Having problems with thyristor commutation circuit

Thread Starter

radityaar

Joined Jul 2, 2018
17
I am trying to build a commutation circuit for thyristor. I have made a simulation on LTSPICE beforehand which you can see on the picture below.

I tried assembling the circuit on a breadboard and have realized that the second thyristor does not turn off the first thyristor. Does anyone what the problem is?
 

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ericgibbs

Joined Jan 29, 2010
8,861
hi,
Could you explain the event/action you are expecting across the two TYN1012 thyristors, that will turn OFF U1 when U8 is triggered ON.?

E
 

Thread Starter

radityaar

Joined Jul 2, 2018
17
Firstly when thyristor U1 is ON it should charge the capacitor until it reaches around -VS(supply voltage). When the thyristor U8 is is turned ON, the capacitor should discharge a current that forces the thyristor U1 into the zero crossing which will turn it off. The simulation seems to have the output I need, but when i tried assembling on a breadboard, the thyristor U1 doesn't seem to want to turn off. Perhaps there are some things I need to add to the simulation for the actual circuit to work
 
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Bordodynov

Joined May 20, 2015
2,418
I have glitches with LTspice. Does not find the library for the LM7805. After update. So I added the model to the schema.
I have made changes to the scheme:
1. Corrected the voltage source
2. Charged the filtering capacitors ic = 20
3. added a diode and tristor leakage compensation resistor for a guaranteed discharge of the capacitor, at an elevated temperature the leakage is increased and it may be necessary to decrease the resistor value
4. Reduced the capacitor from 100 μF to 1 μF.
I did a similar circuit for the electric fishing rod.
PlotF.png
 

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ericgibbs

Joined Jan 29, 2010
8,861
hi,
The current is flowing in the 120R and is decaying exponentially, is the load in the actual circuit [ which doesn't work] purely resistive or is an inductive load.?
E
EDIT:
On the actual circuit add 100nF and 10uF on the Vout's of the 7805's and 100nF's on the Vinp
 

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Thread Starter

radityaar

Joined Jul 2, 2018
17
@Bordodynov thank you!what is the importance of the leakage compensation resistor?the simulation seems to be working fine without it.
@ericgibbs ah I see, I had assumed that the exponential decay was how the output should be due to the capacitor discharge. The load is purely resistive
 

Thread Starter

radityaar

Joined Jul 2, 2018
17
I am sorry.
When I wrote about the leak, I had in mind my circuit for switching thyristors by direct current.
No problem, I have another question though, I have assembled the circuit on a breadboard and it seems that the capacitor doesn't charge when I turn on the main thyristor, do you have any idea why?
 

ericgibbs

Joined Jan 29, 2010
8,861
hi,
Checking in simulation it shows it charging OK.
Is the 1uF a polarised cap.?
How are you measuring the voltage across the cap.?
E
EDIT:
If I change the .tran startup conditions I get some confusing plots for the state of the Cap voltage.??
 
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Thread Starter

radityaar

Joined Jul 2, 2018
17
It seems i used a polarized cap.
hi,
Checking in simulation it shows it charging OK.
Is the 1uF a polarised cap.?
How are you measuring the voltage across the cap.?
E
EDIT:
If I change the .tran startup conditions I get some confusing plots for the state of the Cap voltage.??
I am using a non- polarized cap, i put a probe on the point between the capacitor and the thyristor. Can you show me the plots and startup conditions you used?
 

Thread Starter

radityaar

Joined Jul 2, 2018
17
hi,
This is using the 1meg and 1uF cap.
Note .tran.
E
I'am actually a bit new to LTSPICE, what does the startup uic command do for the simulation?The results using that command seems to be giving me similar results to what I'am encountering with the actual circuit
 
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