Regulator

[argonrepublic]

This regulator is very simillar to mine. I can not find schematics for mine. One transistor is A1015, it is giving me -11 volts. The other is a C1815 it is giving about + 5.5 volts. There are no diodes on my board. Which leg of transistor should I follow? Does the "A" and "C" designate. EBC locations?
How does a transistor regulate voltage?
Thanks
Joe

[Stocker]

3 seconds on Google gets you this.

Politics aside, Google is really a neat thing.

[AndrewT]

Hi,
it's a transistor assisted Zener.
Output volts = Zener volts - Vbe drop of transistor.

Zener current varies due to the output pulling only a small change in base current. Therefore Zener voltage is fairly consistent.

I think there is no feedback in this circuit so it follows there can be no oscillation.

[AuroraB]

A1015 = 2SA1015, C1815 = 2SC1815...
a typical japanese way of shorting the transistor codes.
Nothing to do with the placement of terminals....

[argonrepublic]

I love this site. "3 seconds, politics aside....". That's very cool. Thanks for the help. I still don't get it but It'll make sense in a day or so. I have pulled all of the opamps and ICs , there are no zeners on this board so I am confused. What the heck is controlling these? I might wait a couple more days. I find when I patiently look at these circuits, I learn and get results ,which is happening. When I first started, I would recklessly probe, shunt and hardwire in attempt to make it work NOW. I did more damage than good.
Thank you all for education
Joe

[anatech]

Hi Joe,
As AndrewT suggested, it's only a transistor assisted zener diode. There is no feedback and therefore no active regulation.

What this does is reduce the current variations through the zener by the DC beta of the transistor. This is compared to the same thing using only a zener diode. Therefore the regulation, or variation of voltage caused by a current change is improved.

More complicated regulators use feedback to correct the output voltage. Voltage changes caused by current variations are reduced still further. Performance is greatly enhanced.

The main trick is to determine how much performance is needed. There is no advantage gained if the improved regulation from a more complicated circuit does not enhance the operation of the load, or circuit(s) that are powered from the reguator.

I don't know if that helps.

-Chris

[argonrepublic]

Everything helps. I am still confused because I have no zener Anywhere on my PCB.

[pinkmouse]

Can you draw what you do have?

[AndrewT]

Hi,
even a pic of the top and bottom sides of the PCB should let us reverse engineer the volt reg.

[Stocker]

A pair of resistors can serve for the voltage setting, just as well as a zener diode. So can a potentiometer. It is quite simple to get "about" the voltage you need from a single transistor.