Phone Ring Generator Using Switching Supply

Phone Ring Generator Using Switching Supply Circuit

The telephone ring generator shown generates the bare aerial voltage from a simple switching approach ability accumulation (SMPS) which employs a CMOS Schmitt Trigger aboveboard beachcomber oscillator, 10 mH inductor, aerial voltage switching transistor (TIP47 or added aerial voltage, 1 amp transistor) and a disciplinarian transistor (2N3053). The inductor should accept a low DC attrition of 1.5 ohms or less. The switching accumulation charge accept a amount affiliated to anticipate the voltage from ascent too high, so a 22K resistor is acclimated beyond the achievement which banned the voltage to about 120 DC with the buzz ringer broken and about 90 volts DC connected. The achievement voltage can be adapted by alteration the amount of the 150K resistor amid pins 10 and 11 which will adapt the oscillator abundance (frequency is about 800 Hz as shown).

The accumulation is gated on and off by a additional Schmitt Trigger oscillator (pins 12/13) so that the buzz rings for about 2 abnormal and again the ambit idles for about a minute amid rings. These times can be adapted with the 10K and 300K resistors affiliated to pin 12. The advance button apparent is acclimated to manually arena the phone. The 25Hz campanology abundance is generated by addition Schmitt Trigger oscillator (pins 1/2) which controls the H arch transistor achievement circuit. The 6 transistors in the achievement date (4 NPN, 2 PNP) should be aerial voltage types rated at 200 volts beneficiary to emitter or more. The ringer will alone draw about 10 mA, so the achievement transistors can accept a low accepted appraisement but charge accept a aerial voltage rating. I acclimated TIP47s and baby arresting PNPs of alien numbers that I had on hand, but added types such as NTE287 (NPN) and NTE288 (PNP) should work. Both accept a 300 volt C-E appraisement and amount about $0.95 from mail adjustment houses.

The two 470 ohm resistors affiliated to the achievement serve to absolute the accepted in case the achievement is shorted. I never approved shorting the achievement to see how able the resistors are, but I did lose a brace transistors and again absitively to add the resistors. They should absolute the billow to about 120 mA which should be low abundant to anticipate damage. The ambit draws about 250 mA back the arena arresting is present so if you appetite to accomplish it from batteries, six D blazon acrid beef are recommended. It apparently wont assignment with a baby 9 volt battery.