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.
• Operational Amplifiers...

[@basicaodaeletronica]

AS melhores explicações de como funcionam osciladores

[@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.

[@Vocademy-Electronics-Tech]

Wikipedia, the most reliable source of information on the internet (hoc est taurum stercore), implies they are no longer manufactured. I found them on Amazon but they could have been old stock. A quick search didn't find anything that clearly said they were still manufactured. Thanks for the info.

[@mikesradiorepair]

@@Vocademy-Electronics-Tech DigiKey and Newark show them as still active. Newark shows the manufacturer as Multicomp Pro.

[@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)

[@fano72]

Same here. If you use 4.7k with 220nF, you get 440 Hz which is realistic.

[@fano72]

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

[@odysseus9941]

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

[@Vocademy-Electronics-Tech]

Like most circuits, it requires a DC power supply.