Month: June 2022

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Blown LM358P due to transients

An LM358p is a dual opamp IC which I used in a single supply configuration. I drive the LM358 just shy of its absolute maximum voltage which is +30V. So I gave I supplied 28.8V (+-0.1V). It works flawless but the power supply is a Meanwell switching supply which introduces transient when plugging into the mains supply.

The transient arise when I was plugging in the AC wire to the mains. I used an anchor 6A 3-pin male plug for connection. It was at the brief moment when the transient arise.

The transient which arises apparently has enough power that it blew the epoxy off the silicon and it did with a loud bang.

Blown LM358P due to transients

Doing rough calculation at the moment this happened

Let’s say the transient is double the supply voltage of = 2 x 28.9 V= 57.8V

let’s say the current drawn by the IC is 40mA which is its absolute maximum.

power = voltage x current = 57.8V x 40mA = 2.312W

so for a brief moment, this 2W is radiated by the silicon chip. Which caused the heating up of the epoxy and generating enough expanding force which blew out like that.

but let’s take a more reasonable transient voltage(ISO 7637-2: 2011) of approximately 110V at a rise time of 0.5uS.

so power = 110V x 40mA = 4.4W .

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FAKE BD139 NPN transistors

I have recently found out that there are FAKE transistors in the market. I have a built a circuit design and when I bought the transistor from the Lajpat rai market in Delhi; I assembled the circuit on a test bench for measurements. But I was surprised that the BD139 did not work with 10mA at 30V and they began overheating. They heat up so much that bubbles appear on the front epoxy and it cracked. I thought that maybe it was damaged so I replaced the whole circuit with a new transistor set. But they also didn’t hold and this time they burnt a resistor along with them. I saw flames engulfing the 1/4 Watt resistors.

So I again made the circuit using the minuscule BC546B. Which neither get warm nor went into thermal runaway.

on the BD139 it was marked that it was manufactured by NXP. And I then checked the NXP website and found out that the NXP closed its manufacturing of this transistor in 2001.

There are a lot of BD139 transistors circulating in the market. It is essential that you must buy from a good source.