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| Cheap Fast Rise Time Oscillator |
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| mawyatt:
The 2N3904 would be too slow for this app, a better solution would be a high Ft SiGe HBT like the BFR840, BFP620, BFU725, and others. These inexpensive SiGe devices aren't designed nor specified for pulse use (they are RF devices), however should yield very fast pulse response if applied properly. Best, |
| BillyO:
--- Quote from: mawyatt on February 06, 2023, 03:29:24 pm ---The 2N3904 would be too slow for this app, a better solution would be a high Ft SiGe HBT like the BFR840, BFP620, BFU725, and others. These inexpensive SiGe devices aren't designed nor specified for pulse use (they are RF devices), however should yield very fast pulse response if applied properly. Best, --- End quote --- This then begins to defeat the design criteria of cheap and simple by adding cost and complexity. |
| mawyatt:
--- Quote from: BillyO on February 06, 2023, 03:38:06 pm --- --- Quote from: mawyatt on February 06, 2023, 03:29:24 pm ---The 2N3904 would be too slow for this app, a better solution would be a high Ft SiGe HBT like the BFR840, BFP620, BFU725, and others. These inexpensive SiGe devices aren't designed nor specified for pulse use (they are RF devices), however should yield very fast pulse response if applied properly. Best, --- End quote --- This then begins to defeat the design criteria of cheap and simple by adding cost and complexity. --- End quote --- These are about $0.50 HBTs ;) Best, |
| mawyatt:
These inexpensive SiGe HBTs brings up a question IF they would perform well in an avalanche mode for fast pulse edge production? Anyone given this a try? Best, |
| David Hess:
--- Quote from: magic on February 06, 2023, 09:21:34 am ---Do you expect that ordinary 3904 could be good enough to compete with "bare" LVC logic in terms of rise/fall time? --- End quote --- No, a 2N3904 is too slow. --- Quote ---Or are we talking some special RF transistors? --- End quote --- Nothing exotic is required and RF transistors can be inexpensive. |
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