07-10-2021, 06:50 PM
Basic idea about inductor is that the voltage is proportional to the rate of change of current. V = L * dI/dt if you are familiar with simple calculus.
In a normal TV the line timebase works, to a first approximation, by applying a constant voltage to the scan coils. The current then rises linearly until the spot is at the right edge of the screen. Energy 0.5*L* I^2 is stored in the coil. You then switch off the voltage and the current tries to drop to zero very fast. This generates a high voltage peak which is tamed by resonating the L with some C. This also causes flyback. You then turn on the constant voltage again and the energy stored in the coil is returned to the supply for the left part of the stroke.
This is a very crude explantion but it shows that for normal H scanning it's the L of the scan coils that's dominant.
For the field scan the resistance ofthe scan coils is dominant in the forward stroke. The timebase is rather like an audio amplifier. During flyback you have to apply alarger voltage to get it to happen because the L of the coils matters a lot more.
For SSTV the H scan is so slow that normal audio amp techniques will work pretty well. You'll still get a higher voltage peak during flyback.
In a normal TV the line timebase works, to a first approximation, by applying a constant voltage to the scan coils. The current then rises linearly until the spot is at the right edge of the screen. Energy 0.5*L* I^2 is stored in the coil. You then switch off the voltage and the current tries to drop to zero very fast. This generates a high voltage peak which is tamed by resonating the L with some C. This also causes flyback. You then turn on the constant voltage again and the energy stored in the coil is returned to the supply for the left part of the stroke.
This is a very crude explantion but it shows that for normal H scanning it's the L of the scan coils that's dominant.
For the field scan the resistance ofthe scan coils is dominant in the forward stroke. The timebase is rather like an audio amplifier. During flyback you have to apply alarger voltage to get it to happen because the L of the coils matters a lot more.
For SSTV the H scan is so slow that normal audio amp techniques will work pretty well. You'll still get a higher voltage peak during flyback.
www.borinsky.co.uk Jeffrey Borinsky www.becg.tv
