| Electronics > Repair |
| Need help with a Metcal MX500 |
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| kff:
Also, just curious, why does Q4 need to be double isolated from the heatsink? Is it to reduce capacitance between the gate and ground? |
| wraper:
--- Quote from: kff on February 01, 2015, 06:49:44 pm ---Also, just curious, why does Q4 need to be double isolated from the heatsink? Is it to reduce capacitance between the gate and ground? --- End quote --- Mounting tab is not gate but drain. Considering working frequency likely because of the capacitance. |
| jbryan2:
--- Quote from: kff on February 01, 2015, 06:49:44 pm ---Also, just curious, why does Q4 need to be double isolated from the heatsink? Is it to reduce capacitance between the gate and ground? --- End quote --- Source is tied directly to ground. If the heatsink is tied to ground you had better isolate the tab/drain. |
| jbryan2:
--- Quote from: kff on February 01, 2015, 06:49:44 pm ---Also, just curious, why does Q4 need to be double isolated from the heatsink? Is it to reduce capacitance between the gate and ground? --- End quote --- Oh, and the gate is tied to ground through L10. If you don't isolate the tab/drain then all three pins are - glory be! - tied to ground. It's not going to do much that way. |
| wraper:
--- Quote from: jbryan2 on February 02, 2015, 02:44:10 am --- --- Quote from: kff on February 01, 2015, 06:49:44 pm ---Also, just curious, why does Q4 need to be double isolated from the heatsink? Is it to reduce capacitance between the gate and ground? --- End quote --- Oh, and the gate is tied to ground through L10. If you don't isolate the tab/drain then all three pins are - glory be! - tied to ground. It's not going to do much that way. --- End quote --- As I understand he asked about why 2 layers of insulation, not just one. |
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