UM0670 datasheet(5/43 Pages) STMICROELECTRONICS

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Getting started

UM0670

5/43

Doc ID 15327 Rev 2

Getting started

This section is intended to help designers begin evaluating the board quickly, describing

how the board should be connected with the load and how the jumpers adjust the output

LED current.

As mentioned in the introduction, the board has a nominal output power of 80 W and the

output LED current can be set to 350 mA, 700 mA or 1 A. The LEDs are connected to one

string. Basically, this means if the LED current is set to 350 mA, then the LED voltage should

be approximately 228 V in order to provide output power of 80 W. If the LED current is set to

700 mA, then the LED voltage should be around 114 V. Finally, if the LED current is set

to 1 A, then the LED voltage should be about 80 V. Assuming that a high brightness LED

has (typically) a 3.5 V forward voltage drop, the number of LEDs for the 350 mA output

current is 65, for the 700 mA output current it is 32 and for the output current of 1 A it is 23

(see Table 1). Of course, designers must recalculate the number of LEDs in cases where

the LED has a forward voltage drop other than 3.5 V. If the output LED voltage is different

than that given in Table 1, output LED current precision will be influenced so is

recommended that the total forward voltage drop across all the LEDs is as close as possible

to the calculated output voltages shown in Table 1.

Connect the LED string to the board using connector J2 or J3, being careful to observe the

correct LED polarity (anode + and cathode –). Set the output LED current to 350 mA, 700

mA or 1 A, based on how many LEDs are connected to the output. The output LED current

is set using jumpers JP1, JP2, JP3 and JP4, in accordance with the connection settings

specified in Table 2. It is not necessary to connect a dimming module with a PWM signal,

because if the module is not used the LED brightness is set to maximum level (100%

brightness). Finally, connect an input voltage to the demonstration board between 88 VAC

and 265 VAC, and the LEDs begin illuminating.

Note:

The LEDs cannot be connected during operation, when the input voltage is connected to the

demonstration board. This is because in this case the output capacitor C208 = 0.47 µF is

charged to 400 V and can cause uncontrolled peak LED current.

Table 1.

LED values for different output currents

Output LED current [mA]

Output LED voltage [V]

Number of LEDs for forward

voltage drop 3.5 V

350

228

700

114

1000

Table 2.

Output LED current adjustment on the demonstration board

Jumper

350 mA

700 mA

1000 mA

JP1

Not connected

Connected

Not connected

JP2

Not connected

Connected

Not connected

JP3

Not connected

Connected

JP4

Not connected

Connected

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