What is causing the fault in my thyristor and op amp circuit?

In summary: I've test the comparator part of the circuit by putting an TIP121 transistor in instead of the thyristor and the circuit works fine. I also checked the Voltage from the output pin wit a multimeter by putting one probe on the pin and the other on the ground rail and the Voltage was exactly as I had simulated it.Let's focus on the SCR. You are not able to turn it on by supplying gate current? In place of the piezo buzzer can you connect a 560 ohm resistor + LED (or 9v or 12v light bulb).
  • #1
rollcast
408
0
attachment.php?attachmentid=42879&stc=1&d=1327079870.png


I have tested this circuit on the computer and it works but when I try to make it both on a pcb and breadboard the circuit will not work at all. If i swap the thyristor - TIC106D - for a transistor - TIP121 - the circuit works fine so I think the problem can be isolated down to somewhere between the Op Amp output and the thyristor?

The other unusual thing is that if I short the Cathode pin to the Gate or the Anode pin to the gate, then the buzzer will sound but the thyristor doesn't latch?

Any ideas what is causing the fault.

Thanks
AL
 

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  • #3
Jony130 said:
But TIP106D in not a thyristor
http://www.fairchildsemi.com/ds/TI/TIP105.pdf

Sorry I got the codes the wrong way round.

Transistor I current have in it is TIP 121

Thyristor I tried was a TIC106D
 
  • #4
Try connect 470R resistor parallel to the buzzer.
 
  • #5
What exactly will that do as I can't see it making that much difference?
 
  • #6
We increase the load current so that SCR can latch.
So we ensure that
I_load > I_holding_current
 
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  • #7
Is the 9v supply smooth DC, or are you using a wall wart? Try adding a large electrolytic across the power supply to make sure it is smooth.
 
  • #8
NascentOxygen said:
Is the 9v supply smooth DC, or are you using a wall wart? Try adding a large electrolytic across the power supply to make sure it is smooth.

Its a 9V PP3 battery so the DC supply should be smooth.
 
  • #9
rollcast said:
[The other unusual thing is that if I short the Cathode pin to the Gate or the Anode pin to the gate, then the buzzer will sound but the thyristor doesn't latch?

Shorting the cathode to the gate should not turn on a thyristor. Something seems amiss here. Have you got a second one you could try? Check the connections. The gate would be the smallest lead, I think.

For testing, you could connect the buzzer from the op amp output to ground, to make sure the comparator is working how you think it should. How long are the leads to the LDR? They may be picking up some mains hum.
 
  • #10
NascentOxygen said:
Shorting the cathode to the gate should not turn on a thyristor. Something seems amiss here. Have you got a second one you could try? Check the connections. The gate would be the smallest lead, I think.

For testing, you could connect the buzzer from the op amp output to ground, to make sure the comparator is working how you think it should. How long are the leads to the LDR? They may be picking up some mains hum.

I tried 2 TIC106D Thyristors - by 2 different makers - in the circuit and both behaved the same.

I've test the comparator part of the circuit by putting an TIP121 transistor in instead of the thyristor and the circuit works fine. I also checked the Voltage from the output pin wit a multimeter by putting one probe on the pin and the other on the ground rail and the Voltage was exactly as I had simulated it.
 
  • #11
Let's focus on the SCR. You are not able to turn it on by supplying gate current? In place of the piezo buzzer can you connect a 560 ohm resistor + LED (or 9v or 12v light bulb). Maybe the buzzer is a weird load. Return the 10k gate resistor directly to the +9v instead of relying on the op-amp during this testing phase.

Steering a separate course, it should be possible to do away with the thyristor and convert the comparator to one with hysteresis so it latches on and can drive the buzzer directly with no need for the SCR. Or are you committed to demonstrate use of a SCR?

Can you double check your pin connections: http://www.datasheetsite.com/extpdf.php?q=http%3A%2F%2Fpdfdata.datasheetsite.com%2Fpdf1%2FPhilips%2FC106D.pdf [Broken]
 
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1. What is a thyristor and how does it work?

A thyristor is a type of semiconductor device that acts as a switch, controlling the flow of electric current. It consists of three or four layers of alternating N-type and P-type material, with a gate electrode for control. When a small current is applied to the gate, the thyristor allows a larger current to flow through it, similar to a transistor. However, unlike a transistor, a thyristor will remain in the conducting state until the current flowing through it drops below a certain level.

2. What is an op amp and what is its role in a thyristor circuit?

An op amp, short for operational amplifier, is a type of electronic amplifier that has two inputs and one output, providing a gain to the input signal. In a thyristor circuit, an op amp is typically used to amplify the small current from the thyristor's gate to a level that can trigger the thyristor to turn on. It can also be used to provide a feedback loop to regulate the thyristor's output.

3. How is a thyristor and op amp circuit used in practical applications?

The thyristor and op amp circuit can be used in a variety of practical applications, such as in power supplies, motor control, and lighting control. It is often used to regulate and control the flow of current in a circuit, allowing for efficient and precise control over electrical devices.

4. What are some advantages of using a thyristor and op amp circuit?

One major advantage of using a thyristor and op amp circuit is its efficiency. The thyristor can handle high currents and voltages, while the op amp provides precise control and regulation of the circuit. This combination allows for energy-efficient and cost-effective operation. Additionally, the thyristor has a fast switching speed, making it ideal for applications that require quick response times.

5. Are there any limitations or drawbacks to using a thyristor and op amp circuit?

One limitation of using a thyristor and op amp circuit is that it requires careful design and calibration to ensure proper operation. The op amp must be selected and configured correctly, and the circuit must be designed to avoid false triggering of the thyristor. Additionally, the thyristor's latching behavior means that it cannot be turned off until the current through it falls below a certain level, which can be problematic in certain applications.

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