How to test the functionality of SIDAC?

[seety1981]

How to test SIDAC?

Hii...

I have a SIlicon Bilateral Voltage Triggered Switch (SIDAC) in high voltage lamp ignitor application. So i would like to know how to test the functionality of this components. Please help me!!. Below is the characteristics of the SIDAC:

Model: K220
Breakover voltage,Vbo = 205 - 230 V
Blocking voltage, Vdrm = 165V
Peak of state current at Vdrm. Idrm = 10uA (max)
Continuous on-state DC or RMS current, It = 1.0A (max)
Holding current, Ih = 100mA (max)
Peak on-state voltage,It=1A = 1.5V (max)

I hope the characteristics is clear enough....i really....reallly....need help from you guyzzz...

Regards,

Seety

 

[VVV]

Re: How to test SIDAC?

I answered this question yesterday.

Now that you have the data, it is easy to see what I suggested.

 

[seety1981]

Re: How to test SIDAC?

Thanks for the test procedure. But honestly, I still not really understand about it. I think, I still not understand the meaning of breakover voltage, blocking voltage, peak of state current at Vdrm, continuous on state DC or RMS current, holding current and peak on state voltage. Could you please tell me the meaning of these in the easiest way to understand? I already read the SIDAC datasheet, but I still have no idea about it. So, please help…

Regards,

Seety

 

[VVV]

Re: How to test SIDAC?

The breakover voltage is that at which the SIDAC turns on.
Let's assume you have an adjustable voltage source, inseries with a resistor and you apply that voltage to the SIDAC. As you increase the voltage, the current through the SIDAC increases, but is still VERY low, since the SIDAC is off. When you reach the breakover voltage the SIDAC turns on and almost the entire voltage is applied to the resistor.

Blocking voltage is lower than the breakover voltage and is generally defined at a specificied current, say 10uA. Think of it as the maximum voltage you can apply to the SIDAC without affecting the rest of the circuit. I mean, the SIDAC is used to protect some circuit. It should be open (no current flowing through it) up to a certain voltage. In reality some current flows, but if it's low enough, then it won't affect the protected circuit. Thus, a low current value of about 10uA is selected. So you increase the voltge until the current is 10uA and then measure it. This is the blocking voltage. The 10uA limit could be different for different types or manufacturers, but it's very low, something at which you can still say that the SIDAC is off.
Related to this is the maximum current at the blocking voltage. So you set the voltage to the blocking value and measure the current. I don't know why they give it in the datasheet, since it should be equal to the limit you set when you measure the blocking voltage.

On-state current refers to the maximum current the SIDAC can conduct in the on state, that is after it turns on, due to a high voltage. That is, after the voltage reached the breakover point, the SIDAC turns on and the current is limited by the resistor in series with it (see first answer). Then the resistor should limit the current to a value lower than this maximum on-state current, to make sure the SIDAC does not get damaged.

On-state voltage is the voltage across the SIDAC, at a specified current. The SIDAC turns on the current is limited by the resistor. But the voltage across the SIDAC is not zero, since the SIDAC is not a dead short. Rather, there is a voltage across it, the on-state voltage, which is measured at a specified current.

Holding current is the minimum at which the SIDAC remains on. As you can imagine, at some point the SIDAC should turn off after it has turned on and protected the circuit. That way it is ready for the next voltage spike. What makes it stay on? The current flowing through it. If you decrease that current low enough, the SIDAC will turn off. This minimum current at which the SIDAC is guaranteed to be still on is the holding current. It is much lower than the maximum current. It is usually in the mA range.

 

[seety1981]

Re: How to test SIDAC?

Thanks a lots VVV... your explanation much more clear now...

But, how we can get to know the SIDAC is turns ON or OFF? or are there any method to indicate the SIDAC is turns On or OFF?


Regards,
Siti

 

[VVV]

Re: How to test SIDAC?

Well, when the SIDAC turns on, the voltage drop across it is only 1-2V. So if you measure the voltage across the SIDAC while you increase the test voltage, you will see a high voltage across the SIDAC, increasing as you adjust the power supply. At some point, the voltage across the SIDAC drops abruptly to 1-2V. Then the voltage you measured just before this collapse was the breakover voltage.

A similar method can be applied to see when it turns off. But since you want to also measure the holding current, it is easier to have an ammeter in series with the SIDAC and measure the current through it as you increase the current-limiting resistor (or decrease the power supply voltage) in order to lower the current through the SIDAC. At some point, the current will drop abruptly to zero (or a few uA). Then the current you measured just before that was the holding current.
For this measurement you need to take special precautions to avoid damaging your ammeter. Thus, when measuring the on-drop at max current, use ampere scale.
When you decide to measure the holding current, use mA scale, but use a much larger resistor in series with the SIDAC, such that the maximum current through the SIDAC at the breakover voltage will be lower than the range selected. (In fact, both the breakover voltage and holding current can be measured with the same high resistance, a lower one is only required when testing the on-state voltage drop, since you need high current; by the way, make the on-state voltage measurement really quick, to avoid overheating the SIDAC).

For instance, assume the holding current is expected to be about 100mA and you know the breakover voltage is 220V (you measured it already). Then use a 200mA scale on the ammeter and use a series resistor of 220V/200mA=1.1kΩ Use 1.2kΩ for example.
Then apply enough voltage to turn on the SIDAC, say 225V. The SIDAC should now stay on, provided the holding current is lower than the one flowing through the circuit. If it does not stay on, use a lower resistor and higher range on the ammeter and repeat, until the SIDAC stays on.
Now reduce the power supply voltage slowly while measuring the current. At some point you will see the current drop from mA to µA. That was the holding current, just before the drop.

 

[seety1981]

Re: How to test SIDAC?

Hiii…. I have try as you recommended. But when I’m increase the voltage to 200V, the both resistor were suddenly blow up!!! Hehe… also have a flame on it!!!… So, I include here the circuits for you to check just to make sure it won’t happen again. The circuit also shown the value when the both resistor were blow up.

Regards,

Seety

 

[VVV]

Re: How to test SIDAC?

Hi, there!
Sorry I did not mention that you need power resistors, since at 200V, with only 100mA flowing, you need a 20W resistor. At 1A, that becomes 200W. (Maybe you can skip the on-state voltage measurement, if you do not have the right resistor).
Sorry about that omission.

First of all, you need a DC source, so that the SIDAC will latch on and allow you to do the measurements.
Second, you should measure the voltage across the SIDAC. That is the breakover voltage.

I hope to hear better news.

 

[seety1981]

Re: How to test SIDAC?

Hii...
could you please see the attachment file for power resistor datasheet?? i would like to know if this kind of power resistor is suitable for my case...



regards,

Seety

 

[VVV]

Re: How to test SIDAC?

Yes, that is good. You need to install it on a heatsink, though. The heatsink does not have to be really designed for 20W continuous power dissipation, since you are going to do the measurements fast and then switch off the power.

 

[seety1981]

Re: How to test SIDAC?

Dear VVV,

I include here the circuit connection for you to check. Also, i would like to know the resistance value for power resistor should be.

Thanks and many regards for your support


Seety

 

[VVV]

Re: How to test SIDAC?

The circuit looks OK, except for the value of the resistor in parallel with the filter cap, since the power dissipation would be too high. A resistor value of about 100kΩ would dissipate 0.625W at 250V and it would discharge the cap in about 15sec. Perhaps you should consider such a value, or somewhat lower, say 47kΩ, but 1kΩ seems really too low.

As for the resistor in series with the SIDAC, the value should be about 230V/0.1A=2.3kΩ. Choose 2.2K or somewhat lower. The whole idea is to make sure the current is somewhat higher than 100mA, to maintain the SIDAC on for the duration of the measurement (which should be done fast). You will then reduce the current until the SIDAC turns off.
Two 1kΩ resistors in series are even better. Install them on a heatsink.

With the cap chosen you will have some ripple, but I think the measurements will be OK.

Regards,
VVV