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Re: How to do the "ramp circuit" in the PWM regula
Use any kind of astable ckt plus a current source; for example use a 555 and design it with large duty cycle astable and charge the capacitor with a current source.
if u need it for SMPS, it is not necessary to have a ramp; ie saw tooth with 50% duty cycle and even periodic exponential waveform is acceptable. this is due to the feedback available in the ckt.
a simle way to obtain a ramp is integrating a DC.
An integrator using an operational amplifier is very good. In order to reset the ramp, a switch is placed in parallel with the capacitor. When the switch is opened the ramp starts; when the switch is closed the output goes to 0 and is ready for the next ramp.
Regards
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