Calculating efficiency

Posted by: tofu on 07/21/2015

Hi,

I have a question regarding basics of power supply. How do you calculate power efficiency? I know that the equation is "Efficiency = Pout/Pin". But is Pinfor real power (W) or appearant power (VA)?

I read some application notes and design ideas (for switching mode power supply with Tiny Switch family) found on this website. They all seem to have efficiency better that 70%. I followed and tested the design but I could only get efficiency of 40% (calculated with appearant power). I thought about putting power factor correction on my circuit, but the desins found on this website seems to achieve 80% without the correction..

Since most of the powers are reactive on my circuit, none of the components are getting too hot. But does having big reactive power cause issue in long run?

Sorry for asking many questions.

Thank you for your help

Comments

Thanks for Posting your question into forum . Pin is equal to Voltage*Current*Power factor . How did you design your power supply? What are your output power specifications. Normally all our DER's in the Web are Tested designs? Please download our PI Expert software and Validate your design.

Thanks,

PI-KSAN

Thank you for your reply.

I will try the software and validate the design.

My required specification is power efficiency of 80%, so the design meets the specification if Pin is calculated with power factor.

I am curious, does reactive power cause any issue in the long run? It does not cause any components to heat up, but the power is deliver (and maybe stored?) to the system..

Thank you!

Generally for Power output less than 60 W doesn't need front PFC . For power supply designs above 60W output require front end PFC , What's your power output Specifications?

Regards,

PI-KSAN

Hi,

I have designed a power supply with the IC LNK305 and the measurements tests has showed the same results for full load condition.

The output power is maximum of 470mW, but the input is 1,2W for full load condition. That means the efficiency is aproximatly 40%, and as KSAN said, it doesn't require PFC.

When it's about output of 80mW, the input consumption is 450mW, therefore the efficiency is 18% which is very low.

Since I've followed the reference design, I don't know what else I can do to improve efficiency.

Could please anyone help me with this situation?

Thanks!

How did you design your Power Supply, you said you followed the reference design , whats the reference design number , we generally don't have reference designs with low efficiencies. Is your transformer is Optimised, how did you design your transformer?