In the operation of car audio or connected equipment in stationary the necessary conditions suitable power source, which should give the voltage from 12 to 14.5 In, a stable set in this range, when a maximum current of 20 A. the power supply, the circuit who here has such characteristics.
AC current 220 V from mains power is supplied via a 5 amp fuse F1 on the primary winding of the power transformer T1. It is imported with transformer primary winding and secondary 230 V to 20 V at currents up to 25 A. If necessary, such a transformer can be manufactured independently on the basis of the power transformer from an old colored tube TV, or on the basis of power-frequency transformer with a capacity not below 500 watts for power halogen lamps (12 V) or to obtain for 36 In power equipment by means of winding respectively its secondary winding.
Since the secondary winding voltage of 20 V is supplied to the rectifier bridge VD1. It the finished bridge type Assembly. MW maximum DC 35 A. Ripple rectified voltage smoothing capacitor C1 with a capacity of 22000 UF. In the absence of capacitor such a large capacity, you can replace a few capacitors the smaller capacity connected in parallel, so that in the sum of not less than 20,000 UF (more is possible, but not less).
Constant voltage the capacitor C1 at idle is 26 V.
The stabilizer consists of schematic of the stabilizer on the IC A1 and the output of the voltage regulator transistors VT1-VT5, powerful transistors VT2-VT5 which connected in parallel.
Resistors R5-R8 serve to equalize the current through the transistors, as in the result of the differences in the coefficients of transmission they can under equal conditions be open to different degrees. The resistors connected in the emitter circuits of automatic help install voltage base-emitter under the action of the load current at which the transistors open equally.
IC LM723 is a monolithic IC with adjustable stabilizer the output voltage of the and circuit overload protection. Adjustable output voltage occurs by means of the resistor R3, which, together with resistors R2 and R4 forms a divider output voltage. The setting is the dependence voltage at pin 4 A1 from the output voltage.
The comparator chip operates so that the voltage at the output (pin 10) adjust so that the voltage on the pin 4 was unchanged. Accordingly, the voltage at pin 10 is almost equal to the output. But the maximum allowable output current is small, therefore, to obtain the maximum load current of 20 A required current amplifier, kojima is a circuit transistors VT1...VT5.
Protection circuits overcurrent works by measuring the voltage across the resistance connected in series to the load. The inputs of the current sensor are pins 2 and 3 A1. These conclusions connected parallel to the resistance formed by the resistors R9-R12, connected in series with the load.
It is clear that the following Ohm's law, the voltage across the resistance will increase with increasing current.
Until the voltage between pins 2 and 3 below 0.6 In protection does not work, taking this as a fact that the load current does not exceed the maximum allowable values. At currents approaching to 23-24 And the voltage between pin 2 and 3 reaches 0.6 V and more. This leads to the triggering of protection that reduces the voltage on the output 10 A1 to zero, and thus switches off the load.
Maximum output the current can be set and the other, respectively, by changing the net the resistance of R9-R12, in this case, when selecting the upper threshold of the load current 23 As well of 0.025 Ohms.
Or you can even to organize the adjustment of the maximum output current, in parallel if low-impedance resistors R9-R12 include one variable resistor, somewhere between 10 and 100 Ohms, and the control to alleviate the tension with his engine and one of the extreme conclusions. The resistor will be to be a voltage divider R9-R12. But in this case, resistance R9 R12...need to count on the lower limit adjustment the maximum load current. So through this resistor can be adjusted trip current protection.
The scheme provides quite a good stability of the set output voltage, for example, when the output voltage of 13, under the load 22 And the voltage is reduced only by 40...60 mV.
HL1 led serves to indicate included in the network state. The led indicates HL2 normal mode output power. That is, it burns when there is the output voltage. If it is not lit, but lit HL1 this suggests that the load is short circuit or overload and the output of the stabilizer disconnected protection system current, or blown fuse F2 included at the output of the rectifier.
Transistors VT2-VT5 have to be on a larger radiators, ensure effective cooling. A good option - use plate aluminum radiator together with the fan. In this case, the radiator and fan can be used from a failed power supply unit of the personal computer type AT or ATX. A motor fan can be connected in parallel with capacitor C4.
Details. About the transformer is said in the beginning of the article.
Capacitor C1 - analogue C50-35, import, at 22 thousand microfarads. You can replace multiple smaller capacitors included in parallel.
Rectifier bridge can be replaced by another at a constant current of 30 A or collect it on the diodes are designed for the same current, for example, D, CD, CD.
Transistors can 1N3055 replace CT. Need transistors to capture to close in the parameters. Preferably, one literal symbol, from the same batch, and even better before installation pick them up in as close as possible to the coefficients h21e.
LEDs - normal, flat, almost any. Can use AL307. When there is insufficient brightness can be lowered the resistors R1 and R13.
Resistors R5-R12 - patipatti, wire, resistance of 0.1 Ohm.
If parallel the resistors R9-R12 connect arrow millivoltmeter, on its scale will be possible to determine the load current (accordingly, altering the scale in terms of current).
Author: Gorchuk N. In.