The lighting penetration rate of LED lamps will further increase, which makes thousands of Chinese LED lamp manufacturers rejoicing in the green lighting revolution - because a huge LED market is about to open, and this time it is the Chinese manufacturers who play the leading role. However, it should be seen that in order to popularize LED lamps, not only the cost needs to be greatly reduced, but also the problems of energy efficiency and reliability need to be solved?
1. Do not use bipolar power devices. Since bipolar power devices are cheaper than MOSFETs, usually about 2 cents a piece, some designers use bipolar power devices in order to reduce the cost of LED driving. This will seriously affect the reliability of the circuit, because as the temperature of the LED driver circuit board increases, the effective working range of the bipolar device will rapidly shrink, which will cause the device to fail when the temperature rises and affect the reliability of the LED lamp. Correct The method is to use a metal-oxide-semiconductor field effect transistor device, and its service life is much longer than that of a bipolar device.
2. The MOSFET with a withstand voltage of 600V is relatively cheap. Many people think that the input voltage of LED lamps is generally 220V, so the withstand voltage of 600V is enough, but in many cases the circuit voltage will reach 340V. When there is a surge, 600V It is easy to be broken down, thus affecting the life of LED lamps, it is best to use metal oxide semi-field effect transistors with a withstand voltage of more than 700V.
3. Electrolytic capacitors will naturally age. In addition, the temperature of LED lamps is extremely difficult to control, so the life of electrolytic capacitors will inevitably decrease, thereby affecting the life of LED lamps. In this regard, the vice president of marketing of American Power Integration Company believes that in the LED drive circuit The input part can be considered without electrolytic capacitors. In fact, the use of PI's power chip that can realize dimming can save electrolytic capacitors. PI's single-stage PFC/constant current design allows designers to save large-capacity capacitors. In the output circuit , You can use high voltage ceramic capacitors instead of electrolytic capacitors to improve reliability. "Some people use a 400V electrolytic capacitor for the output when designing a two-stage circuit, which will seriously affect the reliability of the circuit. It is recommended to use Ceramic capacitors for single-stage circuits are fine. For industrial applications that are less concerned with dimming, high temperature environments, and high reliability, electrolytic capacitors are not recommended for design.”
4. If the power of the designed LED lamp is not very high, it is recommended to use the LED driver product integrating the MOSFET, because the advantage of this is that the on-resistance of the integrated MOSFET is less, and the heat generated is less than the discrete one. In addition, the integrated MOSFET is the controller and the FET together. Generally, it has an overheat shutdown function. When the MOSFET is overheated, it will automatically shut down the circuit to protect the LED lamps. This is very important for LED lamps, because LED lamps are generally very Small and difficult to air cooling. "Sometimes it happens that the LED burns and hurts people due to overheating.
5. Adopt the architecture of "PFC (power factor correction) + isolated DC/DC converter", this design will reduce the efficiency of the circuit. For example, if the efficiency of the PFC is 95% and the efficiency of the DC/DC section is 88%, the efficiency of the entire circuit drops to 83.6%! "PI's LinkSwitch-PH device integrates the PFC/CC controller, a 725V MOSFET and MOSFET driver into a single package, increasing the efficiency of the driver circuit to 87%! Such a device greatly simplifies board layout design, saving up to Get rid of the 25 components used in traditional isolated flyback designs! The components eliminated include high voltage bulk electrolytic capacitors and optocouplers." The LED two-stage architecture is suitable for the need to use a second constant current drive circuit for the PFC to drive the LED constant Streaming legacy drives. These designs are outdated and no longer cost effective, so a single stage design is preferable in most cases.
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