modified 10 years ago

UHF Multivibrator

00:55:48

Physicians out there who can explain this effect?
So HF makes diodes conducting... 

published 10 years ago

aquialexjajaja

10 years ago

Diodes recovery time.... At very high frecuencies the voltage is in one direction then in another so fast that when he whants to switch to non-conducting to conducting he is unable to "shutdown" because he need to let the "flow" pass... There some diodes called fast recovery or shottky diodes i think ... Something like that ... These are designed for high frecuencies....

thebugger

10 years ago

This is due to the diode junction capacitance. See a PN junction this small is bound to have some capacitance (5pf in this case) and at such high frequencies like 10Ghz the reactive resistance of the junction capacitance is quite low (3ohms in this case) which means that in reverse direction the diode stops the voltage flow as much as a 3ohm resistor would, so it has almost no effect. It's like a continuous circuit despite the polarities of the diodes. I hope this somewhat clears it up.

thebugger

10 years ago

Another interesting effect is occurring though. Typically these LED's should work at 2V. But the AC source is set to 1V. This effect is again connected to the to the junction capacitance. See the LED's act more like a capacitor right now rather than a diode, so what normally won't energise them now will with the increased current flow (30mA in this case). That's quite interesting.

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