin 5 of U35 which is compared with the triangular waveform at pin 6 of U3B. You need to select a potentiometer resistance range plus the series resistor so that voltage a pin 5 of U3b varies between 2/3Vcc and 1/3Vcc so you can still get the 0-100% duty cycle.
You need to tweak the active load values R14,r18, and r40 once you determine the offset current that you want which is based on the max dim ratio that you require.