1
\$\begingroup\$

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

\$\endgroup\$
3
  • \$\begingroup\$ Can we do it with a zener diode as well?(reverse biased) \$\endgroup\$ Commented Mar 21, 2020 at 10:38
  • \$\begingroup\$ 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. \$\endgroup\$ Commented Mar 21, 2020 at 10:42
  • \$\begingroup\$ 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 \$\endgroup\$
    – across
    Commented Mar 21, 2020 at 11:11

2 Answers 2

2
\$\begingroup\$

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.

\$\endgroup\$
2
  • \$\begingroup\$ Ah ok thanks for your answer. \$\endgroup\$ Commented Mar 21, 2020 at 11:20
  • \$\begingroup\$ Of course it does dave tweed.Electron-hole pairs are created due to quantum tunneling and the strong electric field of the depletion region... \$\endgroup\$ Commented Mar 21, 2020 at 11:24
0
\$\begingroup\$

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.

\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.