TECHNICAL NOTES

 
LINE FREQUENCY
Our standard transformers are designed to operate in 50 or 60Hz circuits. On demand, we furnish toroids with thinner grain oriented steel laminations for operation at frequencies to 2kHz. For higher frequencies, cores are chosen from such composite materials as ferrite or powdered metal.

APPLYING TOROIDS TO RECTIFIER POWER SUPPLIES
When used in rectifier circuits, the advantages of toroids may be optimized if consideration is given to how they are applied. AC current in the transformer's secondary is not only influenced by the DC load current, but, just as important, by the circuit configuration. Common circuit configurations are shown as follows:

Full Wave Bridge(FWB)
     
  Form Factor (K) = 1.8 IL(DC)=DC current load
  IAC=(K) x IDC IS(AC)=RMS circuit in secondary
  K=Form factor associated with circuit type
 
  Full Wave Center Tap (FWCT)
 
     
  Form Factor (K) = 1.3 IL(DC)=DC current load
  IAC=(K) x IDC IS(AC)=RMS current in secondary
    K=Form factor associated with circuit type
     
  Full Wave Center Tap (FWCT) with Choke Input
 
     
  Form Factor (K) = 0.7 IL(DC)=DC current load
  IAC=(K) x IDC IS(AC)=RMS current in secondary
    K=Form factor associated with circuit type
     
  Full Wave Bridge(FWB)
 
     
  Form Factor (K) = 1.8 IL(DC)=DC current load
  IAC=(K) x IDC IS(AC)=RMS current in secondary
    K=Form factor associated with circuit type
     
  FORM FACTOR (K)
 

    IL(DC) = DC current load
    Is(AC) = RMS current in secondary = K x IL(DC)
    K = Form factor associated with circuit type

    The "Form Factor" (K) is related to the rectifier circuit configuration and the wave form of the current in the secondary.

      lAC = K x IDC

    Typical form factor (K) values at capacitor input filter:

      Rectifier Type Form Factor (K)
      FWB 1.8
      FWCT 1.3
      FWCT with choke input 0.7
      FWCT with dual outputs 1.8

AMVECO employs computer aided design techniques to optimize the toroidal transformer parameters. Our computer program takes into account the influence of the circuit Form Factor (K) as shown above. When preparing specifications for toroids, it is important that the capacitor value and the voltage drop across the regulator (if any) is furnished. In some high current applications, a choke input filter will compound savings because inductors yield a lower Form Factor (K). In these circuits, the size of the transformer and the total capacitance are both reduced.