**Peak Inverse Voltage (PIV)**: Maximum voltage across a non-conducting diode**PIV Requirement**: Must be less than diode’s breakdown voltage**Worst Case**: Capacitor-input filter**Symbols for Maximum Reverse Voltage**: PIV, PRV, \(V_B\), \(V_{BR}\), \(V_{R}\), \(V_{RRM}\), \(V_{R(max)}\)

**Half-Wave Rectifier with Capacitor-Input Filter**Critical part: Determines reverse voltage

Worst case: Peak secondary voltage negative, capacitor fully charged

Peak Inverse Voltage (PIV): \[\mathrm{PIV} = 2V_p\]

Example: Peak secondary voltage = 15 V \[\mathrm{PIV} = 2 \times 15\,\text{V} = 30\,\text{V}\]

Diode must have breakdown voltage greater than PIV

**Full-Wave Rectifier with Capacitor-Input Filter**Critical part: Determines peak inverse voltage

Secondary voltage at negative peak

Lower diode: short (closed switch), upper diode: open

Peak Inverse Voltage (PIV): \[\mathrm{PIV} = V_p\]

**Bridge Rectifier with Capacitor-Input Filter**Critical part: Determines peak inverse voltage

Upper diode: short (closed switch), lower diode: open

Peak Inverse Voltage (PIV): \[\mathrm{PIV} = V_p\]

Advantage: Lowest PIV for a given load voltage

Compared to full-wave rectifier: Requires half the secondary voltage for same load voltage

Filter capacitor initially uncharged

At power-on, capacitor acts as a short

Initial charging current may be very large

Surge current: Initial rush of current

Charging path: Resistance of transformer windings and diode bulk resistance

Designer’s choice: Diode with sufficient current rating or use of a surge resistor

Surge resistor: Reduces surge current to safe level

\(R_{surge}\) inserted between bridge rectifier and capacitor-input filter

Surge resistors are infrequent in use

What is the peak inverse voltage if the turns ratio is \(8: 1\) ? The diode has a breakdown voltage of 50 V . Is it safe to use the diode in this circuit?

The rms secondary voltage is:

\[V_2=\frac{120 \mathrm{~V}}{8}=15 \mathrm{~V}\]

The peak secondary voltage is:

\[V_p=\frac{15 \mathrm{~V}}{0.707}=21.2 \mathrm{~V}\]

The peak inverse voltage is:

\[\text { PIV }=21.2 \mathrm{~V}\]

The diode is more than adequate, since the peak inverse voltage is much less than the breakdown voltage of 50 V .