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The five key LED driver design

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The five key LED driver design

Release date:2014-09-09 00:00 Source: Views:

To popularize the LED lamps and lanterns, not only the need to reduce the cost, more technical problems need to be solved. How to solve energy efficiency and reliability of the problem, PowerIntegrations marketing vice President DougBailey share the experience of the high efficient and reliable LED driver design.


A, do not use the bipolar power devices


DougBailey pointed out that due to the bipolar power devices, cheaper than the MOSFET is 2 cents a commonly, so some designers in order to decrease the cost of the LED driver using bipolar power devices, this will seriously affect the reliability of the circuit, because of increase in the temperature of the LED driver circuit boards, effective working range of bipolar devices quickly narrow, it leads to device failure during temperature rise to influence on the reliability of the leds with, the right thing to do is to choose MOSFET device, the service life of the MOSFET device far longer than bipolar devices.


Second, try not to use electrolytic capacitor


What do you want to use in LED driver circuit capacitors? Currently have supporters and opponents, proponents argue that if temperature control circuit board can be good, the purpose of, in turn, to extend the life of the electrolytic capacitor, such as selection of 105 degrees of life of 8000 hours of high temperature electrolytic capacitor, according to the passage of the electrolytic capacitor life estimation formula of "every 10 degrees below the temperature, double life", then its working life in a 95 - degree environment for 16000 hours, the working life of 32000 hours in a 85 - degree environment, the working life of 64000 hours in a 75 - degree environment, if the actual working temperature is lower, so life will be longer! It seems that as long as selects high quality electrolytic capacitor is no influence to the life of the drive power!


From no electrolytic capacitor and supporters say the high ripple current caused by the low frequency blinking may cause physical discomfort for some human eyes, the magnitude of low frequency ripple can also lead to some digital camera equipment appear difference frequency flashing light dark grid. So, high quality light lamps and lanterns or need electrolytic capacitor. But opponents think electrolytic capacitor will natural aging, in addition, the temperature of the LED lamps and lanterns is very difficult to control, so the service life of electrolytic capacitor will reduce, which affect the service life of the LED lamps and lanterns.


DougBailey think about it, in the LED driver circuit input portion can be considered without electrolytic capacitor, actually use PI LinkSwitch - PH will save electrolytic capacitor, PI of single-stage PFC/constant current design can save you big capacity, designers in the output circuit, high voltage ceramic capacitors can be used in place of the electrolytic capacitor to enhance the reliability, "some people in the design of two-stage circuit, the output using a 400 v of the electrolytic capacitor, this will seriously affect the reliability of the circuit, the proposed single-stage circuit with ceramic capacitors are ok." He stressed. "For not too concerned about the dimming function, high temperature environment and the need for high reliability of industrial applications, I strongly recommend not using electrolytic capacitor to design."


Three, MOSFET pressure not less than 700 v


Withstand voltage of 600 v MOSFET is cheaper, many believe that the LED lamps and lanterns of the input voltage is 220 v, so the withstand voltage 600 v, but most of the time circuit voltage to 340 v, when a surge of 600 v MOSFET is easy to breakdown, which affects the service life of LED lamps and lanterns, choose 600 vmosfet may actually save some cost but the pay is the price of the whole circuit board, so, "don't use 600 v voltage of MOSFET, had better choose more than 700 v voltage MOSFET," he stressed.


Four, try to use single stage structure circuit


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


Five, try using MOSFET device


, Doug if the design of high power LED lamps and lanterns is not recommend the use of integrated LED the MOSFET drive products, because it has the advantage of integration on resistance of mosfets, the less the quantity of heat to the score of less, on the other hand, is integrated with FET, MOSFET is controller usually have shut off function, overheat in MOSFET overheat automatically shut off the circuit to achieve the purpose of protection of LED lamps and lanterns, the LED lamps and lanterns is very important, because the LED lamps and lanterns is generally very small and difficult to air cooling. "Sometimes they will LED burn injury due to overheating, but our solution never like this." He said.


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