TDA4505

The TDA4505 is a TV sub-system circuit, for colour television receivers. For a complete colour television receiver only a tuner, a colour decoder and output stages are required.

The TDA4505 has the following features including:(1)vision IF amplifier with synchronous demodulator; (2)tuner AGC (negative going control voltage with increasing signal); (3)AGC detector suited for negative modulation; (4)AFC circuit; (5)video preamplifier; (6)sound if amplifier, demodulator and preamplifier; (7)DC volume control or separate supply for starting the oscillator; (8)horizontal synchronization circuit with two control loops; (9)vertical synchronization (divider system) and sawtooth generation with automatic amplitude adjustment for 50 or 60 Hz mode; (10)transmitter identification (mute); (11)three level sandcastle pulse generation.The horizontal synchronization has two control loops. This has been introduced to generate a sand-castle pulse.Using the oscillator sawtooth facilitates accurate timing of the burst key pulse. Therefore,the phase of this sawtooth must have a fixed relationship to the sync pulse, which is achieved by use of a second loop.

The absolute maximum ratings of the TDA4505 are:(1)operating ambient temperature range:-25 to 65; (2)storage temperature range:-25 to 150; (3)supply voltages:9.5 to 13.2V; (4)supply current:6 to 8.5mA;(5)total power dissipation:2.3W.The TDA4505 embodies a synchronized divider system for generating the vertical sawtooth at pin 2.The divider system has an internal frequency doubling circuit, which allows the horizontal oscillator to operate at its normal line frequency. One line period equals 2 clock pulses.Use of the divider system avoids the requirement for vertical frequency adjustment. The divider has a discriminator window for automatic switching from 60 Hz to 50 Hz mode. When the trigger pulse comes before line 576 the 60 Hz mode is selected, otherwise the 50 Hz mode is selected.To avoid the necessity of a VCR switch, the time-constant of phase detector at strong input signal is sufficiently short to obtain a stable picture during VCR playback. During the vertical retrace period the time-constant is even shorter so that the head errors of the VCR are compensated at the beginning of the scan. During weak signal conditions (information derived from the AGC circuit) the time constant is increased to obtain a good noise immunity.