I am looking to replace a classic 50Hz transformer/rectifier circuit with an SMPS.
The input is to be 230VAC (EU) compliant and the output should be 5V/0.2A minimum while 5V/0.5A is a nice to have. An external adapter is not accepted (the apparatus also has a 230VAC output for pump control).
The cost of the current circuit is less than 2€ (50Hz transformer (1.05€), rectifier, regulator).
I've started by looking in to the lowest cost SMPS controller to find that the total BOM is quickly exceeding the origincal circuit's cost (100kHz transformer 1.1€, controller 0.2€, rectifier, optocoupler).
So the bigger transformer costs less than the smaller 100kHz transformer.
Should I be looking for an SMPS controller with higher switching frequency (does that exists) to get a smaller (cheaper) transformer or is it currently hopeless to design an SMPS that is cheaper that the classic 50Hz transformer centered design?
What is the best approach. Example: find the transformer first and then the controller?
Where's the state of the art of Isolated AC/DC SMPS at today ?
Edits:
- looking at pricings for volumes of 2k to 10k/annum.
- The current power solution parts cost $2.5 (50Hz 220V/1.5VA transformer, bridge, caps and LDO).
- Must I conclude that the best AC/DC SMPS solutions are using around 100kHz, 15x15x15mm transformers, and that smaller (/cheaper) solutions using 1MHz for instance, a smaller transformer do not exist/are not available?
My conclusion after consulting several sources:
– For a custom design the cost of an isolated SMPS is higher than simply rectifying and regulating the transformer output.
Thanks to all contributers for your feedbacks!
Best Answer
You won't be able to make this low qty/yr cheaper than buying direct.
The cost of failure exceeds the savings unless you have done this before. But choosing a transformer 1st tells me otherwise. You always start with detailed specs.
You still have to select many sources and perform DVT to their specs and your requirements with accelerated stress tests. This is probably what you omitted last time.
You cannot expect $0.1/W prices in a 2.5W supply.
You ought to budget 1 month of work doing Design Verification Tests (DVT) with at least 10 units from each supplier.
This should include a teardown reverse-engineering analysis. If you know how to design, then do this. This is essential for high volume users who rely on high quality from the cheapest sources.
Best quality comes from Japanese parent companies like TDK, OKI, etc.
This looks like the best CUI model distributed by DK. $4.43 @ 540 = qty. They do not make them but are custom made for them under their US brand.