High power factor, high efficiency electronic ballast controller ML4831

Abstract: ML4831 is a highly integrated electronic ballast controller produced by Micro Linear Semiconductor Company in the United States. This article introduces the basic working principle, characteristics and typical applications of this circuit. 

1. Overview ML4831 is a high power factor, high efficiency electronic ballast controller with adjustable brightness. It mainly consists of power factor controller, oscillator, preheating shutdown sequence, control gating logic, output driver and overvoltage and overheating protection (see Figure 1). Restart and lamp re-output are controlled by external timing, and taking into account the comprehensive control of different lamp characteristics, the ballast control device can adjust the power of the lamp through frequency modulation (FM) and adjust the lamp power through compensation programming. Power, through compensation programming to adjust the operating frequency of the voltage controlled oscillator (VCO). These functions are integrated on one chip, which can be used in different situations.      　　The main features of the chip are as follows: ●The power factor correction and power adjustment functions are completed by an integrated circuit. ●Low distortion, high efficiency, continuous voltage boost, average current detection power factor. ●Quick start or instant start, the start time is adjustable. ●Lamp current feedback controls brightness. ●Frequency dimming and start-up. ●When the lamp goes out, it can be adjusted to restart to prevent the ballast from heating up. ●Internal over-temperature shutdown protection replaces external sensing protection to ensure the safety of the equipment. ●The overvoltage comparator in PFC can eliminate the loss of control caused by load open circuit. ●Adopts large-amplitude oscillator and standard current multiplier to improve noise immunity. 2. Pin function      　　ML4831 adopts dual in-line 18-pin package, and the pin arrangement is shown in Figure 2. The function description of each pin is as follows: ●EA OUT: PC error amplifier output and correction terminal. ●IA OUT: The output and adjustment node of the PFC average current transconductance amplifier. ●I (SINE): PFC current multiplier input. ●IA+: PFC average current transconductance amplifier non-inverting input and PFC cycle-by-cycle current limit comparator peak current detection point. ●LAMP FB: The inverting input terminal of the lamp arc current sampling (or adjustment) error amplifier is also the brightness control input node. ●LFB OUT: Lamp current error transconductance amplifier output. ●R(SET): external resistor, which sets the maximum frequency Fmax of the oscillator and the R(X)/C(x) charging current. ●INTERRUPT: used for lamp extinguishing detection and restart. Start again after the time interval of this foot. ●R(X)/C(X): preheating timing, brightness lock and interrupt. ●GND: Ground ●P GND: Chip power ground terminal. ●OUT B: MOSFET driver output terminal B of the ballast. ●OUT A: MOSFET driver output terminal A of the ballast. ●PFC OUT: PFC MOSFET driver output terminal. ●VCC: positive power supply of the chip. ●VREF: 7.5V reference voltage buffer output. ●EA_/OVP: PFC error amplifier inverting input and OVP comparator input. 3. Main parameters ●Power supply ICC: 75mA ●Output current. DC current flowing into or out of pins 13, 14 and 15: 250mA ●Multiplier input I (SINE) of pin 3: 10mA ●Input voltage of pins 5, 9 and 18: 0.3VCC~-2V; ●Input voltage of pin 4 : -3～+2V; ●Maximum overload voltage of pins 1 and 6: -0.3～+7.7V; ●Maximum overload current of pins 1, 2 and 3: ±20mA; ●Maximum overload voltage of pin 2: -0.3～ +6V; ●Operating temperature range: -65～+150℃ 4. Introduction to the main unit functions of ML4831 Figure 1 is the internal principle block diagram of ML4831. The functions of several main units are as follows: 4.1 Power factor part The power factor correction circuit in ML4831 Using average current detection boost power factor control circuit. For the working principle of this circuit, please refer to relevant information. 4.2 Multiplier The multiplier of ML4831 is a linear current input multiplier and is a part of the power factor controller. It has strong ability to suppress interference caused by high-power conversion. The rectified DC voltage of the input sine wave voltage is converted into current through the step-down resistor. In this way, very small ground noise is generated on the basis of the PWM (Pulse Width Modulation) comparator. The output voltage of the multiplier is added to the non-inverting input of the current amplifier, forming the reference for the current error amplifier. Its size is calculated according to the formula. VMUL≈[I(SINE)×(VEA-1.1V)]/4.17mA Among them, I(SINE) is the current on the buck resistor; VEA is the output voltage of the error amplifier. The maximum output voltage of the multiplier is 1V. 4.3 Stability of average current and output voltage The pulse width modulator (PWM) in the PFC control part can suppress the positive voltage interference caused by the multiplier output and the negative voltage interference on the current sampling resistor connected to pin 4 and the current connected to pin 4. Negative voltage interference on the sampling resistor. Cycle-by-cycle current limiting is used to protect the MOSFET during high-speed current transients. When the voltage at pin 4 falls below -1V, the pulse width modulator cycle is terminated. 4.4 Overvoltage protection (OVP