Startup

AN3410

18/28

Doc ID 018890 Rev 1

7

Startup

Startup scope photo - cold start, everything discharged, 7 LEDs, 120 V input.

Trace colors:

–

Yellow AC line, 100 V/div, ref +2 div

–

Blue LED voltage, 10 V/div, ref -3 div

–

Green LED current, 100 mA/div, ref -3 div

Figure 16.

Startup waveforms

This startup time is too long for some applications. Some circuitry should be added to

increase the current limit during startup. An R-C series network could be added from U1 pin

1 to ground (pin 8). The network would have no effect once the feedback loop takes over –

the voltage on pin 1 is stable at 2.5 V.

The time can also be reduced by reducing the value of R7, but this will reduce efficiency.