S-Video/PAL Video Converter

Many video devices nowadays have an S-Video video output terminal, such as camcorders, satellite TV receivers, etc. The purpose of this article is to introduce a simple circuit (as shown in Figure 1) that can convert S-Video video output to PAL video output.

1. Circuit working principle

In fact, what we need to do is to mix the brightness and color signals that are separated in the S-Video standard for transmission, and avoid cross-modulation caused by the combination of these two signals of different nature as much as possible. The color signal in the S-Video signal is equivalent to the color component of the PAL signal. Similarly, the brightness signal in the S-Video signal can be regarded as the brightness component in the SECAM or PAL signal. The two independent video signals are input to the input end of the mixer through two matching resistors.

The mixer is implemented with a typical op amp KE5534. Both signals are directly coupled without DC blocking capacitors to avoid various problems caused by changes in the average DC component of the useful signal. The output also passes through a 75Ω resistor to match the connecting cable. In the video channel, there is also a potentiometer to adjust the level to achieve the purpose of adjusting the image contrast.

The power supply of the adapter is +8v and -8v provided by two voltage regulators. The negative power supply can also be -5v. Usually the output signal value is mostly positive.

2. Converter production

The input signal is a four-contact socket for S-Video video terminals, and the output is a common RCA output socket. When installing, pay attention to the polarity of the filter capacitor and the direction of the power supply voltage regulator.