The entire power converter is assembled on a small printed circuit board made of foil fiberglass, transistors and powerful diodes are soldered outward with metal flanges - a massive aluminum radiator is screwed to them. Its dimensions depend on the load connected to the device.
The following photo shows the view from the installation side. Drawing the board and circuit in Layout - on the forum.
Schottky diodes are used as rectifier diodes. I used this device to swing two STK4044s in the car, subjective assessment - very good!
At the output voltage U=+-51V, for normal operation of STK microcircuits at idle, at P=max the drawdown is about 1.5 Volts per arm. I think this failure is hardly noticeable by ear, especially since hardly anyone listens to the amplifier at maximum all the time. The board was designed by hand, one might say in a hurry, so you can improve it at will. In general, this homemade converter for automotive ULF works 100% - I recommend repeating it. The dependence of power on output voltage and speaker resistance of the UMZCH is shown in more detail in the table.
Perhaps the most difficult part of amplifier design is powering the subwoofer channel from the on-board 12 volt network. There are a lot of reviews about it in various forums, but it is very difficult to make a really good converter using the advice of experts, see for yourself when it comes to this part of the design. To do this, I decided to focus on assembling a voltage converter; perhaps this will be the most detailed description, since it outlines two weeks of work, as people say - from<<А>>to<<Я>>.
There are a lot of voltage converter circuits, but as a rule, after assembly, defects, malfunctions, and incomprehensible overheating of individual parts and parts of the circuit appear. Assembling the converter took me two weeks, since a number of changes were made to the main circuit; in the end, I can safely say that the result was a powerful and reliable converter.
The main task was to build a 300-350 watt converter to power the amplifier according to the Lanzar scheme, everything turned out beautifully and neatly, everything except the board, we have a big shortage of chemicals for etching boards, so we had to use a breadboard, but I don’t advise repeating my torment, soldering Wiring for each track, tinning each hole and contact is not an easy job, this can be judged by looking at the back of the board. For a beautiful appearance, wide green tape was glued to the board.
PULSE TRANSFORMER
The main change in the circuit is the pulse transformer. In almost all articles on homemade subwoofer installations, the transformer is made on ferrite rings, but the rings are sometimes not available (as in my case). The only thing that was there was an Alsifer ring from a high-frequency choke, but the operating frequency of this ring did not allow it to be used as a transformer in a voltage converter.
Here I was lucky, I received a couple of computer power supplies almost for nothing; fortunately, both units had completely identical transformers.
As a result, it was decided to use two transformers as one, although one such transformer can provide the desired power, but when winding the windings simply would not fit, so it was decided to remake both transformers.
First, you need to remove the heart; in fact, the work is quite simple. Using a lighter, we heat the ferrite stick, which closes the main heart, and after 30 seconds of heating, the glue melts and the ferrite stick falls out. The properties of the stick may change due to overheating, but this is not so important, since we will not use sticks in the main transformer.
We do the same with the second transformer, then we remove all the standard windings, clean the transformer terminals and cut off one of the side walls of both transformers, it is advisable to cut down the wall free from contacts.
The next part of the work is gluing the frames. You can simply wrap the fastening area (seam) with electrical tape or tape; I do not recommend using various adhesives, as this may interfere with the insertion of the core.
I had experience in assembling voltage converters, but nevertheless this converter cost me all the juice and money, since during the work 8 field workers were killed and the transformer was to blame for everything.
Experiments with the number of turns, winding technology and wire cross-sections led to pleasing results.
So the hardest part is winding. Many forums advise winding a thick primary, but experience has shown that you don’t need much to get the specified power. The primary winding consists of two completely identical windings, each of them is wound with 5 strands of 0.8 mm wire, stretched along the entire length of the frame, but we won’t rush. To begin with, we take a wire with a diameter of 0.8 mm, the wire is preferably new and smooth, without bends (although I used a wire from the network winding of the same transformers from power supplies).
Next, we wind 5 turns along one wire along the entire length of the transformer frame (you can also wind all the wires together with a bundle). After winding the first core, it needs to be strengthened by simply winding it onto the side terminals of the transformer. Afterwards we wind the rest of the wires, evenly and neatly. After winding is completed, you need to get rid of the varnish coating on the ends of the winding; this can be done in several ways - heat the wires with a powerful soldering iron or remove the varnish individually from each wire with a mounting knife or razor. After this, you need to tin the ends of the wires, weave them into a pigtail (it’s convenient to use pliers) and cover them with a thick layer of tin.
After this, we move on to the second half of the primary winding. It is completely identical to the first one; before winding it, we cover the first part of the winding with electrical tape. The second half of the primary winding is also stretched across the entire frame and wound in the same direction as the first; we wind it according to the same principle, one core at a time.
After winding is completed, the windings need to be phased. We should get one winding, which consists of 10 turns and has a tap from the middle. It is important to remember one important detail here - the end of the first half should join with the beginning of the second half or vice versa, so that there are no difficulties with phasing, it is better to do everything from photographs.
After a lot of hard work, the primary winding is finally ready! (you can drink beer).
The secondary winding also requires a lot of attention, since it is this that will power the amplifier. It is wound according to the same principle as the primary, only each half consists of 12 turns, which completely ensures a bipolar output voltage of 50-55 volts.
The winding consists of two halves, each is wound with 3 strands of 0.8 mm wire, the wires are stretched throughout the frame. After winding the first half, we insulate the winding and wind the second half on top in the same direction as the first. As a result, we get two identical halves, which are phased in the same way as the primary. Afterwards, the leads are cleaned, intertwined and sealed to each other.
One important point - if you decide to use other types of transformers, then make sure that the halves of the heart do not have a gap; as a result of experiments, it was found that even the slightest gap of 0.1 mm sharply disrupts the operation of the circuit, the current consumption increases by 3-4 times , the field-effect transistors begin to overheat so that the cooler does not have time to cool them.
The finished transformer can be shielded with copper foil, but this does not play a particularly big role.
The result is a compact transformer that can easily deliver the required power.
The circuit diagram of the device is not simple; I do not advise novice radio amateurs to contact it. The basis, as always, is a pulse generator built on the TL494 integrated circuit. The additional output amplifier is built on a pair of low-power transistors of the BC 557 series, almost a complete analogue of the BC556; from the domestic interior, you can use the KT3107. Two pairs of powerful field-effect transistors of the IRF3205 series are used as power switches, 2 field-effect transistors per arm.
The transistors are installed on small heat sinks from computer power supplies and are pre-insulated from the heat sink with a special gasket.
The 51 ohm resistor is the only part of the circuit that overheats, so a 2-watt resistor is needed (although I only have 1 watt), but overheating is not terrible, it does not affect the operation of the circuit in any way.
Installation, especially on a breadboard, is a very tedious process, so it’s better to do everything on a printed circuit board. We make the plus and minus tracks wider, then cover them with thick layers of tin, since a considerable current will flow through them, the same with the field drains.
We set 22 ohm resistors at 0.5-1 watt, they are designed to remove overload from the microcircuit.
The field gate current limiting resistors and the microcircuit supply current limiting resistor (10 ohm) are preferably half a watt, all other resistors can be 0.125 watt.
The frequency of the converter is set using a 1.2nf capacitor and a 15k resistor; by decreasing the capacitance of the capacitor and increasing the resistance of the resistor, you can increase the frequency or vice versa, but it is advisable not to play with the frequency, since the operation of the entire circuit may be disrupted.
The rectifier diodes were used in the KD213A series; they did the best job, because due to the operating frequency (100 kHz) they felt excellent, although you can use any high-speed diodes with a current of at least 10 amperes; it is also possible to use Schottky diode assemblies, which can be found in the same computer power supplies, in one case there are 2 diodes that have a common cathode, so for a diode bridge you will need 3 such diode assemblies. Another diode is installed to power the circuit; this diode serves as protection against power overload.
Unfortunately, I have capacitors with a voltage of 35 volts of 3300 microfarads, but it is better to select a voltage from 50 to 63 volts. There are two such capacitors per arm.
The circuit uses 3 chokes, the first to power the converter circuit. This choke can be wound on standard yellow rings from power supplies. We wind 10 turns evenly around the entire ring, the wire is divided into two 1 mm wires.
Chokes for filtering RF interference after the transformer also contain 10 turns, wire with a diameter of 1-1.5 mm, wound on the same rings or on ferrite rods of any brand (the diameter of the rods is not critical, length 2-4 cm).
The converter is powered when the Remote Control (REM) wire is connected to the power supply positive, this closes the relay and the converter starts working. I used two relays connected in parallel at 25 amps each.
The coolers are soldered onto the converter block and turn on immediately after the REM wire is turned on. One of them is designed to cool the converter, the other is for the amplifier, you can also install one of the coolers in the opposite direction so that the latter removes warm air from the common case.
RESULTS AND COSTS
Well, what can I say, the converter justified all hopes and costs, it works like a clock. As a result of the experiments, he was able to deliver an honest 500 watts and would have been able to do more if the diode bridge of the unit that powered the converter had not died.
Total spent on the converter (prices shown are for the total number of parts, not for one)
IRF3205 4pcs - 5$
TL494 1pc -0.5$
BC557 3pcs - 1$
KD213A 4pcs - 4$
Capacitors 35V 3300uF 4pcs - $3
Resistor 51 ohm 1 piece - $0.1
Resistor 22 ohm 2 pcs -0.15$
Development board - $1
From this list, I got the diodes and capacitors for free, I think except for the field workers and the microcircuit, everything can be found in the attic, asked from friends or in workshops, so the price of the converter does not exceed $10. You can buy a ready-made Chinese amplifier for a subwoofer with all the amenities for $80-100, and products from well-known companies cost a lot, from $300 to $1000. In return, you can assemble an amplifier of identical quality for only $50-60, even less if you know where to get the parts from , I hope I was able to answer many questions.
The supply voltage of the on-board network of a passenger car is 12v. If we set the impedance of the speaker system to be 4 om , then the maximum power that can be obtained at this supply voltage will be 36w. This is the most theoretical maximum, assuming bridge connection of the amplifier and zero resistance of the output stage transistors in the open state, that is, practically for a digital pulse amplifier. For an analog amplifier, the maximum power will be no more than 20w per channel when bridged. To obtain more power, it is necessary either to use a pulse output stage that generates an audio signal using the pulse-width modulation method, or it is necessary to reduce the impedance of the speaker system. In the first case, the sound will contain an ultrasonic component from PWM, and also, more complex measures will be needed to combat signal distortion. In the second case, the resistance of the voice coil will already be comparable to the resistance of the wires going to it, which, in general, can nullify such measures. There is another way - organizing a voltage supplement in the output stage by rectifying the output signal and a large storage capacitance. But this is also not very good, since it is difficult to obtain a sufficiently linear frequency response, and the dependence of the power transmission coefficient on the magnitude of the input signal may be uneven. Of course, all of the measures listed above to increase the output power of an amplifier powered from a low-voltage source have a right to exist, and if carried out carefully and competently, give good results. But, there is a more traditional way to increase the power of the ULF - simply by increasing its supply voltage using a voltage converter, and even organizing bipolar power supply with it. This method allows you to use in a car not a compromise automobile version of ULF, but almost any ULF circuit used in stationary equipment, capable of providing significantlybetter sound quality than clever circuits of powerful auto-ULFs, with voltage boosters on capacitors and low-impedance speaker systems, because as any amateur will say hl-end - the best sound comes from a simple single-tube cascade without feedback circuits and with a high-impedance output. But this is of course the other extreme.
Whatever the circuit of the “regular” ULF that you plan to use in a car, it requires a supply voltage converter. This converter must produce increased bipolar voltage, in this case±20v with output current up to 4A. Such a power source will be able to power ULF with an output power of up to 60-70w, made according to the traditional design.
The schematic diagram of the converter is shown in the figure. The scheme is largely standard. The master oscillator with a PWM circuit for stabilizing the output voltage is made on microcircuit A1. Nominal generation frequency is about 50 kHz (regulated by resistor r 3). The reference voltage from the output is supplied to the input of the comparator (pin 1) and, depending on the voltage at pin 1, the comparator changes the width of the pulses generated by the microcircuit so as to maintain the output voltage stable. The output voltage value is precisely set by a trimming resistor r 8, which forms this measuring voltage. Chain vd 1- c 3- r 4- r 5 forms a smooth start of the circuit.
Output antiphase pulses are removed from pins 8 and 11 of A1 to be supplied to the output stages, but here they first go to the output transistor driver on chip A2. The task of this microcircuit is to amplify the power of these pulses, since it uses powerful field-effect transistors with low open-channel resistance. Such transistors have significant gate capacitance. To ensure sufficient speed of opening of transistors, it is necessary to ensure the fastest possible charging and discharging of the capacitances of their gates; this is what the driver on A2 serves for.Large capacitors C6 and C7 are installed along the power circuit; they must be soldered with a thick wire directly at the tapping point of the primary winding of the transformer.
For the option giving bipolarsupply voltage (as in the diagram), the secondary winding has a tap from the middle. This tap through inductance l 2 connected to the common wire. On diodes vd 2-vd 5 (Schottky diodes) a rectifier is made that gives positive and negative voltagemarriage. In a single-supply circuit, the secondary winding has no tap, and the negative terminal of the rectifier bridge must be connected to a common negative. In this case, if voltage is required 40v resistor value r 9 should be doubled compared to that indicated on the diagram.
As a basis for the transformer, a carefully disassembled and unwound transformer from the power supply of an old color TV of models of the 3-USTST line is used. It should be noted that the transformer core is glued there quite firmly and not every attempt to separate its halves ends in success. In this sense, in my opinion, it is better to have two such transformers (fortunately, there are now plenty of unnecessary power supplies MP-1, MP-3, etc.). For one transformer, cut the frame along with the winding and remove it. What remains is the core, which, without a frame and winding, can be divided much easier and more efficiently. For the second transformer, carefully break and break the core so as not to damage the frame. As a result of this “barbarism” you get one good core and one good frame.
Now about winding. The winding must hold a large current, so it requires a thick wire. To wind the primary winding, a PEV 0.61 wire folded in three is used. For the secondary, the same wire, but folded in half. Primary winding - 5+5 turns, secondary - 10+10 turns.
Coil l 1 - not a coil, but a ferrite tube placed on a wire. l 2 - 5 turns of PEV 0.61 folded in three on a ferrite ring with a diameter of 28 mm.
Rare transistors fdb 045an can be replaced by others, and the choice is quite large, since a maximum drain-source voltage of at least 50v The drain current is not lower than 70A and the channel resistance in the open state is not more than 0.01 Ohm. Using these parameters, you can select quite a lot of replacement candidates, that is, almost any fet -transistor for car ignition switches and other things.
Capacitors C11 and C12 for voltage not lower 25v other capacitors for voltage not lower 16v.
Gorchuk N.V.
Section: [Power supplies (switching)]
Save the article to:
If your car doesn't have room for a powerful audio system and your car amplifier is out of use, don't give it away or throw it away. It can be used indoors or outdoors; you can use the power supply from your computer to connect it.
WHAT IS THE ARTICLE ABOUT?
Actions
1. Find the power on pin
- The package with the power supply (when purchasing a new one) should contain a pinout diagram. Look for a pin that is labeled like “Power on,” “PS OK,” or other keywords indicating a signal. It will be on the largest connector.
- On new power supplies, 99% of the time this will be a green wire, but for older models (“10+ years”) the wire may be yellow or purple. If your power supply doesn't come with a pinout diagram, check the manufacturer's website for a pinout diagram.
2. Cut the power-on wire from the connector and strip the insulation from the edge
3. Cut the ground wire from the connector and also strip the edge of the insulation
- Refer to the pin diagram to find out what color the ground wire is. 99.9% it will be a black wire.
4. Connect both stripped ends and insulate
5. Connect all 12v wires
stripping their ends together, having previously cut them off from the connector.
- Refer to the pinout diagram to see what color the 12v wires are. In 99.9% of cases these will be yellow wires.
6. Connect all negative wires together, cutting them off from the connector and stripping the ends
- Refer to the pinout diagram to see which color is negative. In 99.9% of cases these will be black wires.
7. Take the twisted yellow 12v wires and attach them to the “+” terminal of the amplifier
- Some amplifiers may simply label "12v" instead of "+".
8. Take the twisted black wires and attach them to the “-” terminal of the amplifier
9. To connect “+” or “12v” to the “REM” or “REMOTE” source on the amplifier, use a discarded piece of wire
10. Connect the signal source, speakers and our power supply to the amplifier
- Now you can plug in the power supply and enjoy the music!
- You can add a switch in step 4. Simply connect both ends of the wire to the switch. This will give you the ability to turn off the power with a button instead of having to unplug and plug in the power source.
Rice. 1 mono-board car audio amplifier with separate power voltage converters
Voltage converter in the power supply circuit of car amplifiers, like any power source, has some output resistance. When powered from a common source, a relationship arises between the channels of multi-channel audio amplifiers, which is greater, the higher the output impedance of the power source. It is inversely proportional to the power of the converter.
One of the components of the output resistance of the power supply is the resistance of the supply wires. In high-end models, copper buses with a cross-section of 3...5 mm are used to power the output stages of the audio power amplifier. This is the simplest solution to problems with power supply to an audio amplifier, improving dynamics and sound quality.
Of course, by increasing the power of the power source, the mutual influence of the channels can be reduced, but it cannot be completely eliminated. If you use a separate converter for each channel, the problem is eliminated. In this case, the requirements for individual power supplies can be significantly reduced. Typically, the level of crossover attenuation of car amplifiers with a common power supply is 40...55 dB for budget models, and 50...65 dB for more expensive ones. For car audio amplifiers with separate power supplies, this figure exceeds 70 dB.
Supply voltage converters are divided into two groups - stabilized and unstabilized. Unstabilized ones are noticeably simpler and cheaper, but they have serious disadvantages. At power peaks, the output voltage of the converter decreases, which leads to increased distortion. If you increase the power of the inverter, it will reduce the efficiency at low output power. Therefore, unstabilized converters are used, as a rule, in inexpensive amplifiers with a total channel power of no more than 100... 120 W. At higher amplifier output power, preference is given to stabilized converters.
As a rule, the power supply is mounted in the same housing with the amplifier (Fig. 1 shows a monoboard of a car audio amplifier with separate supply voltage converters), but in some designs it can be made in the form of an external unit or a separate module. To turn the car amplifier into amplifier operating mode, the control voltage from the head unit (Remote output) is used. The current consumed by this pin is minimal - a few milliamps - and is in no way related to the power of the amplifier. Car amplifiers must use protection against load short circuits and overheating. In some cases, there is also protection for acoustic systems from DC voltage in the event of failure of the amplifier output stage. This part of the circuit for modern car amplifiers has become almost standard and may differ in minor changes.
Rice. 2 Diagram of a stabilized power supply for a car audio amplifier "Monacor NRV 150"
In the first automobile amplifiers, power supplies used voltage converters made entirely of discrete elements. An example of such a circuit for a stabilized power supply for a car audio amplifier "Monacor HPB 150" (Fig. 2). The diagram retains the factory numbering of elements.
The master oscillator is made using transistors VT106 and VT107 according to a symmetrical multivibrator circuit. The operation of the master oscillator is controlled by a key on transistor VT101. Transistors VT103, VT105 and VT102, VT104 are push-pull buffer cascades that improve the shape of the master oscillator pulses. The output stage is made of parallel-connected bipolar transistors VT111, VT113 and VT110, VT112. The matching emitter followers on VT108 and VT109 are powered by reduced voltage taken from part of the primary winding of the transformer. Diodes VD106 - VD111 limit the degree of saturation of the output transistors. To further speed up the closing of these transistors, diodes VD104, VD105 were introduced. Diodes VD102, VD103 ensure smooth startup of the converter. From a separate winding of the transformer, a voltage proportional to the output is supplied to the rectifier (diode VD113, capacitor C106). This voltage ensures fast closing of the output transistors and helps stabilize the output voltage.
The disadvantage of bipolar transistors is the high saturation voltage at high current. At a current of 10... 15 A, this voltage reaches 1 V, which significantly reduces the efficiency of the converter and its reliability. The conversion frequency cannot be raised above 25...30 kHz; as a result, the dimensions of the converter transformer and losses in it increase.
The use of field-effect transistors in the power supply increases reliability and efficiency. The conversion frequency in many blocks exceeds 100 kHz. The advent of specialized microcircuits containing a master oscillator and control circuits on a single chip has significantly simplified the design of power supplies for powerful automotive amplifiers.
Rice. 3 Simplified circuit of an unstabilized power supply voltage converter for a Jensen car amplifier
A simplified diagram of an unstabilized power supply voltage converter for a four-channel car amplifier "Jensen" is shown in Fig. 3 (the numbering of elements in the diagram is conditional).
The master oscillator of the voltage converter is assembled on a KIA494P or TL494 microcircuit (domestic analogue - KR1114EU4). The protection circuits are not shown in the diagram. In the output stage, in addition to the types of devices indicated in the diagram, you can use powerful field-effect transistors IRF150, IRFP044 and IRFP054 or domestic KP812V, KP850. The design uses separate diode assemblies with a common anode and a common cathode, mounted through insulating heat-conducting pads on a common heat sink together with the output transistors of the amplifier.
The transformer can be wound on a ferrite ring of standard size K42x28x10 or K42x25x11 with magnetic permeability μ e = 2000. The primary winding is wound with a bundle of eight wires with a diameter of 1.2 mm, the secondary winding with a bundle of four wires with a diameter of 1 mm. After winding, each of the bundles is divided into two equal parts, and the beginning of one half of the winding is connected to the end of the other. The primary winding contains 2x7 turns, the secondary winding contains 2x15 turns, evenly distributed around the ring.
Choke L1 is wound on a ferrite rod with a diameter of 16 mm and contains 10 turns of enameled wire with a diameter of 2 mm. Chokes L2, L3 are wound on ferrite rods with a diameter of 10 mm and contain 10 turns of wire with a diameter of 1 mm. The length of each rod is 20 mm.
A similar power supply circuit with minor changes is used in car amplifiers with a total output power of up to 100... 120 W. The number of pairs of output transistors, transformer parameters and the design of protection circuits vary. In voltage converters of more powerful amplifiers, feedback on the output voltage is introduced and the number of output transistors is increased.
To distribute the load evenly and reduce the influence of the scatter in the parameters of the transistors in the transformer, the currents of the powerful transistors are distributed over several primary windings. For example, in the Lanzar 5.200 car amplifier power supply converter, 20 are used! powerful field-effect transistors, 10 in each arm. The step-up transformer contains 5 primary windings. Each of them is connected to 4 transistors (two in parallel in the shoulder). For better filtering of high-frequency interference, individual smoothing filter capacitors with a total capacity of 22,000 μF are installed near the transistors. The terminals of the transformer windings are connected directly to the transistors, without the use of printed conductors.
Because car audio amplifiers operate under very severe temperature conditions, some designs use built-in cooling fans that blow air through heat sink ducts to ensure reliable operation. The fans are controlled using a temperature sensor. There are devices with both discrete control ("on-off") and with smooth adjustment of the fan speed.
Along with this, all amplifiers use thermal protection of the units. Most often it is implemented on the basis of a thermistor and comparator. Sometimes standard integrated comparators are used, but in this role they most often use conventional op-amp operational amplifier microcircuits. An example of a thermal protection device circuit used in the already discussed four-channel car amplifier "Jensen" is shown in Fig. 4. In the diagram, the numbering of parts is conditional.
Thermistor R t 1 has thermal contact with the amplifier housing near the output transistors. The voltage from the thermistor is applied to the inverting input of the op-amp. Resistors R1 - R3 together with the thermistor form a bridge, capacitor C1 prevents false alarms of the protection. With the length of the wires with which the thermistor is connected to the board being about 20 cm, the level of interference from the power supply is quite high. Through resistor R4, positive feedback is provided from the output of the op-amp, turning the op-amp into a threshold element with hysteresis. When the case heats up to 100 °C, the resistance of the thermistor decreases to 25 kOhm, the comparator is triggered and the high voltage level at the output blocks the operation of the converter.
The output transistors of the amplifier and the key transistors of the power converter are most often used in plastic cases, TO-220. They are attached to the heat sink either with screws or spring clips. Transistors in metal cases have somewhat better heat dissipation, but since they need to be installed through special heat-sinking pads, their installation is much more complicated, so they are used in car amplifiers much less often, only in the most expensive models.
