TDA2579B Philips Semiconductors, TDA2579B Datasheet - Page 9

• Manufacturer Part Number: TDA2579B
• Description: Horizontal/vertical synchronization circuit
• Manufacturer: Philips Semiconductors

Philips Semiconductors
Preliminary specification
Horizontal/vertical synchronization circuit
TDA2579B
Supply (pins 9, 10 and 16)
The IC has been designed such that the horizontal oscillator and output stage can start operating by application of a very
low supply current into pin 16.
The horizontal oscillator starts at a supply current of approximately 4 mA. The horizontal output stage is forced into the
non-conducting stage until the supply current has a typical value of 5 mA. The circuit has been designed so that after
starting the horizontal output function a current drop of
1 mA is allowed. The starting circuit has the ability to derive the
main supply (pin 10) from the horizontal output stage. The horizontal output signal can also be used as the oscillator
signal for synchronized switched mode power supplies. The maximum allowed starting current is 9.7 mA (T
= 25 C).
amb
The main supply should be connected to pin 10, and pin 9 should be used as ground. When the voltage on pin 10
increases from zero to its final value (typically 12 V) a part of the supply current of the starting circuit is taken from pin 10
via internal diodes, and the voltage on pin 16 will stabilize to a typical value of 9.4 V.
In a stabilized condition (pin V
10 V) the minimum required supply current to pin 16 is 2.5 mA. All other IC functions
10
are switched on via the main supply voltage on pin 10. When the voltage on pin 10 reaches a value of 7 V the horizontal
phase detector circuit is activated and the vertical ramp on pin 3 is started. The second phase detector circuit and burst
pulse circuit are started when the voltage on pin 10 reaches the stabilized voltage value of pin 16 which is typically 9.4 V.
To close the second phase detector loop, a flyback pulse must be applied to pin 12. When no flyback pulse is detected
the duty factor of the horizontal output stage is 50%.
For remote switch-off pin 16 can be connected to ground (via a npn transistor with a series resistor of
500 ) which
switches off the horizontal output.
Horizontal oscillator, horizontal output transistor, and second phase detector (pins 11, 12, 14 and 15)
The horizontal oscillator is connected to pin 15. The frequency is set by an external RC combination between pin 15 and
ground, pin 9. The open collector horizontal output stage is connected to pin 11. An internal zener diode configuration
limits the open voltage of pin 11 to
14.5 V.
The horizontal output transistor at pin 11 is blocked until the current into pin 16 reaches a value of
5 mA.
A higher current results in a horizontal output signal at pin 11, which starts with a duty factor of
40% HIGH.
The duty factor is set by an internal current-source-loaded npn emitter follower stage connected to pin 14 during starting.
When pin 16 changes over to voltage stabilization the npn emitter follower and current source load at pin 14 are switched
OFF and the second phase detector circuit is activated, provided a horizontal flyback pulse is present at pin 12.
When no flyback pulse is detected at pin 12 the duty factor of the horizontal output stage is set to 50%.
The phase detector circuit at pin 14 compensates for storage time in the horizontal deflection output stage. The horizontal
output pulse duration is 29 s HIGH for storage times between 1 s and 17 s (flyback pulse of 12 s). A higher storage
time increases the HIGH time. Horizontal picture shift is possible by forcing an external charge or discharge current into
the capacitor at pin 14.
September 1990
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