Specifications

CA10 Course Notes
Sharp Electronics (UK) Limited
CE Technical Support Group Page 25
Beam current limiter
Beam current limiting is carried out to remove the risk of forward X-ray emissions, to stabilise the EHT
and control picture brightness. Feedback to control the beam current is taken from the bottom end of the
EHT over winding as shown in the diagram below.
Figure 26 : Beam Current Limiter Circuit
Feed back for the beam current limiter is taken from the bottom end of the EHT over winding on pin 8 of
T601. This produces a DC voltage which is fed into pins 22 ( B LIM ) and 50 ( EHT IN ) of IC201. When
the beam current increases, the voltage on pin 8 of T601 will rise, conversely as the beam current
decreases the voltage on this pin drops.
Beam limiting input of IC201
Pin 22 ( B LIM ) will ensure that the picture brightness is maintained within limits should the beam current
increase or decrease by varying the amplitude of the video signal. Should the beam current become
excessive, then IC201 will reduce the amplitude of the video signal so that the screen blanks out ( raster
still present, but no picture ). If the beam current then increases still further, the video signal will be
reduced below the black level to give an ultra black picture.
Figure 27 : Signal Present on Pin 22 ( BLIM ) of IC201