1、 Capacitance filtering
In parallel with a capacitor at the output end, this kind of circuit is relatively simple, only a large electrolytic capacitor, the output voltage changes with the change of output current, the external characteristics are relatively soft, and the output characteristics are very poor, so it is suitable for circuits with small load current change, and the load current is not large; in order to reduce the pulsation component, sometimes a large one and a small one will be paralleled capacitance.
2、 Inductive filtering
Inductance filtering is to connect an inductor. Because the inductance has self inductance effect, when passing through the current, the two ends of the inductor will produce electromotive force to resist the change of current value, so it can play a filtering role. With the increase of current, part of it will be stored in the inductance to make the current increase slowly; at the same time, when the current decreases, the reverse emf will hinder it in turn At the same time, its external characteristics are also relatively hard, so it is suitable for large current load.
3、 Complex filtering
1. LC filter (inverted L filter)
LC filter is composed of inductance and capacitance. In order to reduce the ripple voltage, a load and capacitor are usually connected to the circuit in parallel. In this way, after the inductance and capacitance filtering, the output load end can get a smooth DC. This filter can also play a good filtering effect when the current changes and fluctuates.
2. LC – π filtering
This kind of filter adds a capacitor on the basis of LC filter, so the output voltage ripple is smaller, its filtering effect is better than LC filter, but at the same time, the charging and striking current of rectifier diode is larger.
3. RC – π filtering
This kind of filter is similar to LC – π filter, but the inductance is replaced by resistance. Because resistance has the function of reducing voltage, when combined with capacitance, more pulsating AC components will drop on the resistance to reduce the impact on load, and finally realize filtering. This circuit is suitable for small load current and low output voltage ripple.