LED torch using NSI45090JDT4G constant current regulator
A very simple LED torch circuit can be designed using the NSI45090JDT4G adjustable constant current regulator (CCR) designed by ON Semiconductor ,using extreme few external components .
NSI45090JDT4G device is designed to provide a cost effective solution for regulating current in LEDs.
This Constant current regulator is based on patent-pending Self-Biased Transistor (SBT) technology and regulates current over a wide voltage range. It is designed with a negative temperature coefficient to protect LEDs from thermal runaway at extreme voltages and currents.
The Radj pin allows Ireg(SS) to be adjusted to higher currents by attaching a resistor between Radj (Pin 3) and the Cathode (Pin 4). The Radj pin can also be left open (No Connect) if no adjustment is required.
The maximum current that can be adjusted using this chip is around 160 mA , and the maximum input voltage is around 45 volts .
The D1 from the circuit shown here is used for reverse battery protection .
Bellow you can see how simple is to design a circuit using this chip ( all data shown bellow are for this schematic ) .
LED’s = ((Vin − QX VF − D1 VF)/LED VF)
Example: Vin = 12 Vdc, QX VF = 3.5 Vdc, D1VF = 0.7 V
LED VF = 2.2 Vdc @ 30 mA
(12 Vdc − 4.2 Vdc)/2.2 Vdc = 3 LEDs in series.