HEF 4047

Monostable/astable multivibrator

Other names for this product: HEF4047, 4047, CD4047,

Courtesy/Thanks to: Philips Semiconductor

Description: The HEF4047B consists of a gatable astable multivibrator
with logic techniques incorporated to permit positive or
negative edge-triggered monostable multivibrator action
with retriggering and external counting options.

Inputs include + TRIGGER, - TRIGGER, ASTABLE,
ASTABLE, RETRIGGER and MR (Master Reset).
Buffered outputs are O, O and OSCILLATOR OUTPUT. In
all modes of operation an external capacitor (Ct) must be
connected between CTC and RCTC, and an external
resistor (Rt) must be connected between RTC and
RCTC (continued on next page).


Astable operation is enabled by a HIGH level on the
ASTABLE input. The period of the square wave at O and
O outputs is a function of the external components
employed. ‘True’ input pulses on the ASTABLE or
‘complement’ pulses on the ASTABLE input, allow the
circuit to be used as a gatable multivibrator. The
OSCILLATOR OUTPUT period will be half of the O output
in the astable mode. However, a 50% duty factor is not
guaranteed at this output.

In the monostable mode, positive edge-triggering is
accomplished by applying a leading-edge pulse to the
+ TRIGGER input and a LOW level to the - TRIGGER
input. For negative edge-triggering, a trailing-edge pulse is
applied to the - TRIGGER and a HIGH level to the
+ TRIGGER. Input pulses may be of any duration relative
to the output pulse. The multivibrator can be retriggered
(on the leading-edge only) by applying a common pulse to
both the RETRIGGER and + TRIGGER inputs. In this
mode the output pulse remains HIGH as long as the input
pulse period is shorter than the period determined by the
RC components.

An external count down option can be implemented by
coupling O to an external ‘N’ counter and resetting the
counter with the trigger pulse. The counter output pulse is
fed back to the ASTABLE input and has a duration equal
to N times the period of the multivibrator. A HIGH level on
the MR input assures no output pulse during an ON-power
condition. This input can also be activated to terminate the
output pulse at any time. In the monostable mode, a HIGH
level or power-ON reset pulse must be applied to MR,
whenever VDD is applied.