# Peak value

As a peak value is designated according to DIN 40110-1 ( "AC quantities") the largest amount of the instantaneous values of an alternating signal ; this is a periodic signal with the equivalent value zero, e.g. B. an alternating voltage . With sinusoidal alternating signals , the peak value is called the amplitude .

Periodic variable (above)
Alternating variable (below)
1 = maximum value
2 = minimum value
3 = peak-valley value
4 = peak value
5 = period duration

## Determinations

For periodic quantities that are not necessarily alternating quantities, e.g. B. mixed current , the maximum value and the minimum value are named in DIN 40110-1 ; If there are several maximum values ​​within a period, the largest value is called the peak value . In the same standard, the distance between maximum and minimum is referred to as the oscillation width or peak-valley value (formerly peak-peak value). ${\ displaystyle {\ hat {y}}}$ ${\ displaystyle {\ check {y}}}$  ${\ displaystyle {\ underset {{} ^ {\ lor}} {\ overset {{} _ {\ land}} {\! y}}}}$

In electrical engineering , the term peak value is used particularly frequently, e.g. B. at the peak value of the current and at the peak value of the voltage . There are also the names or in use (pronounced I-roof and U-roof ). Borrowed from English , p stands for peak . Indices must always be appended to the formula symbol ; according to DIN 1313 is in no way the unit symbol , e.g. B. V for volts , to be provided with a mark. ${\ displaystyle I _ {\ mathrm {s}}}$${\ displaystyle U _ {\ mathrm {s}}}$${\ displaystyle {\ hat {\ imath}}}$${\ displaystyle {\ hat {u}}}$${\ displaystyle U _ {\ mathrm {p}}}$

Measuring devices that do not record the course over time usually give the rms value .

## Typical functions with peak values

Alternating quantities and their peak values

Periodic functions meet the condition

${\ displaystyle y (t + T) = y (t)}$

with the period . Alternating variables also meet the condition for the mean value ${\ displaystyle T}$

${\ displaystyle {\ bar {y}} = 0 \ quad {\ text {or}} \ quad \ int _ {0} ^ {T} y (t) dt = 0}$.

Examples that can be found in technology are:

${\ displaystyle y (t) = {\ hat {y}} \ cdot {\ begin {cases} 1 & {\ text {if}} 0
${\ displaystyle y (t) = {\ hat {y}} \ cdot {\ begin {cases} {\ frac {4} {T}} (t - {\ frac {1} {4}} T) & { \ text {if}} 0 \ leq t \ leq {\ frac {T} {2}} \\ - {\ frac {4} {T}} (t - {\ frac {3} {4}} T) & {\ text {if}} {\ frac {T} {2}} \ leq t \ leq T \ end {cases}}}$
• Sawtooth function
${\ displaystyle y (t) = {\ hat {y}} \ cdot {\ frac {2} {T}} (t - {\ frac {T} {2}}) \ qquad {\ text {if}} 0

## Applications

The dielectric strength of capacitors must be measured according to the peak value, not the effective value. This is calculated with the sine curve

${\ displaystyle U _ {\ mathrm {s}} = {\ sqrt {2}} \ cdot U _ {\ mathrm {eff}}}$

However, they are often specified for rms values ​​of an alternating voltage.

The power grid in Europe has an effective value of 230 V (or 400 V between the outer conductors) for end consumers. The peak value is

${\ displaystyle 230 ~ \ mathrm {V} \ cdot {\ sqrt {2}} = 325 ~ \ mathrm {V}}$

A capacitor fed by a mains rectifier is charged almost to this voltage.

The peak value of the voltage applied to a surge arrester or a suppressor diode at the peak current that can be diverted (e.g. 100 A) is called the protection level . The downstream electronics to be protected must at least withstand this peak value.

The peak values ​​of audio signals (speech, singing, music) are often much higher than the rms value. Audio amplifiers must therefore have a high headroom in order not to cause distortion (clipping) at these peak values.

Many electronic components are specified differently with regard to their maximum parameters for single and repeated peak values. This applies, for example, to diodes , capacitors, inputs of analog and digital integrated circuits or MOSFETs .

Examples
• A 1N400x rectifier diode is suitable for an average current value of 1 A, but withstands a peak current of 30 A once (during an 8.3 ms half cycle on a 60 Hz network) and periodically well over 1 A peak current.
• Y interference suppression capacitors are designed for continuous operation at up to 250 V AC, but can withstand short overvoltage events of up to 5 kV.
• The PL500 electron tube has an average anode voltage of less than 1000 V, but can withstand a peak voltage of up to 7 kV for less than 18 µs and less than 22% of the period.

## Measurement

Simplified circuit for measuring the peak value

A precision rectifier can be used to measure the peak value , and the DC voltage generated in this way is then displayed on a voltmeter . In the simplified circuit of a precision rectifier shown opposite, the AC voltage to be measured is rectified and feeds a capacitor whose voltage corresponds to the peak value after one period of the input voltage. The switch parallel to the capacitor serves to reset after the measurement. ${\ displaystyle V _ {\ mathrm {in}}}$

Historically, glow lamps were also used to measure the peak value , as these have the property of only igniting at a certain voltage. The AC voltage to be measured is fed to the glow lamp via a capacitive voltage divider with a variable capacitor . The value of the variable capacitor is changed until the glow lamp ignites. If the ignition voltage of the glow lamp is known, the peak value of the AC voltage supplied can be determined via the division ratio of the capacitive voltage divider.