buck converter and regulator

Question

First: I want to use DC DC Stop Down Buck Converter, im using this one: - https://www.aliexpress.com/item/10pcs-24V-12V-to-5V-3-3V-3V-DC-DC-1A-Step-Down-Converter-Voltage-Regulator/32671102728.html

Because i want to power arduino, did i need and LM7805 Regulator? Idea is: 24v to 5v to LM7805 and to Atmega328. Is need in this case Regulator or not ?

Second: I want to use DC DC Boost Step Up Converter, im using this one: - https://www.aliexpress.com/item/10PCS-DC-DC-Boost-Step-UP-Converter-1-5-3V-3-7V-4-5V-to-5V/32669914226.html

Because i want to power arduino did i need and LM7805 Regulator ? Idea is: 1.5v/3v/3.7v to 5V to LM7805 and to Atmega328. Is need in this case Regulator or not?

Thanks.

Answer 1

If your buck regulator provides a 5 volt output with sufficient current to power the load then you don't need an additional regulator. Apart from this, for a 7805 to operate correctly it needs at least 7 volts as an input for it to regulate to 5 volts correctly.

Answer 2

A 7805 is a poor choice due to the old term LDO mean low dropout using BJT's , since now it considered a "high" dropout regulator (2-2.5V) compared to using similar regulators with MOSFET switches.

A better choice, considering you also suggested that you need an AC to 24DC supply is to combine all the output requirements into a DC spec and choose a better AC-DC solution that satisfies all your requirements that is readily consumer and commercially available.

Start by defining your AC input and all your DC output peak and avg maximum currents and voltages, not by saying how do my make these arbitrary cheap looking solutions work without knowing the details.