| Electronics > Beginners |
| 4026 Max Current Output |
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| JonPyro:
Hi all, Looking at the cd4026b datasheet for max output current to drive my led 7seg all I can find is output source minimum of 1mA @ 5v. https://www.google.com/url?sa=t&source=web&rct=j&url=http://www.ti.com/lit/ds/symlink/cd4026b.pdf&ved=2ahUKEwiq2Ya9q5_gAhU1sXEKHRDdBQcQFjAMegQIBxAB&usg=AOvVaw2sxqS5kuCGFQoooETF1JPy Googling it I have found many answers ranging from 1mA to 15mA. Even their example at the bottom of the datasheet shows them driving an led display through transistors! I remember years ago at school we used to use max 15mA per segment as a rule of thumb, however, can anyone tell me how I can find out from the datasheet? I notice they give output wattage of the transistors, could you work this backwards? |
| Benta:
Look at Fig. 6, 7, 8 and 9 in the data sheet. |
| JonPyro:
--- Quote from: Benta on February 03, 2019, 11:53:11 am ---Look at Fig. 6, 7, 8 and 9 in the data sheet. --- End quote --- So if I am reading figure 8 correctly, you should limit the output to 4mA at 5V and about 19/20mA at 10V and 29/30mA at 15V? |
| Ian.M:
Its worse than that. If you look closely at the static electrical characteristics on page 2 and analyse the available data, you'll see that you need to derate those curves by 3% of the current for every 10 deg C temperature rise + the power dissipation heats the die significantly if you push the current too far along those curves from the origin. You certainly wont get a sustained 30mA at 15V Vcc from more than one output without destroying the chip, as that will breach the abs. max. dissipation limits on page 1. |
| JonPyro:
They don't make this easy! Ignoring your 3% for a second. Looking at the first page max output wattage is 100mW......so 30mA @ 15v is 450mW :o |
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