FAQ
Q1: Can the Clipper be used to measure negative voltages? For example the reverse recovery voltage on an IGBT ?
A1: The Clipper can measure down to -1.8V in HI mode, and -0.8V in LO mode. More information on this will follow soon.
A1: The Clipper can measure down to -1.8V in HI mode, and -0.8V in LO mode. More information on this will follow soon.
Q2: What is the maximum negative voltage the Clipper can tolerate?
A2: When a negative voltage is applied to the input terminal, the Clipper acts as a current source to the DUT. With -2V applied on the input, the Clipper supplies approx 60mA. The series protection is provided by a 10 Ohm resistor, therefore the limiting factor here is the power dissipation capability of this resistor. For example, short pulses of -5V or less will not damage the Clipper. We will provide more details of the exact values soon.
A2: When a negative voltage is applied to the input terminal, the Clipper acts as a current source to the DUT. With -2V applied on the input, the Clipper supplies approx 60mA. The series protection is provided by a 10 Ohm resistor, therefore the limiting factor here is the power dissipation capability of this resistor. For example, short pulses of -5V or less will not damage the Clipper. We will provide more details of the exact values soon.
Q3: What load does the Clipper apply to the DUT?
A3: The Clipper has a constant current load of around 350µA, when the input is positive. For negative input voltages, the Clipper sources current to the DUT, up to around 60mA.
Q4: How do you connect the Clipper to the DUT?
A4: The Clipper is supplied with some PCB mounting SMA sockets and adapters. The Sockets can be wired to the DUT as shown in the picture above (Red for positive Drain, Black for negative Source).
Q5: What Oscilloscope conversion resolution is required for best results?
A5: A perfetly acceptable measurement can be obtained with an 8-bit Oscilloscope. Since now the input sensitivity can be set to 100mV per division to measure a 500mV Drain voltage.
Q6: Whats the best way to measure RdsON ?
A6: In the development phase, Ids can be measured using a standard inductive current loop probe, by creating a physical wired "loop" on the circuit board. Alternatively, an inductive loop sensor can be used around the Drain leg of the Transistor under test. This will allow one Oscilloscope channel to measure Ids. With Vds from the clipper being measured on a second Oscilloscope channel, then the MATH function can calculate and display Vds/Ids = Rds.
In the Production phase, since the target Ids is known, the effective change in RdsON can simply be measured by looking at the Vds output from the Clipper. This depends on prior knowledge of Ids, but can be sufficient for a basic fault test or production screening.
Q7: How can the Clipper be used to measure the Thermal Performance and SOA ?
By looking at the stability of RdsON (see Q6 above) the effectiveness of the full thermal dissipation path can be seen. For example, if the Heatsink is not attached correctly (e.g. is not properly mounted, or thermal paste missing or insufficient) then the RdsON will increase as the junction temperature increases. Thermal equilibrium should be reached and the RdsON will remain constant. This of course needs to be within the Safe Operating Area (SOA) of the component, otherwise Pd and Tj will increase catastrophically.
Q8: What is the typical response time to a step input?
A8: The output waveform has a setting time of <100nS.
Q9: Can the Clipper be used to measure the Drain-Source voltage on the High-Side of a bridge?
A9: This is tricky, as the high common mode voltage will cause an offset problem. Also, an Isolated Oscilloscope would be required. Best would be a differential Clipper. If there is interest here we can loko at developing this product.
Q10: Is the DUT load different before and after switching?
A10: As long as the DUT voltage is positive, then no. The load presented by the Clipper is always the same, and is a constant current of 350µA.
A3: The Clipper has a constant current load of around 350µA, when the input is positive. For negative input voltages, the Clipper sources current to the DUT, up to around 60mA.
Q4: How do you connect the Clipper to the DUT?
A4: The Clipper is supplied with some PCB mounting SMA sockets and adapters. The Sockets can be wired to the DUT as shown in the picture above (Red for positive Drain, Black for negative Source).
Q5: What Oscilloscope conversion resolution is required for best results?
A5: A perfetly acceptable measurement can be obtained with an 8-bit Oscilloscope. Since now the input sensitivity can be set to 100mV per division to measure a 500mV Drain voltage.
Q6: Whats the best way to measure RdsON ?
A6: In the development phase, Ids can be measured using a standard inductive current loop probe, by creating a physical wired "loop" on the circuit board. Alternatively, an inductive loop sensor can be used around the Drain leg of the Transistor under test. This will allow one Oscilloscope channel to measure Ids. With Vds from the clipper being measured on a second Oscilloscope channel, then the MATH function can calculate and display Vds/Ids = Rds.
In the Production phase, since the target Ids is known, the effective change in RdsON can simply be measured by looking at the Vds output from the Clipper. This depends on prior knowledge of Ids, but can be sufficient for a basic fault test or production screening.
Q7: How can the Clipper be used to measure the Thermal Performance and SOA ?
By looking at the stability of RdsON (see Q6 above) the effectiveness of the full thermal dissipation path can be seen. For example, if the Heatsink is not attached correctly (e.g. is not properly mounted, or thermal paste missing or insufficient) then the RdsON will increase as the junction temperature increases. Thermal equilibrium should be reached and the RdsON will remain constant. This of course needs to be within the Safe Operating Area (SOA) of the component, otherwise Pd and Tj will increase catastrophically.
Q8: What is the typical response time to a step input?
A8: The output waveform has a setting time of <100nS.
Q9: Can the Clipper be used to measure the Drain-Source voltage on the High-Side of a bridge?
A9: This is tricky, as the high common mode voltage will cause an offset problem. Also, an Isolated Oscilloscope would be required. Best would be a differential Clipper. If there is interest here we can loko at developing this product.
Q10: Is the DUT load different before and after switching?
A10: As long as the DUT voltage is positive, then no. The load presented by the Clipper is always the same, and is a constant current of 350µA.