Hello,

I am trying to derive an equation for this regulator, so I can put them on the excel file. Please refer to the attached image.
On the case that D1 is on (zener breakdown mode), and Q1 is forward-active, I derived the equation of iBB and found it strange.

From the equation, as RL goes higher, iBB becomes lower. I have simulated this circuit on LTSpice and got the result the other way around.
However, I checked the equation I derived step-by-step, and found nothing wrong.

Could you please help me check it?

Best Regards,
BlackMelon

 

Where is causing Rin?

 

Rin is in series with Vin. Please see the circuit.

 

hi BM,
Please post your LTS asc file, we can compare results.
E

 

hi BM,
Please post your LTS asc file, we can compare results.
E

Here is the .asc file.

 

hi BM,
First question would be why have you chosen such high values for the resistors.?
The Zener current is in the pA range and the Load current uA,

Rin serves no purpose

E
Update:
You are driving a 13V zener with a 12V source voltage, how is that going to work.?

 

hi BM,
Run this version of your circuit.
E

 

Oh Dear!.... This is quite embarrassing but I think I know it. I put +12V at the input voltage, while I use 13V zener diode.
Ps. I have just also simulated at R1 = 1k, Rin = 10 ohm, RL = 10 to 30 ohms at get the same relationship as the equation (and your curve). Thank you very very much!!!! ^_^

 

And next time I really have to check the biases current. I mean current through the diodes and the bases, see if they match the curves on the datasheet and be able to turn the device on. May be last night I was too drunk. = ='

 

hi.
OK, so derive your regulator equations, see how they match with your simulation, let's know the result.
E

 

Rin is in series with Vin. Please see the circuit.

I see Rin.
My question was, what is its purpose, why is it there?

 

Rin serves no purpose

Actually I think it does. It represents the real world output impedance of the supply; eg the internal resistance of a battery or the windings of a generator, or even the dynamic impedance of a power supply (ΔV/ΔI). Though 10ohm is much higher than reality - .01 - 0.1ohm is more realistic.

 

hi guys,
In the TS's own words...
May be last night I was too drunk. = ='

E