Relaxation Oscillators - Solid-state Devices and Analog Circuits - Day 6, part 10

Vocademy - Free Vocational Education

Relaxation oscillators exploit a sudden change in a circuit parameter when the circuit reaches a given voltage or current. This change does not reverse until a different threshold is reached (hysteresis). In the simplest example in this video, a neon light starts to conduct when a parallel capacitor charges to about 90 volts. The conducting bulb discharges the capacitor. The bulb stops conducting at around 60 volts, allowing the capacitor to charge again. Other relaxation oscillators use different mechanisms, but the common characteristic is one voltage of current triggering a change in the circuit but a different voltage or current reversing the change.

[basicaodaeletronica]

AS melhores explicações de como funcionam osciladores

[eytansuchard]

In modern days, low frequency for power switching, e.g. 8 K Hz, can use a Thyristor. Someone posted a circuit with BT151 with circuit voltage of 5 volts.

[mikesradiorepair]

They still make normal (non programable) UJT's. I have a 50 or so 2N4870 which is still made. For the life of me I can't remember what I stock them for but I would have bought them for inventory if they were in something I work on.

[odysseus]

😄Can I run this oscillator with AC or DC supply voltage?

[david_pilling]

Could use an SCR/thyristor instead of Unijunction - same semiconductor layers, different connection. If you really want something that is officially still manufactured.

[gregwmanning]

Thanks for video
I got 10.34Hz not 1kHz using formula provided earlier and values provided later. I may have miss-applied the formula? f = 1 / (2 x Ln(3) x 22u x 2k)

[fano]

Maybe a cool pwm audio oscillator, we should try that.

[aziaufa]

I just dont understand at all how this works. Every single simulation behave differently (tinkercad, ltspice, proteus)