Non Isolated AC/DC Power Supply Design (4W, 5V, 800mA). LNK-30X not possible?
Hi
I have used LNK-304 in the past to design 5V 100mA non isolated AC-DC power supply by referencing through datasheet & application notes. We now have a requirement for a power supply with the following specifications :
Design : Must be Non Isolated
Vin : AC 220V (Preferred design for Vin 90-265)
Vout : 5V
Iout : approx 700mA
so,
Pout : approx 4W
Topology : Buck (any other possibilities?)
Size : Compact
My understanding is that LNK-30X cannot provide output currents above 360mA?
So, I am looking for some help on which power chip/design to follow for these requirements.
Any help is greatly appreciated.
Thanks & Regards
Shoaib
Comments
But we need transformerless design due to size/cost contraints as this product is potentially going to be higher in quantities. Can any other switch be used for that. I have not spotted any reference design or application note for any switch other than LNK30X.
Thanks
Power Integrations does not have any reference designs for your output current level for a transformerless power supply. The problem with the LNK306 is the peak current is not high enough for a 700 mA load. You would need a device with 1 amp or greater peak drain current rating. Topswitch can meet that requirement, however the feedback current on the control pin needs to be 6 to 8 mA. This makes the design a bit more difficult.
Z. Cochrane
Thank you very much for the support. So, LNK30X can definitely be not used and TOPSwitch is very difficult to achieve? So, does that mean we can't have a non isolated buck solution with Power Integrations products? What level of support can we get from Power Integrations as the product is potentially going to be 100,000 per annum.
Thanks
Our TOPSwitch and TinySwitch families may also be used in a non isolated buck configurations.
I've attached a couple of (old) examples of schematics. One used TinySwitch-II but TinySwitch-III would also work. The same is true for the TOP223 example, here TOPSwitch-JX could be used.
For the volumes you mention I would encourage you to contact your local sales office for direct support.
Cheers PI-Chekov
Hi
Thank you very much for the reply. Its been helpful. I have built & now testing a Buck Converter based on TOP224 using some old refernce design. I have attached my circuit diagram and have tried to explain the problem below.
Attached Files
--------------
1- BickConv.pdf is the design reference document
2- PowerSupplyCct.jpg is the circuit diagram of our design cicuit
3- PrototypeBuilt.jpg is the actual prototype build of our design
Expectations
------------
I am expecting to get output of approx 5.8V @ 0.8mA (max). 5.8V is what I understand is the minimum output from TOP224 in Buck topology? (Ref BuckConv.pdf page 2 line 5)
Test Obervations
------------------
1- Test load of 20 Ohms.
Vout = 5.4V
=> Iout = 270mA
Vout ripple = 100mV
Inductor giving very low audible noise
2- Test load of 10 Ohms
Vout = 5.0V
=> Iout = 500mA
Vout ripple = 250mV
Inductor giving considerable audible noise
Problems & Questions
--------------------
1- Should not Vout be 5.8V?
2- With the chosen components in the design, is the circuit not able to provide 800mA of Iout?
3- Why does Vout drop with increased load? What is limiting factor here?
4- Why does Vout ripple increase with increased load? What is limiting factor here?
5- In what ways can the circuit be improved? Is it going to be reliable for 10 years?
6- How much heat is expected to be generated by this circuit? Any special care on that?
7- Are the design fundamentals right for what we are trying to acheive?
Looking forward to a details response.
Thank you very much for your support.
Any further guidance will be highly appreciated.
Thanks
You can increase the output current if you use a non-isolated flyback of tapped buck topology. However, cost of using a transformer in a non-isolated design may not be cost effective.
Z. Cochrane