Hi DogydaveYou dont need the series 1K resistors from the led outputs, the current limit is set by the resistor on pin 7, as for extra leds, use a PNP transistor with a 100 ohms base resistor from the ouptuts and feed the leds with 1K series resistors.
Hi DodgydaveYes the transistor BC556B is fine, put the leds and 1k resistors on the Collector to ground, Emitters to V+,
Hi Alec_tWhat is the typical Vf of the LEDs?
Is a supply voltage greater than 9V available to power the LEDs?
Sorry to keep asking but could I just up the power supply to 12v. And when you say 3v drop do you mean that's 3v max down to the lowest working voltagePaddy, if your leds have a volt drop of 3V,then four in series is 12V volt drop, may be better to put 3 in series with 150 to 330 ohms resistor, that would give an led current of 10 to 20mA.
Hi DodgydaveYes you can use a 12v supply , looking at the voltage drops of each colour, the yellow have the lowest and the blue the highest, so four yellow leds will be 8 V, whereas four blue leds will be 14V,
So its better to put 3 leds in series,with resistors of 330 ohms for the yellow, and 100 ohms for the other colours,otherwise the brightness will be different on each colours.
thanks daveHi Paddy, each led has a different voltage drop, so 3 reds will give a voltage drop of approx 9v, whereas 3 yellows are 6v, so 20mA for the reds needs a 300 ohms resistor,and 20mA for the yellow needs a 150 ohms.
Red resistor is 6v/20mA = 300
Yellow resistor is 3v/20mA =150
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