Timeline for Can a Zener diode maintain constant base current to a transistor?
Current License: CC BY-SA 4.0
19 events
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| Jul 12, 2022 at 11:34 | comment | added | Antonio51 | Right. At one "voltage" ... Temp Coeff of Zener can be "equal" to zero ... :-) I forgot. | |
| Jul 11, 2022 at 18:24 | comment | added | winny | @Antonio51 That’s not entirely true. They are flat around 5 V. | |
| Jul 9, 2022 at 6:17 | answer | added | PStechPaul | timeline score: 0 | |
| Jul 8, 2022 at 19:13 | answer | added | Kuba hasn't forgotten Monica | timeline score: 1 | |
| Jul 8, 2022 at 16:36 | answer | added | Antonio51 | timeline score: 1 | |
| Jul 8, 2022 at 15:35 | comment | added | Antonio51 | Zener only is not really a "good" idea ... Zener series with a diode should be a better "device". Zener has a "positive" temperature coefficient (if the bias point is well chosen) and diode has a "negative" temperature" coefficient ... So the temperature effect can be "compensated" ... | |
| Jul 7, 2022 at 20:10 | comment | added | DKNguyen | Why two sources? | |
| Jul 7, 2022 at 20:09 | comment | added | Kyle B | You can achieve a pretty good constant current source with 2 transistors. i.e. edn.com/… | |
| Jul 7, 2022 at 19:37 | comment | added | jonk | @coulombs For constant current design using discrete BJTs, consider reading this. | |
| Jul 7, 2022 at 18:47 | comment | added | John D | @coulombs With an emitter degeneration resistor you could improve the circuit. Since you haven't added any performance specs or requirements it's hard to comment beyond that. The early effect, the previously mentioned tempcos, and part-to-part variation if you're building more than one of these will all impact performance. | |
| Jul 7, 2022 at 18:06 | comment | added | coulombs | @JohnD I read that beta can increase with temperature: electronics.stackexchange.com/questions/490868/…, but there seems to be a way to counteract it by adding an ohmic load to the emitter. The resistor-zener series appears to be a standard circuit used for voltage regulation. As I see it, the zener diode circuit and transistor circuit work fine on their own. Is putting them together really so impractical? | |
| Jul 7, 2022 at 17:03 | answer | added | GodJihyo | timeline score: 2 | |
| Jul 7, 2022 at 16:59 | comment | added | LvW | If you want a single BJT stage with a collector current as constant as possible you should be aware that the BJT is a voltage-driven device. Therefore, use a low-resistive voltage devider at the base (advantage: Base voltage nearly independent on the base current and its pretty large uncertainty) and use a current stabilizing emitter esistor RE. | |
| Jul 7, 2022 at 16:46 | history | edited | Null♦ | CC BY-SA 4.0 |
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| Jul 7, 2022 at 16:44 | comment | added | John D | The temperature coefficients of the zener and Vbe, as well as the part-to-part variation in beta and several other factors make this idea impractical. A better alternative would be a current mirror, and better yet an op-amp/bjt or FET current source. | |
| Jul 7, 2022 at 16:34 | review | Close votes | |||
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| Jul 7, 2022 at 16:06 | history | edited | JRE | CC BY-SA 4.0 |
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| Jul 7, 2022 at 16:03 | history | edited | coulombs | CC BY-SA 4.0 |
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| Jul 7, 2022 at 15:55 | history | asked | coulombs | CC BY-SA 4.0 |