USB port - 6-15 volt power supply. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Power Supplies
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Nowadays, USB is the universal computer port to which a wide variety of devices are connected. A sufficiently powerful 5 V voltage source is output to USB, so many devices not only exchange data through it, but are also powered from the USB port. These are various scanners, webcams, portable CD or DVD drives, modems, etc. On the Internet, you can find descriptions of very stupid knick-knacks powered by USB - microvacuum cleaners, tea heaters, and even microcoffee makers.
In principle, many other peripheral devices can be powered from USB, even those not designed for this, but there are some limitations. In particular, by the supply voltage, which is only 5 V. Despite the fact that peripherals powered by their own network adapters usually require a higher voltage.
The figure shows a diagram of a simple adapter that allows you to increase the voltage taken from the USB port to 6 ... 15 V (depending on the resistances of resistors R5 and R6), provided that the load current does not exceed 150 mA.
The circuit is based on a DC-DC boost converter based on the LM3578AM chip. Since the converter is a pulse converter, an inductance L1 is installed at the input, which prevents the penetration of impulse noise both into the computer circuit and from the computer into the circuit of the powered device, the A1 chip contains a PWM pulse generator and an output key. The key goes to pins 6 and 5. Pin 7 is the input of the protection control circuit, which determines the current through the key by the magnitude of the voltage drop across the resistance of resistors R2-R4. And when it exceeds the allowable value, protection is triggered.
The voltage pumping occurs on the inductance L2. Then this alternating voltage is rectified by the Schottky diode VD1 and smoothed out by capacitors C6 and C7. The output voltage is stabilized by comparing the voltage taken from the R5-R6 divider with the reference voltage generated by the stabilizer, which is part of the microcircuit.
Control input - output 1. The values of resistors R5 and R6 in the diagram are shown to obtain a nominal output voltage of 9 V:
- for a voltage of 6 V - R5 \u47d 6K, R9,1 \uXNUMXd XNUMX kOhm;
- for a voltage of 12 V - R5 \u110d 6K, R10 \uXNUMXd XNUMX kOhm;
- for voltage 15 V - R5=130K, R6=9,1 kOhm.
In principle, you can get a different voltage by choosing the appropriate resistances of resistors R5 and R6. The ratio of their resistances should be such that, with the required output voltage, there is a voltage of 1 V at pin 1 A1.
Mounting the converter is most conveniently done on a small printed breadboard.
Inductors L1 and L2 - ready-made, industrial production.
Author: Zhurbin A.
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