Design of high brightness LED driver power supply based on MIP553 chip
“Aiming at the shortcoming of electrolytic capacitors limiting the life of the existing LED drive circuits, a design method of an LED drive circuit without electrolytic capacitors is proposed. The method adopts Panasonic MIP553 chip with built-in PFC dimmable LED drive circuit, and is combined with an external non-isolated bottom edge chopper circuit as the basic circuit structure, and outputs a stable current to meet the needs of LED work. At the same time, a protection circuit is designed to protect the load. The experimental results show that the controller chip can work stably, and can achieve a constant voltage output of 27V and a constant current output of 350mA.
Aiming at the shortcoming of electrolytic capacitors limiting the life of the existing LED drive circuits, a design method of an LED drive circuit without electrolytic capacitors is proposed. The method adopts Panasonic MIP553 chip with built-in PFC dimmable LED drive circuit, and is combined with an external non-isolated bottom edge chopper circuit as the basic circuit structure, and outputs a stable current to meet the needs of LED work. At the same time, a protection circuit is designed to protect the load. The experimental results show that the controller chip can work stably, and can achieve a constant voltage output of 27V and a constant current output of 350mA.
LED (Light Emitting Diode) has become a new generation of green lighting source with many advantages such as energy saving, environmental protection, high brightness and long life. With the maturity of LED lighting technology, it will eventually be used in all aspects of life and become the new favorite of lighting sources. However, driving power with high efficiency, low cost, high power factor and long life is the key to the luminous quality and overall performance of LED lamps.
The LED light bulbs on the market today are about 40 times longer than incandescent light bulbs, which is equivalent to 40,000 hours. Because the LED is a DC current drive part, it directly converts electrical energy into light energy through the flowing current, so it is also called a photoelectric converter. Because there is no friction and mechanical loss, the efficiency of energy saving is higher than that of ordinary light sources. However, when the AC power supply is turned on, it is generally a DC stabilized power supply that uses rectifier parts and a smoothing circuit. The electrolytic capacitors necessary in the smoothing circuit will rise by 10°C due to the surrounding temperature and self-heating, and the life will be cut in half. So electrolytic capacitors hinder the life of LED lighting fixtures.
In order to improve the life of the driving power supply, simplify the circuit, reduce the cost and improve the power density, it is necessary to remove the electrolytic capacitor. Therefore, a high-brightness LED driving power supply without electrolytic capacitor is proposed in this paper.
1 The basic working principle of LED power supply
Adopt BUCK converter and IPD control to realize switching power supply, output constant current and voltage, and drive LED lights. The overall block diagram of the circuit is shown in Figure 1.
In the main circuit part, a filter is connected immediately after the commercial power supply. Its function is to filter out the high-order harmonics in the power supply and the surge in the power supply, so that the control circuit is less disturbed by the power supply. The input rectifier part adopts an integrated rectifier bridge, which converts the alternating current whose level floats up and down the zero point into a one-way pulsating direct current through the unidirectional conduction characteristic of the diode, and then outputs the direct current voltage under the action of the filter capacitor and the inductance. After adjustment and control by MIP553 and BUCK circuit, the voltage for LED is output.
2 The specific design of LED power supply
2.1 Design of the input circuit
In order to prolong the service life of the LED driving power supply and make it match with the LED, the electrolytic capacitors in the circuit must be removed.
The design index of the circuit is: input AC voltage Vm: 198-264VAC/50Hz; output voltage Vo: 27VDC; output current Io: 0.35A.
The input circuit includes a noise filtering device, a safety fuse device and an input rectifying device, as shown in Figure 2.
The noise filter device is mainly composed of capacitors C1/C2/C3 and Inductor L1, and its function is to reduce electromagnetic interference (EMI) in the frequency band less than 1MHz. This device can also be linked after the AC AC, before the rectifier, the filtering effect is the same. The safety fuse is composed of a fuse and ZNR1. The fuse mainly prevents the circuit from quickly cutting off the circuit to protect the load when the peak current of the hazardous circuit is generated; ZNR1 is a surge absorber, which absorbs static electricity and surges from the input terminal to protect circuit behind. The input rectifier device converts alternating current into direct current, and the selection of the input rectifier bridge: the voltage stress of the rectifier bridge diode is:
Considering the margin, choose TSC GBL205 (VR=600V, IFAN=1A).
2.2 Design of the output circuit
The output circuit consists of the basic BUCK circuit and a Zener diode DD1. As shown in Figure 3.
2.2.1 Buck converter and its advantages
Buck converter, also known as buck converter, series switching regulator, three-terminal switching buck regulator, is a single-tube non-isolated DC/DC converter whose output voltage is equal to or less than the input voltage.
The input current is in operation is, when the switch is closed, is>0; when the switch is open, is=0, so is is pulsating, but the output current io is continuous and stable under the action of inductors, diodes and capacitors of. Especially suitable for providing operating current for LEDs.
The selection criteria of FRD1: the rated current is greater than 2 times the output current, the rated voltage is greater than the input voltage, and the reverse recovery time should be within 100ns, considering the margin, the parameters of FRD1 are: 15A, 600V, trr=50ns. Select T1 and Cout in a similar way, then their parameters are: T1: 680μH; Cout: 1μF, 50V.
2.2.2 Zener diode DD1
In a certain range of low input voltage, if there is no reverse device like DD1, there will be reverse current flowing through the IPD at the moment when the switch is turned off, and the IPD is not allowed to have such current, because this This reverse current will cause damage to the IPD.
Each stress on DD1: IDD>2・Io=2×0.35=0.7A, UDD>Uo, reverse recovery time trr
MIP553 chip realizes wide voltage 85~277V/AC input, built-in MOS, simple and stable structure, no need for electrolytic capacitors, supports isolation or non-isolation solutions, single power supply output power 6~30W, constant current output
The drain current of MIP553 is controlled by pins CL and EX, so the settings of the resistors RCL and REX connecting these two pins will directly affect the size of the drain current. The maximum drain current can be determined by REX. Considering this maximum drain current flows through the LED, care should be taken when setting the reference value.
Among them, it is assumed that the input voltage is 100V, the output voltage is 28V, the current is 400mA, and the maximum drain current is set to 1.0A.
The functions of CVDD, CEX, and CCL are to stabilize the operation of MIP553 and suppress external noise. Therefore, its value should be chosen properly. CVDD, stabilizes the voltage of VDD, suppresses the flickering of the LED, the characteristics are not affected by temperature, and does not generate additional noise, the reference standard value is between 1 ~ 10μF; CEX, suppresses external noise from entering the EX pin, its reference standard value is 470 Between ~1000pF; CCL, suppress external noise from entering the CL pin, if its value is too large, then the pF value will be seriously affected, so its value should be less than 1000pF.
2.4 Simulation results
Use Multisim to simulate the circuit, and the result obtained is shown in Figure 5.
As can be seen from Figure 5, the output voltage is stable at 27V and the current is stable at 0-35A, which meets the design requirements.
3 Challenges of LED Power
As a new type of electric light source, LED has obvious advantages in the production of large luminous three-dimensional characters and luminous signs. It has low control voltage, low cost and high reliability. Although LED products have an increasingly fierce development trend in domestic and foreign markets, LED lighting is an emerging industry after all, and it has not yet been widely popularized. Therefore, LED driving power inevitably faces challenges in various aspects: First, due to the positive The voltage varies with current and temperature, and its “color point” also drifts with current and temperature. In order to ensure the normal operation of the LED, it is required that its driver must be Limit current. Secondly, if LED dimming is required, pulse width modulation dimming technology is usually used, and the typical PWM frequency is 1 to 3 kHz. Finally, the power handling capability of the LED driver circuit must be sufficient and robust to withstand multiple fault conditions and be easy to implement.
LED is an energy-saving, high-efficiency and environmentally friendly green lighting, and it is very important to study its driving circuit. This paper introduces the LED driving power supply designed by MIP553, and proves the stability of its output current through simulation, which has a good application prospect.