# Is DC a RMS value?

The RMS value of a fluctuating voltage or current is its effective value. The corresponding steady DC (constant) value produces the same result. A light attached to a 6V RMS AC source, for example, will shine with the same brightness when linked to a constant 6V DC supply. However, a light attached to a 60Hz waveform-containing 6V RMS source will not work properly if connected to a constant 6V DC supply.

So, no, DC does not equal RMS. But they have about the same magnitude if you look at it over time. If you were to take the average value of DC then yes, that would be about equivalent to the RMS value of the signal.

In practice, people use power supplies that convert an AC signal into a DC signal before supplying it to their devices. The output of these supplies must be capable of handling the peak values of the input signal while still providing a constant voltage or current. For example, if the input signal has large peaks but also varies a lot between positive and negative values, the output will have large peaks but may also vary a lot between positive and negative values. This is called "peak clipping" and most modern power supplies avoid this problem by using expensive components that are designed to handle high currents during short periods of time.

If you connect a DC circuit to an AC signal, you are doing two things at once.

## What is the RMS voltage in DC?

The RMS, or root mean square current/voltage, of an alternating current/voltage represents the d.c. current/voltage that dissipates the same amount of power as the alternating current/average voltage's power dissipation. The RMS value for sinusoidal oscillations is the peak value divided by the square root of 2. For other waveforms, the RMS value should be calculated from its integral over time.

The RMS value for a direct current (DC) voltage is defined as the maximum value of the voltage across any load connected to it. Because power is the product of voltage and current, the RMS value of a DC voltage is also called its peak value. A DC voltage source cannot provide more than this peak value no matter what load is connected to it; thus, it cannot supply power beyond this limit. However, a DC voltage source can provide much less peak voltage when some type of amplifier is used instead, which acts like a variable resistor to reduce the voltage before it reaches the load.

For example, if a DC voltage source provides 5 volts but if we connect a resistor to reduce the voltage to 3 volts, then the power supplied to the resistor will be 1 watt, so its temperature will rise by 1 degree Celsius. Without the resistor, the voltage would reach 15 volts and cause damage to other components on the circuit board.

## What is the difference between RMS and average current?

The average value represents the DC component of the AC signal, but the RMS value represents the effective value that would create heat through a resistor like DC. DC currents are always risk, so they should be limited by regulation.

The peak current on the other hand refers to the maximum value that can be delivered for a short period of time. It is usually expressed in amperes. Peak currents should be limited by power supplies or drivers to prevent damage from overheating.

Peak currents are generally much higher than the average current used by LEDs. An LED will not burn out even if exposed to peak currents because it has internal resistance that limits the current it will draw at any one time. However, excessive peak currents may cause premature aging of the LED or lead to electrical failure of the device depending on voltage/current ratios.

Average current is defined as the total amount of current flowing into an LED per unit time. This number can be calculated with this formula: Average current = Voltage x Frequency where Voltage is equal to RMS current / Root 2 (for sinusoidal current).

## What is the average RMS and peak value?

The square root of the mean (average) value of the squared function of the instantaneous values is the RMS value. Because an alternating current voltage rises and falls with time, it requires more alternating current voltage to achieve a given RMS value than a direct current voltage. For example, 169 volts peak AC is required to create 120 volts RMS (.5 VA), but only 120 volts DC is needed.

Peak value means the highest value that any one element of the signal reaches. In an AC waveform, this is the maximum voltage across any single point on the circuit. With direct current, the peak value is the same as the rms value because there are no high peaks to exceed any given level.

For sinusoidal signals, the peak value is exactly twice the rms value. For square waves, the peak value is equal to the rms value.

For audio signals, 0.1 volt is usually considered loud, while 1 volt is usually considered very loud. A speaker can be damaged by excessive power so these levels are used to indicate how much power is being delivered to the speaker.

For microphone signals, 0 dBFS (decibels full scale) indicates that the peak amplitude of the sound captured by the microphone was 100 decibels (dB). 10 dBFS indicates that the peak amplitude of the sound captured by the microphone was 10 decibels below full scale.

## Why do we measure AC in terms of RMS?

AC voltages (and currents) are usually provided as RMS values in common use since this allows for a reasonable comparison with stable DC voltages (and currents), such as from a battery. A 6V AC supply, for example, indicates 6V RMS with a peak voltage of around 8.6V. A current of 12A RMS would have a peak value of about 100A.

Since power is voltage times current, 6V RMS at 12A results in 50W of power being drawn from the source. This is more than the average household appliance load so it cannot be used to turn any device on or off. To provide less than 50W of continuous power would be dangerous since it could cause overheating and fire.

The reason why we don't get exactly 6V RMS across the line is because of distortion caused by impedance in the wiring between the unit measuring the voltage and the unit receiving it. The amount of distortion depends on the length of cable involved and also on its specific resistance. Impedance varies with frequency so at low frequencies like half-wave rectified mains voltage this effect is minimized. At high frequencies the voltage drop across the cable becomes significant and causes distortion.

Distortion can be reduced by using longer cables but this is expensive and not always possible. It can also be compensated for by using active circuits called "voltmeters" which introduce additional distortion but allow very accurate measurement over a wide range of inputs.

##### John Wiley

John Wiley is a man of many interests. He's got his hands in many different fields of science and technology, but what he really loves is solving problems and helping people. John has been working in the tech industry for years now, and he feels very lucky to be able to do what he loves every day.

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