I'm building a PWM regulator for an incandescent bulb. Some of thos was described in a thread called "RMS Approximation of PWM/Square wave". In any case. Since there is no inductor/diode/cepacitor in the output stage I'll be using an RMS converter (LTC1968). For the PWM section I'm using the MIC1557 (SOT-23 size 555 equiv) for a R-C sawtooth to a comparator (TLV7211a) inverting input. I can choose the frequency (probably in the 200-800Hz range). The feedback is sent through the LTC1968 RMS converter to the FB pin (0.8V) of a tiny (SC-70) 5mA voltage regulator (OnSemi NCP102). It's really just a powerful error amplifier. The Output of that is sent to the non-inverting input of the comparator. So if the feedback voltage drops, the NCP102 increases voltage ot the non-inverting input of the TLV7211, thus increasing duty cycle. I've tested this type of layout on breadboard using different components. I got to thinking though. Question: Would it be possible to use a resistor divider between the MIC1557 and comparator to reduce the voltage of the sawtooth and feed it to the NON-inverting comparator input and send the RMS converter output directly to the INVERTING input of the comparator? That way, a falling output voltage would cause a reduction in voltage to the INVERTING input and increase duty cycle? I could reduce the component count. I realize there is no true reference voltage in the system, but since the
1557 is fed from a fixed 5V source, the sawtooth would be a constant 5*1/3 to 5*2/3 V. Thoughts guys?- posted
15 years ago