Hi,

I'm trying to find a replacement diac for HT60 in the attached AC DC circuit board. The closest available I've found was the NTE6412 but it's not readily available in Canada. Would the DB4 be an acceptable replacement? The breakover voltage is 32v-40v. HT60 has a breakover voltage of 56V-70V. The incoming voltage is 120VAC.

This is for the promedia 5.1 speaker system where the daughter board amongst other components are prone to frying. My plan to make the system more robust was to up the watt rating on resistors and up the temp rating on capacitors, and potentially add a fan. The boards are all inside the subwoofer.

Thanks ahead of time!

 

The fan should fix the problems.
Just my thoughts. It worked for me with a Philips crt TV, to save buying a very expensive chip, for a customer.
Good luck..........

 

Thank you twohats. Do you have any suggestion on the replacement diac? I feel like the breakover voltage shouldn't matter too much. But circuit design is definitely not my expertise.

 

Sorry, no.
Good luck.............

 

I believe the diac is there to kick off the oscillator when the supply starts up so its voltage may not be critical.

 

The HT-60 breaks over at 60V.
I wonder if two 32V diacs in series would do the job. It should take 64V before either starts to break over, then the first one triggering should ensure the second triggers.
As its purpose is only to get the oscillator started, I hardly think it’s going to be too critical.

 

I wonder if two 32V diacs in series would do the job.

Probably not. Whichever one has the lowest leakage will see the greater voltage and then when that one breaks over the full voltage will be seen across the other one and it too will breakover. So I would expect that the resultant voltage will be less than 60V

 

I believe the diac is there to kick off the oscillator when the supply starts up so its voltage may not be critical.

Thanks Albert, where's the uncertainty? Or are you 95% certain and it's just a disclaimer?

 

Probably not. Whichever one has the lowest leakage will see the greater voltage and then when that one breaks over the full voltage will be seen across the other one and it too will breakover. So I would expect that the resultant voltage will be less than 60V

According to the datasheet of a ST 32V diac, the maximum leakage is 10uA, but the maximum breakover current is 100uA.
It would be much handier to know the minimum breakover current, but it suggests that the leakage wouldn't be enough to make it break over; but not something you could definitely rely upon.

 

Thanks Albert, where's the uncertainty? Or are you 95% certain and it's just a disclaimer?

I have not done the analytical maths on the circuit nor gone thoroughly through the datasheets for all the components. I am not familiar with this particular circuit. Given all that I cannot be certain.

 

How wrong can this go? Is it something I can try with the lower voltage replacement without making a catastrophic failure? I'm not going to hold you to it. I'd just like an opinion from someone that is less clueless than me.

 

How wrong can this go? Is it something I can try with the lower voltage replacement without making a catastrophic failure? I'm not going to hold you to it. I'd just like an opinion from someone that is less clueless than me.

I don't know. They used a 60V device for a reason but I don't know that reason.