The "error" signal can be applied directly to pin 9 or if you want to use the additional opamp to pin 2. This is how voltage across the Ct capacitor (pin 5) and OSC output (pin 4) looks like in working circuit.Īnd here you have the voltage across Ct capacitor and two outputs. This sawtooth wave swings between 0.9V and 3.2V. And you can set the oscillator frequency by choosing corresponding values for RT and Ct capacitor.Īnd the output waveform from the oscillator is "send" to PWM comparator. SG3525 has the internal sawtooth oscillator. Otherwise, the output of the comparator is low. Notice that when the value of the input "error" signal is greater than that of the sawtooth wave, the output of the comparator is high. This diagram explains everything you need to know.Īs you can see we have a comparator and two signals at the input.Īt noninverting we apply the "error" voltage and at the inverting input, we apply sawtooth waveform from the internal/external oscillator.Īnd by changing the voltage at noninverting input we can change the duration of the output pulse. It may be used in conjunction with pin 1 to provide feedback compensation.įirst, you need to ask yourself a question know how analog PWM work. What kind of "feedback" are we talking about? Why can't I just connect input voltage, define the frequency and dead time using the capacitor and resistor as shown in the diagram, and use the output of the IC? I don't understand what this is used for, or if it is even necessary to have a functioning circuit. If you are wondering what that is, you can think of it as a comparator that controls the increase or decrease of the duty cycle for the “feedback” that you associate with Pulse Width Modulation (PWM). Pins 1 (Inverting Input) and 2 (Non Inverting Input) are the inputs to the on-board error amplifier. This is for instance a site with explanations: Įverything is clear except for what pins 1 and 2 exactly do. I want to build a PWM circuit and it seems the SG3525 is a good candidate for the job, however I don't completely understand all pins and I can't find any comprehensible info (for my skill level) on the internet.
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