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But I'm not so sure if it's ok to directly connect buck converter and the LDO to a single 20V,5A power supply rail. It depends on the behavior of your supplies and of the rail, but in general that's not a problem. What could be a problem even with just the one converter to 18V is that if that rail is coming from a switching regulator that's does ...

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To minimize the effect of switched current of the buck converter on other parallel things (your LDOs), it might be a good idea to put an EMI filter on the input of the buck. Be sure to design the filter to avoid buck controller instabilities by damping it properly.

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If your sensor uses 50mW on 3V3 that is 15mA. With a linear regulator it will draw 15mA from 24V, about 360mW. This doesn't require a heat sink, so the linear regulator will probably be cheaper than the switcher. However if you keep it powered for 10 years, drawing 360mW, it will still end up using 32 kWh of energy which costs more than a simple and cheap ...

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A switching step down power supply is always the choice if you want to limit the power loss in the voltage level conversion. This can be especially important for battery power sources or if there are regulatory requirements on standby power consumption. It is fairly easy analysis to compute the power loss in a switching regulator versus a linear regulator ...

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In general PFC converters in general have to fulfill two criteria. Firstly, the input power equals the output power (neglecting converter losses), meaning that \begin{align} V_{in,rms} \cdot I_{in,rms} = V_{out} \cdot I_{out} \end{align} Secondly, the shape of the input current has to follow the shape of the input voltage to ensure high power factor and ...

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Probably you are using the LM2576-ADJ version. This version requires an external voltage divider (two resistors), to provide 1.235V on FEEDBACK pin (pin 4). So, if you connected FEEDBACK pin directly to the output, you should expect 1.235V on output - an you can see it in case of input voltage equal 12V ;) The next question is: why there is 3.3V on output ...

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