Current Draw

Using my multimeter, measured 436mA drawn before the LDOs, for the OSD circuit. Does not include MCU current.

Measured 260mA drawn after the LDOs on the 3.3V supply. Measured 70mA on the 1.8V supply. (All using the Amps scale, on the 10A unfused input).

If this is accurate, then I might be able to achieve around 360mA using a switching power supply with 80% efficiency (not including MCU current draw).

New Approach, New Ideas

Now looking at making a new board, using the AD724 clocked in sync with the incoming video signal’s colourburst. This is looking like quite a challenge. The basic principle has been shown to work, but it requires a lot of ICs. Am considering using the AD8001 as the pixel switch as it has “excellent video characteristics” according to the datasheet, which also gives a reference circuit for exactly that. However it requires a dual +-5V supply and I am not sure what is the best way to provide this. More research needed. Could it be as simple as 2 +5V LDOs, with the positive rail of one and the negative rail of the other, becoming GND?

Am also wondering how much of the 550mA used by my existing design, is due to losses by the inefficient linear voltage regulators? If I changed them to switch-mode regulators, could I bring the power down to 300mA? And could I do this while keeping noise within acceptable limits? I will try to measure the actual current drawn by the video chips from the LDO regulators. To date I have only measured total current drawn from the 5V USB power supply which includes losses from the LDOs.