Trystan Casey
In electronics, electrical ripple refers to the residual periodic variation of the DC voltage within a power supply derived from an AC source. This phenomenon, known as ripple voltage, arises from the incomplete suppression of the alternating waveform after rectification. Ripple voltage is undesirable for sensitive electronic equipment as it can lead to heating and damage of capacitors, cause errors in digital circuits, and result in incorrect outputs and data corruption. The presence of ripple voltage can also reduce the resolution of electronic test and measurement instruments. To mitigate the effects of ripple voltage, various techniques and components are employed, such as smoothing capacitors, voltage regulators, and electronic filters.
| Characteristics | Values |
|---|---|
| Definition | Ripple is the residual periodic variation of the DC voltage within a power supply which has been derived from an alternating current (AC) source. |
| Other names | Ripple voltage, ripple current, surge current |
| Cause | Incomplete suppression of the alternating waveform after rectification |
| Origin | Output of a rectifier, generation and commutation of DC power |
| Reduction methods | Smoothing capacitors, voltage regulators, electronic filters, capacitor or inductor filters |
| Effects | Reduced resolution of electronic test and measurement instruments, errors in digital circuits, incorrect outputs in logic circuits, data corruption, heating and damage of capacitors |
| Parameters | RMS value of the ripple, average value of the output of the rectifier, peak-to-peak value of the voltage, conversion ratio, ripple factor, form-factor |
| Applications | Fourier analysis, AC/DC power conversion, DC power generation |
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Ripple voltage
Mathematically, ripple factor, denoted as γ, is defined as the ratio of the root mean square (RMS) value of the ripple voltage to the absolute value of the DC component of the output voltage, usually expressed as a percentage. The ripple factor provides insight into the purity of the DC output from a rectifier, with a smaller ripple factor indicating a purer DC output.
To minimise or eliminate the negative effects of ripple voltage, several techniques and components can be employed:
- Smoothing capacitors: Capacitors can be used to convert the ripple voltage into a smoother DC voltage. Aluminum electrolytic capacitors with capacitances of 100uF or more are commonly used for this purpose.
- Π-filter (pi-filter): This low-pass filter consists of two smoothing capacitors and a choke to provide high impedance to the AC ripple, effectively reducing its impact.
- Inductors: Inductors can be placed in series with the power supply output to oppose sudden changes in current, thereby reducing the amplitude of the ripple.
- Voltage regulators: Switched-mode power supplies often include voltage regulators that inherently filter out ripple voltage due to their non-linear characteristics.
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Ripple current
In electronics, a ripple is a residual periodic variation of the DC voltage within a power supply derived from an AC source. This ripple is caused by the incomplete suppression of the alternating waveform after rectification. A ripple current, specifically, refers to the AC component present in the output current of an AC power supply or switching power supply. It usually exists in the form of a periodically varying sine wave with the same frequency as the input power supply.
The ripple current is a critical parameter to consider when selecting a capacitor for a specific application. The size of the ripple current is directly related to the capacity of the capacitor. To reduce its impact, a capacitor with a large enough capacity must be selected to ensure it can withstand the ripple current requirements. The ripple current can be calculated using the formula: Ripple current (Ir) = Ipk x (1-e^(-t/RC)). Here, Ipk is the peak value of the output current, R is the resistance value, and C is the capacitance value.
The presence of a ripple current can have several effects on capacitors. Firstly, it can lead to a heating effect, where the current passing through the capacitor generates power consumption, causing the capacitor to heat up. If the ripple current is large or sustained for a long period, the capacitor may overheat, impacting its performance and reducing its operational life. Secondly, ripple current increases the core temperature of a capacitor, leading to stress changes in its internal materials. This results in ageing and a shortened life for the capacitor.
To address the issues caused by ripple current, filtering measures can be implemented to reduce the low-frequency power supply ripple. This can be achieved by increasing the DC/DC converter closed-loop gain circuit or using a pre-stage pre-stabilizer circuit to enhance the ripple suppression effect. Additionally, large discrete components like high ripple-current-rated electrolytic capacitors, large iron-core chokes, and wire-wound power resistors can be used to reduce the ripple before passing the current to sensitive IC components.
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Reducing ripple
Ripple (or ripple voltage) is the residual periodic variation of the DC voltage within a power supply derived from an AC source. It is caused by the incomplete suppression of the alternating waveform after rectification. In other words, it is the amount of AC voltage that appears on a DC voltage.
Ripple is undesirable for many electronic applications. It can cause heating and damage to capacitors, and it can reduce the resolution of electronic test and measurement instruments. It can also cause errors in digital circuits, incorrect outputs in logic circuits, and data corruption.
Ripple can be reduced using the following methods:
Voltage Regulators
Voltage regulation is based on a different principle than filtering. It relies on the peak inverse voltage of a diode or series of diodes to set a maximum output voltage. Voltage regulators can be made with a series resistor to drop voltage, followed by a shunt zener diode whose Peak Inverse Voltage (PIV) sets the maximum output voltage. If the voltage rises, the diode shunts away current to maintain regulation. The output of a regulator is free of ripple due to the non-linear characteristics of these devices.
Smoothing Capacitors
Smoothing capacitors can be used to convert the ripple voltage into a smoother DC voltage. Aluminum electrolytic capacitors are commonly used for this purpose and have capacitances of 100uF or more. The repeated DC pulses charge the capacitor to the peak voltage. The capacitance value and working voltage are important factors when selecting a capacitor.
Low Pass Filters
A low pass filter can be used to reduce ripple voltage. This type of filter uses frequency response to calculate the parameters of L and C.
Common Mode Choke Filters
Common mode choke filters are commonly used as EMI filters. They can limit switching noise that may be transmitted to the output side of a converter. While there is still leakage inductance inside the common mode filter, it can still have some effect on ripple voltage suppression.
Pi-Filters
A pi-filter is a more effective method of reducing ripple voltage. This low pass filter consists of two smoothing capacitors and a choke to provide high impedance to the AC ripple.
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Effects of ripple
Electrical ripple, specifically ripple voltage, is the residual periodic variation of the DC voltage within a power supply derived from an AC source. It is caused by the incomplete suppression of the alternating waveform after rectification. Ripple current, on the other hand, refers to the pulsed current consumption of non-linear devices.
Ripple has several undesirable effects on DC circuits. Firstly, it causes heating in components, which can lead to the damage of capacitors over time. This heating effect is due to the increased dissipation in parasitic resistive portions of circuits, such as the ESR of capacitors, DCR of transformers and inductors, and the internal resistance of storage batteries. The dissipation is directly proportional to the current squared times resistance (I^2 x R).
Secondly, ripple can cause noise and distortion in the circuit. This noise can reduce the resolution of electronic test and measurement instruments, and even lead to incorrect outputs in logic circuits and data corruption. On an oscilloscope, ripple will manifest as a visible pattern on the screen.
Thirdly, ripple can be problematic for voltage regulation. The regulator circuit can filter out ripple, but only if the minimum level of the ripple waveform does not go below the voltage being regulated. Voltage regulators are based on a different principle than simple filtering, relying on the peak inverse voltage of diodes to set a maximum output voltage.
Finally, ripple can be reduced by using electronic filters, specifically smoothing filters, which can increase or decrease DC output. These filters work by providing high impedance at the ripple frequency. A more effective method is to use a π-filter (pi-filter), which consists of two smoothing capacitors and a choke to provide high impedance to the AC ripple. Large discrete components, such as high ripple-current-rated electrolytic capacitors, large iron-core chokes, and wire-wound power resistors, can also reduce ripple to manageable proportions.
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Ripple factor
Electrical ripple is a phenomenon observed in power supply outputs, where there is a residual periodic variation in the DC voltage derived from an AC source. This ripple effect is caused by the incomplete suppression of the alternating waveform after rectification, resulting in fluctuating voltages that can impact the performance of electronic components.
The ripple factor is a critical parameter that quantifies the ripple content in the waveform. It is denoted as gamma (γ) and is defined as the ratio of the root mean square (RMS) value of the alternating current (AC) component in the rectified output to the average value of the rectified output. Mathematically, the ripple factor can be expressed as:
> ! [\gamma = \frac{V_{RMS}}{V_{DC}}](https://latex.codecogs.com/png.latex?%5Cgamma%20=%20%5Cfrac%7BV_%7BRMS%7D%7D%7BV_%7BDC%7D%7D)
Where:
- VRMS is the root mean square value of the AC component in the rectified output.
- VDC is the average value of the rectified output.
The ripple factor is a dimensionless quantity and always has a value less than 1. It helps to express the DC ripple as a fraction of the AC input, providing insight into the voltage fluctuations without needing to know the exact AC input.
The RMS value of the ripple can be calculated using the following formula:
> ! [RMS = \sqrt{\frac{1}{T}\int_{0}^{T}(i_{L}-I_{dc})^{2}d(\omega t)}](https://latex.codecogs.com/png.latex?RMS%20=%20\sqrt{\frac{1}{T}\int_{0}^{T}(i_{L}-I_{dc})%5E{2}d%28\omega%20t%29})
Where:
- IL is the load current.
- Idc is the average value of the rectified output.
- T is the time period.
The effective value of the load current (Irms) can also be calculated as:
> ! [I_{rms} = \sqrt{\frac{1}{T}\int_{0}^{T}(i_{L})^{2}d(\omega t)}](https://latex.codecogs.com/png.latex?I_%7Brms%7D%20=%20\sqrt{\frac{1}{T}\int_{0}^{T}(i_{L})%5E%7B2%7Dd%28\omega%20t%29})
By understanding the ripple factor and measuring the ripple content, engineers can design appropriate filtering and regulation techniques to minimise the ripple and improve the performance of electronic devices.
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Frequently asked questions
Electrical ripple is the residual periodic variation of the DC voltage within a power supply derived from an AC source. It is also known as ripple voltage.
The electrical ripple is caused by the incomplete suppression of the alternating waveform after rectification. It can also be caused by the generation and commutation of DC power.
The presence of an electrical ripple can cause errors in digital circuits, incorrect outputs in logic circuits, and data corruption. It can also reduce the resolution of electronic test and measurement instruments.
The electrical ripple can be reduced by using smoothing capacitors, which convert the ripple voltage into a smoother DC voltage. Aluminum electrolytic capacitors are commonly used for this purpose and have capacitances of 100uF or higher.
