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Elliott Sound Products Project 89
Switchmode Power Supply For Car Audio
Sergio Sánchez Moreno and Rod Elliott

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Foreword
This contributed project is a result of considerable collaboration between Sergio and myself, and should not be seen as necessarily a complete project in itself, but a stepping stone to understanding switching power supplies, how they work, and what you can do with them.
Be warned - there is considerable risk. Because of the extremely high current available from a car battery, a tiny mistake may easily lead to catastrophic failure. All electronic components are said to contain smoke (wire contains an enormous amount), and a slip of the soldering iron can liberate an unbelievable quantity. Seriously though, the risk of severe burns and the possibility of causing a fire in your car are very real, and should not be underestimated. 300A from a car battery can do a vast amount of damage in a few milliseconds - should the fuse not blow (you will use a fuse, won't you?), then the damage can be extensive.
At various points in Sergio's part of the article, I have included some additional information.
Please see the special note at the end of this article for important information about the project.

Introduction
The difficulties of installing a hi-fi system in a car are many, although there is no doubt that the most important is the limitation of the vehicle supply voltage. As most readers already know, the nominal voltage of a car battery is 12V, reaching about 13.8V when charging (i.e. engine running).
The maximum RMS. audio power from a given voltage V is somewhat less than:
Pmax = ( V / ( 2 x √2 ) )² / RL
... where RL is the speaker nominal impedance.
Thus, for a 13.8V system, this power is limited to about 6W on a 4 Ohm load. Note that the lower the resistance of the speaker, the higher the maximum power (this is the reason most audio speakers have a 4 ohm nominal impedance instead of the more common 8 ohm in home systems).
This may be simplified to some extent ...
P = ( V / 3 )² / RL
and a typical calculation based on a 13.8V supply gives ...
P = ( 13.8 / 3 )² / 4
P = 4.6² / 4 = 5.29 Watts
This allows for standard losses, and is acceptably accurate at this voltage - the only real way to know is to measure the amp, since the losses vary depending on the topology of the output stage.
Power output can be increased by a factor of nearly 4 by using bridging techniques, explained in more detail in ESP project 14, so we can obtain up to about 24W on a 4 ohm speaker. This can be enough for the midrange and high frequencies, but is obviously very limited for a subwoofer application, for example. (Moral: distrust of '4 x 45W' head units is well advised, for they certainly aren't talking about RMS power).
So, what can be done to increase available audio power? The answer is a simple derivation of the above formula - either decrease load impedance or increase supply voltage. The lower the impedance, the more current is needed, making the construction of low impedance output stages more difficult (there are some other practical limits), so let's increase supply voltage.
Switch Mode Power Supply Basics
The vast majority of high-powered audio amplifiers use SMPS (Switch Mode Power Supplies) to generate higher voltages from the available 12 (13.8) volts. An extensive theoretical explanation on how these things work is beyond the scope of this article, but these are some fundamental ideas you should know about switch mode power supplies (SMPS) for car amps:
The DC voltage at the battery has to be switched in some form to generate an AC waveform suitable for a transformer. As you already know, a transformer basically converts the AC voltage in its primary to a scaled version of it in its secondary, the scale factor being the turns ratio of the primary to the secondary . (Again, take this as an extreme simplification). A transformer doesn't allow DC voltages to pass, and there is electrical (galvanic) isolation between both windings.

The AC waveform is usually a square wave that is relatively easy and efficient to generate. The frequencies usually fall between 25kHz and 100kHz or more, thus allowing smaller transformers than the used in main appliances (its construction is also different, their cores are not laminated, but made from ferrites or iron powder). The switching elements have to be capable of high currents and must also be fast and have low switching losses. Usually, power MOSFETs or high speed bipolar transistors are used (some SMPS designs use SCRs but these are in the minority).

Once this waveform is stepped-up by the transformer, it has to be rectified again and filtered back to DC, since that is what we want. For audio applications, we usually need a symmetrical supply, +/-35V, for example. The rectification is done with a diode bridge, as it would be using a conventional transformer at 50 or 60 Hz. Note that for the frequencies we are talking about, fast or ultra-fast d

Kết quả (Việt) 1:

ESP Logo Elliott Sound sản phẩm dự án 89 Switchmode nguồn cung cấp cho âm thanh xe hơiSergio Sánchez Moreno và Rod ElliottShare|Lời giới thiệuDự án góp này là kết quả của sự hợp tác đáng kể giữa Sergio và bản thân mình, và không nên được xem như là nhất thiết phải là một dự án đầy đủ trong chính nó, nhưng một bước đá để hiểu biết chuyển đổi nguồn, như thế nào họ làm việc, và bạn có thể làm gì với chúng.Được cảnh báo - là có nguy cơ đáng kể. Bởi vì rất cao hiện nay có sẵn từ một pin xe, một sai lầm nhỏ có thể dễ dàng dẫn đến thất bại thảm họa. Tất cả các thành phần điện tử được cho là chứa khói (dây có chứa một số lượng lớn), và một phiếu sắt hàn có thể giải phóng một số lượng không thể tin được. Nghiêm túc mặc dù, nguy cơ bị bỏng nặng và khả năng gây ra một đám cháy trong xe của bạn là rất thực tế, và không nên đánh giá thấp. 300A từ một pin xe hơi có thể làm một số lượng lớn các thiệt hại trong một vài mili giây - nên các cầu chì không thổi (bạn sẽ sử dụng một cầu chì, phải không?), sau đó thiệt hại có thể được mở rộng.Tại các điểm khác nhau ở của Sergio của bài viết, tôi đã có một số thông tin bổ sung.Xin vui lòng xem lưu ý đặc biệt ở phần cuối của bài viết này cho các thông tin quan trọng về dự án.Giới thiệuNhững khó khăn của việc cài đặt một hệ thống hi-fi trong một chiếc xe rất nhiều, mặc dù có là không có nghi ngờ rằng quan trọng nhất là hạn chế của chiếc xe cung cấp điện áp. Như hầu hết các độc giả đã biết, điện áp trên danh nghĩa của một pin xe hơi là 12V, đạt khoảng 13.8V khi sạc (tức là động cơ chạy).The maximum RMS. audio power from a given voltage V is somewhat less than:Pmax = ( V / ( 2 x √2 ) )² / RL... where RL is the speaker nominal impedance.Thus, for a 13.8V system, this power is limited to about 6W on a 4 Ohm load. Note that the lower the resistance of the speaker, the higher the maximum power (this is the reason most audio speakers have a 4 ohm nominal impedance instead of the more common 8 ohm in home systems).This may be simplified to some extent ...P = ( V / 3 )² / RLand a typical calculation based on a 13.8V supply gives ...P = ( 13.8 / 3 )² / 4P = 4.6² / 4 = 5.29 WattsThis allows for standard losses, and is acceptably accurate at this voltage - the only real way to know is to measure the amp, since the losses vary depending on the topology of the output stage.Power output can be increased by a factor of nearly 4 by using bridging techniques, explained in more detail in ESP project 14, so we can obtain up to about 24W on a 4 ohm speaker. This can be enough for the midrange and high frequencies, but is obviously very limited for a subwoofer application, for example. (Moral: distrust of '4 x 45W' head units is well advised, for they certainly aren't talking about RMS power).So, what can be done to increase available audio power? The answer is a simple derivation of the above formula - either decrease load impedance or increase supply voltage. The lower the impedance, the more current is needed, making the construction of low impedance output stages more difficult (there are some other practical limits), so let's increase supply voltage.Switch Mode Power Supply BasicsThe vast majority of high-powered audio amplifiers use SMPS (Switch Mode Power Supplies) to generate higher voltages from the available 12 (13.8) volts. An extensive theoretical explanation on how these things work is beyond the scope of this article, but these are some fundamental ideas you should know about switch mode power supplies (SMPS) for car amps:The DC voltage at the battery has to be switched in some form to generate an AC waveform suitable for a transformer. As you already know, a transformer basically converts the AC voltage in its primary to a scaled version of it in its secondary, the scale factor being the turns ratio of the primary to the secondary . (Again, take this as an extreme simplification). A transformer doesn't allow DC voltages to pass, and there is electrical (galvanic) isolation between both windings.The AC waveform is usually a square wave that is relatively easy and efficient to generate. The frequencies usually fall between 25kHz and 100kHz or more, thus allowing smaller transformers than the used in main appliances (its construction is also different, their cores are not laminated, but made from ferrites or iron powder). The switching elements have to be capable of high currents and must also be fast and have low switching losses. Usually, power MOSFETs or high speed bipolar transistors are used (some SMPS designs use SCRs but these are in the minority).Once this waveform is stepped-up by the transformer, it has to be rectified again and filtered back to DC, since that is what we want. For audio applications, we usually need a symmetrical supply, +/-35V, for example. The rectification is done with a diode bridge, as it would be using a conventional transformer at 50 or 60 Hz. Note that for the frequencies we are talking about, fast or ultra-fast d