09-12-2021, 06:49 PM
The error is that it's not ampere-turns that cause saturation. An unloaded transformer will saturate just as easily as a loaded one. If you take any iron cored transformer and wind up the voltage applied to a winding, at some point the current will start to increase rapidly as the core enters saturation. The voltage at which you get saturation will fall linearly as you reduce frequency.
This is why some US transformers, designed for 60Hz, will saturate and overheat on 50Hz even with correct mains voltage.
Your problem is also made worse by using a sigle ended output stage where the primary of the transformer is also carrying DC.
To calculate the scan power, assume that the load is resistive. As you correctly state, the reactance of the frame coils is a secondary effect at 12.5Hz. You need 50Vp-p which is approx 18V RMS. Using V^2/R gives 18x18/511 = 0.63W average power. In other words, not very much.
This is why some US transformers, designed for 60Hz, will saturate and overheat on 50Hz even with correct mains voltage.
Your problem is also made worse by using a sigle ended output stage where the primary of the transformer is also carrying DC.
To calculate the scan power, assume that the load is resistive. As you correctly state, the reactance of the frame coils is a secondary effect at 12.5Hz. You need 50Vp-p which is approx 18V RMS. Using V^2/R gives 18x18/511 = 0.63W average power. In other words, not very much.
www.borinsky.co.uk Jeffrey Borinsky www.becg.tv
