# How do i calculate the timing of an oscillator

i am designing a modified square wave inverter. i am using SG3524 as my pulse width modulator. i desired to have 25% duty cycle... i know my period T is the inverse of my frequency which is 50Hz so my period is 20ms. i discovered that for me to get a complete output waveform, the switching process will go through four stages in which i will share my period in 4 making 5ms per each stage. My challenge is how to get my parameters right for the pulse width modulator to give me the desired result in terms getting the values for the timing i.e the formula to apply to get the ON time which is 5ms. here is the diagram of the modulator. how do i calculate for pin 6 and pin 7 which my RT and CT respectively.

• A circuit diagram would help, not a pin-out picture of the chip. – Andy aka Aug 30 '13 at 11:46
• That's not a circuit diagram - that's the internal workings of the chip. Surely you don't expect someone to design a circuit around a chip of your choice without you doing any work. So far, chip selection seems to be the only work you've done and I would say that your choice of chip versus your question title and content is not that good. – Andy aka Aug 30 '13 at 12:56
• Does the SG3524 not have a single-ended mode? That will make things a bit more interesting... – Ignacio Vazquez-Abrams Aug 30 '13 at 13:22
• 1.what is the formula to use when you are setting ON and OFF time when using an oscillator in an inverter circuit? 2. what is the relationship of this with the choice of RT and CT?..thats all i needed to know. – Matt Aug 30 '13 at 13:42

f = 1.3 / Rt*Ct