SINGLE CHOKES (EMI)
Single chokes are used for the suppression of differential mode interference or differential mode noise (DMN). DMN is generated by switching devices. They occur usually at frequencies below
1MHz.
Cores for Single chokes are usually made out of iron powder or metal powder with one winding. Various materials with different properties are available.
All iron powder cores are susceptible to thermal aging. This means an increasing core loss when exposed to elevated temperatures for extended periods of time. The cores we use have a very little
and defined thermal aging.
This type of chokes may work as storage choke where there is only little requirement and the cost plays a role.
Areas of application
- EMI suppression of DMN in phase-controlled circuits like dimmers
- EMI suppression of DMN in SCR circuits
- EMI suppression of DMN in triac circuits
- EMI suppression of DMN in circuits with solid state relays
- storage choke in applications like SMPS and DC/DC converters below 50kHz
- current rise limiter choke in circuits like frequency converters
Technical characteristics:
The inductance rating, also known as AL value, of iron or metal powder cores is quite low compared to ferrite. The inductance of a choke depends on the AC flux density in the core and falls off
at high values. The nominal inductance which is found in a data sheet is the value at no load current. The quality and quantity of EMI suppression depends not only on the inductance value of a
choke but also on core size and material.
Since DMN occurs only up to 1MHz chokes are usually wound in more layers if needed. Coupling capacitance doesn't really affect it.
Materials:
- F: standard material
- FV: special material for EMI suppression of DMN in phase-controlled circuits
- K: lower loss material
- L: lower loss material and application at high temperature (no aging)
- MS: very low loss material (dI/dt-chokes)
- MP: lowest loss material (dI/dt-chokes)