Power limit circuit

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Equation 6

Equation 7

Equation 8

Equation 9

Equation 10

3

Power limit circuit

A power limit circuit can be added to LED balancing circuit 3 to limit the overall power when

there is a large voltage variation for parallel strings of LEDs. Figure 4, Figure 5 and Figure 6

show a power limit circuit (in bold) which has two LED strings. Voltage variation may be due

to a number of factors:

●

low voltage drop in a LED string

●

high voltage drop in a LED string

●

shortened LED string

Figure 4 shows the power limit circuit comprised of R11, R12 etc. If there is a low drop in the

LED string D1 and D2 (Figure 4), the voltage at V1 (Q1 collector) is high and Q11 is turned

drops. The power supply source, which has a constant current source, tries to supply the

required current, and will raise the output voltage up to the power supply output voltage limit.

removed.

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