switch mode power supply diodes

Question

Hello I have a question on switch mode power supply diodes. Usually switch mode power supplies have a rectifying diode at the transformer output. Do these diodes regulate the transformer output or do they just rectify the output?

For example a transformer with a 12 volt output ac when the diode is put on the output and then filtered charges the capacitor at peak voltage will then be higher

so what i want to know is i have a switch mode power supply that has a winding and the a diode i have never seen before (a black diode with a green band) and there is no voltage regulator just a 35v capacitor and inductor and then another capacitor like the circuit shown on the output So is this type of diode a normal diode how would i determine what it is (also the SMPS is out of a dvd player) it has a similar winding but negative. which works but this diode is burned out I know diodes have a voltage drop that why I'm asking this i just want to substitute it.

Answer 1

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.