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Topic: 3w RGB color bar (BOM w/ TLC5940, Fets, UNL's (Read 4 times) previous topic - next topic

sjim

#20
Feb 09, 2013, 09:07 am Last Edit: Feb 09, 2013, 09:14 am by sjim Reason: 1
since my output from the 3chRGB controller... each color output ranging from 12v and below, I will need to regulate before connecting to the ADJ pin bc the zxld1360's ADJ pin max is +6v. It seems the only way to do so is use a NPN transistor so the 1360 only receives voltages from 0 to +6 volts, is this the correct way to do this?  In reading the specs, do I regulate the NPN operational at +6v or is it +2.5v (according to the DC voltage method) ?
+
(1360's specs)
Driving the ADJ input via open collector transistor
The recommended method of driving the ADJ pin and controlling the amplitude of the PWM waveform is to use a small NPN
switching transistor as shown below:
This scheme uses the 200k resistor between the ADJ pin and the internal voltage reference as a pull-up resistor for the
e.

• Drive with DC voltage (0.3V < VADJ < 2.5V) to adjust output current from 25% to 200% of
IOUTnom
• Drive with PWM signal from open-collector or open-drain transistor, to adjust output current.
• Adjustment range 25% to 100% of IOUTnom for f>10kHz and 1% to 100% of IOUTnom for f <
500Hz
• Connect a capacitor from this pin to ground to increase soft-start time. 
(Default soft-start time = 500µs. Additional soft-start time is approximately 500µs/nF)

johnwasser


I will need to regulate before connecting to the ADJ pin bc the zxld1360's ADJ pin max is +6v.


No, because the outputs of the RGB controller are Open Collector and the zxld1360 datasheet says you can use an Open Collector signal directly.

"Open Collector" means the output pin is internally connected to the Collector of an NPN transistor.  When the NPN transistor is off the output pin is floating. When the NPN transistor is ON the pin is pulled to ground.  In those cases where you need a HIGH/LOW signal from an Open Collector output you must provide a pull-up resistor.

Since the zxld1360 accepts an Open Collector output as an input it must have an internal voltage source.
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sjim

Would I a pull-up in this scenario, like a 10k pull-up between ADJ and controller's output?   
would it be close to this model below?
(each color 350ma)

3ch RGB controller output1(12v >)  -> 10kpull-up -> Adj 
10kpullup -> c1=100nF -> Grnd

12v -> Vin -> Rsense(.1ohm) -> RGB(eg.Red) -> 47uH -> Lx

I think also it might better to the use the ZXLS1350(350ma) vs 1360(1a)

Chagrin


Would I a pull-up in this scenario, like a 10k pull-up between ADJ and controller's output?   
would it be close to this model below?
(each color 350ma)

3ch RGB controller output1(12v >)  -> 10kpull-up -> Adj 
10kpullup -> c1=100nF -> Grnd


The RGB controller output goes to the gate of an NPN transistor, the collector connects to the open collector output, and the emitter connects to GND.

sjim

How about this config to drive 1x3wRGB (r=2.5v, b/g=3.5v) at 350ma per color

(eg. 3chRGB Controller output for Red(only) from 12vDC > 3ch RGB controller(each separate output to) > NPN > ZXLD1352

12v+ ----47k 5% .25w----\  prevent flicker when power on
R  -------10k -------------/ (gate) BC848(npn)-collector -> ADJ(zxld1352)
B                                   (emitter)--GND           
G

Grnd  ---- power grnd of zxld

Any better way or different part configurations for doing so?  The ZXLD1352 has 1000:1 dimming vs 100:1 for the 1350 (assuming would this give better dimming spectrum)

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