TC62D902FG

2014-10-01

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11. Description of Operation

The basic circuit of this product is a flyback power supply.

An average LED current value is controlled by the peak current value ( IS ) of the secondary,

and the pulse width ( tS ) and the duty cycle control..

Start-Up Resistor)

This device is supplied operating current from the VCC terminal. The UVLO release voltage

threshold of the VCC pin in this case is a maximum of 13 V, the static operating current is a

maximum of 15 μA and the operating supply current is a maximum of 2.5 mA.

Therefore, start-up resistor R ( VCC ) can be calculated below.

R(VCC) ≦ (IC activation voltage/15μA) - (UVLO release voltage13V/2.5mA)

In the normal operation, this device gets an operating current from the bias side of the

transformer. It selects so as not for the VCC pin to exceed 24 V in the turn-ratio of the secondary

and the bias. When the turn-ratio is 1, the secondary voltage and the bias voltage are the

same almost.

Bias Voltage = LED VF / Turns ratio of Secondary and bias.

For example, if the VF of the LED is equal to or less than 24 V, the turn-ratio of the secondary and

the bias is 1:1. When the VF of the LED is bigger than the high value of VCC, it adjusts with the

turn-ratio or the Zener diode.

RSEN

ISEN

VSEN

Q1

VIN

VIN(peak)

VCC

Start-Up resistor

R(VCC)

1V

1V

VF

VF+1V

VF+1V

VF

GND

Ntr=Pri:Sec

Option Zener Diode：

When Vcc over than 24V.