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[SOLVED] how can i operate 12v LED series using 5 volt signal

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Micro Lover

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hi everyone
i m designing a digital clock that's working perfectly on seven-segments(Small one,one), but i want to make it on led, i got one PCB from market,
One segment of each digit is designed in series included 6 LEDs (In each segment). so one segment will glow 12 v, how can i glow seven-segment which will turn-on on 12 volt aprox, and i have a aprox 4.5 voltage signal

untitled.JPG
 

You can use a NPN transistor, feed the 4.5v control signal through a resistor to the base, emitter to the gnd and collector to the cathode of the leds (you will probably need a series resistor too) and the anode of the led to the +12v.
What I describe is a low side switch, it is connected in the ground side of the led and provides the gnd to the led when it is on, the positive supply is always connected to the other side of the led.

An alternative is to use a ULN2003 chip, connect each 12v led thread (6 led segment) in place of the relays
ULN2003_relay.jpg

Alex
 
thnx alexan_e
but the problem is still
can u help me some more????
i m sending u ZIP file.....
plz...
 

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  • New Folder.zip
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If you are using some external buffers, as for example the ULN2003-2004 series and the PNP transistors, you need to change the program in order to revers the logic levels data on the output ports or to connect another inverter gates, so that the outputs remain unchanged (the two inversion functions would "cancel" each other out so that there would be no inversion from input to final output).
 

See some examples for the hardware modification: :grin:
 

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  • Inverter display 1.GIF
    Inverter display 1.GIF
    33.4 KB · Views: 72
  • Inverter display 2.GIF
    Inverter display 2.GIF
    28.7 KB · Views: 67
  • Inverter display 3.GIF
    Inverter display 3.GIF
    33.8 KB · Views: 72
Last edited:

@Micro Lover
Your PNP transistors can't turn off because you have +12v at the emitter and you drive the base with 0 or 5v, in either case the transistor is on.
You can use a NPN as a level translator driving the PNP transistor like the schematics shown above by mister_rf

Alex
 

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