Define Peak Inverse Voltage (PIV) of SCR and explain the equation used for calculating the PIV of SCR in single phase rectifiers.
The correct answer and explanation is :
Peak Inverse Voltage (PIV) of SCR
The Peak Inverse Voltage (PIV) of a Silicon Controlled Rectifier (SCR) is the maximum voltage that can be applied to the SCR in the reverse direction without causing it to break down or become damaged. It is a critical parameter for the SCR in applications where the rectifier circuits reverse bias the SCR during operation. PIV determines the maximum reverse voltage the SCR can handle before it is subjected to a reverse breakdown, which could permanently damage the device.
PIV in Single-Phase Rectifiers
In a single-phase full-wave rectifier using SCRs, the SCRs alternate between conducting and blocking phases. During the non-conducting period, the SCR needs to withstand the reverse voltage that can be applied across it.
When the SCR is in the blocking state (reverse bias), the voltage across it can rise to the maximum value of the input AC supply voltage. The PIV is crucial to prevent the SCR from being damaged when subjected to high reverse voltage.
Equation for PIV in Single-Phase Rectifiers
The equation to calculate the PIV of an SCR in a single-phase full-wave rectifier is as follows:
[
PIV = V_{max}
]
Where:
- ( V_{max} ) is the peak value of the AC input voltage.
In a single-phase AC supply, the peak voltage (( V_{max} )) is related to the RMS value (( V_{rms} )) by the equation:
[
V_{max} = \sqrt{2} \times V_{rms}
]
Therefore, the PIV of the SCR in a single-phase full-wave rectifier is equal to the peak value of the AC supply voltage. The SCR must be able to withstand this voltage during the half-cycle when it is reverse biased.
Explanation:
In a single-phase full-wave rectifier circuit using SCRs, two SCRs are used, and each conducts during half of the input cycle. When an SCR is not conducting, it must handle the reverse voltage that the AC supply generates during that time. If the SCR’s PIV rating is exceeded, it could undergo reverse breakdown, damaging the component. Hence, the PIV rating is essential for ensuring that the SCR is chosen with sufficient voltage capacity for the application.
Image:
Here is a diagram of a single-phase full-wave rectifier circuit using SCRs, showing the AC input waveform, the conducting SCRs during the positive and negative half cycles, and the Peak Inverse Voltage (PIV) across the non-conducting SCR during the reverse bias period. This diagram helps to visualize how PIV is relevant in the SCR’s operation.