• SN74LS112N pinout diagram, DIP-16 top view: dual J-K flip-flop with preset and clear, pin 8 GND, pin 16 VCC
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SN74LS112N Logic Gates IC

SN74LS112N Logic Gates IC

₦350.00 NGN
₦350.00 NGN
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What it is

The SN74LS112N has two independent J-K flip-flops in a 16-pin DIP. Each has its own clock, J and K inputs, Q and Q outputs, and active-LOW preset and clear inputs. Outputs change on the falling edge of the clock. The inputs are fully buffered, so the flip-flop never loads the signals driving it.

It has the same logic as the older 74LS76, but with the standard power pinout (VCC pin 16, GND pin 8). That makes it the easiest dual J-K flip-flop to use on a breadboard or PCB.

Function table (each flip-flop)

PRE CLR CLK J K Q Q Mode
L H X X X H L Preset (async set)
H L X X X L H Clear (async reset)
L L X X X H* H* Not allowed (unstable)
H H ↓ L L Q0 Q0 Hold
H H ↓ H L H L Set
H H ↓ L H L H Reset
H H ↓ H H Q0 Q0 Toggle
H H H X X Q0 Q0 No change

↓ = falling (HIGH-to-LOW) clock edge. X = don't care. Q0 = previous state. *Pulling PRE and CLR LOW together forces both outputs HIGH, and the final state is unpredictable when they are released. Avoid it.

Pinout (DIP-16, top view, notch at the top)

Pin Signal Function Pin Signal Function
1 1CLK FF1 clock (falling edge) 16 VCC +5 V supply
2 1K FF1 K input 15 1CLR FF1 clear, active-LOW
3 1J FF1 J input 14 2CLR FF2 clear, active-LOW
4 1PRE FF1 preset, active-LOW 13 2CLK FF2 clock (falling edge)
5 1Q FF1 output 12 2K FF2 K input
6 1Q FF1 inverted output 11 2J FF2 J input
7 2Q FF2 inverted output 10 2PRE FF2 preset, active-LOW
8 GND Ground 9 2Q FF2 output

Specifications

Parameter Value
Logic family 74LS (low-power Schottky TTL)
Function Two independent J-K flip-flops, negative-edge-triggered, with preset and clear
Package DIP-16 (PDIP, through-hole)
Supply voltage (VCC) 4.75 V min / 5 V nom / 5.25 V max
Absolute max supply / input voltage 7 V
Input HIGH threshold (VIH) 2.0 V min
Input LOW threshold (VIL) 0.8 V max
Output HIGH voltage (VOH) 2.7 V min / 3.4 V typ at −0.4 mA
Output LOW voltage (VOL) 0.35 V typ / 0.5 V max at 8 mA
Output current −0.4 mA source (HIGH) / 8 mA sink (LOW)
Clock frequency 0–30 MHz guaranteed (fmax 30 MHz min, 45 MHz typ)
Propagation delay (clock / async input → Q, Q) 15 ns typ / 20 ns max (2 kΩ, 15 pF)
Setup time (J, K before clock ↓) 20 ns (data) · 25 ns (CLR inactive) · 20 ns (PRE inactive)
Hold time (after clock ↓) 0 ns
Minimum pulse width CLK HIGH 20 ns · PRE / CLR LOW 25 ns
Supply current (whole chip) 4 mA typ / 6 mA max
Input current (LOW) J, K: −0.4 mA max · PRE, CLR, CLK: −0.8 mA max
Operating temperature 0 °C to 70 °C

Using flip-flops

  • Tie CLR and PRE HIGH for normal operation. They are active-LOW. If one floats or is pulled LOW, it overrides the clock and the flip-flop looks "stuck". This is the most common reason these chips seem dead.
  • Debounce switches before they reach CLK. A mechanical push-button bounces and produces several clock edges per press, so a toggle circuit appears to skip. Use an RC filter plus a Schmitt trigger (74LS14) or an SR latch built from two 74LS00 gates.
  • Divide-by-2 / toggle: tie J and K HIGH. Q flips on every falling clock edge, so Q runs at half the clock frequency.
  • Ripple counter: with J = K = HIGH, feed flip-flop 1's Q into flip-flop 2's CLK to get a 2-bit binary counter (÷4). Chain more chips for more bits.

Wiring it up

  • 5 V only. 74LS is TTL logic and needs 4.75–5.25 V on VCC. It will not run reliably from 3.3 V.
  • Decouple it. Put a 100 nF ceramic capacitor between VCC and GND, as close to the chip as you can.
  • Don't leave inputs floating. An open TTL input usually reads HIGH, but it picks up noise and gives random glitches. Tie unused inputs to VCC (directly or through 1 kΩ) or to GND.
  • Arduino Uno / Nano / Mega (5 V): connect directly, no level shifting needed.
  • ESP32, Raspberry Pi, STM32 and other 3.3 V boards: a 3.3 V output driving a 74LS input is fine (HIGH threshold is 2.0 V). The other direction is not: a 74LS output can sit around 3.4–3.6 V when HIGH, which is above what 3.3 V-only pins accept. Use a divider (1 kΩ in series, 2 kΩ to GND) or a level shifter, or use the 74HC/74HCT version of the chip instead.
  • Driving LEDs: 74LS outputs sink current (8 mA) much better than they source it (0.4 mA). Wire the LED and a 680 Ω–1 kΩ resistor from +5 V to the output, so the LED lights when the output is LOW.

In the package

1 × SN74LS112N in a 16-pin plastic DIP (through-hole, 2.54 mm pin pitch, 7.62 mm / 0.3" row spacing). It drops straight into a breadboard across the centre channel. For soldered builds, use a DIP socket so the chip can be swapped.

The markings depend on the batch: you may get Texas Instruments (SN74LS…N), Hitachi/Renesas (HD74LS…P) or another second-source maker. They are all the same standard 74LS part: same pinout, same logic, same 5 V ratings.

Which J-K flip-flop do I need?

  • SN74LS73N: clear only, 14 pins, power on pins 4 and 11.
  • SN74LS76N: preset and clear, 16 pins, power on pins 5 and 13 (older part).
  • SN74LS112N (this chip): preset and clear, 16 pins, standard corner power. Recommended for new builds.

Datasheet

Texas Instruments SN74LS112A datasheet (PDF)

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