What is Power Ripple?
When the output of the power supply is working, a phenomenon of fixed frequency fluctuation caused by the switching of the power supply itself, the ripple is generally synchronized with the switching frequency of the power supply, and is generated by the charging and discharging of the capacitor, PWM adjustment, etc.
In a word, it’s an AC interference single on the DC signal, and the frequency of it is the same as the frequency of switching.
How is power ripple generated?
Normally power supplies include linear power supplies and switching power supplies, the output DC voltage is required a fixed value, which is obtained by fixating, filtering, and stabilizing from the input AC voltage. Because the filtering is not 100% clean, the DC voltage contains some AC voltage part like 20%, where ripples were produced.
Ripple is a complex signal with disorganized that fluctuates up and down around the output DC voltage. There are many factors that produce power ripple, even if you use battery power, it will be affected by load ripple.
For linear power supplies
When the frequency of electricity supply is 50Hz, the ripple comes from it, the frequency of ripple voltage is usually 50Hz*n, n depends on the rectification type of circuit.
for half-wave rectification, n=1;
for full-wave rectification, n=2;
for 3-phase full-wave rectification, n=6;
The output ripple of the linear power supply is an integer multiple of 50Hz, it’s quite easy to be reduced.
For Switching power supplies
The generation of ripples is complex, the frequency value is bigger and hard to be reduced.
It includes
- low-frequency ripple,
- high-frequency ripple,
- common mode noise,
- noise generated by switching components,
- ripple noise from the control loop circuit,
Normally the ripples of switching power supplies are bigger than linear power supplies.
High-frequency ripple
The high-frequency ripple comes from the switching conversion circuit.
- The switch tube of the switching power supply needs time for rising and falling when it is turned on and off, at the same time, there is a noise with the multiplier frequency as the switch rise and falls appearing.
- And, when the diode reverses recovering, its equivalent circuit will cause resonance and generate noise with frequency Mhz.
- The leakage inductance of the high-frequency transformer will also produce high-frequency interference.
These noises are generally called high-frequency ripple noise and are usually much larger in magnitude than the ripple.
Common mode noise
There is a parasitic capacitance between the power device and the radiator bottom plate and the primary and secondary sides of the transformer, and the wire has a parasitic inductance. Therefore, when the voltage is applied to the power device, the output end of the switching power supply will generate a common mode ripple noise.
Noise generated by switching components
As the switch is switched on and off, the current in the inductor also fluctuates around the RMS value of the output current. Therefore, a ripple at the same frequency as the switch will also appear at the output.
Ripple noise from the control loop circuit
In the actual circuit, the control loop needs time to respond and cannot be adjusted linearly, so the output voltage will fluctuate instantaneously, and it may even cause the power supply system to oscillate, and make ripple noise.
Why need to reduce the ripple of power adapters?–disadvantages of ripple.
When debugging the product, you will encounter the following phenomena:
- There is a humming noise in the speaker or receiver, which may be caused by a sine wave-like ripple signal in the audio range pushing the cone of the speaker or the receiver of the phone to form a noise;
- When debugging the signal amplification system, it can be seen that the ripple voltage modulates the amplified signal and forms clutter;
- For display devices, If there are thin horizontal bars scrolling up or down on the background of the Display image, it may be caused by excessive power supply ripple of the intermediate frequency unit such as modulation and correction in the exciter.
All of the above phenomena may be caused by ripples. If the ripple voltage is high, it may cause the electronic products to generate harmonics, modulation, etc., which may influence the normal operating situation; reduce the efficiency of the power adapter; affect the logical relationship of the digital circuits; interfere with the transmission of the signals, etc. A stronger ripple will produce surge voltage or current, the surge might burn electrical devices. So reducing power ripple is very important.
