Fast Speed EHT compensation circuit
Publication Date: 2005-Dec-22
The IP.com Prior Art Database
Title: Fast Speed EHT compensation circuit
EHT=Extra High Tension.
CRT=Cathode Ray Tube.
The need for horizontal yoke's current modulation
When picture is black (low light output), the EHT of the CRT is higher, this will result in a decrease in the picture width as a higher amount of horizontal deflection current is required in the yoke to deflect the beam.
When the picture is full white (high light output), the EHT is lower, this will result in a larger picture width as a lower amount of horizontal deflection current is required in the yoke to deflect the beam. The amount of horizontal yoke's deflection current needs to be controlled for correct picture width at all beam current condition.
Prior Art-- Present circuit configuration
Presently the EHT information is derived from EHT produced by the windings of the line output transformer charging the capacitance formed by the EHT anode and the aquadag of the picture tube.
This EHT information is not a direct representation of the actual drive on the video amplifier as the beam current is drawn from the anode's capacitance of the picture tube during scan period, which then charges the anode's capacitance only during flyback period.
The EHT information, which is obtained from the windings of the line output transformer that produces the EHT voltage by charging the anode-aquadag capacitance of the picture tube, has a large time constant. Therefore, it is not a direct representation of the EHT variation. This has resu...