Electrical – what should be the reverse voltage of diode


In AC/DC converter using 240V/12V step down transformer,the diode used for rectification should have reverse voltage of more than 12v.

what should be the diode reverse voltage,if it should rectify directly 240V AC from mains(step-down transformer is not used)

should the reverse voltage be more than rms voltage-230 AC or peak to peak voltage 320V

Best Answer

You need at least the peak voltage. That is 230V + 10% * SQRT(2) ~ 360 Vpeak.
(Mains voltage isn't solid 230V, it has margin)

However, you also need to survive transients (IEC 61000-4-4). Which is why you use slightly higher Vr. Diodes of 600V to 800V are common and 1000V to 1200V are becoming affordable as well.

Make sure to protect the input with an appropriate varistor (MOV) and fuse.