zappedagain
Electrical
- Jul 19, 2005
- 1,074
This is continuing the discussion started in thread240-309895
Are there any guidelines for the value of the bypass capacitor from the primary to secondary of a flyback transformer to eliminate (reduce) the common mode currents that can cause EMI issues?
Other than stating that the capacitor voltage needs to be at least as high as the transformer isolation voltage I haven't seen any other specifications for this part. A few articles give a typical range (2.2-4.7 nF). I'd think the transformer manufacturers would define it, but I haven't seen that in the datasheets of several or the larger flyback transformer manufacturer's datasheets. I'm disappointed in how many application notes I see that don't even show the bypass capacitor; is this a trick of the EMI/EMC trade and not power supply design?
Z
Are there any guidelines for the value of the bypass capacitor from the primary to secondary of a flyback transformer to eliminate (reduce) the common mode currents that can cause EMI issues?
Other than stating that the capacitor voltage needs to be at least as high as the transformer isolation voltage I haven't seen any other specifications for this part. A few articles give a typical range (2.2-4.7 nF). I'd think the transformer manufacturers would define it, but I haven't seen that in the datasheets of several or the larger flyback transformer manufacturer's datasheets. I'm disappointed in how many application notes I see that don't even show the bypass capacitor; is this a trick of the EMI/EMC trade and not power supply design?
Z