Timeline for BJT Constant Current, Resistor Equations
Current License: CC BY-SA 4.0
4 events
| when toggle format | what | by | license | comment | |
|---|---|---|---|---|---|
| Jul 18, 2018 at 21:32 | vote | accept | TFD_Jon | ||
| Jul 18, 2018 at 21:32 | |||||
| Jul 7, 2018 at 3:08 | comment | added | jonk | @TFDyellow Do you feel you understand the concept here? The basic idea is that R1 provides more than enough base current for Q2. However, Q1 monitors the drop across R2 and "sinks" excess current from R1 before it can get to the base of Q2, when and where needed. So Q1 is monitoring the voltage across R2, adjusting how much current it sinks away from Q2's base. All the I/O pin does is supply an excess amount and allows Q1 to figure out how much to sink away in order to hold one VBE drop across R2. | |
| Jul 7, 2018 at 2:52 | comment | added | TFD_Jon | Thanks Jonk. I agree with your answer, and see this as another approach as Sparky mentioned (creating constant voltage at Vb; using transistor rather than diodes). | |
| Jul 6, 2018 at 4:33 | history | answered | jonk | CC BY-SA 4.0 |