It never hurts to own a car, aside from the nest cigarette lighter, and a service connector, adapted to USB or even miniUSB. Such adapters useful in many cases, for example, to power the peripheral equipment PC, charge mobile phones, video recorders of events and just the fact that structurally developed under USB power. And this is quite possible.
With a relatively small load currents (up to 0.5 A) when not needed to achieve maximum efficiency, it is possible to simplify the electrical circuit for voltage regulators, provided that the input voltage is already quite stable. This is exactly the case.
The device is made on the basis of the DC-DC Converter on-chip MSA ON Semiconductor. MSA combines the comparator generator pulses (up to 100 kHz), the driver's internal temperature-compensated the reference voltage source and powerful output key (Fig. 1).
Fig. 1. Scheme internal nodes SA and its analogues
The input voltage of the chip is from 3 to 40 V, maximum output current, specified in reference data, - 1.5 A. However, in my opinion, this current the chip is in a DIP-8 (photo 1) can be given only in emergency, emergency and short mode. Safe current for this chip installed without radiator and other elements of the ventilated cooling shall not exceed - 0,3...0,4 A. In our case, this corresponds to a task.
The electrical circuit of the Converter is presented in figure 2.
Fig. 2. Electric circuit device adapter for USB on-a-chip MSA
By the way, there are different ways of increasing the output current of the chip MSA. For example, if you increase the inductance of the inductor, the voltage and current in the load also can be increased.
The output of the Converter there is no need to install the oxide capacitor large capacity. First, the input voltage in the car enough stable, and second, the internal protection circuits MSA triggered, not allowing the Converter to operate normally.
Details
Analog circuits MSA - CREW; possible replacement for AR, NJM2360, KS34063.
In the device used resistors MLT-0.25 or similar imported type MF-25. Oxide capacitors C1 and NW - type K50-29 or similar.
Diode VD2 - diode 1N5819 Schottky replaceable on 1N5817 1N5818 or. This a diode with a current capacity equal to the load current.
The inductor L1 is a coil on the rod with a length of 8 mm ferrite brand contains 40 NC of turns of wire sew with a diameter of 0.75 mm. Active resistance L1 is not greater than 0.1 Ohm's. Such a coil can be purchased at the shop of electronic components in a ready form to example, the DM chokes magnetic circuit with the core). The only condition: the throttle And must withstand current up to 1A inclusive (with a margin).
The Zener diode VD1 in this case protects the input circuit of the Converter on chip DА1 overvoltage. You can replace the 1N4745А (with voltage stabilization 16 In) or even eliminate entirely, because this chip designed for input voltages up to 40 V.
Figure 4 shows the USB-connector, mounted in automotive splitter, within which is mounted a printed circuit Board device (photo 1).
Photo 1. Appearance of the device is modified splitter
Photo 2. External view of the circuit Board mounted with discrete elements and chip
Author: A. Kashkarov