KA7810 voltage regulator unusual behavior... - Page 1
Forum section: electronics / beginners

author: zimzom
author_rank: Regular Contributor
timestamp: April 03, 2014, 12:30:48 pm
content: 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 railpin 3 then goes to the positive rail.a1 to + raila2 to - raile2 to - DCe3 to + DCc1 to KA7810 voutc2 to KA7810 grndc3 to KA7810 vinWhen 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?

author: David_AVD
author_rank: Super Contributor
timestamp: April 03, 2014, 09:03:58 pm
content: Schematic?Do you have bypass capacitors?

author: zimzom
author_rank: Regular Contributor
timestamp: April 04, 2014, 03:26:48 am
content: Quote from: David_AVD on April 03, 2014, 09:03:58 pmI 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?

author: David_AVD
author_rank: Super Contributor
timestamp: April 04, 2014, 04:38:57 am
content: 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 !

author: zimzom
author_rank: Regular Contributor
timestamp: April 04, 2014, 04:52:37 am
content: 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.

author: mariush
author_rank: Super Contributor
timestamp: April 04, 2014, 05:46:33 am
content: 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 voltsAnd even then a decoupling capacitor would be helpful.