The resistor that suppresses voltage and current glitches at the entrance of the power chip always explodes. Could you tell me why?

Zikiost

The resistor that suppresses voltage and current glitches at the entrance of the power chip always explodes. Could you tell me why? [Copy link]

 

RT, the power chip used is EG1192L from Yijingwei, and VCC is 24V or 48V.

A 1 ohm 1210 0.5W chip resistor is used at the entrance to suppress voltage and current glitches. However, during customer use, the three-proof paint on the resistor surface turned yellow at high temperature many times, and the measured resistance value was about 5k. This occurred in both high and low temperature impact tests and room temperature tests, and the probability of occurrence in high and low temperature impact tests was higher. Could you please tell me what the possible reason is? Thank you

Also attached is the waveform

Yellow-VCC input Light blue-15V output Dark blue-current passing through R55

qwqwqw2088

Circuit boards coated with conformal coating may decompose or change color in high temperature environments.

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Title: "The resistor that suppresses voltage and current glitches at the entrance of the power chip always explodes"

This is the resistor at the entrance burst or damaged, this is a circuit design problem, related to overcurrent, overvoltage, improper thermal design, including mechanical stress, etc.

qwqwqw2088

Voltage glitches may generate transient high voltage on the resistor, exceeding the maximum voltage tolerance of the resistor
. Is there any external electromagnetic interference that causes voltage or current abnormality?
It seems inappropriate to use a 1 ohm resistor to suppress voltage and current glitches .

qwqwqw2088

suggestion,

Replace the three-proof paint with one with good heat resistance.
Read the EG1192L manual again, or communicate with the official website to see if the circuit is improperly designed
. Confirm whether the resistor used can withstand the designed current.
Is the actual circuit heat dissipation considered?

tagetage

It's a hardware design issue, resistors should not be placed.

Zikiost

tagetage posted on 2024-6-6 22:12 It is a hardware design problem, resistors should not be placed.

What could you ask?

My understanding is that the surge current at the moment of power-on will generate high voltage on the parasitic inductance of the PCB trace, which may exceed the maximum withstand voltage of the chip and cause damage to the chip. In addition, adding a resistor can also suppress the LC oscillation after power-on.

fjdeepblue

It is likely that the resistor power is insufficient and overheating occurs. Replace it with a resistor with a higher power.

tagetage

The surge current at the moment of power-on will generate high voltage on the parasitic inductance of the PCB trace, which may exceed the maximum withstand voltage of the chip and cause damage to the chip. The parasitic inductance of the PCB is very small and can be ignored for the input of power chips.

And adding a resistor can also suppress the LC oscillation after power-on. -------- Adding a resistor to a DC chip has a bad effect. There is no LC oscillation in a DC chip.

I'm a hardware engineer, and I can tell from one look at your circuit that it must have been drawn by a hardware novice.

不亦心

First of all, it is not recommended to connect resistors in series. Secondly, if you must do so, you cannot connect ordinary thick-film resistors in series, and you need durable alloy resistors. Thirdly, when measuring surge current, you must discharge the circuit capacitors, the current probe bandwidth should be large, the oscilloscope should have full bandwidth and do not turn on bandwidth limit, the input voltage source rising slope should be fast enough, and finally, turn on direct hot plugging first. Finally, you can roughly estimate the resistor loss based on the input capacitor energy, and see whether the selection is reasonable according to the resistor pulse power curve.

beyond_笑谈

If there are multiple voltage rails, the resistor can be replaced with an inductor or a magnetic bead. Or the resistor can be a surge type.