Hello,
I was looking for efficient way to power an esp32 board with mains voltage (220V) and found a link .
the site also shows a circuit diagram as given below:
So I want to know what equivalent re-settable fuse can be used instead of 72°C thermal fuse.
or if anyone knows a better way to power then please suggest.
I guess the thermal fuse is in physical contact with the housing of that HLK-PM03 buck converter module and is to break the circuit if the module begins to overheat. If it does overheat for any reason then the module cannot anyway be used any more. So, in this instance, a non-resettable fuse is a good choice.
You can't use a standard wall adapter, a.k.a. phone charger?
The ESP32 will destroy itself before those fuses blow. What's the purpose?
The ESP32 has an on board Vreg just supply it with 5V.
I wanted an alternative that when it blows I don't have to replace it.
I am an infant when it comes to electrical circuitry so was hoping to get a solution here.
I want to test it in an industrial environment and fetching data using MQTT & Node-RED.
See reply #2. Resetting after a catastrophic failure is a terrible idea. By catastrophic, I mean a failure that likely causes permanent damage to the device.
So HLK-PM03 Converter will also allow high voltage and will ultimately fry my ESP board and thermal fuse is the best option here. 
What makes you think that?
I work with industrial control units, they have a fuse and an MOV for protection.
I think you are over thinking the situation.
If this is your project;
Can you show us under side of the PCB, to see how you have used the PCB to isolate mains into the converter from the DC output.
Have you removed the solder pads between input and output?
You should also fit an LED to indicate that the 3V3 supply working.
Tom... 
PS. Those Hi-Link units are very reliable and the load that you will be presenting to it will be much lower than the 3W it can handle.
I haven't started building it yet, wanted to understand circuity before blowing up my ESP board. Want to use it as an Iot device on a machine in an industrial environment. Hence, I want it to be robust as it can get before trying it out.
Below is a diagram on how I will be using inputs, by using opto-couplers to isolate the board. And same I want when supplying power.
Hi,
Is there a reason for trimpots on the inputs to what appear to be OptoIsolators?
It looks like the output of the opto will pull the ESP32 input HIGH when active, but you have no pulldown resistor to pull the input down to gnd when the opto is not active.
It might be better if you drew a schematic.
Hand drawn and photographed is perfectly acceptable.
Please include ALL hardware, component names and pin labels.
Can I suggest you use some protoboards and a small 5V supply, or if all your load will be are those inputs, 5V from the USB programming cable.
Forget the mains power and PCB for a while.
What is the application of your project?
Thanks.. Tom..
You can't "roll your own" power supply in an industrial situation. You MUST use galvanically isolated APPROVED power supplies.
This impacts you legally, technically, and voids your fire insurance if not done properly.
BUY an approved 5v supply and be done with it. Love those UL, CSA and EU worldwide, any voltage/frequency, medical grade power supplies!
Its just to cope with operating range of PC817 while using a proximity sensor (24V). I can replace it with a resistor.
Wanted it in compact enclosure. So was avoiding any external power source and preferred it on a single pcb.
what if I use this (link)
If it isn't INTERNATIONALLY RECOGNIZED don't use it.
update: Says its UL & CE approved. Go for it. Be sure to use ALL UL/CE approved components for anything NEAR the mains. Also, creep distances and hipot need to be observed/tested. Keep the approval docs as part of your engineering support package.
FYI: UL approved power supplies seldom fail on their own and essentially NEVER fail in a hazardous configuration.
The LESS you add, the better off you are. If you need input (or output) protection, SPECIFY it, don't build it. Power (mains) is one of many aspects of design where its more cost effective, and safer legally, to buy, rather than build. Let the PS vendor bear the costs of approvals and the product liabilities.
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