Modern portable computers, so-called, laptops, are popular. They are much more comfortable with their stationary counterparts. The laptop can be put in a bag and take with you, for example, on a business trip, to use them during field work. And even as a home entertainment center" laptop more convenient, as it takes up minimal space. However, in my opinion, there is one very important disadvantage - most laptops are powered from a network source voltage of 19V, making it impossible for them to direct power from the vehicle electrical system (12-14V). And this is very important, especially in fieldwork, as own capacity laptop battery usually lasts no more than two hours of work in active mode. But what if you, at some object you need a whole day to process some data, but there is no power source except the onboard network "UAZ", where you came?
Surely there must be some network adapters enable you to connect your laptop to the car, but almost in a broad sell them there, and if there is, then the price of "under-ordering from Germany" is produced close to the price of a laptop.
The following is a description of a relatively simple circuit adapter (DC-DC Converter) that increase the voltage of the vehicle electrical system to 19V needed to power the laptop. And supporting this voltage is stable.
Fig. 1
The adapter is made on the basis of chip LM3524, representing a high frequency switching DC-DC Converter pumped across the inductor, output current up to 200mA output current which, in this scheme, upgraded to 3.5-4A with a powerful transistor switch (transistors VT1 and VT2).
Look at the diagram carefully. The voltage of the vehicle electrical system is supplied to the supply circuit chips D1 and an output key using the fuse P1 and a low-resistance wire resistor R6, softening the generator start-up and running in the circuit overload protection. The current consumption of the chip D1 determines the voltage on R6, arriving at the inputs of congestion control - conclusions 4 and 5 of D1. The voltage across R6 is greater, the greater the load current (actual current consumption from the source).
A pair of output transistors of the chip D1 connected in parallel (the emitter-conclusions 14 and 11, collectors - conclusions 12 and 13). Loaded the collectors of the output transistors a resistor R10. With this resistor the pulses are key to the non-inverting transistors VT1 and VT2. Transistor VT1 is advanced inverter, and s as the output transistor VT2 use powerful key field effect transistor with a low resistance of the open channel. Due to the small resistance of the open channel, despite significant current, power it dissipates is small, and the radiator is almost not required. Only "guarantee" it has radiator plate from the output transistor, a vertical scan of the TV type 3-USCT (plate sizes approximately Hm).
Pumping voltage occurs across the inductor L1. Diode VD2 rectifies the pulses of self-inductance and the capacitor C11 to be a certain DC voltage.
To stabilize the output voltage used by the comparator, the inputs of which the outputs 1 and 2 of D1. On pin 2 through a divider R1-R2, the reference voltage is supplied from the internal regulator circuit (the output of the stabilizer, o 16). The output 1 is energized from the output of the power source, a lower divider R3-R4-R5. The magnitude of the output voltage depends on the ratio between the shoulders of the divisor, and set a trimming resistor R4 (actually, in the range from 15 to 22 volts). It is desirable that the resistor R4 was multi-turn, so its installation is more accurate and more stable.
Coil L1 is wound on a ferrite ring cores outer diameter of 28mm. A total of 30 turns of wire sew 1,56.
Diode VD2 (diode the Schottky) should allow for a direct constant current of at least 5A.
Transistor BU278 can be replaced by any other similar transistor, for example, BUZ21L Transistor S can be replaced by any n-p-n transistor in common use, for example, CT.
Chip LM3524 it is advisable to choose DlP-case (easier to solder). You can replace the same chip SG3524, but another production.
Resistor R6 - wire, of a power not less than 2W.
All capacitors must be rated for a voltage not lower than 25V.
The establishment comes down to setting the output voltage trimming resistor R4. It is desirable that R4 was reusable. Can R4 preliminary to replace a variable resistor, and after adjusting to measure its resistance. Then, to gain the necessary resistance to permanent resistors (through a serial or parallel connection), and install this "Assembly" instead of R4.
The transducer was assembled on the PCB layout, therefore, the circuit wiring tracks not elaborated upon.
When connected to a vehicle power supply is necessary to strictly observe the correct polarity. Otherwise, the Converter fails. Optimally - connecting directly to the battery terminals. In this case, there will be a minimum of interference from both the Converter and the inverter. Transmitter housing must be shielded.
Author: V. Why; Publication: www.radioradar.net