| Electronics > Beginners |
| NPN Transistor as a switch: what's the use of the emitter resistor? |
| << < (7/7) |
| soldar:
Related: https://www.eevblog.com/forum/beginners/understanding-transistors/msg1211771/#msg1211771 |
| bson:
--- Quote from: KE5FX on March 21, 2019, 01:34:37 am ---Win Hill actually just posted a nifty example of this practice as an appetizer for the 'X-chapters' volume for AoE 3. Some grad students needed to dump 200 amps into an LED in a hurry, and they came to him for advice when their first attempt failed to achieve the leading-edge speed they needed. It made for an interesting case study. Arguably, he's not trying to avoid saturation on the transistor's part, so much as he's trying to ensure that the LED sees the same current across the entire pulse as it heats up over time. Similar basic motivation, though. --- End quote --- 200A pulses into a LED... That's mad science territory! :o Can't wait to get a copy! |
| Zero999:
--- Quote from: bson on March 23, 2019, 03:53:26 am --- --- Quote from: KE5FX on March 21, 2019, 01:34:37 am ---Win Hill actually just posted a nifty example of this practice as an appetizer for the 'X-chapters' volume for AoE 3. Some grad students needed to dump 200 amps into an LED in a hurry, and they came to him for advice when their first attempt failed to achieve the leading-edge speed they needed. It made for an interesting case study. Arguably, he's not trying to avoid saturation on the transistor's part, so much as he's trying to ensure that the LED sees the same current across the entire pulse as it heats up over time. Similar basic motivation, though. --- End quote --- 200A pulses into a LED... That's mad science territory! :o Can't wait to get a copy! --- End quote --- I've been there and done that. I wouldn't recommend a BJT. Use a MOSFET instead. If the duty cycle is low, then the MOSFET can be driven, via a small transformer. I posted some of the schematics for someone who asked about making a high powered LED flash. https://www.eevblog.com/forum/projects/ultra-short-ultra-fast-led-flash/ |
| Navigation |
| Message Index |
| Previous page |