Bridge Rectifier with Zener Regulator load current doesn't change even when load resistor is replace

Status
Not open for further replies.

Thread Starter

xso111

Joined Oct 12, 2017
24
trying to build a DC supply using a zener regulator with
1k ohm load
1k ohm series resistor
3300uF cap
1n4728a zener diode
x4 1n4002g rectifier diode(0.58V threshold)
12V secondary

schematic


in the load with 1k ohm resistor i'm getting 2.6V, and 0.26mA current(is this current too low?) then i changed the load resistor to 100ohm and the current didn't even buldge it is still 0.26mA.

isn't the load current supposed to be I = V / R? so my load current with 1k ohm resistor should be 2.6/ 1000 = 2.6mA, not 0.26mA like what i'm measuring.
 

dl324

Joined Mar 30, 2015
12,911
How is this different from your other thread?

How are you measuring current?

The load on a zener regulator should be less than a tenth of the zener current. Why are you still trying to operate the zener at such a low current?

Clipped, reduced whitespace schematic:
zenerClip.jpg
 
Last edited:

Thread Starter

xso111

Joined Oct 12, 2017
24
How is this different from your other thread?

How are you measuring current?

The load on a zener regulator should be less than a tenth of the zener current. Why are you still trying to operate the zener at such a low current?

Clipped, reduced whitespace schematic:
View attachment 139201
sorry for being persistent.

the problem i had with the previous thread was i'm getting a negative current when measure(bought a new DMM and the negative current was solved).

if i may ask can you please elaborate "The load on a zener regulator should be less than a tenth of the zener current"

my professor tasked us to just make a working Voltage regulator
 

dl324

Joined Mar 30, 2015
12,911
if i may ask can you please elaborate "The load on a zener regulator should be less than a tenth of the zener current"
Zener voltage varies with current, especially when you're operating close to the knee. If the load causes the current to change significantly, the zener voltage will change.

A rule of thumb we use is that load current should be less than a tenth of the zener to minimize zener voltage variation. And you need to be operating at a current well beyond the knee so you're in the low impedance region.

This is why other forms of regulation are better.
my professor tasked us to just make a working Voltage regulator
He should have given you some specifications to shoot for - such as load regulation.

This is a project to you, but to us it's homework, so this post should be in the Homework Help forum. We know not to just give answers there...
 

be80be

Joined Jul 5, 2008
2,051
It's hard to say but if you use dc voltage to sim because i cant see the transformer setting
you get a better idea
Screenshot from 2017-11-12 14-07-35.png
 
Status
Not open for further replies.
Top