Dear all, I applied positive bias on gate, there is significant high leakage current on the transistor. However, when I applied negative bias on gate, the leakage current is insignificant. What can I infer from this?
Yes, applying a positive or negative bias on the gate of certain power semiconductor devices can result in different leakage currents (IGSS - Gate-to-Source Leakage Current). Leakage currents refer to the small currents that flow through the device when it is supposed to be in the off-state (blocking state). The magnitude and direction of the IGSS depend on the type of power semiconductor device and its internal structure. Two common types of devices where the bias on the gate affects the IGSS are MOSFETs and Insulated Gate Bipolar Transistors (IGBTs):
1. MOSFETs:
- For N-channel MOSFETs: When a positive voltage (VGS) is applied to the gate (relative to the source), it enhances the flow of electrons in the channel, turning the MOSFET "on" or into its conducting state. In this case, the IGSS is typically very low because the MOSFET is in the on-state.
- For P-channel MOSFETs: When a negative voltage (VGS) is applied to the gate (relative to the source), it enhances the flow of holes in the channel, turning the MOSFET "on." In this case, the IGSS is also typically very low because the MOSFET is in the on-state.
- For both types, when the gate voltage is zero (VGS = 0), the MOSFET should be off. In this off-state, there is a small reverse leakage current (IGSS) flowing through the gate-to-source junction, which is usually very low but can be affected by temperature and other factors.
2. IGBTs:
- When a positive voltage (VGE) is applied to the gate (relative to the emitter), it enhances the conductivity of the IGBT, and it enters the on-state. In this state, the IGSS is generally low.
- When a negative voltage (VGE) is applied to the gate (relative to the emitter), it reduces the conductivity of the IGBT, but it might not turn off completely, and some leakage current (IGSS) can flow through the device.
It's important to note that the magnitude of IGSS is usually quite small in both MOSFETs and IGBTs when they are in the off-state. However, in high-voltage applications or situations where minimizing power loss is crucial, leakage currents become more critical, and device selection and proper driving techniques become important factors to consider. Additionally, the characteristics of IGSS may vary between different device families and manufacturers.
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