KA7810 voltage regulator unusual behavior...

[zimzom]

got my breadboard out, there is a 14v dc input from a ac/dc transformer unregulated. I use a dc socket to connect to the board. positive to vin(pin 1) grnd to grnd. (pin 2)

pin 2 then goes to the negative rail
pin 3 then goes to the positive rail.

a1 to + rail
a2 to - rail
e2 to - DC
e3 to + DC
c1 to KA7810 vout
c2 to KA7810 grnd
c3 to KA7810 vin
 
When I connect the power, I am only getting the difference between the unregulated voltage and the regulated. (2-3v) where has the other 10v gone?

[David_AVD]

Schematic?

Do you have bypass capacitors?

[zimzom]

Schematic?

Do you have bypass capacitors?

I used this video...



I thought it was weird not using the bypass caps but i figured the guy knew what he was doing. I should have followed the datasheet. I didn't use the led as I just wanted to measure the voltage output..

In fairness, the guy is using the 5v version - but even that has bypass caps in the datasheet.

Agraa its my own fault,  I should have trusted the datasheet and not youtube. WIll now stomp out to get the thallium caps lol. Thinking this through further perhaps using the battery source is a "clean" enough source for the IC not to have an issue where as a wall socket DC converter would have ripple problems?

[David_AVD]

Hmmm... not sure I'd trust the advice of the guy in that video if he can't get something as simple as a regulator correct !   

[zimzom]

Youtube magic lol.  I thought I was on to a winner, electronics videos where the presenter has English as a first language.

Again I should have known when there was no heat sink on the voltage regulator..

Hhmmm, will get some ferrite beads today, another thing to add to the list.

[mariush]

Decoupling capacitors are not really necessary when you power a linear regulator from a battery, and the cables going from regulator to battery are very small (a few centimeters).
However, it almost never hurts to have a decoupling capacitor and in some cases even a large input capacitor (especially in battery operated circuits) would help a lot.
In the video the guy used a 9v battery with short wires and the regulator outputs 5v so there's a large difference between input and output voltage.. it works.

You used an ac/dc transformer, unregulated, so I'm not even sure that you actually used a capacitor after rectification to smooth out the output of the bridge rectifier.. without a capacitor after the rectifier, you're going to have voltage going from 0 to some high voltage and back. The capacitor must be large enough to keep the voltage all the time above Vout + at least 2 volts

And even then a decoupling capacitor would be helpful.