Output not regulating
Hi
I have used PIExpert to design a power supply using LNK626. Circuit Image attached.
The output of the system is designed to be 4V however the system when unloaded reaches till 20V starting from 4V
When loaded with 10 ohms load, the system output is only 1V.
We are not using the exact resistors mentioned but 6.11k and 11.6k with a ratio very close to the design value.
But that does not explain the huge change in output from 1V to 20V. Please assist
Comments
Thanks for getting back.
The system.is designed to give a maximum of 1.2A at 4V
At 10 ohms load. The expected current was only 50% loading
The transformer was manufactured locally and we had specified the output from PIExpert to our manufacturer.
In order to be sure of its construction we are checking the design again. Can you specify some tests we can do to confirm the transformer is fine.
Regards
Hello pk_rulz
I think you may need a pre-load here to maintain the no load output regulation. it is stated in page 8 of the application note of LNK-CV. below is the link:
https://ac-dc.power.com/sites/default/files/product-docs/an45.pdf
For designs where output voltage regulation must be maintained at zero load, start with a resistor value that represents a load of approximately 25 mA at the nomimal output voltage. For example, for a 5 V output use a pre-load resistor value of 2 kW.
For designs where the output voltage can rise under no-load conditions, select the pre-load resistor value such that the output voltage is within the maximum output voltage specification. Limit the maximum voltage rise at no-load to <50% of the normal output voltage to minimize increases in input power due to increases in the primary clamp and bias winding dissipation.
Since a pre-load resistor also increases the no-load losses, where the specification allows, adjust the no-load voltage to trade-off lower no-load input power with high no-load output voltage as needed.
Best Regards
Hi sir,
I would like to design four mulitple Dc ouput auxiliary. I am using PIExpert Suite 8.6. Accoring to design parameters i.e. universal input and four isolated output as
1. 30v, 0.05A
2. 30v, 0.05A
3. 12v, 0.35A
4. 10v, 0.05A
Total peak power is : 7.7W
I am facing with warning :Reduce VOR, or design with smaller device. I not able to undestand what is the meaning of smaller device. Attached circuit diagram for your frerence. please help me, first time I am designing SMPS for multiple output. Very new in power supply design.
| Attachment | Size |
|---|---|
| LinkSwitch-CV_PIDesign26716.uds (289.5 KB) | 289.5 KB |
Hi Kapila,
Thank you for choosing Power Integrations.
LinkswitchCV is a family of devices consisting of different part numbers corresponding to your required output power and application. RIght now you are using a LNK625PG, smaller device means trying out a LNK624PG. For your case however, you are correct in choosing LNK625PG for your 7.7W output based on the datasheet output power table. A second option is to reduce VOR. Reducing VOR will result in a longer output diode conduction time.
You can try out the different suggestions of the PIexpert design tool until you come up with a design which will work to meet your specifications.
Some comments based on your PIexpert file.
1. Try to slightly increase your total input capacitor.
2. Your transformer may saturate especially at high ambient temperature. Try redesigning the transformer with lower inductance or higher KP.
Hope this helps.
Hello pk_rulz,
Thank you very much for using PI product.
I have a few question about the design before we dig in.
How much is your output power?
did you use the transformer PIExpert suggested, can you share the transformer construction if possible
Best Regards