With the gradual development of LED lighting , more and more customers will get the phone in front of the habit of shooting LED lamps , by observing the presence or absence of strobe lighting and determine whether the harm to the human eye . This approach is not entirely correct.
The traditional fluorescent directly for AC 50Hz , its strobe is 100Hz, when taken with a digital camera because the sampling frequency is different, there will be water ripples . The LED lighting is a DC power supply , the light emitted by the light source which will also be in the form of direct current ( DC superimposed on the basis of said minor fluctuations or pulsations ) , from a physical perspective, the luminous indeed much lower volatility the degree of fluctuation in the light source of alternating current job . However , the input AC power supply in the form of still difficult to completely avoid AC ripple through the LED light sources. So , when there will be a digital camera with led street lighting Manufacturer flicker of existence .
There are camera flashes can conclude that the human eye will hurt it? Fact, " the frequency of the human eye is sensitive to light of volatility in the low frequency range ," such as the frequency of ambulance warning light is about 8-10 Hz , most likely to make eye discomfort , which led to the alert. These frequencies are far below the normal range of the optical frequency of the AC power source to work , so " there does not exist a normal eye when the light source is not a comfortable situation to work under the current frequency of civilian power ." Currently a wide range of sources around the world are using the optical frequency 50-60 Hz ( including LED displays , LED TV ) , so that the LED lamps output ripple current 100Hz can affect the human eye is more imprecise comfort of this statement .
Vision can feel the strobe mainly by two factors :
1, the output ripple frequency is low
Individuals under special conditions ( for example : region from matte suddenly into light region ) strobe will be felt around 100Hz , old movie frame rate of 24fps, but if the illumination flicker frequency is about 60Hz, all no law to endure , computer monitors and televisions out of the old standard frame rate , it is easy to understand. 2, the output ripple of the output voltage or current 100Hz ripple , when the ripple voltage is less than 5% , can not feel flicker . Then the ripple current may be smaller than 5% , to achieve a bit difficult.
Phone or video camera frame rate is generally around 30 , high-speed motion camera can reach 400fps. Shooting strobe lights, strobe frequency if the device can not exceed the set shooting frame rate four times on the device will be taken even see the lights flash has serious shake -hui , the results taken as well. So, shoot the old CRT monitor display , often see a bar move up.
Lower frequency strobe , although we can not be felt immediately , but long-term in this light, people get tired easily , prone to myopia and other eye diseases.
Purely in terms of the current LED power supply requirements are satisfied no flicker can be done . Roughly as follows:
1 . Increase the output of electrolytic capacitors
(2) using passive PFC valley-fill program
3 using two programs (AC / DC, DC / DC)
The first plan " to increase the output of electrolytic capacitors " , this program can be used theoretically AC ripple electrolytic capacitors absorb some , but the actual experience tells us that when the ripple control within a certain range of the future ( 10% ) , difficult to further reduce , regardless of the cost unless Cadogan electrolytic capacitors , eliminating not fundamentally .
The second way " using passive PFC valley-fill program," This program is the most mainstream kind of approach. Non-isolated solutions commonly Shanghai Shanghai Jing Feng Ming or the duty cycle of the source program . Isolation scheme can be used ChipLink or IWATT ( the earliest programs , has basically been eliminated ) . Circuit works as follows . Using two large capacitors and three diodes for power factor correction , because in the back of the rectifier bridge has a large electrolytic capacitor , so the AC ripple absorption, the current through the inductor or transformer to the secondary part of DC .
Transformer
However, valley-fill program there are some problems, first non-isolated valley type programs exist uncontrolled output load voltage , lamp beads likely to cause damage to fill . Secondly , you can not make 90-265V full voltage input , fill half of the valley valley only circuit output voltage electrolytic filter circuit valley , the valley-fill after the rectifier rectifier output voltage lower than the average rectified output voltage of a lot, there are may use the valley-fill in the low voltage input is insufficient load . Moreover, both isolated and non -isolated valley-fill program , harmonic test simply can not pass. Power factor can not be completely up to 0.9 . Therefore, such led street lighting Manufacturer can not fully meet UL, CE certification standards. Annex pages of test data .
The third way is to adopt a two-stage program in the Division I power on the basis of the existing isolation level back plus DC / DC, will be able to completely eliminate the effects of exchange ripple . Electrical parameters can fully meet the certification standards. However, this solution has some increase in cost , requires a power management chip Cadogan and some peripheral circuits , to increase the total cost of around $ 7. The following is a power of two common tests no flash :
Currently the United States a well-known chip design company is developing a true internal adjustment through the chip to achieve no flicker . The technology uses a buck-boost after the first approach, the entire process is completed using a single chip to achieve a smooth DC output in ensuring the PFC and THD premise. Currently the product is in the development stage , has not yet introduced .
More info you can visit:http://www.lead-lighting.com/products/sid106-1.htm
没有评论:
发表评论