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Gold Member Username: GlasswolfWisteria, Lane USA Post Number: 9438 Registered: Dec-03 | Voltage regulation PWM is used in efficient voltage regulators. By switching voltage to the load with the appropriate duty cycle, the output will approximate a voltage at the desired level. The switching noise is usually filtered with an inductor and a capacitor. One method measures the output voltage. When it is lower than the desired voltage, it turns on the switch. When the output voltage is above the desired voltage, it turns off the switch. Audio effects PWM is sometimes used in sound synthesis, in particular subtractive synthesis, as it gives a nice effect similar to chorus or slightly detuned oscillators played together. The ratio between the high and low level is typically modulated with a low frequency oscillator, or LFO. A new class of audio amplifiers based on the PWM principle is becoming popular. Called "Class-D amplifiers", these amplifiers produce a PWM equivalent of the analogue input signal which is fed to the loudspeaker via a suitable filter network to recover the original audio. These amplifiers are characterised by very good efficiency figures (>= 90%) and compact size/light weight for large power outputs. above supplied by: www.wikipedia.com see also: http://en.wikipedia.org/wiki/Switched-mode_power_supply Power Supplies: The purpose of the supply is to convert the auto's battery voltage to a higher voltage. For example, if an amplifier is to produce 100 watts into a 4 ohm speaker, we need 20 volts RMS. This implies that we need about +/-28 volts. (20 volts R.M.S. = 28.28 volts peak). We call that the "rail" voltage. Since the amplifier's output transistors cannot pull all the way up to this rail, we actually need a slightly higher voltage. The process is to convert the 12 volts DC into AC, feed it to a transformer and convert it back to DC again. Converting the 12 volt battery voltage to AC is simple, a PWM (pulse width modulator) IC feeds a bank of MOSFETS (MOSFETs are switching transistors perfectly suited for this task). The 12 volt power is switched at a very high frequency, somewhere between 40 and 150 kHz. Slower switching speeds require a larger transformer, but high speeds have more switching loss. Advanced transformer core materials, faster rectifiers, and clever winding methods have enabled us to utilize very high frequencies. Some of today's better amplifiers have very small power supplies that produce enormous amounts of power. Regulated Power Supplies Most early audio amplifiers contained unregulated power supplies. Regulated supplies require very high quality filter capacitors (called "low ESR" capacitors), output chokes, and an optically isolated voltage feedback circuit. Regulation occurs by controlling the switching pulse width from 0 - 100% to compensate for changes in the battery and rail voltage. The same action occurs when the audio level increases. As the amplifier draws more power from the supply, the rail voltage drops. Again, the regulator circuitry senses this drop and responds with an increased pulse width. The high frequency PWM waveform is rectified (converted to DC) and applied to the output filter choke and capacitors. This output of this circuit is the + and - DC rails that feed the power amplifier. Unregulated Power Supplies Unregulated power supplies are less expensive than regulated supplies. They do not require an output choke, voltage sense or isolation circuitry. Because the duty cycle is nearly 100%, capacitor ripple current is much lower in unregulated supplies. Lower ripple current requires less expensive capacitors throughout. Often we hear that unregulated designs have more "headroom". That means that the amplifier will produce extra power during transients. Most home audio amplifiers employ unregulated power supplies. The power supplies in these amplifiers run at 60 Hz, thus the filter capacitors must be 200-500 times larger than those used in high frequency switchers. The extra capacitance in home audio amplifiers results in extra headroom. Headroom for anything other than very short transients simply doesn't exist in the unregulated designs. The following is an example of specifications for an unregulated vs. regulated amplifiers. Unregulated designs have a higher supply voltage at low power, causing higher voltage on the output transistors. This reduces the amplifier's efficiency. Small amplifiers (less than 100 watts) cannot justify the extra cost of the regulation circuitry, so we often see unregulated supplies in these amplifiers. Pros and Cons of Regulated / Unregulated Supplies Some designers try to keep their supplies regulated down to battery voltages as low as 9.5 volts. The supply compensates by increasing the current. The following table shows voltage and currents for a 500 watt over-regulated amplifier operating at full power. The current increases dramatically at the lower voltages. Because of higher currents at the lower voltages, the supply efficiency drops further, requiring even more current. At higher voltages, the pulse width reduces, causing increased ripple current. This high current creates heat in the filter capacitors and can destroy the capacitor's electrolyte. Some manufacturers do not use capacitors of sufficient quality for this range of regulation. These amplifiers may not perform up to specification just one year after installation. Also, the extra current at low voltages is extra hard on a battery that is already suffering! So, we recommend that amplifiers stay in regulation down to about 11 - 11.5 volts. Any properly working charging system can easily keep the battery voltage well above this. above supplied from: http://www.wickedcases.com/caraudio/amplifiers.html |
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Silver Member Username: BananakrillVallejo, California Post Number: 138 Registered: Jul-04 | Wow, I haven't seen you post a thread in a long time. Thanks for the info though! |
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Silver Member Username: Mikechec9Chicago/atlanta Post Number: 774 Registered: May-05 | i tell you.. it's obvious you're an sq geek when you look forward to the word of the week, lol (of course i'm talking about me). i've really got to get more of a life. until then, keepem comin glass. they're more than appreciated. i'm soakin this stuff up. |