Step up DC / DC Converter with LT1615

Interesting DC / DC converter Linear Technology has presented the company, this chip is the boost converters that allow you to get the maximum voltage in 34B with the input voltage from 1.2V to 15V. It comes in a compact package of 5 pin SOT23, while for work requiring minimal external circuitry. These chips can be used, for example, a high voltage for the LCD screen or for the varicap.

Para LT1615 internal ditunjukkan pada gambar. Ini berisi saklar monostable untuk 400ns, yang menentukan transistor off. Jika tegangan pada umpan balik turun di bawah 1.23V, transistor menyala dan arus dalam kumparan mulai meningkat. Yang meningkatkan medan magnet dalam kumparan. Ketika arus dalam kumparan mencapai 350 mA monostable beralih dari transistor dalam 400ns berikut. Ketika arus dalam kumparan tidak dapat langsung hilang dan terus mengalir dalam arah yang sama seperti sebelumnya, tetapi menurun hampir linear. Ini saat biaya dioda Schottky (SS24 – 40V/2A) output kapasitor. Sementara tegangan pada FB (Pin 3) lebih besar dari 1.23V, tidak ada yang terjadi, segera setelah tegangan turun di bawah 1.23V siklus berulang. Histeresis pada pin FB 8 mV. Tegangan output dapat dihitung dengan menggunakan rumus berikut:

Vout = 1,23 V x (R1 + R2) / R2

The value of resistor R1 can be chosen in the range megaohm as the current flows into FB more than nanoamper.

When power is applied or when the output is shorted, the device enters the power-up. While the voltage at FB is less than 0.6V, the output current integrated circuits is limited to 250 mA instead of 350 mA and the monostable switch increased to 1.5us. These measures reduce the output current in the coil and the diode, while the output voltage rises.

To reduce the noise produced by the chip, input and output must have the bypass capacitors. At the same time they should be located as close as possible to the chip itself.

The choice of inductance is described in detail in the description of the chip LT1615 site Linear Technology . Usually it is 4.7 uH for the output voltage less than 7V. For higher voltages to be used in the inductance of 10uH. The calculation of this inductance is given in the description of this chip . Schottky diode must have a reverse voltage is much greater than the output voltage. Recommended Diodes MBR0530 or SS24.

Log in / SHDN can be used to disable the transmitter, it is necessary to connect it to the ground. If voltage is more than 0.9V, the transmitter is turned on.

In this circuit, this converter can be used to produce a bipolar voltage, which can be used, for example, to power operational amplifiers.