How to eliminate the ripple and noise of switching power supply and improve the stability of switching power supply?
The operating frequency of the switching power supply is relatively high, usually tens of KHz, so the ripple and noise will be much larger relative to the industrial frequency power supply. We can design a suitable filter circuit to reduce the ripple and noise. circuit to reduce ripple and noise Suitable filter capacitors can effectively reduce the ripple and noise of switching power supply. In high frequency switching power supply, the capacitance of the filter capacitor is not as large as possible. Need to consider the capacitance impedance and frequency characteristics. The capacitor needs to have Lower equivalent impedance to have a good filtering effect. Because the frequency of the power supply increases, the capacitance value will drop sharply, so when selecting the filter capacitor we need to consider the ESR (Equivalent Series Resistance). Try to use a filter capacitor with a small ESR value.
The size of the capacitance value can be referred to the previous formula: C>0.289/{fx(U/I) x ACv}.
ACv is the ripple factor in %.
Adding inductor filter can effectively reduce the ripple and noise of switching power supply.
Inductors can isolate AC and pass DC, so we can use inductors to filter and reduce the ripple and noise of switching power supply.
When using inductive filtering, we need to pay attention to the power of the inductor.
Switching power supplies generally use LC filtering.
In order to achieve a better filtering effect, generally use a combination of LC filtering, some switching power supply circuits will be added to the dipole filtering, that is, adding another level of LC filtering circuit. Add LDO (low dropout linear regulator) filtering can significantly reduce the ripple and noise of the switching power supply LDO (low dropout linear regulator) there is a noise rejection ratio of the LDO (LDO) has a noise rejection ratio. So adding a low dropout linear regulator is the most effective way to reduce the ripple and noise of switching power supply. But the cost and power consumption will increase.
