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BC847BW
(Rev.:2012)

Phase Cut Dimmable Non-isolated Buck Converter for LED Retrofit Bulb with ICL8002G & CoolMOS™ 600V C6

Infineon Technologies 

AN-EVALLED-ICL8002G-B2

Phase Cut Dimmable Non-isolated Buck Converter for LED Retrofit Bulb with ICL8002G & CoolMOS™ 600V C6

13

Common Questions and Troubleshooting Hints

13.1

Q&A

How does ICL8002G realize dimming control and power factor correction?

Both dimming control and PFC are achieved with the input mains voltage sensing with the VR pin. This signal is

used to set the peak current of the primary winding and consequently allows both PFC and phase-cut dimming

functionality by regulating the cycle energy.

Is it possible to test the demo board with different LED modules with big variations in total forward

voltages?

The operation range of output voltage is specified in Table 1. The demo board will switch into protection mode

when tested with LED load with out-of-range forward voltage either due to Vcc overvoltage protection or Vcc

undervoltage protection. Modifications on the transformer design are necessary for applications with different

output voltage.

13.2 Design and Troubleshooting Hints

Why is there no light output after the LED load is connected and power is on?

Please verify the following:

• Connectivity of AC input and LED load

• LED module’s polarity

• Whether LED module’s forward voltage is out of the range specified in Table 1

How to change output current?

The easiest way to set the desired output current is to adjust the VR pin’s voltage and shunt resistor. However,

care must be taken to ensure that the transformer is not driven into saturation. Moreover, the VR pin’s voltage

should be kept below 3.7V for maximum power factor.

How to change the open circuit protection to Auto Restart Mode?

If Auto Restart Mode is preferred for output open circuit protection, R7 and/or R12 can be adjusted so that Vcc

overvoltage threshold (Vvccovp = 25V) is reached first before OVP threshold (Vzcovp = 3.7 V) is reached.

Please note that with changing R12, the voltage foldback correction will be affected and as a result the line

regulation will be affected. In this case R9 can be tuned for better line regulation.

Why is the LED flickering in my dimming application? How to improve?

Flickering can be either caused by IC auto-restart or by dimmer's uneven conduction phase angle. For the auto-

restart case, the ICL8002G’s Vcc voltage should be maintained between Vvccovp and Vvccoff over the whole

dimming range. This can be achieved by proper transformer turn ratio design and, if necessary, a voltage

regulation circuit for the Vcc. For dimmer’s uneven conduction case, it is advised to tune the damping and

bleeder circuits.

How to improve system efficiency?

For applications which require higher efficiency, first of all, an active damper circuit can be used to replace the

lossy passive damper circuit. Switching frequency can be reduced so as to minimize the switching loss and this

may require bigger inductor size. Low ESR capacitor can be used for the output capacitor to improve efficiency.

Using a higher current rated MOSFET for Q5, however, may not necessarily produce higher efficiency as the

switching loss may dominate the total power loss of the MOSFET.

How to modify the board for non-dimmable LED bulb application?

For non-dimmable application, the highlighted damping and bleeder circuits as shown in Figure 2 can be

removed for better efficiency and cost reduction.

Application Note

21

Version 1.1, 2012-08-03

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