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Underdamped sine wave generation with thyristor (SCR)

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iraquois

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I am trying to generate an underdamped sine wave on 50ohm resistor. To do this I use LC circuit. In my circuit:
edaoardsch.png

First to charge C1. V1 sends pulse and after full charge V1 stops. To have an oscillation V2 sends pulse to U1 ( SCR). But here the problem is I got very short periot of oscillation.
edaboardsignal.png



and also second problem is : There is distortion on indcutor like :


edaboarddist.png

How can I extend the oscillation period and how to prevent the distortion?
Or should I change the topology ?
 

Hi,
How can I extend the oscillation period

50 Ohms dissipate a lot of energy. While the energy stored in the 6uF is relatively low.

time constant is R x C = 50 Ohms x 6uF = 300us. (This formula does not give exact values for your circuit... but it gives a rule of thumb)

--> so either increase C or increase R to get a higher time constant.

Klaus
 

Hi,


50 Ohms dissipate a lot of energy. While the energy stored in the 6uF is relatively low.

time constant is R x C = 50 Ohms x 6uF = 300us. (This formula does not give exact values for your circuit... but it gives a rule of thumb)

--> so either increase C or increase R to get a higher time constant.

Klaus
Even if I remove 50ohm still ringing is too short just adds 1 more period. And values for capacitance and inductance are for to have near 10khz signal. And simple circuit with just L and C gives good ringing.
 

Hi,

how do you measure it? With a 50 Ohms measurement tool?

Klaus
 

consider a diode in series with R1 to limit back-feed into V2 when the SCR fires ...
 
R1 loads the LC circuit also during negative oscillation period. Better connect trigger voltage source between gate and cathode.
 

keep doubling C and halving L until the ckt is under-damped ...
 

also unless you continuously fire the SCR the ringing will stop after the gate drive is removed ....
--- Updated ---

freq - 6.5kHz ( undamped ) the Q of this ckt is very low - hence the lack of long cycle ringing ...
 
Last edited:

consider a diode in series with R1 to limit back-feed into V2 when the SCR fires ...
R1 loads the LC circuit also during negative oscillation period. Better connect trigger voltage source between gate and cathode.
Thanks a lot for all comments. I tried diode with R1 and also connecting pulse signal(V2) to cathode. Still no change.

also unless you continuously fire the SCR the ringing will stop after the gate drive is removed ....
--- Updated ---

freq - 6.5kHz ( undamped ) the Q of this ckt is very low - hence the lack of long cycle ringing ...
Actually normally if I try to simulate 6uF and 50uH oscillation it looks like that:
signal.png
So as far as I see values look okey. Problem is in the circuit I think.
I will keep trying to design another circuits and will edit if I can get solution :).
And if you have advice please share. Thanks for all efforts.
 
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