CD4017

The CD4017B is a five-stage Johnson decade counter from the CD4000B CMOS family, supplied in a 16-pin package with ten decoded active-high outputs Q0 to Q9, an active-low carry output Q5-9, two clock inputs and an overriding asynchronous master reset. Because a Johnson counter uses five flip-flops to produce ten decoded states, only one output is ever high at a time and the decoded outputs are spike-free — a decisive advantage over ripple counters when the outputs drive thyristors, relays or LED strings directly. Internal circuitry also provides automatic code correction: after any illegal state the counter returns to a valid counting sequence within eleven clock pulses.

The part is fully static, so the clock can be stopped indefinitely or run from a few hertz up to several megahertz depending on supply. TI supplies CD4017B with 5 V, 10 V and 15 V parametric ratings across a recommended supply range of 3 V to 15 V, and specifies operation from −55 °C to +125 °C for the standard catalog part. Output drive follows the classic CD4000B curve: about 0.5 mA minimum sink at VDD = 5 V, 1.3 mA at 10 V and 3.4 mA at 15 V, so outputs can drive a logic input, an LED with a series resistor or a small MOSFET gate, but not a relay coil directly. Static supply current is in the microamp range, and the clock inputs have Schmitt-trigger action that tolerates very slow rise and fall times.

Designers use the CD4017 in three recurring patterns. First, as a divide-by-N counter: feeding output Qn back to the master reset truncates the count, giving divide-by-2 through divide-by-10 from a single chip. Second, as a sequencer: each decoded output enables one step of a process, an LED chase, a stepper phase pattern or a relay bank. Third, as a 1-of-10 decoder, where four or fewer address-driven inputs select one of ten loads; the Q5-9 carry output allows cascading several devices for longer chains. Dual clock inputs let one edge be used for counting while the other gates the counter, and the carry output stays high during states 0 to 4 so it can ripple-clock the next stage.

Sourcing is straightforward. TI's CD4017BE (PDIP-16, 25 per tube), CD4017BM96 (SOIC-16, 2,500 per reel) and CD4017BPWR (TSSOP-16, 2,000 per reel) are all active production parts, and pin-compatible second sources include Nexperia's HEF4017BT, onsemi's MC14017B and Toshiba's TC4017BP. Note that HEF4017B parts are specified from −40 °C to +125 °C with a recommended 3 V to 15 V supply and a lower absolute maximum, so check the vendor's limiting values before applying 18 V rails. MOQ is 1 tube or 1 reel with 1-2 day dispatch from Shenzhen stock; the part is cheap enough that counterfeit risk is modest, but kit-market lots are sometimes remarked CD4022 or CD4017 clones with weaker output drive — measure sink current at your operating supply if the count sequence is driving loads directly.