Automotive laptop power supply. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Power Supplies

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Modern portable computers, the so-called laptops, enjoy well-deserved popularity. They are incomparably more convenient than their stationary counterparts. You can put a laptop in a briefcase and take it with you, for example, on a business trip, use it when working on the road. And even as a home "entertainment center", a laptop is more convenient, as it takes up minimal space. However, in my opinion, there is one extremely important disadvantage - most laptops are powered by a 19V mains supply, which makes it impossible to directly power them from the car's on-board network (12-14V). And this is very important, especially when working on the road, since the capacity of the laptop's own battery is usually enough for no more than two hours of work in active mode. But what if you, at some facility, need to process some data for a whole day, and there is no power source at hand except for the on-board network of the UAZ on which you arrived?

Of course, there must be some kind of network adapters that allow you to connect a laptop to a car, but practically they are not widely sold, and if there are, then the price "under order from Germany" is close to the price of a whole laptop.

Below is a description of a relatively simple adapter circuit (DC-DC converter), which increases the voltage of the car's on-board network to 19V, which is necessary to power a laptop. And maintaining this voltage stable.

Fig. 1

The adapter is based on the LM3524 microcircuit, which is a high-frequency pulsed DC-DC converter pumped by inductance, with an output current of up to 200mA, the output current of which, in this circuit, is increased to 3,5-4A using a powerful transistor switch (on transistors VT1 and VT2).

Let's take a closer look at the diagram. The voltage from the car's on-board network enters the power supply circuit of the D1 microcircuit and the output key through the fuse P1 and the low-resistance wire resistor R6, which softens the start of the generator and operates in the overload protection circuit. The current consumption of the D1 chip is determined by the voltage at R6 supplied to the overload control inputs - pins 4 and 5 of D1. The voltage at R6 is the greater, the greater the load current (and the actual current consumption from the source).

A pair of output transistors of the D1 microcircuit are connected in parallel (emitters - pins 14 and 11, collectors - pins 12 and 13). Collectors of output transistors are loaded with resistor R10. From this resistor, the pulses are fed to a non-inverting key on transistors VT1 and VT2. Transistor VT1 serves as a preliminary inverter, and s as an output transistor VT2, a powerful field-effect key transistor with a low open channel resistance is used. Due to the low resistance of the open channel, despite the significant current, the power dissipated on it is small, and the radiator is practically not required. Exclusively "for a guarantee", a plate radiator is installed on it from the output transistor of a vertical scanning TV of the 3-USCT type (a plate measuring approximately 25x35mm).

The voltage pumping occurs on the inductance L1. The diode VD2 rectifies the self-induction pulses and a certain constant voltage appears on the capacitor C11.

To stabilize the output voltage, a comparator is used, the inputs of which are pins 1 and 2 of D1. At pin 2, through the divider R1-R2, a reference voltage is supplied from the internal stabilizer of the microcircuit (the output of the stabilizer is pin 16). Pin 1 is supplied with voltage from the output of the power source, reduced by the divider R3-R4-R5. The value of the output voltage depends on the ratio of the shoulders of this divider, and is set by the trimmer resistor R4 (in fact, in the range from 15 to 22 volts). It is desirable that the resistor R4 be multi-turn, so its installation will be more accurate and stable.

Coil L1 is wound on a ring ferrite magnetic circuit with an outer diameter of 28 mm. Only 30 turns of wire PEV 1,56.

Diode VD2 (Schottky diode) must allow direct direct current of at least 5A.

The BU278 transistor can be replaced by any other similar transistor, for example, BUZ21L. The BC548 transistor can be replaced by any general purpose npn transistor, for example, KT503.

It is advisable to choose the LM3524 chip in a DlP package (it is more convenient to solder). You can replace the same SG3524 chip, but of a different production.

Resistor R6 - wire, with a power of at least 2W.

All capacitors must be rated for at least 25V.

Establishment comes down to setting the output voltage with a tuning resistor R4. It is desirable that R4 be multi-turn. You can pre-replace R4 with a variable resistor, and after adjusting, measure its resistance. Then, dial the required resistance from fixed resistors (by series or parallel connection), and install this "assembly" instead of R4.

The converter was assembled on a breadboard printed circuit board, so the track layout was not worked out.

When connecting to the vehicle on-board network, polarity must be strictly observed. Otherwise, the converter will fail. Optimum - connection directly to the battery terminals. In this case, there will be a minimum of interference, both from the converter and to the converter. The transmitter housing must be shielded.

Author: Karavkin V.; Publication: radioradar.net

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