Low power 5V supply using TOPswitch
Hello,
I am using PI Expert software generated design for SMPS of 5.1Volts output at 0.8amp. This power supply is used to operate a relay board with 10 relays. This power supply should work for over 5 years at continuous application (24hours). My peak current consumption is 0.8amp and average current consumption is in the range of 0.3-0.5amps (at 5.1Volts). I have manufactured PCBs and tested this design and it is giving very good result in 1% accuracy load regulation.
My question is that how can I calculate, test and ensure that this power supply design will work in our products for over 5 years of continuous usage.
Also I would appreciate any feedback on the design to make it better
Regards
Devansh
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Thanks Sir for the detailed reply.
1. Derating - I have designed the circuit for 0.8amp of current requirements, however my current consumption is in the range of 0.2 to 0.4 amp. I am using higher rated components than suggested by the PI design software.
2. Surge - For surge I have currently used MOV and also to protect components, I am using the OV protection of the TOP switch (over 400volts). Kindly let me know if there is any better solution for surge protection
3. HALT - I would be really thankful if you can let me know the procedure for this test.
- Electrolytic caps - Yes as suggested in the design software, I am using low ESR capacitors where suggested.
- Optocoulers - Currently I am using PC817B. Would it be better option to higher CTR version like the PC817C. Kindly let me know.
This is going to be my first product range using the TOPswitch and I hope I am able to design correctly so that i can get very good reliability.
Regards
Devansh
Hi Devansh,
HALT is quite complicated, most of the big power supply companies has it as part of their QA or separate reliability department to test and compute the expected life of power supply. It needs methodological measurement and computation. You can read below link or google on HALT so you can study and fully understand.
http://www.tek.com/sites/tek.com/files/media/document/resources/HALT_HASS_WP.pdf
For those that doesn't have the capability to do the HALT test, the rule of thumb is to design your components at 50% derating or below (resistors, capacitors, diodes).
MOV for surge is fine.
Higher CTR is good but the main consideration is your forward current (If) away from saturation but sufficient enough to provide feedback at all condition.
Hi devanshsharma,
Thank you for using Power Integrations' part.
Regarding your question, you have alot of factors to consider. Reliability is big part of our design process to make sure that our products will meet or exceed its expected life. That is why we need to pass all the safety standards and reliability test. Below are my inputs that you needs to consider.
1. Derating: In your case I think you need atleast 50% derating. Meaning your components should operated 50% or below its rated power, voltage or current.
2. Surge: You needs to pass the surge requirement based on your application. This will make sure that your design can handle day to day unwanted line disturbances.
3. HALT: Highly Accelerated Life test is a standard test to predict the expected life of the power supply.
Most of the weakest components of the power supplies are Elyctrolytic Capacitors and Optocouplers.
Elyctrolytic Caps: Use low ESR, high life 5000hrs series.
Optocouplers: Make sure that you have good CTR design to maximize life.
Topswitch FIT rate is 0.4685, (MTBF=2,134,302,000). Failure rate estimated by de-rating the high temperature reliability test data to an application use junction temp of 55°C using activation energy of 0.7eV and was calculated with a 60% confidence level.
I might not covered everything but hopefully it can help you to meet your design requirements.