Oznog
Active Member
What's a simple, cost-effective way to get 5v power out of 110v, with on-board components? Preferably isolated.
Sure, there are those 110v-5v USB power, isolated transformer "mini-wall-warts"- only a couple of bucks. But that's not an on-board solution, I can't have a second power cord, and can't wire this wart up inside the case.
I didn't see any cheap, tiny transformers on Mouser. There were some 110v-to-5v modules but they were quite expensive- ~$6 IIRC- and weren't even isolated. Whatever components those 5v USB wall supplies use, I can't find them.
A FWB with large cap followed by a large resistor and 5v zener would do it, but the heat is substantial. If the circuit's drawing 50mA, that's 7.5W in the resistor at all times, even when it's "off" (the controller's asleep) and drawing no current. That resistor would be expensive and the plastic case wouldn't even be safe with that much heat sourcing inside it.
In theory you could rip apart the wart, pull the components, and reuse them on the board. But for production that's not desirable at all, it's a problem to source and extract the components and there's no guarantee the device will always contain the same components.
Sure, there are those 110v-5v USB power, isolated transformer "mini-wall-warts"- only a couple of bucks. But that's not an on-board solution, I can't have a second power cord, and can't wire this wart up inside the case.
I didn't see any cheap, tiny transformers on Mouser. There were some 110v-to-5v modules but they were quite expensive- ~$6 IIRC- and weren't even isolated. Whatever components those 5v USB wall supplies use, I can't find them.
A FWB with large cap followed by a large resistor and 5v zener would do it, but the heat is substantial. If the circuit's drawing 50mA, that's 7.5W in the resistor at all times, even when it's "off" (the controller's asleep) and drawing no current. That resistor would be expensive and the plastic case wouldn't even be safe with that much heat sourcing inside it.
In theory you could rip apart the wart, pull the components, and reuse them on the board. But for production that's not desirable at all, it's a problem to source and extract the components and there's no guarantee the device will always contain the same components.