Why did this zener diode explode?

Thread Starter

fablau

Joined May 14, 2020
167
Thank you Mr Chips for drawing the circuit in a logical manner! Much appreciated. I'm confused by HS3-1. Is it negative or positive or switching between the two? The problem I'm having is seeing how the PEMOS transistor switches properly, as surely it's source needs to be connected to the +32 volt supply. I can see R3 pulls the gate to +32 and turns the transistor off, and OPT1 provides the voltage from D4 to turn it on, but surely only if the source id connected to +32v.What have I overlooked?
The NEMOS transistor circuit I can see clearly ( now that the circuit has been redrawn properly), though I think R4 value is too high to turn the transistor off quickly, same comment to R3.
Thank you Martin for your notes.

Yes, H3-1-2 can vary its polarity by switching between the two, so that the magnet can either attract or repel.

The stable 32V is just to trigger the MOSFET gates through the optocouplers. That's independent by the power coming from H3-1-2.

As for R3 and R4, what value would you suggest to make it faster? From my tests 10k works just fine for my application, but if I can improve that, even better... maybe 5k would be better?
 

Thread Starter

fablau

Joined May 14, 2020
167
I wonder how many of (for example) the NEMOSFET transistors could be switched on at the same time by the controller? With several pull down resistors now in parallel the 12v zener voltage collapses and the transistors fail to switch on properly. Same logic applies to the PEMOS transistors. Easy to see now there's a neat and logical drawing.
The controller should be able to turn on-off 9 MOSFETs at the same time max, in any combination. Of course, if attract is what you want, P-channel MOSFETS are used and vice-versa. So you could have 4 P-channel MOSFET turning on to attract from 9 magnets and 5 N-channel MOSFETs turning on to repel at the same time.

Your point of using a single zener to trigger multiple gates is a good one and I thought about that a lot. From my experiments, that doesn't seem to be an issue, but how would you suggest to better doing it? Dedicate a single Zener-resistor line for each MOSFET or do you have any other ideas?

Thanks for your feedback, appreciated!
 

Martin_R

Joined Aug 28, 2019
132
he controller should be able to turn on-off 9 MOSFETs at the same time max, in any combination.
Ok. So, what's the time between one transistor turning off and it's opposite number turning on? If it's too short then both transistors would be on, causing the demise of both. Also if the transistor is slow to turn off then it has a portion of time in its linear mode, and it will get hot. For R3 and R4 I would try 470R, but you would have to replace the zeners with 7812/7912 types regulators to supply the voltage due to incread current demand.
 

BobaMosfet

Joined Jul 1, 2009
2,053
Hello everyone.

Please, help me to understand why D1 of the circuit below exploded when I increased the voltage to 32v. Everything was working perfectly at 22V, then I increased the voltage to 32v and D1 exploded. As you can see from the schematics, that diode drives nine N-Channel MOSFETS when they are activated through the corresponding optocouplers driven by an external controller connected to the Digital Inputs. My guess is that I have exceeded the breakdown voltage, but per specifications, it should be fine and I didn't expect that to happen.

Here are some details about the used components:

Here is the Zener diode I have used:

https://datasheet.lcsc.com/lcsc/1810122016_MDD-Microdiode-Electronics-BZT52C12_C173429.pdf

And here is the N-Channel Mosfet I have used:

https://datasheet.lcsc.com/lcsc/1811141141_HL-Haolin-Elec-5N04_C237240.pdf


The max voltage the circuit should be able to support is max 40v, even though I don't think ever go over 32v. The max current out of the MOSFETs shouldn't be over 0.5 amp each, but of course, they can be all turned on for a max total output of 4.5 amps (but I don't think that should be related to the Zener blowing up, please, correct me if I am wrong).

The circuit's purpose is to drive an array of electromagnets that can either attract (in which case P-channel MOSFETs are used) or repel (in which case N-channel MOSFETs are used instead).

Eager to know your thoughts, let me know if you need more information, and thank you in advance to anyone!

View attachment 241096
What is the actual number of the zener diode you used- the datasheet covers several. here are the important parameters:

1623769854620.png

Do you see the Pd value? and the junction temperature values? The other specs on the next page down are for each different zener- which is why we need to know what the actual diode you use is.

You exceeded the Pd value - it's that simple.
 
Hello everyone.

Please, help me to understand why D1 of the circuit below exploded when I increased the voltage to 32v. Everything was working perfectly at 22V, then I increased the voltage to 32v and D1 exploded. As you can see from the schematics, that diode drives nine N-Channel MOSFETS when they are activated through the corresponding optocouplers driven by an external controller connected to the Digital Inputs. My guess is that I have exceeded the breakdown voltage, but per specifications, it should be fine and I didn't expect that to happen.

Here are some details about the used components:

Here is the Zener diode I have used:

https://datasheet.lcsc.com/lcsc/1810122016_MDD-Microdiode-Electronics-BZT52C12_C173429.pdf

And here is the N-Channel Mosfet I have used:

https://datasheet.lcsc.com/lcsc/1811141141_HL-Haolin-Elec-5N04_C237240.pdf


The max voltage the circuit should be able to support is max 40v, even though I don't think ever go over 32v. The max current out of the MOSFETs shouldn't be over 0.5 amp each, but of course, they can be all turned on for a max total output of 4.5 amps (but I don't think that should be related to the Zener blowing up, please, correct me if I am wrong).

The circuit's purpose is to drive an array of electromagnets that can either attract (in which case P-channel MOSFETs are used) or repel (in which case N-channel MOSFETs are used instead).

Eager to know your thoughts, let me know if you need more information, and thank you in advance to anyone!

View attachment 241096
Hello everyone.

Please, help me to understand why D1 of the circuit below exploded when I increased the voltage to 32v. Everything was working perfectly at 22V, then I increased the voltage to 32v and D1 exploded. As you can see from the schematics, that diode drives nine N-Channel MOSFETS when they are activated through the corresponding optocouplers driven by an external controller connected to the Digital Inputs. My guess is that I have exceeded the breakdown voltage, but per specifications, it should be fine and I didn't expect that to happen.

Here are some details about the used components:

Here is the Zener diode I have used:

https://datasheet.lcsc.com/lcsc/1810122016_MDD-Microdiode-Electronics-BZT52C12_C173429.pdf

And here is the N-Channel Mosfet I have used:

https://datasheet.lcsc.com/lcsc/1811141141_HL-Haolin-Elec-5N04_C237240.pdf


The max voltage the circuit should be able to support is max 40v, even though I don't think ever go over 32v. The max current out of the MOSFETs shouldn't be over 0.5 amp each, but of course, they can be all turned on for a max total output of 4.5 amps (but I don't think that should be related to the Zener blowing up, please, correct me if I am wrong).

The circuit's purpose is to drive an array of electromagnets that can either attract (in which case P-channel MOSFETs are used) or repel (in which case N-channel MOSFETs are used instead).

Eager to know your thoughts, let me know if you need more information, and thank you in advance to anyone!

View attachment 241096
Hello everyone.

Please, help me to understand why D1 of the circuit below exploded when I increased the voltage to 32v. Everything was working perfectly at 22V, then I increased the voltage to 32v and D1 exploded. As you can see from the schematics, that diode drives nine N-Channel MOSFETS when they are activated through the corresponding optocouplers driven by an external controller connected to the Digital Inputs. My guess is that I have exceeded the breakdown voltage, but per specifications, it should be fine and I didn't expect that to happen.

Here are some details about the used components:

Here is the Zener diode I have used:

https://datasheet.lcsc.com/lcsc/1810122016_MDD-Microdiode-Electronics-BZT52C12_C173429.pdf

And here is the N-Channel Mosfet I have used:

https://datasheet.lcsc.com/lcsc/1811141141_HL-Haolin-Elec-5N04_C237240.pdf


The max voltage the circuit should be able to support is max 40v, even though I don't think ever go over 32v. The max current out of the MOSFETs shouldn't be over 0.5 amp each, but of course, they can be all turned on for a max total output of 4.5 amps (but I don't think that should be related to the Zener blowing up, please, correct me if I am wrong).

The circuit's purpose is to drive an array of electromagnets that can either attract (in which case P-channel MOSFETs are used) or repel (in which case N-channel MOSFETs are used instead).

Eager to know your thoughts, let me know if you need more information, and thank you in advance to anyone!

View attachment 241096
May I comment something?
Function of Zener diode looks like to protect over voltage input to LED of opto-couplers, not single.
First of all, BZT52 series is just 500mW type zener in best condition and actual performance will be only 400mW at 25 degree C condition as (max TJ - Room Temp ) / 305 degreeC/W.
This poor device only can handling max. 40mA by 12V type and no margin of high transient voltages.

I would like to recommend some resistor in series with zener diode (Maybe Zener voltage will reduce) for current limit or put more zeners to share the current.

Thanks and I hope this will be little help to you.
 

Thread Starter

fablau

Joined May 14, 2020
167
Ok. So, what's the time between one transistor turning off and it's opposite number turning on? If it's too short then both transistors would be on, causing the demise of both. Also if the transistor is slow to turn off then it has a portion of time in its linear mode, and it will get hot. For R3 and R4 I would try 470R, but you would have to replace the zeners with 7812/7912 types regulators to supply the voltage due to incread current demand.
Good points! Actually, it is in the milliseconds' realm, I'd say 1-2 milliseconds? Is that too short of a time?

And your idea to provide current via 7812/7912 types regulators is a very good one as well, I'll try that. Thank you!
 

Thread Starter

fablau

Joined May 14, 2020
167
What is the actual number of the zener diode you used- the datasheet covers several. here are the important parameters:

View attachment 241336

Do you see the Pd value? and the junction temperature values? The other specs on the next page down are for each different zener- which is why we need to know what the actual diode you use is.

You exceeded the Pd value - it's that simple.
Yes, so sorry, I didn't specify the model number, here it is:

BZT52C12

Here is a shot of its specs:

zenerSpecs2.png
 

Thread Starter

fablau

Joined May 14, 2020
167
May I comment something?
Function of Zener diode looks like to protect over voltage input to LED of opto-couplers, not single.
First of all, BZT52 series is just 500mW type zener in best condition and actual performance will be only 400mW at 25 degree C condition as (max TJ - Room Temp ) / 305 degreeC/W.
This poor device only can handling max. 40mA by 12V type and no margin of high transient voltages.

I would like to recommend some resistor in series with zener diode (Maybe Zener voltage will reduce) for current limit or put more zeners to share the current.

Thanks and I hope this will be little help to you.
Very good points. I have measured the current through the zener as I posted earlier, and actually that goes up to 200mA. According to the sheet I posted above just now it handles not more than 5mA?? Am I reading that right? Oh dear... if so, this is a terrible design indeed...
 

BobaMosfet

Joined Jul 1, 2009
2,053
Very good points. I have measured the current through the zener as I posted earlier, and actually that goes up to 200mA. According to the sheet I posted above just now it handles not more than 5mA?? Am I reading that right? Oh dear... if so, this is a terrible design indeed...
You clearly need to learn some things :) (we all started knowing nothing):

Title: Understanding Basic Electronics, 1st Ed.
Publisher: The American Radio Relay League
ISBN: 0-87259-398-3
 

Thread Starter

fablau

Joined May 14, 2020
167
You clearly need to learn some things :) (we all started knowing nothing):

Title: Understanding Basic Electronics, 1st Ed.
Publisher: The American Radio Relay League
ISBN: 0-87259-398-3
Yes, I feel now like a baby playing with matches.

Ok, thanks for the book suggestion, I'll definitively check it out!
 

sparky 1

Joined Nov 3, 2018
732
Last edited:

Thread Starter

fablau

Joined May 14, 2020
167

Martin_R

Joined Aug 28, 2019
132
Thank you Martin for your notes.

Yes, H3-1-2 can vary its polarity by switching between the two, so that the magnet can either attract or repel.

The stable 32V is just to trigger the MOSFET gates through the optocouplers. That's independent by the power coming from H3-1-2.
Is H3-1-2 referenced to 0v? Your circuit confuses me somewhat. H3-2 and 2 swop polarity as you say, yet doing so against a fixed +32v and ground seems a recipe for disaster. I've altered the circuit to eliminate the 32v rail. See attached circuit, L1 is your coil. By the way, how is the polarity swopped, are you just using an ac transformer?
 

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Thread Starter

fablau

Joined May 14, 2020
167
Is H3-1-2 referenced to 0v? Your circuit confuses me somewhat. H3-2 and 2 swop polarity as you say, yet doing so against a fixed +32v and ground seems a recipe for disaster. I've altered the circuit to eliminate the 32v rail. See attached circuit, L1 is your coil. By the way, how is the polarity swopped, are you just using an ac transformer?
This is very interesting... I am wondering if all that works even when H3-1-2 switch polarity?

To answer your question, I am switching polarity by turning on/off the inputs on the L298N as any regular h-bridge.
 

Thread Starter

fablau

Joined May 14, 2020
167
What are you attracting with your electromagnet?
Do you know that an electromagnet does not repel by simply reversing the current?
I am working on a project that moves objects on a surface with electromagnets underneath.

What do you mean by " electromagnet does not repel by simply reversing the current"? Please, tell me more... thanks :)
 
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