stardustsailor
Well-Known Member
No matter if Linear or Switching .I hate to disagree with you but I have designed and built linear power supplies and even rewound transformers fro old microwave ovens and linear power supplies are not efficient. they are designed to produce a clean stable output. PWM voltage or current regulation is much more efficient. just compare the size of the heatsink on both types of power supplies to see how much heat they are designed to dissipate.constant current would be better because the forward drop decreases as the temperature goes up and with constant voltage well regulated supplies this can lead to thermal runaway that could destroy the diode. constant current supplies track this voltage drop so total input power declines as temperature rises. providing some protection for the diode.
Constant Voltage Output Power Supplies ,are not ideal for driving leds.
Neither PWM voltage is ideal .
Leds should be driven(powered) with a Constant Current regulation ,as their Vf changes dramatically depending on diode's junction temperature .
So for example if at Tj =25C (say ambient/room temp) a led driven at 1000mA ,has a Vf of 30 V ..
If the junction temperature rises to 85C ,for the same amount of current to pass through ,the diode now has a Vf of
22 V ...
If a CV power supply is used ,the power supply will continue to apply a 30 V voltage to the led ...
The current passing through the diode will be way more than 1000mA ..
The led will overheat ,which will lead to even lower Vf ,thus higher current passing .
The led will soon get fried ....
If a CC power supply was used instead ,the power supply will 'sense' the drop of led's Vf
(as it tracks changes at circuit 's overall "resistance' ) and lower the output voltage to 22V ,
so tghat 1000mA will continue to pass through the led ...
The led will soon stabilise to a stable operating state,electricall-wise ..
As for the type of voltage regulation used for CC led drivers ,is almost always the switching type ..
Which is much more efficient (thus runs cooler,needs smaller heatsinks/transformers ) and compact sized ..
But it has a 'filthy ' output ,full of ripple 'noise' ..
And contaminates with noise the mains AC ..
SDS's advice : Use an EMI filter at the AC inlet of Switching power supplies .
It somewhat 'cleans' lots of ripple noise at their output ..
And reduce the contamination to the AC mains .
http://www.schaffnerusa.com/en/technical-library/emc-emi-filters.html
http://www.schaffner.com/en/products/emcemi.html