triac is failing everytime..

[deepakchikane]

Dear All,

here i am attaching the ckt diagram of my project..

please help me out for why :sad: is failing every time (without gate triggering)

plz plz plz

 

[thylacine1975]

Which triac? T1 or T2 (or both)?

Without understanding your circuit's intended operation (what is the transformer for? What's it's ratio? What's the supply voltage/impedance?) a warning flag has popped up in my mind about your design exceeding the triac(s) di/dt and/or dV/dt limits. Series resistance (perhaps with some inductance) with whichever device is switching will undoubtedly help...

 

[deepakchikane]

Which triac? T1 or T2 (or both)?

Without understanding your circuit's intended operation (what is the transformer for? What's it's ratio? What's the supply voltage/impedance?) a warning flag has popped up in my mind about your design exceeding the triac(s) di/dt and/or dV/dt limits. Series resistance (perhaps with some inductance) with whichever device is switching will undoubtedly help...

dear sir,
t1 & t2 ar the same..

transformer is of 230v to 16 v

i dont have other details


t1=btb24 by fairchild

 

[thylacine1975]

I suspect what's happening is that on application of power, the resulting high dV/dt rate (across their MTx terminals) is triggering the triacs into conduction. Very large currents will then flow through the conducting triacs from the [low impedance] mains supply, undoubtedly killing them (quickly!)

Try adding a resistance (a 100W incandescent globe is a good indicator/indestructable load resistor) between the triacs, perhaps combined with 100 uH(ish)+ of inductance to limit the commutating currents/dI/dt. This will let you get a feel for the intended switching behaviour without destroying any more triacs. You can remove them later (or have a relay switch them out if they prove essential to surviving initial turn-on/mains transients) if you like.

 

[deepakchikane]

I suspect what's happening is that on application of power, the resulting high dV/dt rate (across their MTx terminals) is triggering the triacs into conduction. Very large currents will then flow through the conducting triacs from the [low impedance] mains supply, undoubtedly killing them (quickly!)

Try adding a resistance (a 100W incandescent globe is a good indicator/indestructable load resistor) between the triacs, perhaps combined with 100 uH(ish)+ of inductance to limit the commutating currents/dI/dt. This will let you get a feel for the intended switching behaviour without destroying any more triacs. You can remove them later (or have a relay switch them out if they prove essential to surviving initial turn-on/mains transients) if you like.

hello sir,

i thnk you are into the right direction...

as i switched it with variacs it functions well...

but with the direct mcb it occurs problems..


do u have any solutions so that i can connect in proper way without harming triacs..

allready i failed 23 triacs from last weeks...

hoping for favourable reply as soon as possible

 

[chuckey]

Put a .01 MF capacitor* inseries with a 100 ohm resistor across each triac. Now when the mains is switched on the very fast switching edge sends current down throuth the snubber network and not into the gate of a triac.
* make sure it is rated for 230 V AC and is a type X or Y - rated fro mains use.
Frank

 

[deepakchikane]

Put a .01 MF capacitor* inseries with a 100 ohm resistor across each triac. Now when the mains is switched on the very fast switching edge sends current down throuth the snubber network and not into the gate of a triac.
* make sure it is rated for 230 V AC and is a type X or Y - rated fro mains use.
Frank

chuckey..

any mathematical calculation for snubber design for this..

as my resistor getting burnt
plzz

 

[deepakchikane]

chuckey...

plz refer the circuit above posted....

my triac which is in ac path getting failed when i am giving some loads to the secondary side...

secondary side voltage is 220 volt with 12 amp..

in no load conditions,
it is not harming triac which is in path of ac
plz help me out fast

 

[mdorian]

Hi , my guess is also a dv/dt failure. Do not let the gates floating . Put some RC protection circuit ( use a high power resistor not a 250mW one) ,connect the gates to cathodes and see if it still fails. If not , use some low impedance driver to drive T1 and T2. I really don't understand the use of T1. Witch is 220V side and witch 16V side on the transformer? Do you supply this circuit with 220V?

 

[chuckey]

Xc = 10^6/ 2 x PI X .01 X 50 ~ 10^6/ PI ~ 300 k , So resistor current should be 240/300 mA ~ .8 mA, P100 = 100 X .64 micro watts or 6.4 mW . its good to see that the 100R resistor is soaking up power because the dissipation from the steady state AC is only 6.4 mW. However there should be no real heat, just a burst of power during the first few 1/2 cycles of the mains when powering or depowering. If its running hot, either the cap is too big in value, or its leaky, or there is something putting big transients down the AC line.
Frank

 

[deepakchikane]

Xc = 10^6/ 2 x PI X .01 X 50 ~ 10^6/ PI ~ 300 k , So resistor current should be 240/300 mA ~ .8 mA, P100 = 100 X .64 micro watts or 6.4 mW . its good to see that the 100R resistor is soaking up power because the dissipation from the steady state AC is only 6.4 mW. However there should be no real heat, just a burst of power during the first few 1/2 cycles of the mains when powering or depowering. If its running hot, either the cap is too big in value, or its leaky, or there is something putting big transients down the AC line.
Frank

chuckey..
thanxx for the above mathematical expression..

do i use the same formula for the smps snubeer calculations...
& also things also in mind that when i am connecting two triac in a serias then there is not failures of triac anymore..
is this due the peak voltgae or dv/dv issues..??

- - - Updated - - -

Hi , my guess is also a dv/dt failure. Do not let the gates floating . Put some RC protection circuit ( use a high power resistor not a 250mW one) ,connect the gates to cathodes and see if it still fails. If not , use some low impedance driver to drive T1 and T2. I really don't understand the use of T1. Witch is 220V side and witch 16V side on the transformer? Do you supply this circuit with 220V?

T1 is used to short the primary of transformer..


the winding which is in series with the load is the 16 volt winding & triac is in parallel with the primary 230 vac windings..

 

[chuckey]

At switch on, you have mains fed via the 16v winding to the load. if T1 is not already turned on, there will be a massive voltage generated by the 230V winding applied to T1 and T2. So the first thing to think about is to stop the full 230v being applied across the 16V winding. 16V rms ~ 46V p-p, put some 50V high power zeners across the 16v winding?, or some sort of delay circuit, to make sure T1 is ON before mains is applied. You could apply this technique to the secondary instead, this is what the T1 snubber is doing, the high voltage transient is being soaked up via the cap then putting real power into the resistor.
i am not sure what the circuit is mean't to do, either to switch the outgoing voltage to the load up by 16V, or to reduce it by the magic 16 V?
Frank

 

[deepakchikane]

At switch on, you have mains fed via the 16v winding to the load. if T1 is not already turned on, there will be a massive voltage generated by the 230V winding applied to T1 and T2. So the first thing to think about is to stop the full 230v being applied across the 16V winding. 16V rms ~ 46V p-p, put some 50V high power zeners across the 16v winding?, or some sort of delay circuit, to make sure T1 is ON before mains is applied. You could apply this technique to the secondary instead, this is what the T1 snubber is doing, the high voltage transient is being soaked up via the cap then putting real power into the resistor.
i am not sure what the circuit is mean't to do, either to switch the outgoing voltage to the load up by 16V, or to reduce it by the magic 16 V?
Frank

chukey:
i am not getting you.

as there is no problem for the T1 (which will short the ac winding-primary)..

the another problems is when i am switching the secondary then my T2,that is connected in live to neutral (which will picture my pri winding ) which damaging the path triac

i also connected the snubber of 4.4nF/1KV WITH 50 OHM RESISTOR across triac.. but my triac is failling everytime...

but when i connect two triac serias then this problem ends for the first trial,but for second trial it takes out the both triacs..

i am out of my brains logics from wher the problem it is...

 

[mdorian]

Maybe switching 1 and 2 pins of the transformer ? Take off both thriacs and see the voltage on T2. Switch pins 1 and 2 and see if it show less.

 

[FvM]

The circuit operation mode is still partly unclear.

How about load current, voltage induced in the primary winding by the load current? How do you assure that the primary voltage doesn't exceed the maximum triac voltage?

Regarding triac triggering, what's the trigger circuit, do you perform zero voltage switching? Otherwise the other triac will be most likely triggered by exceeding dV/dt rating, causing catastrophic failure of both triacs.

 

[deepakchikane]

The circuit operation mode is still partly unclear.

How about load current, voltage induced in the primary winding by the load current? How do you assure that the primary voltage doesn't exceed the maximum triac voltage?

Regarding triac triggering, what's the trigger circuit, do you perform zero voltage switching? Otherwise the other triac will be most likely triggered by exceeding dV/dt rating, causing catastrophic failure of both triacs.

fvm

i want to use this ckt to switch the transformer primary whenever used..
t1 & t2 are alternatively switched on
T1=is used for the bypass the primary so that it induces some vtgs into the secondry.. resulting the load volatge will be added or reduced..

now the about exceeding voltages.. BTA 24 is having 2500vrms blocking capacity..
i dont know y still it is danaging the triac...

do u have any idea how i can do the same operations..??

 

[FvM]

BTA 24 is having 2500vrms blocking capacity

You're confusing package insulation with triac voltage blocking.

Anyway, maximum dV/dt isn't a matter of voltage rating as such. If you are igniting one triac at the wrong time, you'll risk dV/dt induced triggering of the other one.

 

[deepakchikane]

You're confusing package insulation with triac voltage blocking.

Anyway, maximum dV/dt isn't a matter of voltage rating as such. If you are igniting one triac at the wrong time, you'll risk dV/dt induced triggering of the other one.

fvm
please read the bta 24 datasheets...

 

[FvM]

fvm
please read the bta 24 datasheets...

Yes, that's what I did. I'm referring to the ST datasheet. But 2500 V blocking voltage of a triac is absurd anyway.

 

[deepakchikane]

i want to trigger both triacs alternatively..