CD4047B — CMOS Low-Power Monostable / Astable Multivibrator

Overview

The CD4047 (CD4047B / CD4047BE) is a versatile CMOS low-power monostable (one-shot) and astable (free-running) multivibrator IC manufactured by Texas Instruments and onsemi. Available in a 14-pin through-hole DIP-14 and surface-mount SOIC-14 package, it requires only one external resistor ( $R$ ) and one external capacitor ( $C$ ) to set its timing period.

Operating across an ultra-wide voltage range of $3.0\text{V}$ to $18.0\text{V}$ DC with microamp quiescent power consumption, the CD4047 is distinguished by its built-in internal binary toggle flip-flop. In astable mode, this internal divider guarantees an exact, mathematically perfect $50\%$ duty cycle on its complementary outputs ( $Q$ and $\bar{Q}$ ), while providing a doubled-frequency signal at $OSC_{OUT}$ . Because of this feature, the CD4047 is one of the most famous and widely deployed ICs for driving push-pull DC-to-AC power inverters (12V to 220V/110V 50Hz/60Hz inverters), ultrasonic transducers, and precision square-wave clock generators.

Quick reference


Device Type	CMOS Monostable / Astable Multivibrator
Operating Modes	Astable (Free-Running), Monostable (Positive/Negative Edge, Retriggerable)
Package	14-pin DIP (DIP-14 / PDIP-14) / 14-pin SOIC
Supply Voltage Range ( $V_{DD}$ )	$3.0\text{ V}$ to $18.0\text{ V}$ DC ( $20\text{ V}$ absolute max)
Duty Cycle Accuracy	Exact $50.0\%$ Duty Cycle on $Q$ and $\bar{Q}$ outputs
Outputs	$Q$ (Pin 10), $\bar{Q}$ (Pin 11), $OSC_{OUT}$ (Pin 13, $2\times f_Q$ )
Astable Frequency Formula	$f_Q = \frac{1}{4.4 \times R \times C}$ , $f_{OSC} = \frac{1}{2.2 \times R \times C}$
Monostable Pulse Width	$t_{pulse} = 2.48 \times R \times C$
Quiescent Current	$0.02\ \mu\text{A}$ at $5\text{V}$ typ ( $0.05\ \mu\text{A}$ at $10\text{V}$ )

Pinout (DIP-14 Package)

text

                            ┌───┴───┐
                    C-EXT  1│ 1   14│ VDD (+3V to +18V)
                    R-EXT  2│       │13 OSC OUT (2x Frequency)
                RC-COMMON  3│ CD4047│12 RETRIGGER
                 /ASTABLE  4│   B   │11 /Q (Complementary Output)
                  ASTABLE  5│ DIP-14│10 Q  (True Output)
                 -TRIGGER  6│       │9  EXT RESET (Active-High)
                 VSS (0V)  7│       │8  +TRIGGER
                            └───────┘

Pin	Name	Type	Description
1	`C-EXT`	Timing Input	Connect external timing capacitor $C$ between Pin 1 and Pin 3
2	`R-EXT`	Timing Input	Connect external timing resistor $R$ between Pin 2 and Pin 3
3	`RC-COMMON`	Timing Common	Common junction for external $R$ and $C$ components
4	`/ASTABLE`	Digital Input	Active-LOW Astable Enable (Connect to $V_{SS}$ / GND for astable mode)
5	`ASTABLE`	Digital Input	Active-HIGH Astable Enable (Connect to $V_{DD}$ for astable mode)
6	`-TRIGGER`	Digital Input	Negative-edge trigger input (Monostable mode; tie to $V_{DD}$ in astable)
7	`VSS`	Power	Common Ground reference ( $0\text{ V}$ )
8	`+TRIGGER`	Digital Input	Positive-edge trigger input (Monostable mode; tie to GND in astable)
9	`EXT RESET`	Digital Input	External Master Reset (Active HIGH; tie to GND for normal operation)
10	`Q`	Digital Output	Buffered true multivibrator output ( $50\%$ duty cycle)
11	`/Q`	Digital Output	Buffered complementary inverted output ( $50\%$ duty cycle)
12	`RETRIGGER`	Digital Input	Retrigger control input (Monostable mode; tie to GND in astable)
13	`OSC OUT`	Digital Output	Master oscillator output ( $f = 2 \times f_Q$ , non-50% duty cycle)
14	`VDD`	Power	Positive Supply Voltage ( $+3.0\text{ V}$ to $+18.0\text{ V}$ )

Typical Application Circuit: 50Hz / 60Hz Inverter Push-Pull Driver

text

                       +12V DC Supply
                             │
                      ┌──────┴──────────────────────────┐
                      │                                 │
                [Pin 14: VDD]                     [Pin 5: ASTABLE]
                      │                                 │
                [ 100nF Cap ]                     [Pin 6: -TRIGGER]
                      │                                 │
               [Pin 4: /ASTABLE] ──┐                    │
               [Pin 7: VSS] ───────┼────────────────────┤
               [Pin 8: +TRIGGER] ──┤                    │
               [Pin 9: RESET] ─────┼──────────┐         │
               [Pin 12: RETRIGGER] ┘          │         │
                                             GND       +12V
  Timing Network (50Hz on Q & /Q):
    Pin 1 (C-EXT) ────[ C = 100nF (0.1µF) Film ]────┐
                                                     ├──── Pin 3 (RC-COMMON)
    Pin 2 (R-EXT) ────[ R = 47kΩ Resistor ]──────────┘
    
  Complementary MOSFET Gate Drive:
    Pin 10 (Q)  ──────────────────► [Gate of Push-Pull MOSFET 1 (e.g. IRFZ44N)]
    Pin 11 (/Q) ──────────────────► [Gate of Push-Pull MOSFET 2 (e.g. IRFZ44N)]

Calculating Astable Frequency

$f_Q = f_{\bar{Q}} = \frac{1}{4.4 \times R \times C}$ $f_{OSC} = \frac{1}{2.2 \times R \times C}$

For 50 Hz Output: $C = 100\text{ nF} (0.1\ \mu\text{F})$ , $R = \frac{1}{4.4 \times 50 \times 10^{-7}} \approx 45.4\text{ k}\Omega$ (use $39\text{k}\Omega$ in series with a $10\text{k}\Omega$ trim pot).
For 60 Hz Output: $C = 100\text{ nF}$ , $R \approx 37.8\text{ k}\Omega$ ( $33\text{k}\Omega + 10\text{k}\Omega$ trimmer).

Common mistakes

Leaving unused trigger / control inputs floating: CMOS inputs must never float. In astable mode:
- Connect Pins 4, 7, 8, 9, 12 to GND ( $V_{SS}$ )
- Connect Pins 5, 6, 14 to $+V_{DD}$
Using low-quality electrolytic timing capacitors: Electrolytic capacitors suffer from high leakage currents that disrupt the charge/discharge ramp across pins 1–3. Always use polypropylene, Mylar film, or C0G ceramic capacitors for timing component $C$ .

Notes

CD4047 vs NE555: Unlike the 555 timer which requires external flip-flops or diode networks to produce a $50\%$ duty cycle, the CD4047 produces inherently perfect $50\%$ complementary outputs with a single RC network.

Interface	Timing Pins (C-EXT, R-EXT, RC-COMMON), Control Inputs (ASTABLE, -TRIGGER, +TRIGGER, RETRIGGER, RESET), Outputs (Q, Q-BAR, OSC-OUT)
Supply	3–18 V
Package	14-pin DIP (DIP-14 / PDIP-14) / 14-pin SOIC