telephone sine wave ringer circuit

[bala karthik]

hi
i am in need of generate 75 Vrms 25hz sine wave as ringer for my pbx system.

now my design inputs are follows:-

+5V
+13.8V
+33V
-120V

*6vrms 25Hz sinewave
or
*16Vrms 25Hz sinewave

with the help of my earlier design i gave my reference sine wave(16v by w.b osc) to the push pull amplifier whose supply voltages are +5V and -120V. unfortunately i got only 12V sine wave at the output. could any one help me to design a push pull amplifier to get 75Vrms sine wave.

my design has some limitation so dont want any suggestion to use sinewave generator ics pls
allmy need is to get design formula for the push pull amplifier to get 75Vrms sine wave.
thank you

 

[betwixt]

A push-pull amplifier, even in bridge configuration would not generate 75V unless you used the -120V supply.

Suggestion: Use a standard small mains transformer in reverse. For example, use a 115/12V transformer and drive its 15V side from an amplifier running from the 13.8V supply. To get 75V out you only need to drive it about 8V so it should be easy to produce from a small amplifier. The transformer only needs to be rated at say 10VA so it would be very small. This method also has the advantage that the ringer voltage is isolated from the PSU so it is easier to interface.

I used this method in telecoms test equipment for many years.

Brian.

 

[bala karthik]

great idea.......... but my design has some restrictions. my pbx system should work in battery backup(12v 7AH). in mypower supply using SMPS transformer 230VAC is converted into 13.8V 2A to charge the battery . there it self +5v regulated and +33V & -120V generated using another smps transforme (pot core) so the design wont go for another transformer. any alternate idea ...? can any one guide me to design a puh pull amplifier to generate 75V sine wave....?

 

[crutschow]

If the 75Vrms sinewave needs to drive a grounded load (load common with the power supply common) then you need a transformer since 75Vrms is 210Vpp.