NE5565 electronic ballast controller - power circuit - circuit diagram - Huaqiang Electronic Network

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The NE5565 is an electronic ballast controller from Philips. This bipolar monolithic IC integrates a power factor correction (PFC) controller and a self-oscillating half-bridge driver with various control and protection features. Using the NE5565 to design fluorescent electronic ballasts can reduce component count, reduce size, reduce weight, and improve ballast reliability and safety.

1. The internal structure of NE5565 and its main features

The EN5565 is available in a 20-pin dual in-line narrow-body plastic package, as shown in Figure 1.

The NE5565 is mainly composed of a power factor (PF) amplifier, a DC error amplifier, a PWM controller, a half-bridge oscillator, an output buffer, a voltage regulator, a lamp voltage regulator, a lamp current rectifier and undervoltage lockout protection, and capacitive load protection. Circuit composition such as overcurrent protection, as shown in Figure 2.

The pin functions and pin input and output ratings of the NE5565 are listed in Table 1.

The NE5565 controller includes two switching power supply control circuits: the first is a PFC boost converter controller, which can increase the electronic ballast power factor to above 0.99, the current harmonic distortion is extremely low, and the AC transient voltage Protection is provided; the second is a half-bridge oscillator circuit that converts the DC high voltage of the PFC output into a high frequency AC voltage. The half-bridge controller drives two external high-voltage power MOSFETs for lamp current regulation, peak lamp voltage limiting, and power switch protection. The NE5565 has an operating temperature range of 0 to +85 °C.

The main features of the NE5565 are:

● The same chip can complete PFC and ballast dimming control;

● AC current harmonic distortion is very low;

● Variable frequency mode;

● Programmable preheating and ignition to achieve three-step soft start;

● Lamp overvoltage protection;

● It can eliminate the overshoot generated when the load is cut off and realize overvoltage protection.

2. Main functions of NE5565

The typical application circuit of the NE5565 is shown in Figure 3. T1 is a high-frequency transformer of a half-bridge oscillator, and T2 is a lamp current detecting transformer.

2.1 Voltage adjustment (voltage regulator)

The 7.42V reference voltage output from the VREF pin serves as a reference for the control logic voltage. Vcc is typically 12.7V and Vcc is at least 9.3V before VREF is output. The accuracy of VREF is ±3.5% in the range of 0 to 85 °C.

2.2 lamp voltage regulator

Under preheating, ignition, and lamp shutdown conditions, the highest open circuit voltage across the lamp load must be limited. During voltage regulation, the lamp voltage is controlled by the arc voltage of the lamp and is not controlled by the control circuit. When the VLAMP pin voltage exceeds VREF, the lamp voltage comparator detects the VLAMP pin voltage. During this time, the lamp voltage reaches the maximum allowable open circuit voltage value, and the VLAMP voltage is reduced by the fast frequency increase circuit. The RXCX time constant determines the frequency offset time of the startup circuit (ratio 2:1).

2.3 Low voltage lock protection

When the PFC and half-bridge control circuits should be turned on or off, the protection circuit uses the Schmitz trigger to detect the DC supply voltage of the Vcc pin and determine the upper and lower trip points of the supply voltage. The PFC and half-bridge control circuits remain off until Vcc rises from zero volts to the upper voltage limit (11V). Once Vcc exceeds the upper voltage, the PFC and half-bridge oscillator circuits begin to operate. When Vcc is below the lower limit voltage (10V), the PFC and half-bridge circuits are turned off. The PFC and half-bridge oscillators are not allowed to operate until Vcc exceeds the upper limit trip point. The minimum delay is set by the component external to the DMAX pin.

2.4 Light start and PFC over voltage protection

The half bridge undervoltage lockout circuit samples the DC output voltage of the PFC. Before the PFC output voltage reaches the set value (such as 400VDC), the undervoltage lockout circuit prohibits the lamp from igniting. When the OV pin input voltage exceeds 5/7 VREF, the inverter frequency is normally ignited from the maximum value when the lamp is warmed up. At the lower frequency offset, the ignition procedure begins.

The overvoltage protection circuit prevents the PFC DC output voltage from exceeding the set value. When the overvoltage comparator input pin OV voltage is much higher than VREF, the PFC buffer gate drive output OUTP is turned off to prevent the PFC DC output voltage from further increasing. The overvoltage protection circuit only protects the overvoltage or overshoot generated by the PFC circuit and does not suppress the transient voltage of the AC line.

2.5 Capacitive load protection

A capacitive load protection circuit is used to prevent the half-bridge power transistor from failing when the lamp is removed. When the frequency exceeds the resonant frequency of the half-bridge LC load network, the primary voltage will lead the primary current. The protection logic detects the phase relationship between the LC network resonant current and the voltage. The IPRIM pin input voltage is the primary current signal of the LC network. If the IPRIM pin voltage is higher than -100mV (positive), that is, when the gate drive signal is high, the system malfunctions and the frequency of the half-bridge oscillator rises.

2.6 Half Bridge Oscillator

The half-bridge oscillator is a triangular wave generator that generates a square wave signal to drive the buffer circuit. The oscillation frequency is determined by the resistance value and capacitance value of the RT and CT pins, and the CT pin voltage is the triangular wave voltage.

2.7 output buffer driver

The output buffer is used as a level shifter to convert the low-level logic signals of the half-bridge oscillator and the pulse-width modulator into a 10V drive signal to drive the two power switches of the external half-bridge circuit. The OUTH half-bridge buffer/driver circuit drives an external level shifting circuit and then drives the half-bridge power switch. The OUTP output can directly drive a MOSFET or a circuit that combines external level shifting with a power MOSFET.

2.8 Pulse Width Modulator

The PWM control circuit is used to control the duty cycle of the PFC. The PWM frequency is determined by the half bridge oscillator. The ramp voltage appears on the CP output pin and is synchronized with the half-bridge oscillator. Therefore, at the valley point of the CT triangle wave, the CP pin ramp voltage starts. When the CP pin ramp voltage exceeds the DC pin output voltage, the capacitor connected to the CP pin discharges. The resistors and capacitors connected to the DMAX pin control the maximum duty cycle, soft-start function, and half-bridge cut-off time.

2.9 Overcurrent protection

The current value can be detected by a resistor connected to the CSI pin. When the CSI voltage is -500mV, the overcurrent protection circuit is triggered and the OUTP output is turned off. When an overcurrent occurs in the PFC input circuit, the capacitor on the DMAX pin is forced to discharge.

2.10 Power Factor Amplifier

To modulate the duty cycle of the PFC power switch, the rectified peak AC voltage and phase are sensed by the PF amplifier and the power factor input is received through the PF pin. When the AC voltage reaches a peak and zero crossing, the input voltage of the PF pin is 1V and 0V, respectively.

2.11 DC Error Amplifier

This circuit is used to provide negative feedback of the PFC DC output voltage. The DC output voltage of the PFC is input to the DC pin through a resistor divider and filter network. The reference voltage of the DC error amplifier is VREF. The DC error amplifier output should be connected to a filter capacitor to eliminate switching noise.

2.12 lamp current rectifier

A lamp current rectifier is used to provide negative feedback control of the average lamp current. The lamp current transformer (T2) and the load resistor convert the lamp current signal into a voltage that is applied to the L1 and L12 pins, and the CRECT pin provides a full-wave rectified output. External resistors and capacitors determine the gain and time constant of the circuit. The differential error amplifier compares the CRECT pin voltage to the internal 2/7 VREF reference voltage and adjusts the frequency of the half-bridge oscillator to minimize the error voltage to force the average lamp current to be constant.