L6585DE PFC and Ballast Control Integrated Circuit

Start sequence of old or damaged lights

When an old lamp is connected to a ballast, the impulse voltage may be higher than the nominal value or the safety threshold. In this case, the lamp may remain unlit for a longer period of time than the ignition time. In both cases, during ignition, due to a decrease in frequency, the voltage at the output of the ballast can easily reach dangerous values. If the lamp tube ruptures, the same situation will occur: the lamp cannot ignite and the lamp voltage must be limited. During ignition, L6585DE is connected to the HBCS pin through a resistor that senses the current flowing into the lamp through a sensor. If the voltage of the HBCS pin reaches 1.6 V, a small amount of current will sink from the EOI pin, resulting in a slight increase in frequency. From a macro perspective, the modified result of this frequency is frequency regulation, resulting in current regulation and lamp voltage limitation. Once the voltage of the HBCS pin reaches 1.6 V, the TCH pin begins to charge Cd: when the TCH voltage reaches 4.63V, the TCH pin is no longer free (such as during preheating), but sinks 26ua, causing Cd to release faster. When the TCH voltage reaches 1.5 V, pull down the pin and check the HBCS voltage. If the voltage is higher than 1.05 V, the IC stops working. If the lamp ignites during this shortened TCH cycle, the EOI pin stops sinking current. If it reaches 1.9 V, the IC enters operation mode and the TCH pin is immediately pulled down. It is worth noting that the shortened TCH cycle time depends only on the Cd value. It is recommended to start with selecting Cd to obtain protection time, and then continue selecting Rd to obtain the required TPRE

QQ image 20200926095332.png

Old lamp management in operating mode  diode

In operating mode, old lights may exhibit three different abnormal behaviors:

Rectification effect

Overcurrent

Hard Swap Event

Rectification effect

The rectification effect and the increase in the difference in ohmic resistance between the two are related to the cathode. Therefore, when the lamp current flows in, the equivalent resistance of the lamp is higher in one direction than in the other. The current waveform is distorted and the lamp current is no longer zero. The offline pin is the input of the internal window comparator, which can be triggered by voltage changes caused by rectification effects. The reference of this comparator and the amplitude of the window can be connected to set the appropriate resistor for the EOLP pin as shown in the table below:  diode