Introduction to several battery-powered LED controllers

For white LEDs with a forward voltage of 3.5 to 4.2V (at 20mA), a boost converter is usually required. A charge pump (such as MAX682 to MAX684) can be used together with MAX1916 to form a driver circuit for this type of LED , as shown in Figure 1. MAX682 to MAX684 can convert a 2.7V input voltage into a 5.05V output, and the output current can reach 250mA, 100mA, and 50mA respectively. The LED can be turned off using the shutdown control pin of MAX684 or the enable control pin of MAX1916. In the circuit of Figure 1, when MAX684 is in shutdown mode, the power supply current drops to 22μA; when RSET=43kΩ, the LED current is 22mA;

Figure 2 shows an LED current control circuit using a charge pump. The typical value of the feedback regulation voltage is 1.235V, Ipk=1.235/R SENSE, and a 24Ω current sensing resistor can provide 50mA current to the diode. When the charge pump is working, the output voltage rises to the LED turn-on voltage, and the LED starts to conduct. The typical forward voltage of a white LED is 3.5 (1±0.1) V. Adding the feedback regulation voltage, the bias voltage provided by the output of the MAX1759 is 4.735V. The ripple of the output voltage of this circuit is within 40mV, which will not cause significant changes in the LED output and is usually not noticeable to the human eye. In addition, there is no DC path between the input and output of the circuit in Figure 2 when it is off.