switch mode power supply diodes
CR2 is a normal diode. At least it's a normal fast diode, a slouch like 1N4004 will not do. It's likely to be a schottky, which is fast and lower forward drop then a silicon diode. 

Regulation of output voltage is achieved by adjusting the amount of power Q1+T1 pushes into the output pi filter. 

The box marked 'ref' is really a difference amplifier with one input set to a reference voltage, which detects the output voltage, and controls the power transferred as required.