Relaxation oscillator

Question

I was wondering how inside the relaxation oscillator heating is not produced inside the BJT junction causing destruction of the transistor.

schematic

^{simulate this circuit – Schematic created using CircuitLab}

and this is what I propose:

schematic

^{simulate this circuit}

Instead the reverse bias bjt , we can use a Zener diode right in reverse bias. After the Zener breakdown voltage is reached any lightbulb connected in series will be turned on , when the Zener breakdown voltage is not reached it wont be turned on. — Jelly Strawberry, Mar 21 '20 at 10:42
Could you show me the circuit you're referring to? To my knowledge a simle bjt or a zener diode circuit will not work as relaxation oscillator because you need negative resistance region(ujt) to discharge. Zener diode and bjt just cutoff and stay there. Nothing happens afterwads. @JellyStrawberry — across, Mar 21 '20 at 11:11

Dave Tweed · Answer 1 · 2020-03-21T11:38:38.370

2

Heating IS produced inside the transistor. You can easily calculate how much (voltage × current, averaged over time), and show that it is well within the transistor's ratings.

You can't substitute a zener diode for the transistor, because it doesn't have the negative resistance characteristic that the transistor has.

edited Mar 21 '20 at 11:38

answered Mar 21 '20 at 11:17

Dave Tweed

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Ah ok thanks for your answer. – Jelly Strawberry Mar 21 '20 at 11:20
Of course it does dave tweed.Electron-hole pairs are created due to quantum tunneling and the strong electric field of the depletion region... – Jelly Strawberry Mar 21 '20 at 11:24

score 0 · Answer 2 · answered Mar 21 '20 at 17:25

The 2N2369 used to be popular for 500 picosecond risetime pulses, in relaxation circuits.

Given the dominant spec on that transistor was the 1.6 GHz Ftau, th precise dopings and thicknesses would vary from vendor to vendor. Back then either Motorola or Fairchild likely would have provided the device.

Relaxation oscillator

2 Answers2