Operational Amplifiers (OpAmps) are among the most commonly faked chips on the market. When you purchase these from AliExpress and other non-trustworthy sources, with sophisticated OpAmps, you almost inevitably get worthless copies that do not work at all as expected.
In this article, you learn what is commonly inside fake OpAmp chips, how they behave, and how you can identify them quickly.
Why Fakes?
Chinese sources like AliExpress and similar sites are huge market places: the operator of such platforms isn’t selling you anything. Instead, the platform brings buyers and sellers together, and you are faced with all kinds of “shops” that have no reputation. Because of this, there is minimal accountability, and when sellers send you fake items, they do not need to fear a public outcry. If their reputation is finally at a low, they simply open up a new shop with a different name.
Do not get me wrong: market places such as AliExpress can be great sources for cheap and good components, especially for DIY makers with a low budget. However, there are notorious items (such as OpAmps) that you better not buy there as they seem to be almost always falsified.
How Fake Chips Work
Fake OpAmps often look indistinguishable from genuine parts. Inside the package, you find a wrong dye (if you had the means to open and investigate the chip under a microscope). The dye really is from a much cheaper and much more basic OpAmp, and just the internal wiring has been changed to match the pin layout of the faked OpAmp.
So fake OpAmps typically do work. However, you are really using a completely different OpAmp with much inferior specifications.
It’s not just the wasted money: when you accidentally use a fake OpAmp in good faith in your circuit, it might damage other parts, and you will be wasting a lot of time trying to find your error in a circuit that actually has no error, when the circuit isn’t working. So if you do get OpAmps from untrusted sources, before using them, make sure you perform a basic test (see below).
Identifying Fake OpAmps
The only way of identifying fake OpAmps without opening them and examining their dye is to test some key specs and see if they match.
A great way is testing rail-to-rail capability as this differentiates modern high quality OpAmps from cheap and old designs used in fake OpAmps.
For this test, you use a simple voltage follower circuit. Here is a sample for a MCP6002, one of the most popular and most commonly faked OpAmp:
Do not forget to also supply the chip with power. VSS (MCP6002 pin 4) goes to GND, and VDD (MCP6002 pin 8) connects to the supply voltage, i.e. 3.3V.
When you now connect a voltage to the non-inverting input (pin 3), your voltmeter at the output pin (pin 1) should measure close to this voltage. So when you apply GND to pin 3, the output should be 0V, and likewise when you apply 3.3V, the output should be close to 3.3V.
Cheap OpAmps found in most fakes cannot output rail-to-rail voltages, so when you test a fake OpAmp, it most likely outputs much less voltage. When you i.e. apply 3.3V, your voltmeter may measure just 1.7V.
Why Testing OpAmps Is Important
The simple voltage follower test from above is a good way to perform a basic test. If the rail-to-rail capabilities don’t match the specifications, then all the other specifications will most likely be off as well.
A fake OpAmp may not just degrade your circuit, it may in fact cause damage or even fire hazards. Genuine MCP6002 OpAmps for example can source and sink around 20mA whereas faked OpAmps can only handle a few mA (if at all).
Recommendations
I am a great fan of market places like AliExpress: you can get competitively priced quality components, and the very same components would cost you up to ten times more on local market places such as Amazon. Especially when it comes to LED or microcontroller boards, the quality you get from AliExpress and others is typically acceptable.
Some components however should not be purchased there because they seem to be routinely faked. This includes OpAmps and power transistors.
Such components should always be purchased at trusted sellers such as Mouser, DigiKey, and similar.
Prices for components aren’t that much different. What makes these distributors problematic is their shipping cost. Ordering small quantities is prohibitive once €20 shipping cost is added. That’s why you should start a list, and add all the components you may want to stock. Maintain this list for a while until the volume of your order qualifies you for free shipping. At Mouser, for example, orders above €50 (€60 with included VAT) ship free.
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(content created Aug 20, 2024 - last updated Aug 28, 2024)