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Will the failure of the MOS tube cause the external voltage to charge the battery at a high voltage? [Copy link]

 
This post was last edited by tongshaoqiang on 2024-10-16 19:09

As shown in the two figures above: the circuit is powered by batteries and external 24VDC. When there is external power (DC-DC, BL8037 provides 24V to 3.62V), the battery does not work. The circuit power supply is controlled by MOS2 and MOS3. After communicating with the battery manufacturer, we found that some customers have MOS failure, which causes the external 24V to charge the battery, resulting in the battery burning.
I checked several points of MOS tube failure, but I still don't understand them. Let me ask you, if two MOS tubes fail in the above switching control circuit, will there be a situation where 24V is added to both ends of the battery?
(My own analysis will not work. It will only happen when R3 is short-circuited and MOS3 has a GD short-circuit; R3 is short-circuited and MOS2 has a GS SD short-circuit, and MOS3 has an SD short-circuit;)

WST2339.pdf

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WST2339

BL8037_V1.6_en.pdf

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BL9307

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Use 24V voltage to directly power the G pole. If the voltage is too high, it should be reduced to about 12V. Connect a 0.25A fuse resistor or fuse in series in the middle. When the MOS tube burns out, the fuse burns out, and the 24V power supply is disconnected.   Details Published on 2024-10-18 11:14
 
 

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Didn't you mention what type of battery???

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Disposable lithium battery   Details Published on 2024-10-17 07:57
 
 
 

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It's not a lithium battery.

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The failure of the MOS tube itself will not directly cause the external voltage to charge the battery at a high voltage.

Unless the DC-DC chip BL8037 fails and causes a short circuit

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Thanks for knowing! The short circuit of the input and output of BL8307 will cause a 24V high voltage at the drain of MOS2. If the DS of mos3 can withstand this high voltage and does not cause the DS of MOS3 to break down and short-circuit, the battery will not be charged at a high voltage, right?  Details Published on 2024-10-17 14:01
 
 
 

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tagetage posted on 2024-10-16 20:06 Didn’t you mention what type of battery? ? ?

Disposable lithium battery

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It is not suitable to design the circuit like this for disposable lithium batteries. It is OK to directly connect the positive output of the battery to a Schottky diode to prevent reverse current. What kind of MOS should be used? The current is particularly large? ? ?  Details Published on 2024-10-17 10:10
 
 
 

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I used the XL1509 chip, 12V to 5V, but there was no overload protection. After overload, the internal MOS tube broke down directly, and the input voltage was directly added to the output end, causing the capacitor to explode, almost causing my eyes to burst. It seems that there is only short circuit protection, but no overload protection.

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The main characteristic of MOS failure is that G, S, and D are short-circuited with each other, which is possible.

Moreover, in your circuit diagram, MOS3 is always on. What is the meaning of its existence?

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No, when the external input power supply is connected, the gate of MOS3 is about 8V, the S pole is 3.62V, and Pmos is turned off.  Details Published on 2024-10-17 14:10
 
 
 

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tongshaoqiang posted on 2024-10-17 07:57 Disposable lithium battery

It is not suitable to design the circuit like this for disposable lithium batteries. It is OK to directly connect the positive output of the battery to a Schottky diode to prevent reverse current. What kind of MOS should be used? The current is particularly large? ? ?

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The current is not very large. In 4G communication, there will be a very short-term peak current of 1A, and a longer period of time is 300mA.  Details Published on 2024-10-17 14:12
 
 
 

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qwqwqw2088 posted on 2024-10-17 07:50 The failure of the MOS tube itself will not directly cause the external voltage to charge the battery at a high voltage unless the DC-DC chip BL8037 fails and causes a short circuit

Thanks for knowing!

The short circuit of the input and output of BL8307 will cause a high voltage of 24V to exist at the drain of MOS2. If the DS of mos3 can withstand this high voltage and does not cause the DS of MOS3 to break down and short-circuit, the battery will not be charged with a high voltage, right?

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Shawn.TAO posted on 2024-10-17 08:53 The main feature of MOS failure is that G, S, and D are short-circuited with each other, which is possible. And in your circuit diagram, MOS3 is always on, so there is...

No way

When the external input power supply is on, the gate of MOS3 is about 8V, the S pole is 3.62V, and Pmos is off.

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I didn't notice that MOS3 is a PMOS, I thought it was also an NMOS. It looks fine.  Details Published on 2024-10-18 10:10
 
 
 

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tagetage posted on 2024-10-17 10:10 It is not appropriate to design the circuit like this for disposable lithium batteries. It is OK to directly connect the positive output of the battery to a Schottky diode to prevent reverse current. What MOS should be used? Electric...

The current is not very large. In 4G communication, there will be a very short-term peak current of 1A, and a longer period of time is 300mA.

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@ maychang senior, please give me some guidance. Common consequences of MOS tube failure

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MOS tube is damaged, often GS short circuit, three motors short circuit is also common. If MOS3 GD short circuit, then obviously VDD_24 24V voltage will charge the battery at VCC_BAT. However, the current is not large, because of R3, the current will not exceed 2mA.  Details Published on 2024-10-17 15:07
 
 
 

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tongshaoqiang posted on 2024-10-17 14:13 @maychang senior, please give me some guidance. Common consequences of MOS tube failure

MOS tube is damaged, often GS short circuit, three motors short circuit is also common. If MOS3 GD short circuit, then obviously VDD_24 24V voltage will charge the battery at VCC_BAT. However, the current is not large, because of R3, the current will not exceed 2mA.

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Thanks for the reply! If both MOS2 and MOS3 have GDS short circuit, there will be a large current to charge the battery at VCC_BAT, so the battery will explode, right? But there is a chance that both MOS2 and MOS3 have GDS short circuit, but it will not be too high, right? In this way, does every circuit have a possibility of being unusable?  Details Published on 2024-10-17 15:37
 
 
 

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maychang posted on 2024-10-17 15:07 MOS tube damage, often short circuit between GS, three motors are also common short circuit. If the GD of MOS3 is short circuited, then obviously the 24V voltage of VDD_24 will...

Thanks for the reply senior!

If GDS short circuit occurs in both MOS2 and MOS3, a large current will be available to charge the battery at VCC_BAT, and the battery explosion will occur, right?

There is a chance that both MOS2 and MOS3 will have a GDS short circuit, but it is not too high, right? Does this mean that every circuit has a potential risk of being unusable?

Just like the rechargeable batteries we use, they all have protection boards for charge management. If the protection board fails, there is also a risk of the battery exploding. Is it true that there are no explosions in current batteries? (I feel something is wrong again. The Lebanese pager exploded with the battery, right?) I am confused.

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It is not necessary for both MOS2 and MOS3 to be damaged. As long as the GD of MOS3 is short-circuited, 24V will charge the battery at VCC_BAT. I feel that MOS tube damage is more likely to occur during the welding assembly process. After being installed in the whole machine, as long as the design is correct, the probability of damage is not high.  Details Published on 2024-10-17 15:52
It is not necessary for both MOS2 and MOS3 to be damaged. As long as the GD of MOS3 is short-circuited, 24V will charge the battery at VCC_BAT. I feel that MOS tube damage is more likely to occur during the welding assembly process. After being installed in the whole machine, as long as the design is correct, the probability of damage is not high.  Details Published on 2024-10-17 15:49
 
 
 

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tongshaoqiang posted on 2024-10-17 15:37 Thank you for your reply! If both MOS2 and MOS3 have GDS short circuit, there will be a large current to charge the battery at VCC_BAT, so that the battery will explode...

It is not necessary for both MOS2 and MOS3 to be damaged. As long as the GD of MOS3 is short-circuited, 24V will charge the battery at VCC_BAT.

I feel that MOS tube damage is more likely to occur during the welding assembly process. After installation in the whole machine, as long as the design is correct, the chance of damage is not high.

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tongshaoqiang posted on 2024-10-17 15:37 Thank you for your reply! If both MOS2 and MOS3 have GDS short circuit, there will be a large current to charge the battery at VCC_BAT, so that the battery will explode...

The pagers in Lebanon did not explode with batteries, but instead had explosives placed inside. The detonation was controlled by the signal received by the pager. When no detonation signal was received, the pager could be used normally.

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tongshaoqiang posted on 2024-10-17 14:10 No way. When the external input power supply is connected, the gate of MOS3 is about 8V, the S pole is 3.62V, and Pmos is turned off

I didn't notice that MOS3 is a PMOS, I thought it was also an NMOS. It looks fine.

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Use 24V voltage to directly power the G pole. If the voltage is too high, it should be reduced to about 12V. Connect a 0.25A fuse resistor or fuse in series in the middle. When the MOS tube burns out, the fuse burns out, and the 24V power supply is disconnected.

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