LED lamps and lanterns drive power supply design experience - (AddTime ：2013-03-07)

200W led Flood light and lanterns to popularity, not only need to drastically reduce the cost, more need to solve the problem of energy efficiency and reliability, and how to solve these problems, PowerIntegrations marketing vice President DougBailey Shared the efficient high reliable 200W led Flood light and lanterns design five advice.

A, do not use bipolar power device
DougBailey points out that because of the bipolar power MOSFET device than cheap, generally is about 2 cents a, so some designers in order to reduce LED drive costs and the use of bipolar power device, this will seriously affect the reliability of the circuit, because with the LED driver circuit temperature ascend, bipolar devices of the effective scope of work to unwind quickly, this can lead to a device in the temperature rise fault which affect the reliability of the 200W led Flood light and lanterns, the right way is to choose MOSFET device, MOSFET device life much longer than bipolar devices.

Second, the MOSFET pressure not less than 700 v
Withstand voltage 600 v MOSFET is cheaper, many believe that 200W led Flood light and lanterns of input voltage is generally 220 v, so withstand voltage 600 v enough, but a lot of times circuit voltage to 340 v, the surge, 600 v MOSFET is easy to breakdown, which affect the 200W led Flood light and lanterns life, actually choose 600 vmosfet may save some cost but pay may be the circuit board price, so, "don't choose 600 v pressure of MOSFET, had better choose pressure more than 700 v MOSFET." he stressed.

Third, try not to use electrolytic capacitor
LED drive circuit whether or not to use electrolytic capacitor? There are supporters has opponents and supporters say if the circuit board temperature control, in order to extend the electrolytic capacitor life purpose, such as selection of 105 degrees of life for 8000 hours of high temperature electrolytic capacitor, according to the passage of the electrolytic capacitor life estimation formula "to reduce temperature every ten degrees, life doubled," then it in 95 degrees environment of working life for 16000 hours at 85 degrees, under the environment of working life for 32000 hours at 75 degrees, under the environment of working life for 64000 hours, if the actual working temperature is lower, so they will live longer! By this token, as long as the selection of high quality electrolytic capacitor to drive power of life does not have any effect!

There's supporters say the no electrolytic capacitor with high ripple current and lead to low frequency scintillation will for some human cause physical discomfort, a large range of low frequency ripple can also lead to some digital camera equipment appear difference frequency flashing light and dark grid. So, the high quality light lamps and lanterns still need electrolytic capacitor. But opponents think electrolytic capacitor will be natural aging, in addition, the temperature of the 200W led Flood light and lanterns is very difficult to control, so electrolytic capacitor life will decrease, thus affecting the life of the 200W led Flood light and lanterns.

To this, DougBailey think, in the LED driver circuit input part can consider don't electrolytic capacitor, actually use the PI LinkSwitch - PH can save electrolytic capacitor, PI of single-stage PFC/constant current design can allow the designer to save large capacity, in the output circuit, can use the high pressure ceramic capacitor instead of electrolytic capacitor so as to enhance the reliability, "some people in the design of two stage circuit, the output is based on a 400 v electrolytic capacitor, which would seriously affect the circuit reliability, it is suggested that the single circuit with ceramic capacitor can." He emphasized. "For not too concerned about dimming function, high temperature environment and need high reliability industrial application for, I strongly suggest not using electrolytic capacitor design."

Four, use as far as possible MOSFET device
If the design of 200W led Flood light and lanterns power is not very high, Doug suggest using integrated the MOSFET LED drive products, because the advantage of this is integrated MOSFET conduction resistance less, the quantity of heat of generation to score made less, in addition, is the integration of MOSFET is controller and FET together, usually have overheating shut off function, in the MOSFET overheating automatically shut off the circuit to achieve the purpose of protection of 200W led Flood light , the 200W led Flood light and lanterns is very important, because the general 200W led Flood light and lanterns is very small and hard to air cooling. "Sometimes happen due to overheating LED combustion hurt, but we plan never so." He said.

Five, try to use single stage structure circuit
Doug said some LED circuit used two stage structure, namely "PFC (power factor correction) + isolated DC/DC converter" architecture, the design will reduce the efficiency of the circuit. For example, if PFC of efficiency is 95%, and the DC/DC part of efficiency is 88%, the efficiency of the whole circuit will be reduced to 83.6%! "The PI LinkSwitch - PH device at the same time will PFC/CC controller, a 725 vmosfet and MOSFET drive integrated into a single package, the efficiency of the driving circuit, rising to 87%!" Doug points out, "this device can greatly simplify the circuit board layout design, can save the most traditional isolation flyback type used in the design of 25 element! Save components including high pressure large capacity electrolytic capacitor and light coupling device. Doug said LED two stage structure suitable for must use the second constant current drive circuit can cause the PFC drive LED constant current old driver. These designs are out of date and no longer is cost effective, so in most cases all had better use single stage design.