NE556Dual bipolar timer
Two independent clocks. One compact IC.
NE556 combines two independently controlled timer circuits in a 14-pin IC. Each channel has its own trigger, threshold, control, reset, output and discharge contact; only the power rails are shared. External resistors and capacitors set a repeating waveform or a single timed pulse. Our two-clock example makes the difference visible: channel 1 cycles slowly while channel 2 runs about ten times faster. The package switch compares NE556N through-hole PDIP-14 with NE556DR SOIC-14. Select any pin to inspect its function, or adjust the two timing networks below to explore the calculated results.
Outputs and dischargeTiming inputsReset and controlShared supply
NE556NPDIP-14Top view
NE556DRSOIC-14Top view
Click a lead or use the arrow keys. Top view
PIN 1 · Outputs and discharge
Open-collector discharge1DISCH
Function
Discharges the external timing capacitor when this channel is LOW.
How to connect
Connect to the junction of RA and RB.
Electrical note
This is a switching node, not a second push-pull output.
PIN 2 · Timing inputs
Threshold input1THRES
Function
Ends the HIGH interval when the timing node exceeds the upper reference.
How to connect
Join to 1TRIG and the timing capacitor.
Electrical note
Nominal reference: 2/3 VCC with CONT unmodulated.
PIN 3 · Reset and control
Control voltage1CONT
Function
Sets the comparator reference for timer 1.
How to connect
Bypass to ground with 10 nF in the example.
Electrical note
Changing CONT changes both thresholds and the timing equations.
PIN 4 · Reset and control
Active-low reset1RESET
Function
Forces this output LOW and turns on its discharge switch.
How to connect
Tie to VCC for continuous operation.
Electrical note
Do not leave reset floating; it overrides trigger and threshold.
PIN 5 · Outputs and discharge
Push-pull output1OUT
Function
Timer 1 output, independent of the other channel.
How to connect
Connect a high-impedance scope or a current-limited LED.
Electrical note
Output swing depends on load; it is not rail-to-rail.
PIN 6 · Timing inputs
Trigger input1TRIG
Function
Starts the HIGH interval when the input falls below the lower reference.
How to connect
Join to 1THRES in the astable example.
Electrical note
Nominal reference: 1/3 VCC. A sustained LOW trigger can hold the output HIGH.
PIN 7 · Shared supply
GroundGND
Function
Common return for both channels.
How to connect
Connect all local ground symbols to supply return.
PIN 8 · Timing inputs
Trigger input2TRIG
Function
Starts the HIGH interval when the input falls below the lower reference.
How to connect
Join to 2THRES in the astable example.
Electrical note
Nominal reference: 1/3 VCC. A sustained LOW trigger can hold the output HIGH.
PIN 9 · Outputs and discharge
Push-pull output2OUT
Function
Timer 2 output, independent of the other channel.
How to connect
Connect a high-impedance scope or a current-limited LED.
Electrical note
Output swing depends on load; it is not rail-to-rail.
PIN 10 · Reset and control
Active-low reset2RESET
Function
Forces this output LOW and turns on its discharge switch.
How to connect
Tie to VCC for continuous operation.
Electrical note
Do not leave reset floating; it overrides trigger and threshold.
PIN 11 · Reset and control
Control voltage2CONT
Function
Sets the comparator reference for timer 2.
How to connect
Bypass to ground with 10 nF in the example.
Electrical note
Changing CONT changes both thresholds and the timing equations.
PIN 12 · Timing inputs
Threshold input2THRES
Function
Ends the HIGH interval when the timing node exceeds the upper reference.
How to connect
Join to 2TRIG and the timing capacitor.
Electrical note
Nominal reference: 2/3 VCC with CONT unmodulated.
PIN 13 · Outputs and discharge
Open-collector discharge2DISCH
Function
Discharges the external timing capacitor when this channel is LOW.
How to connect
Connect to the junction of RA and RB.
Electrical note
This is a switching node, not a second push-pull output.
PIN 14 · Shared supply
SupplyVCC
Function
Positive supply shared by the two timers.
How to connect
Apply regulated +5 V; place 100 nF directly between pins 14 and 7.
At a glance
Dual bipolar timer
Choose a separate RC network for each timer. Reset can stop either channel while the other continues.
4.5–16 VRecommended supply
2 Separate timing networksIndependent timers
0–70 °C · NE gradeAmbient range
14 PDIP / SOICPhysical contacts
Operating profile
NE556N
Operating conditions
Key parameters and their test conditions
- Supply
- 4.5–16 VConditions / notes: Recommended operating range
- Ambient temperature
- 0 to +70°CConditions / notes: NE556N / NE556DR
- Output loading
- Up to ±200 mA specifiedConditions / notes: Check output drop and package dissipation; not a promise of rail-to-rail swing
- Example supply
- 5 VConditions / notes: Common to both channels
- Local decoupling
- 100 nFConditions / notes: Directly across pins 14 and 7
Package details
Follows the selected physical package
- Manufacturer
- Texas Instruments
- Part number
- NE556N
- Package
- PDIP-14
- Connections
- 14 pins
- Mounting
- Through-hole
- Lead pitch
- 2.54 mm
- Package code
- dip
- Thermal reference
- Board and package dependent; see manufacturer data
Connections by function
Select a pin to open its function, electrical notes and wiring guidance.
Outputs and discharge4 pins
Timing inputs4 pins
Reset and control4 pins
Shared supply2 pins
Outputs and discharge4 pins
Timing inputs4 pins
Reset and control4 pins
Shared supply2 pins
Charge a timing capacitor
With the discharge switch open, each capacitor charges through its RA + RB network. The output remains HIGH until the upper threshold is reached.
Discharge and repeat
The latch then drives the output LOW and connects DISCH to ground. The capacitor discharges through RB until the lower threshold starts another cycle.
Run both channels independently
The two networks share power, not a clock. Using 10 µF for channel 1 and 1 µF for channel 2 with equal resistors gives approximately a ten-to-one frequency ratio. They are not synchronized.
The calculator shows nominal steady-state timing. Capacitor leakage, tolerances, trigger conditions, load and supply noise affect a real circuit.
Two timing networks. Two waveforms.
Adjust each channel and compare its ideal steady-state timing.
Timer 1 OUT · pin 5
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——
Timer 2 OUT · pin 9
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Supply: 5 V. Each graph uses its own time scale. Nominal astable timing, not an electrical simulation. Output amplitudes, tolerances, leakage, startup and loading are not modeled. Both RESET inputs are assumed HIGH; CONT is unmodulated.
Pin reference
Select a pin to explore its function and connection.
14 pins
| Pin | Signal | Type | Function |
|---|---|---|---|
| 1DISCH | Open-collector discharge | Discharges the external timing capacitor when this channel is LOW. | |
| 1THRES | Threshold input | Ends the HIGH interval when the timing node exceeds the upper reference. | |
| 1CONT | Control voltage | Sets the comparator reference for timer 1. | |
| 1RESET | Active-low reset | Forces this output LOW and turns on its discharge switch. | |
| 1OUT | Push-pull output | Timer 1 output, independent of the other channel. | |
| 1TRIG | Trigger input | Starts the HIGH interval when the input falls below the lower reference. | |
| GND | Ground | Common return for both channels. | |
| 2TRIG | Trigger input | Starts the HIGH interval when the input falls below the lower reference. | |
| 2OUT | Push-pull output | Timer 2 output, independent of the other channel. | |
| 2RESET | Active-low reset | Forces this output LOW and turns on its discharge switch. | |
| 2CONT | Control voltage | Sets the comparator reference for timer 2. | |
| 2THRES | Threshold input | Ends the HIGH interval when the timing node exceeds the upper reference. | |
| 2DISCH | Open-collector discharge | Discharges the external timing capacitor when this channel is LOW. | |
| VCC | Supply | Positive supply shared by the two timers. |
No pins match. Try a signal name or choose All pins.
Operating conditions
NE556 grade
Manufacturer specifications 5 parameters
| Parameter | Value | Conditions / notes |
|---|---|---|
| Supply | 4.5–16 V | Recommended operating range |
| Ambient temperature | 0 to +70°C | NE556N / NE556DR |
| Output loading | Up to ±200 mA specified | Check output drop and package dissipation; not a promise of rail-to-rail swing |
| Example supply | 5 V | Common to both channels |
| Local decoupling | 100 nF | Directly across pins 14 and 7 |
No specifications match. Try a parameter name or a unit.
Recommended operation is distinct from absolute stress limits.
Thresholds and output levels
25°C · stated test conditions
Manufacturer specifications 5 parameters
| Parameter | Value | Conditions / notes |
|---|---|---|
| Trigger at 5 V | 1.67 V typical; 1.1–2.2 V limits | Each channel |
| Threshold at 5 V | 3.3 V typical; 2.4–4.2 V limits | Each channel |
| LOW output | 0.1 V typical; 0.25 V maximum | 5 V supply; sinking 5 mA |
| HIGH output | 3.3 V typical; 2.75 V minimum | 5 V supply; sourcing 100 mA |
| Supply current | 6 mA typical; 12 mA maximum | 5 V; outputs LOW; no external load |
No specifications match. Try a parameter name or a unit.
These test points must not be extrapolated to every load or temperature.
Timing equations
Nominal RC relationships
Manufacturer specifications 5 parameters
| Parameter | Value | Conditions / notes |
|---|---|---|
| Astable HIGH | ln(2) × (RA + RB) × C | Capacitor charges through both resistors |
| Astable LOW | ln(2) × RB × C | Capacitor discharges through RB |
| Frequency | 1 / [ln(2) × (RA + 2RB) × C] | Use Ω, F and seconds |
| HIGH duty cycle | (RA + RB) / (RA + 2RB) | Above 50% in the ordinary two-resistor circuit |
| Monostable pulse | Approximately 1.1 × R × C | Trigger must return HIGH before the timing interval ends |
No specifications match. Try a parameter name or a unit.
Ideal ratios assume unmodulated CONT. The initial power-on interval differs from steady-state cycles.
Two-clock circuit
5 V · independent outputs
Manufacturer specifications 8 parameters
| Parameter | Value | Conditions / notes |
|---|---|---|
| RA1 / RA2 | 10 kΩ | VCC to respective DISCH pin |
| RB1 / RB2 | 100 kΩ | DISCH to respective timing node |
| C1 | 10 µF | Timing node 1 to GND; positive terminal to timing node |
| C2 | 1 µF | Timing node 2 to GND; positive terminal to timing node |
| Nominal f1 / f2 | 0.687 Hz / 6.87 Hz | Ideal values; component tolerances omitted |
| HIGH duty cycle | 52.38% | Both channels |
| Control bypass | 10 nF per channel | Pins 3 and 11 to GND |
| Reset | Pins 4 and 10 to +5 V | Neither input floats |
No specifications match. Try a parameter name or a unit.
The illustrated scope is a high-impedance load. Use a series resistor for any LED.
Control behavior
Applied independently to each timer
Manufacturer specifications 5 parameters
| Parameter | Value | Conditions / notes |
|---|---|---|
| RESET LOW | OUT LOW; DISCH conducting | Overrides other inputs |
| TRIG below lower reference | OUT HIGH; DISCH open | When RESET is inactive |
| THRES above upper reference | OUT LOW; DISCH conducting | When trigger is above its reference |
| Both timing inputs between references | Retain latch state | Hysteresis prevents chatter in a clean RC cycle |
| Unused channel | Hold RESET LOW and define its inputs | Do not assume floating pins are harmless |
No specifications match. Try a parameter name or a unit.
Input priority follows RESET, then trigger, then threshold.
Package and pin reference
NE556N · PDIP-14
Manufacturer specifications 5 parameters
| Parameter | Value | Conditions / notes |
|---|---|---|
| Pitch | 2.54 mm | Through-hole |
| Timer 1 | DISCH 1; THRES 2; CONT 3 | RESET 4; OUT 5; TRIG 6 |
| Timer 2 | TRIG 8; OUT 9; RESET 10 | CONT 11; THRES 12; DISCH 13 |
| Shared power | GND 7; VCC 14 | Never reuse the eight-pin NE555 numbering |
| Orientation | Top view | Pin-one mark and notch identify the numbering |
No specifications match. Try a parameter name or a unit.
Match the exact mechanical package before manufacturing a PCB.
Independent pulse generators
Generate two low-frequency timing signals from separate networks.
Manufacturer application guideSequential timers
Use one channel to initiate another with a correctly shaped trigger pulse.
Manufacturer application guidePulse shaping
Configure either timer as a one-shot with a defined trigger and reset path.
Manufacturer application guideTake it into ProTech
Find NE556 in the Components Library to place its schematic symbol and connect its pins.
Reference page · circuit simulation model not yet availableOpen ProTech