Charger Ripple and No-Load Ripple: What They Mean and How Engineers Test Them

Charger Ripple and No-Load Ripple: What They Mean and How Engineers Test Them
 
When engineers test a charger, output voltage is only one part of the story.
A charger may show a stable 5V, 9V, 15V, or 20V on a multimeter, but if you connect an oscilloscope, the output is never perfectly flat.
You may see a small periodic waveform, high-frequency spikes, switching noise, or even a noticeable sawtooth waveform when the charger has no load.
This is where charger ripple and no-load ripple become important.
 
For charger manufacturers, ripple is not simply a number printed on a test report. It is related to the power supply topology, switching frequency, transformer design, output filtering, control loop, PCB layout, capacitors, load condition, and even the measurement method.
A charger with 20mV ripple and another charger with 80mV ripple may both work normally. But the difference can tell engineers a lot about the design and stability of the power supply.
This article explains charger ripple from a manufacturer's and power electronics engineer's perspective.
 
What Is Charger Ripple?
Charger ripple is the AC component that remains on the DC output voltage of a charger.
Ideally, a 5V charger would produce a perfectly flat 5V DC output.
In the real world, it looks more like this: DC output + periodic ripple + high-frequency noise + switching spikes. The ripple is normally measured in millivolts peak-to-peak (mVpp).
For example, if an oscilloscope shows:
• Maximum voltage: 5.025V
• Minimum voltage: 4.975V
Then the peak-to-peak variation is: 50mVpp
The important point is that ripple is a variation around the DC output voltage. It does not mean that the charger is continuously changing from 5V to a completely different voltage. A well-designed switching power supply will inevitably exhibit a certain level of ripple.
The engineering goal is to control it within an acceptable range, not necessarily eliminate it completely.
 
Why Does a Charger Have Ripple?
Modern USB chargers are switching power supplies.
Inside a typical charger, the AC input is converted and processed through several stages before the final regulated DC output reaches the USB port.
A simplified structure looks like: AC Input → Rectification → Switching Stage → Transformer → Secondary Rectification → Filtering → USB Output
 
Switch-level circuits rapidly switch the current on and off.
While this switching action is essential for achieving efficient power conversion, it also generates voltage or current fluctuations. Subsequently, output-side capacitors, inductors, transformers, and feedback control systems work together to smooth the waveforms.
However, some residual ripple remains. Several factors influence the final ripple level: Switching frequency, Transformer design, Output inductance, Output capacitor quality, PCB layout, Control-loop response, Switching topology, Load current, ESR of capacitors, EMI filtering, Rectification method, Snubber design, Cable and test fixture, etc.
This is why two 65W chargers with the same output specification can produce very different ripple waveforms. What Is No-Load Ripple?
No-load ripple, sometimes called zero-load ripple, refers to the output ripple measured when the charger is operating with little or no external load.
This is a particularly interesting condition for modern USB-C chargers.
At first, it sounds simple: No load should mean almost no ripple.
In practice, that is not necessarily true.
In fact, some chargers show a more unusual waveform at no load than they do under normal load.
You may see:
• Sawtooth waveforms
• Burst-mode pulses
• Periodic switching packets
• Low-frequency modulation
• High-frequency spikes
• Intermittent output activity
This can be completely normal depending on the power supply architecture.
 
Why Does No-Load Ripple Sometimes Look Worse?
The main reason is power-saving operation. When a charger has no device connected, it does not need to continuously transfer significant power to the output.
Keeping the main switching circuit operating at full activity would waste unnecessary energy. Therefore, many modern chargers enter a light-load or burst-mode operating condition.
Instead of switching continuously, the controller may:
1. Start switching
2. Transfer energy to the output
3. Detect that output voltage is high enough
4. Reduce or stop switching
5. Allow the voltage to fall slightly
6. Start switching again
This cyclic process produces a visible waveform on the oscilloscope; the resulting waveform may resemble a sawtooth or burst pattern. However, this does not necessarily indicate a defect in the charger.
Actual charger measurements often show this behavior. For example, laboratory testing of USB chargers has documented sawtooth waveforms at zero load associated with power-saving operation.
 
No-Load Ripple vs Full-Load Ripple
One of the common mistakes when evaluating charger quality is testing only one operating condition.
A charger should ideally be evaluated under multiple conditions.
For example:

Test Condition	What Engineers Look For
No load	Burst mode, standby behavior, spikes
Light load	Control-loop stability
25% load	Normal regulation
50% load	Ripple and efficiency
75% load	Thermal and electrical stability
Full load	Maximum ripple, temperature and stability
Dynamic load	Transient response

The waveform can change considerably between these conditions.
A charger might show relatively low ripple at 5V/0A but higher ripple at 5V/3A.
That is not unusual. The important question is whether the output remains stable and within the relevant design and compliance requirements across its intended operating range.
 
Is No-Load Ripple Dangerous?
Not necessarily. This is an important distinction.
Seeing a waveform on an oscilloscope does not automatically mean that the charger is unsafe.
Engineers need to look at:
• Ripple amplitude
• Spike amplitude
• Frequency
• Waveform shape
• Duration
• Output voltage regulation
• Load condition
• Protection behavior
• Thermal performance
• EMC performance
• Product specifications
A small sawtooth waveform at no load may simply indicate that the charger has entered a low-power switching mode.
On the other hand, unusually large spikes, unstable output, excessive oscillation, or abnormal voltage excursions can indicate an engineering problem.
This is why waveform analysis is more useful than looking at one mV number alone.
 
Ripple vs Noise: Are They the Same Thing?
Not exactly. The terms are often used together, but engineers can distinguish between them.
Ripple
Ripple generally refers to a relatively periodic voltage variation associated with the power conversion process.
Typical causes include:
• Switching operation
• Rectification
• Capacitor charging/discharging
• Switching frequency
• Output filter characteristics
 
Noise
Noise is a broader term.
It can include:
• High-frequency switching noise
• Random electrical noise
• EMI coupling
• Switching spikes
• Ringing
• PCB coupling
• External interference
In an oscilloscope waveform, both can appear at the same time.
This is why a simple peak-to-peak measurement does not always tell the complete story.
A measurement guide from Cadence, for example, points out that power-supply evaluation commonly considers peak-to-peak voltage, RMS voltage and frequency-domain characteristics rather than relying on only one measurement.
 
What Does mVpp Mean?
When engineers talk about charger ripple, one of the most common specifications is: mVpp
This means: millivolts peak-to-peak
For example: 40mVpp, means the measured difference between the highest and lowest observed voltage excursion is 40mV.
It is different from:
• mVrms
• mV peak
• average voltage
• noise density
These measurements cannot simply be treated as interchangeable.
 
For charger manufacturing, the test condition must therefore be clearly defined.
A statement such as: Ripple: <50mV, is not very useful without knowing:
• At which output voltage?
• At what load?
• What bandwidth?
• What oscilloscope?
• What probe?
• What test fixture?
• Was the measurement AC-coupled?
• Was the ground connection optimized?
Without this information, two suppliers may report completely different numbers for essentially the same hardware.
 
How Do Engineers Measure Charger Ripple?
The main instrument is an oscilloscope.
A typical engineering setup includes:
• Oscilloscope
• Appropriate probe
• Electronic load
• USB-C PD trigger or analyzer
• Short measurement connection
• Defined bandwidth
• Controlled load condition
The USB-C output must first be configured to the desired voltage.
 
For example: 5V output.
The engineer measures ripple at: 5V / 0A. Then: 5V / 1A, 5V / 2A, 5V / 3A, depending on the charger's rated output.
For a PD charger, the same process can be repeated at different negotiated voltages: 5V, 9V, 12V, 15V, 20V.
For higher-power USB-C PD products, additional voltage levels may be relevant depending on the supported PD specification.
USB-IF currently maintains formal USB Power Delivery specifications and compliance test documents, including PD 3.2 documentation and current compliance-test specifications.  Why the Oscilloscope Probe Matters
This is one of the most overlooked parts of ripple testing.
A poor measurement setup can make a good charger look bad.
The ripple being measured may only be tens of millivolts.
But a long oscilloscope ground lead can act like an antenna and pick up switching noise.
The engineer may then see large spikes that are partly created by the measurement setup itself.
For this reason, professional testing normally uses a short ground connection or an appropriate probing method. (The bandwidth setting also matters.)
 
For example, one test setup for a USB-C PD reference design used a 20MHz bandwidth limit and a carefully controlled probe configuration for ripple and noise measurements.
This is an important lesson for B2B buyers: Do not compare ripple numbers from two suppliers unless the test conditions are comparable.
 
Why Can a Long Ground Lead Create Fake Ripple?
Imagine the actual output ripple is only 20mV. But the probe ground wire picks up switching noise from the charger.
The oscilloscope may then display: 20mV actual ripple + additional induced noise.
The reported result could become much higher.
This is why engineers often pay attention to:
• Probe grounding
• Measurement loop area
• Bandwidth
• Probe capacitance
• Cable length
• Test fixture
• Ground reference
A professional power-supply test is not simply: Connect probe → press Measure → read mV.
The measurement itself needs to be engineered.
 
What Causes High Ripple in a Charger?
When ripple is higher than expected, engineers normally investigate the circuit rather than immediately replacing one component.
Several areas can contribute.
1. Poor Output Capacitors
The output capacitor absorbs and smooths current fluctuations.
Its:
• Capacitance
• ESR
• Temperature rating
• Lifetime
• Ripple-current capability
all affect the output waveform.
A capacitor with unsuitable characteristics can increase ripple significantly.
 
2. Poor PCB Layout
PCB layout has a major influence on switching power supplies.
High-current loops should be kept controlled.
Poor routing can increase:
• Parasitic inductance
• EMI
• Ringing
• Switching spikes
• Ground noise
A schematic can look perfect while the physical PCB layout still creates problems.
 
3. Transformer Design
In an isolated charger, the transformer is one of the most important components.
Engineers need to consider:
• Core selection
• Winding structure
• Leakage inductance
• Winding resistance
• Insulation
• Turns ratio
• Switching frequency
Poor transformer optimization can affect both efficiency and ripple.
 
4. Output Filter Design
The output filter is another critical area.
Depending on the topology, the design may use:
• Capacitors
• Inductors
• LC filters
• Additional filtering stages
Increasing capacitance alone is not always the best solution.
The filter needs to work with the converter's switching frequency and control loop.
 
5. Control-Loop Design
The feedback loop determines how the charger responds to changes in output voltage and load.
An incorrectly compensated control loop may cause:
• Oscillation
• Slow response
• Excessive ripple
• Poor transient performance
This is why ripple should not be treated as an isolated component problem.
 
6. Switching Frequency
Higher switching frequency can help reduce the size of magnetic components and filters.
This is one reason modern GaN chargers can achieve high power density.
However, higher frequency also creates additional challenges involving:
• Switching losses
• EMI
• PCB layout
• Gate drive
• Transformer losses
• High-frequency noise
So higher frequency is not automatically better.
The complete design has to be optimized.
 
Does GaN Automatically Mean Lower Ripple?
No. This is another common misunderstanding.
GaN can provide advantages such as:
• Faster switching
• Lower switching losses
• Higher power density
• Smaller magnetics
• Improved efficiency
But GaN itself does not guarantee a specific ripple level.
 
A GaN charger with poor PCB layout can still have significant switching noise.
Likewise, a well-designed silicon-based charger can have a very clean output.
The final ripple depends on the complete power architecture.
This is one reason why engineers should evaluate the actual electrical performance rather than assuming: GaN = low ripple.
 
For more information about how GaN changes charger architecture, see our related guide:
👉 GaN Chargers vs. Traditional Chargers: What's the Difference and Why Does It Matter?
👉 What Is GaN Charger Technology?

Does Higher Charger Power Mean Higher Ripple?
Not automatically. A 100W charger does not necessarily have higher ripple than a 30W charger.
However, higher-power designs generally create more demanding engineering conditions.
For example, a 100W USB-C charger may need to manage:
• Higher input power
• Higher output current
• Higher switching energy
• Greater thermal stress
• More complex power conversion
• More demanding transient conditions
As power increases, the design margin becomes more important.
 
This is particularly relevant for 65W chargers, 100W chargers, 120W chargers, 140W chargers, 180W chargers, and 240W USB-C PD chargers.
The charger must maintain stable output not only at light load but also during high-power operation.
 
Why No-Load Ripple Is Especially Interesting for USB-C Chargers
Modern USB-C PD chargers are not simple fixed-voltage adapters.
The output voltage can change according to the negotiated power profile.
For example, a charger may provide: 5V, 9V, 12V, 15V, 20V; depending on the product design and negotiated operating condition.
USB Power Delivery also allows more flexible power delivery and, with newer specifications, supports significantly higher power levels than earlier USB charging implementations. USB-IF states that PD 3.1 expanded USB-C power delivery capability up to 240W.
Therefore, engineers need to evaluate output behavior under different operating points rather than assuming that a single 5V measurement represents the entire charger.
 
What Should a Factory Test Before Mass Production?
From a charger manufacturer's perspective, ripple testing is only one part of electrical validation.
A proper engineering validation process may include:
Output Voltage — Check whether the output remains within the specified voltage range.
Ripple and Noise — Check the output waveform under different loads.
Load Regulation — Check how much the output changes as the load changes.
Line Regulation — Check how the charger behaves when the AC input voltage changes.
Transient Response — Check the response to rapid load changes.
Efficiency — Measure energy conversion efficiency.
Standby Power — Measure power consumption with no external load.
Temperature Rise — Check internal and external temperature under defined conditions.
Protection — Verify OVP, OCP, OTP, SCP, Other applicable protections
EMC — Evaluate conducted and radiated emissions according to the target market and applicable standards.
A charger manufacturer should not judge product quality from ripple alone.
 
Is Lower Ripple Always Better?
This is a surprisingly complicated question.
In general, lower unwanted ripple and noise are desirable, but engineers should not chase the smallest number at any cost.
For example, adding excessive filtering may:
• Increase component count
• Increase cost
• Increase PCB area
• Increase leakage or inrush considerations
• Affect transient response
• Affect efficiency
• Complicate thermal design
The goal is not: "Make ripple as close to zero as possible." The better engineering objective is: "Achieve stable, reliable and appropriately clean output with a balanced design."
This is especially important for mass-produced chargers where cost, size, efficiency, reliability and certification all have to work together.
 
What Ripple Level Is Acceptable for a Charger?
There is no single universal number that can be applied to every charger.
A 5W USB charger, a 65W GaN charger and a 240W USB-C PD charger have different architectures and operating conditions.
Ripple requirements also depend on:
• Product specification
• Applicable standards
• IC manufacturer recommendations
• Customer requirements
• Target market
• Output voltage
• Load condition
• Test bandwidth
• Measurement method
Public charger tests show that ripple can vary considerably with voltage and load.
 
Some tested USB-C chargers, for example, have measured ripple in the tens of millivolts peak-to-peak, while no-load operation can produce distinct sawtooth waveforms.
Therefore, B2B buyers should avoid asking a factory only: "Is your ripple below 50mV?"
A better question is: "Please provide the ripple test condition, waveform and measurement method."
That gives the engineering team much more useful information.
 
How Should B2B Buyers Evaluate a Charger Ripple Test Report?
If you are sourcing USB-C chargers from a factory, ask for more than one number.
A useful test report should identify:
1. Output Voltage
For example: 5V / 9V / 12V / 15V / 20V
2. Load
For example: 0A, 1A, 2A, 3A, full load
3. Ripple Measurement
Preferably: mVpp, with the test conditions clearly stated.
4. Oscilloscope Settings
Ask about Bandwidth limit, Probe type, Coupling, Time base, Vertical scale.
5. Waveform
The waveform itself can sometimes reveal problems that a single numerical result hides.
6. Test Equipment
For higher-level engineering validation, the equipment model and test setup can be useful for traceability.
 
Ripple Testing at No Load: What Should Engineers Watch?
No-load testing is particularly useful for checking charger standby behavior.
Engineers should look for:
• Stable DC output
• Normal burst-mode behavior
• Excessive spikes
• Abnormal oscillation
• Unusual low-frequency fluctuations
• Unexpected audible noise
• Output instability
• Excessive standby power
A sawtooth waveform alone does not necessarily indicate a failure.
The key question is whether the waveform is expected for the controller and topology being used and whether the output remains within the intended operating limits.
 
Can Ripple Damage a Phone or Laptop?
Normally, a properly designed and compliant charger should provide a stable output suitable for its intended application. However, excessive electrical noise or abnormal output behavior is not something manufacturers should ignore.
The risk is not simply the ripple number. Engineers need to consider the entire output waveform and system interaction.
Modern devices have their own power-management circuits, but the charger still needs to provide a stable power source.
This is especially important when designing chargers for:
• Smartphones
• Tablets
• Laptops
• Monitors
• Docking stations
• Gaming devices
• IoT products
• Consumer electronics
For USB-C PD products, compatibility and interoperability are also important because the charger and device negotiate power according to the supported profiles. USB-IF's compliance program specifically addresses USB PD behavior and power profiles.
Related Reading: Why Does My Charger Get Hot? Is It Dangerous? Causes, Solutions and Manufacturer Insights.
 
Ripple Is Only One Part of Charger Quality
This is perhaps the most important point from a factory perspective.
A charger with low ripple is not automatically a good charger.
A professional charger design needs to balance: Ripple + Noise + Efficiency + Thermal Performance + Safety + EMC + Transient Response + Reliability
 
For example, a charger may have excellent ripple performance but poor thermal performance.
Another charger may have excellent efficiency but unacceptable EMI.
A third charger may have good electrical performance but insufficient protection.
The final product must undergo a comprehensive engineering validation process. For this reason, professional charger manufacturing is far more than simply assembling components onto a PCB (Printed Circuit Board).
 
How Manufacturers Reduce Ripple in Charger Design
When engineers need to improve ripple performance, the solution depends on the root cause.
Possible improvements include:
Optimize Output Capacitors
Select suitable capacitance, ESR, ripple-current rating and temperature characteristics.
 
Improve PCB Layout
Minimize high-current loop areas and control switching paths.
 
Optimize Transformer Design
Reduce leakage-related ringing and improve magnetic performance.
 
Improve Snubber Design
Control excessive switching spikes and ringing.
 
Optimize Output Filtering
Use the appropriate filter structure for the switching topology.
 
Tune the Feedback Loop
Improve stability and transient response.
 
Improve Switching Control
Optimize switching frequency and operating modes.
 
Improve Grounding
Reduce unwanted coupling between noisy and sensitive sections.
 
Improve Measurement Setup
Before modifying the hardware, confirm that the measured ripple is real.
This last point matters more than many people expect.
Sometimes the first "problem" is not the charger.
It is the test setup.
 
What Does a Good Charger Engineering Team Look At?
At the prototype stage, engineers may focus heavily on waveform quality.
During mass production, the focus becomes broader.
A mature charger manufacturing process should control:
• Incoming components
• PCBA quality
• Transformer consistency
• Soldering quality
• Firmware
• Output voltage
• Functional testing
• Aging testing
• Safety testing
• Protection functions
• Final product inspection
 
Electrical performance must remain consistent from prototype to mass production; this is precisely where factory engineering expertise plays a critical role.
It is not enough for a prototype to perform exceptionally well just once; that same electrical performance must be consistently reproducible across thousands of units.
 
Final Thoughts: No-Load Ripple Is Not Automatically a Problem
Charger ripple is a normal characteristic of switching power supplies.
The output of a modern USB charger is never a perfectly flat DC line. There will be some combination of ripple, switching noise and transient components.
No-load ripple can look especially unusual because the charger may enter burst-mode or other power-saving operating conditions.
A sawtooth waveform at zero load does not automatically mean the charger is defective.
What matters is:
• How large the ripple is
• What frequency components are present
• Whether there are excessive spikes
• How the charger behaves under load
• Whether the output remains stable
• Whether the design meets its applicable requirements
• Whether the measurement method is reliable
 
From a manufacturer's perspective, the real objective is not to produce an impressive ripple number on a test sheet.
It is to build a charger that delivers stable power, predictable behavior, safe operation and consistent performance in mass production.
That is the difference between testing a charger and actually engineering one.
 
FAQ: Charger Ripple and No-Load Ripple
Q1: What is ripple in a charger?
Charger ripple is the small AC voltage variation that remains on top of the DC output of a switching power supply. It is commonly measured in millivolts peak-to-peak (mVpp) using an oscilloscope.
 
Q2: What is no-load ripple?
No-load ripple is the ripple measured when the charger has little or no external load connected. Modern chargers may enter burst mode or another low-power operating mode under this condition, which can create a visible sawtooth or pulsed waveform.
 
Q3: Is no-load ripple normal?
Yes, it can be normal. Many switching chargers reduce switching activity when there is no load to minimize standby power. This can produce a periodic waveform that looks different from the waveform under load.
 
Q4: Does no-load ripple mean the charger is bad?
No. A no-load waveform should be evaluated together with its amplitude, frequency, output voltage stability, spikes, standby behavior and the design's expected operating mode.
 
Q5: How is charger ripple measured?
Engineers normally use an oscilloscope with a controlled load and appropriate probing technique. The output is tested at defined voltages and loads, and the peak-to-peak ripple is recorded.
 
Q6: What does mVpp mean?
mVpp means millivolts peak-to-peak. It represents the difference between the highest and lowest voltage excursion observed during the measurement.
 
Q7: What is the difference between ripple and noise?
Ripple is generally a periodic variation associated with the power conversion process. Noise is a broader term that can include high-frequency switching noise, random electrical noise, EMI coupling and switching spikes.
 
Q8: Does GaN automatically reduce charger ripple?
No. GaN can improve switching efficiency and power density, but ripple still depends on the complete charger design, including PCB layout, transformer, filtering, control loop and switching architecture.
 
Q9: Does a higher-wattage charger have more ripple?
Not necessarily. A well-designed 100W or 140W charger can have good ripple performance. Higher power simply creates more demanding electrical and thermal design requirements.
 
Q10: What causes excessive charger ripple?
Common causes include unsuitable output capacitors, poor PCB layout, transformer leakage inductance, inadequate filtering, poor snubber design, control-loop instability and switching-related noise.
 
Q11: Can an oscilloscope show more ripple than actually exists?
Yes. Poor probing, a long ground lead, excessive measurement-loop area or unsuitable bandwidth can introduce additional noise into the measurement.
 
Q12: Should I ask a charger factory for a ripple test report?
Yes, especially for B2B projects. Ask the manufacturer to provide the output voltage, load condition, mVpp result, waveform, bandwidth setting and measurement method so that the data can be compared properly.
 
Reviewed by: Charger Engineer - Michael
Review Date: September 4, 2026