#### Icanmakeit67

Joined Sep 23, 2018
131
I was playing around with the IC CD4026 and using a CC 7 segment display. I’m wondering how to make my own 7SD using 4 LEDs per segment. Would parallel or series be best for the sets of 4 LEDs? Would I need to use a transistor for each segment? I would appreciate opinions/design help.
Thank You

#### Jerry-Hat-Trick

Joined Aug 31, 2022
579
You could arrange for each segment to be four LEDs in series with one resistor to limit the current or four in parallel with each LED needing its own series resistor. Obviously, 4 in series is the simplest construction but you’ll need a higher supply voltage. From the data sheet the supply voltage can be up to 15 volt and 3mA should be sufficient current for high brightness LEDs.

Red LEDs typically have a voltage drop of 1.8V so four in series will drop around 7.2V. With a 10V supply a 1K series resistor should limit the current to around 2.8mA

If you only have a supply voltage lower than the drop across four LEDs then you need to put the four LEDs in parallel, each with their own series resistor and to have around 3mA through each LED you will need a transistor for each segment

#### MisterBill2

Joined Jan 23, 2018
19,006
OR, for 5 volt operation you can use two parallel sets of 2 LEDs in series which will draw less current than 4 in parallel.

#### dl324

Joined Mar 30, 2015
17,008
Would parallel or series be best for the sets of 4 LEDs?
In your LED fade post, you said you always use a 9V power source.

If the forward voltage of the LEDs are low enough at a couple mA, you can put all 4 in series with a current limiting resistor.
Would I need to use a transistor for each segment?
Only if you want more current than CD4026 can source.