White Horse Laboratories offers MOSFET device testing
MOSFET devices are essentially switches. They are quite common and not particularly complex devices. What makes them different than other switches (transistors and mechanical switches, for example) is the fact that they turn on and off extremely quickly, which makes them very effective and precise in controlling the amount of current flowing thru an application. This makes them very useful for many products including pulse width modulation motor controls, Class D amplifiers, DC-DC converters, and all kinds precision power supplies.
Unlike some devices which rely on proprietary programming with complex packages and functionality, what differentiates good MOSFET devices and manufacturers from substandard products is the robustness of their construction in terms of materials and insulation, allowing them to function for extended life-cycles with high current with precise on/off switching. As they are relatively simple components, the design of the wafer is not complex or proprietary so most major manufacturers purchase high-grade wafers from specialty wafer fabrication companies. Production of the components is frequently outsourced to a contract manufacturer to keep costs down and allow the manufacturer to focus their internal resources on devices of higher complexity and shorter life-cycles.
What this has created, however, is an atmosphere in which it is relatively easy for substandard and counterfeit devices to circulate into the market.Contractors can sell sub-standard products rejected by the OEM, or even their own products, into the market. If components have the same package and are sold unmarked, they can easily be marked with original, but fake, OEM laser-etched marking. As the dies are generally procured rather than produced internally, decapsulation analysis is usually ineffective in identifying OEM traceability markings.
The most effective way to verify you are purchasing devices that function to the specifications you require is through electrical testing. The most common problems found with substandard MOSFET devices is that the key parameters do not function exactly as specified by the manufacturer. They may work initially, but not exactly as designed, causing them to fail in application after assembly when the component fails and allows excess current to flow thru the product, ultimately resulting in short circuits (burns out other components).
White Horse has developed a unique and proprietary platform for electrically testing these devices, focusing on Rds(on), BVdss, Idss, Switching Speed, Gate Charge, and Gate Threshold Voltage. The RDS(on) is the internal resistance of the MOSFET when it is switched on. This is tested by measuring the amount of current passing thru the MOSFET, the voltage over Drain (output pin) and Source (input pin) then dividing the voltage by the current. Rds(on) is frequently referred to as a MOSFET’s “critical” parameter.
The Switching Speed of a MOSFET is the delay between switching on and off, meaning how quickly it can switch from an “off” to an “on” state. The faster the switching speed, the more precise the component can be in controlling current flow. Switching Speed is tested using an oscilloscope to measure the delay from when current is introduced to when the current flows through the scope.
BVdss (Voltage between Drain and Source) is the maximum voltage the component can withstand between drain (output) and source (input). BVdss is tested by grounding the gate and applying the maximal specified voltage over drain and source, observing the current flow between them, generally a very low current of several micro amps (µA). Idss (Drain to Source Leakage Current) is the acceptable amount of leakage current that can pass through the drain to source junction at a specified voltage, usually the rated BVdss.
Most manufacturers will specify Idss along with BVdss. High leakage current causes higher power dissipation and loading when connected with other parts of a circuit. Gate Threshold Voltage is the minimum amount of voltage that can be applied to the gate pin to turn-on the MOSFET. It has a unique range value depending on the manufacturer design and intended application. Common values are 2V-4V for high voltage application and 1V-2V for logic-compatible devices.