This instructable describes a half hour project and it by itself will be kept short.
The product created is a simple cheap tester for voltage regulators from the 78XX series.
Step 1: Project Purpose
Why did I do this tester?
Main reason: I buy a lot of parts in sites like Aliexpress, Banggood end etc. There you can find a big quantities of electronic parts for a very low prices. Sometimes the prices are lower than if you buy them directly from the producer (even in big quantities). Sometimes also these parts are product clones with low quality, or even non functional. Few weeks ago I bought a pack of 100 voltage regulators 78L05 for less than 2 USD. I wanted to be sure that I can rely on them - so I wanted to test them (at least 10-20) to have an idea what I have bought.
To be able to test them in a fist way I needed some simple tester. The main constrains when building it - minimum price, minimum size, to be more or less universal - that means I can use it also for different versions of the LM7805 regulator, or even for few member chips of the 78XX series voltage regulators.
Here it goes...
Step 2: The Tester Structure
Because the output voltage of the 78L05 voltage regulator is 5V - the same as that used in the USB interface, I decided to use as output voltage measurement device the USB voltage-meter, which I had available.It has few advantages - it shows the voltage and the current - you can connect some USB device and in this way you can also add a load to the voltage regulator and know more or less precisely how much current you source . Even unloaded the voltage-meter has its own consumption, which should be enough to load the voltage regulator.
As voltage source I used a DIY 2-12V regulated power supply, but also a 9V or 12v battery can be used. The voltage produced must be minimum 2V higher then the output voltage of the regulator.
The decision to use this type of voltage-meter determined also the tester output connector - female USB socket.
Here is the list of the parts needed:
- USB voltage-meter - of course you can use standard DMM for that purpose, and you can use your USB voltage-meter also for other purposes when you do not test voltage regulators
- a small piece of protoboard
- female A-type USB connector - mine was unsoldered from some old nonworking device
- cylindric pins female header
- some electrolytic 10V capacitor
- two pieces of different colour wires
Step 3: Circuit and Implementation
The circuit can be seen on the picture.
All parts were soldered on the protoboard. The capacitor is needed to filter the output voltage and in some cases for the stability.
Step 4: The Tester in Work
On the movie can be seen how easy is now to test the voltage regulators.
As conclusion :
- with few parts you can build a tester for voltage regulators, which can be used for a fast testing of big number of parts
- the tester can be used if you want to select a part between a bunch of identical ones, but having the precise output voltage at specific current. This part could be used further as voltage reference in precise measurement device. Be sure that the voltage sensing device (the USB voltage-meter or the DMM) used have the required precision.
- knowing the allowed input voltage range of your USB voltage-meter (different for different type, but in the range 3-9V) would allow you to test also another voltage regulators from the 78XX series - 7805 (5 V), 7806 (6 V), 7808 (8 V), 7809 (9 V) and LM78L62 (6.2 volts) or LM78L82 (8.2 volts) as well as the STMicroelectronics L78L33ACZ (3.3 volts).