I bought some 7 segment decoders specifically the CD4543B and the datasheet https://www.ti.com/lit/ds/symlink/cd4543b.pdf mentions "Direct LED Driving Capability"

Does that mean I do not have to use current limiting resistors for each segment? (excluding the dp segment, of course)

I tried adding a 220ohm resistor for one of the segments but I couldn't see a noticeable brightness difference, and none of the segments has burnt out, yet.

I'm using common anode 7 segment displays if it makes a difference

  • \$\begingroup\$ What DC supply voltage do you use? The LEDS might survive having no series resistors, but the chip might overheat (especially with large VDD). \$\endgroup\$ – glen_geek Aug 6 '19 at 23:48
  • \$\begingroup\$ I'm using 5v, I didnt notice the chip warming up though \$\endgroup\$ – Slipstream Aug 6 '19 at 23:50

If you look at page 3, there is no resistor to be seen.

So I guess you are lucky no LED has burnt out yet.

However, you can try with a digital (or analog) multimeter, to measure the current (Amperes). A typical 3 mm LED should not get more than 20 mA (and 40 mA is absolute maximum). General rule is always to stay under 20 mA (while using continuous current).

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    \$\begingroup\$ Thanks, I'll measure the current and have a look \$\endgroup\$ – Slipstream Aug 6 '19 at 23:30

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