Linear Power Supply Power Factor and Passive PFC
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- čas přidán 5. 07. 2024
- In this video I discussed some of the misconceptions around the power factors of linear power supplies and demonstrated simple passive PFC technique with simple LC filters.
00:00 Overview
01:07 Linear power supply power factor
03:21 Power factor with no smoothing capacitor
05:23 Passive power factor correction with LC filtering
07:29 Why linear power supplies typically don’t use PFC
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Excellent demonstration of PFC. Thank you very much.
Another good video. Thanks for sharing. It would be interesting to compare the electronic load with some power resistors - I always have a slight doubt about the electronic load when I get unexpected results...
Great explanation, thank you!
Very clear explanation, great stuff sir. Thankyou so much.
Fascinating...cheers.
This is beyond my knowledge base, however, as the ripple rejection efficiency of the linear regulator effects the circuit's overall power factor, I have a point to consider... Most often, designers rate the additional voltage headroom provided to the V Reg at whatever the dropout voltage is... say 1.5V as being a common amount. However, the data sheets for these regulators state that the best ripple rejection is not attained, until 3V of headroom is supplied. Even when this is not directly stated within the text, the test curves are generated at this higher headroom voltage to provide the best ripple rejection, for marketing purposes. Just a thought...
Would it work before the full wave rectifier?
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With a linear PSU the main transformer is already a large 50/60Hz inductor. Is a second inductor really necessary.
In a SMPS the bridge rectifier and large filter caps are before the transformer, which are the main cause of poor power factor in a SMPS. This is where a passive PFC inductor before the rectifier helps to improve the power factor but is not as good as active PFC.
But active PFC is less reliable because the MOSFETs can and do fail short. Ive repaired power supplys before where the PFC MOSFET had failed short. I replaced the FET if i had a suitable replacement in stock or just left it out. The rest of the PSU usually still works.
A transformer is not inductive in operation...!
Why CC and not CR to show the PF correctly????????
Electronic loads as useful as they are, totally suck in response time, ...crap engineering that is pervasive in the industry.
Good point! Didn't occur to me while shooting the video. Just tried it didn't make much difference in the waveform. The electronic load is definitely not designed to handle the voltage waveform without filtering.
That's due to minimal input voltage i assume, which is 2V for this one if i recall correctly from older video about it... Maybe one could build a load working down to fraction of a V and get better results.
@@KerryWongBlog I thing they have large (maybe 2-10uf, and very low ESR) caps across the load terminals for stability???? But since all but they very latest dummy load use SLOW cpu in the control loop, I do not think the AC stability is the issue, but the slow main control loop cycle time???? ...just speculating here. :)