6.4

Buck Disable

6.5

Internal Dimming Function

6.6

External Dimming Function

6.7

Configuring the PFC Stage for Fixed Output

6.8

Equipment Shutdown

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Test Procedure

1. Ensure the AC source is off.

2. Connect a DC source to J4, pins 1 and 2.

3. Set DC source to 0 V.

4. Apply power to the EVM per Section 6.1.

5. Increase DC source to 3.3 V. This input can accept up to 12 V.

6. Observe output current, A1, drops to zero.

7. PFC voltage, V2, does not change.

1. Ensure the AC source is off.

2. Ensure jumper is present on J3.

3. Apply power to the EVM per Section 6.1.

4. Rotate R26 potentiometer slowly anti clockwise.

5. Observe output current on A1 reduce from nominal 0.9 A to 0.1 A. If LED string is attached observe

LED’s dim.

1. Ensure the AC source is off.

2. Ensure jumper is removed from J3.

3. Connect signal generator to J4, pins 3 and 2.

4. Set signal generator to generator a pulse from 0 V to 3.3 V at 200 Hz with variable duty cycle. Note

when the PWM signal is high the LED light is reduced. 100% duty cycle will turn LED off.

5. Apply power to the EVM per Section 6.1.

6. Vary the duty cycle of the signal generator output.

7. Observe output current, A1, changes. If an LED string is attached observe LED’s dim.

The EVM ships configured as a boost follower PFC. Using a soldering iron some simple component

modifications can change the PFC configuration from boost follower to fixed output voltage.

1. Remove R1, R3, R4, R6, C1 and Q1.

2. Change R11 to 6.49 k

Ω.

3. The EVM now uses a fixed output voltage PFC stage. Repeat tests to see functionality.

1. If DC sources are connected to shutdown pins, J2 and J4, ensure they are set to 0 V.

2. Ensure load is at maximum, this will help discharge C17.

3. Turn off AC source.

4. Monitor PFC output voltage V2. Do not handle EVM until V2 reads less than 50 VDC.

SLUU355A – March 2009 – Revised June 2009

A 0.9-A Constant Current Supply with PFC for 100-W LED Lighting Applications

9

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