The MC34017 Tone Ringer derives its power supply by
rectifying the ac ringing signal. It uses this power to activate
a tone generator and drive a piezo–ceramic transducer. The
tone generation circuitry includes a relaxation oscillator and
frequency dividers which produce high and low frequency
tones as well as the tone warble frequency. The relaxation
oscillator frequency fo is set by resistor R2 and capacitor C2
connected to Pin RC. The oscillator will operate with fo from
1.0 kHz to 10 kHz with the proper choice of external
components (see Figure 1).
The frequency of the tone ringer output signal at RO1 and
RO2 alternates between fo/4 to fo/5. The warble rate at which
the frequency changes is fo/320 for the MC34017–1, fo/640
for the MC34017–2 and fo/160 for the MC34017–3. With a
4.0 kHz oscillator frequency, the MC34017–1 produces
800 Hz and 1000 Hz tones with a 12.5 Hz warble rate. The
MC34017–2 generates 1600 Hz and 2000 Hz tones with a
similar 12.5 Hz warble frequency from an 8.0 kHz oscillator
frequency. The MC34017–3 will produce 400 Hz and 500 Hz
tones with a 12.5 Hz warble rate from a 2.0 kHz oscillator
frequency. The tone ringer output circuit can source or sink
20 mA with an output voltage swing of 37 V peak–to–peak.
Volume control is readily implemented by adding a variable
resistance in series with the piezo transducer.
Input signal detection circuitry activates the tone ringer
output when the ac line voltage exceeds programmed
threshold level. Resistor R3 determines the ringing signal
amplitude at which an output signal at RO1 and RO2 will be
generated. The ac ringing signal is rectified by the internal
diode bridge. The rectified input signal produces a voltage
across R3 which is referenced to RG. The voltage across
resistor R3 is filtered by capacitor C3 at the input to the
Figure 1. Oscillator Period (1/fo) versus
Oscillator R2 C2 Product
150 k ≤ R2 ≤ 300 k
400 pF ≤ C2 ≤ 3000 pF
R2 C2, OSCILLATOR R2 C2 PRODUCT (µs)
When the voltage on capacitor C3 exceeds 1.2 V, the
threshold comparator enables the tone ringer output. Line
transients produced by pulse dialing telephones do not charge
capacitor C3 sufficiently to activate the tone ringer output.
Capacitors C1 and C4 and resistor R1 determine the 10 V,
24 Hz signature test impedance. C4 also provides filtering for
the output stage power supply to prevent droop in the square
wave output signal. Six diodes in series with the rectifying
bridge provide the necessary non–linearity for the 2.5 V,
24 Hz signature tests.
An internal shunt voltage regulator between the RI and RG
terminals provides dc voltage to power the output stage,
oscillator and frequency dividers. The dc voltage at RI is
limited to approximately 22 V in regulation. To protect the IC
from telephone line transients, an SCR is triggered when the
regulator current exceeds 50 mA. The SCR diverts current
from the shunt regulator and reduces the power dissipation
within the IC.
Line Input Resistor
R1 affects the tone ringer input impedance. It
also influences ringing threshold voltage and
limits current from line transients.
(Range: 2.0 to 10 kΩ).
Line Input Capacitor
C1 ac couples the tone ringer to the telephone
line and controls ringer input impedance at low
(Range: 0.4 to 2.0 µF).
(Range: 150 to 300 kΩ).
(Range: 400 to 3000 pF).
Input Current Sense Resistor
R3 controls the ringing threshold voltage.
Increasing R3 decreases the ring–start voltage.
(Range: 5.0 to 18 kΩ).
Ringing Threshold Filter Capacitor
C3 filters the ac voltage across R3 at the input
of the ringing threshold comparator. It also
provides dialer transient rejection.
(Range: 0.5 to 5.0 µF).
Ringer Supply Capacitor
C4 filters supply voltage for the tone generating
circuits. It also provides an ac current path for
the 10 Vrms ringer signature impedance.
(Range: 1.0 to 10 µF).
(1/fo = 1.45 R2 C2 + 10 µs)
MOTOROLA ANALOG IC DEVICE DATA