![12v product pi filter design 12v product pi filter design](https://www.behringersystems.com/cfiles/photos/large/pi360.jpg)
However, for this article, we will focus on the AC/Mains EMI ( Electro Magnetic Interference) power type filter. The general term filter, of course, can also be used for a device on control and signal type lines. Filters accept an electrical signal at its input and deliver a different or modified signal at its output depending upon the filters internal configuration.
![12v product pi filter design 12v product pi filter design](https://i.stack.imgur.com/ZtRQh.png)
The term “signal” can be a communication or power type signal. It is a device usually composed of discrete components which can be placed between circuits, networks, or equipment/systems to either emphasize, de-emphasize or control the frequency components of a desired or undesired signal. For a discussion of the non-ideal character of common mode filter inductors refer to the application note “Common Mode Filter Induction Analysis”.To start at the very beginning, what is an electrical filter? An electrical filter can be passive, active, analog, or digital. Standard filter alignments assume ideal filter components this does not necessarily hold true, especially at higher frequencies. Line filters, with their unique requirements, yet non-critical characteristics, are easily designed using a minimum allowable damping factor. Specific filter alignments may be calculated by manipulating the transfer function coefficients (component values) of a filter to achieve a specific damping factor.Ī step-by-step design procedure may utilize standard filter alignments, eliminating the need to calculate the damping factor directly for critical filtering. The resulting common mode filter configuration would be as follows:Ī second order filter uses two reactive components and has two advantages over the first order filter: 1) ideally, a second order filter provides 12 dB per octave attenuation (four times that of a first order filter) after the cutoff point and 2) it provides greater attenuation at frequencies above inductor self-resonance.
![12v product pi filter design 12v product pi filter design](https://developer.electricimp.com/sites/default/files/attachments/images/designing_analog_hw/pi_filter.png)
For example, attenuation at and above 4000 Hz into a 50 Ω load would require a 1.99 mH (50/(2pi x 4000)) inductor. The value of inductance required of the choke is simply the load in ohms divided by the radian frequency at and above which the signals is to be attenuated. In the case of a low pass common mode filter, a common mode choke is the reactive element employed. The simplest and least expensive filter to design is a first order filter this type of filter uses a single reactive component to store certain bands of a spectral energy without passing this energy to the load. When the inductors, L1 and L2 encounter an identical signal of the same polarity referred to ground (common mode signal), they each contribute a net, non zero flux in the shared core the inductors thus perform as independent components with their mutual inductance responding to the common signal: the mutual inductance then attenuates this common signal. The design of a common mode filter is essentially the design of two identical differential filters, one for each of the two polarity lines with the inductors of each side coupled by a single core:įor differential input current ( (A) to (B) through L1 and (B) to (A) through L2), the net magnetic flux which is coupled between the two inductors is zero.Īny inductance encountered by the differential signal is then the result of imperfect coupling of the two chokes they perform as independent components with their leakage inductances responding to the differential signal: the leakage inductances attenuate the differential signal. The resulting common mode output of the filter in the AC line (via impedance matching circuitry) is then negligible. The direction of common mode noise (noise on both lines occurring simultaneously referred to earth ground) is from the load and into the filter, where the noise common to both lines becomes sufficiently attenuated. Figure 1 shows the use of a common mode filter between the AC line (via impedance matching circuitry) and a (noisy) power converter. Line filters prevent excessive noise from being conducted between electronic equipment and the AC line generally, the emphasis is on protecting the AC line.
![12v product pi filter design 12v product pi filter design](https://i.ytimg.com/vi/Cw15yDfxI3E/maxresdefault.jpg)
The use of standard filter alignments can be utilized to achieve a relatively simple and straightforward design process, though such alignments may readily be modified to utilize pre-defined component values. The selection of component values for common mode filters need not be a difficult and confusing process.