Principle of HID Electronic Ballast Based on Microprocessor

Generally, HID electronic ballasts are designed with dedicated chips, and the functions of these chips are relatively simple. There is no open circuit or short circuit detection function. The MC 34262 chip performs power factor correction (APFC) and provides a 400V DC power supply for the HID lamp. Its working process is to use a zero current detector to detect the current k (Figure 1). When the current is zero, the MOSFET Qo is turned on; the output current I is detected and the voltage V corresponding to it is compared with the threshold voltage Uc calculated in MC34262. If V is greater than VC, the MOSFET Qo is turned off. Under the control of the MC34262 chip, the active power factor correction circuit generates a high-frequency oscillation of about 25kHz to achieve the purpose of correcting the power factor. Threshold voltage:

The microprocessor (MCU) of the electronic ballast has a full-bridge conversion function. The high-1-low driver (lR2 101) drives 4 MOS tubes. Since the HID lamp will encounter acoustic resonance when working at high frequency, the voltage switching frequency of the two ends of the HID lamp is designed to be 125H. "Watchdog" function. When the HID lamp is ignited, the impedance of the HID lamp drops to a low resistance state, which instantly causes a current impact in the circuit, causing the APFC controller to lose its comparison basis and may cause a stop vibration phenomenon. In this case, the "watchdog" technology is used to set the zero current detector to zero, quickly turn on the MOS tube Qo, and restore the MC34262 to normal operation. Fault control function, detects that the electronic ballast has no working voltage monitoring function and lamp current detection function, and has no self-starting function after the APFC stops oscillating. The microprocessor is powerful, flexible in application, and is a general component with a low price. Moreover, with the advancement of technology, the processing speed and electrical performance can meet the requirements of HID ballasts. This article uses Microchip Pic16F71 as the HID electronic ballast microprocessor, which has a main frequency of up to 20MHz and a 4-channel A/D MCU as a full-bridge converter and controller component, see schematic diagram 1. Temperature, HID lamp operating voltage and HID lamp current. If over-temperature, over-voltage and over-current occur, the electronic ballast will execute a fault handling procedure, cut off the 4 MOs tubes, and protect the HID lamp and ballast.