Using the STEVAL-ILL016V2

STEVAL-ILL016V2

2/5

Doc ID 17474 Rev 1

1

Using the STEVAL-ILL016V2

The STEVAL-ILL016V2 is shipped without the jumpers that select transformer taps for

specific numbers of LEDs in each parallel string. Please refer to the schematic diagram in

Figure 1, and place the jumpers in the appropriate positions.

The board operates with any number of LEDs with the capacitors supplied at C14 and C15.

LED ripple current is higher for smaller numbers of LEDs.

The LED voltage limit for open-load protection can be set with R30, instead of R32. Refer to

Figure 1 for voltage divider details.

1.1

Operation

This unit is based on a PFC-flyback power converter. Design equations are provided in

application note AN1059 (available on

application note be studied prior to modifying the design.

There are two current limits, one from the isolated secondary (optically coupled) and one on

the primary side.

The primary side limit responds to the line voltage, and should dominate with the line lower

than 102-108 V. The current limit is set by the parallel combination of R25 and R26. Values

of parts at R10 and divider R5, R6, R11 also affect the primary current. Refer to the L6562A

datasheet, and application notes for the L6561 and L6562 for guidance on modifying the

input side characteristics.

The secondary side limit responds to the average LED current. It should take over when the

line voltage is above 102-108 V. LED current is set with the resistors at R31 (shipped with

0.47

Ω wire-wound, topside) and R35-R38 (unmounted 0805 SMT, bottomside). The

schematic contains a formula for selecting resistor values and guidance for resistor

selection.

In dimmed operation, the primary side current limit dominates – the secondary side limit is

saturated, calling for full output. Current to the LEDs is limited by the dimmer Triac’s

conduction angle.

1.2

Additional capabilities

The demonstration board output can be extended to 30 watts, on the same PCB layout, with

some component changes. Several flexible transformers and higher current input filters have

been designed, and application guidance is available.

1.3

First sample run errata

If present, please remove the incorrect, unneeded components at locations D5 and D6. The

RCD clamp consisting of D8, C4, and R18-20 perform their function. The schematic

incorrectly shows a 133 kW resistor at R32. The sample has the correct value of 330 k

Ω.