Apparent C.O.P. of 1.413469133935024 ...

[broli]

http://www.radio-electronics.com/info/circuits/diode_current_limiter/power_supply_current_limiter.php

[DeepCut]

Thanks broli i'll try that tomorrow.


Gary.

[gyulasun]

Hi Gary,

I fully agree with broli to use a voltage regulator against the run-away situation.
Would like to suggest an off-the-shelf regulator that includes all the neccessary circuits shown in the link, it is produced by most big analog IC manufacturers. It is known as the three terminal 7818 linear voltage regulator, like LM7818, MC7818, uA7818 etc. Gives out exactly 18V at any current up to maximum 1A, seems fully cover your input requirement of DC 18V and .15A current.
Here is a link for a data sheet at random, out of many:
http://www.datasheetarchive.com/MC7818-datasheet.html 

One thing to consider:  linear voltage regulators waste power because of the voltage difference between their input and output. Just think about it: they need a minimum of 2.5V higher voltage than the output 18V to be able to work correctly, they are designed like that. (there are special low drop out regulators too that need only .2 or .3V voltage higher than the output but now you have 29V-19V=10V difference (when you load the output with 220 Ohm resistor) and that is what counts now. So the regulator will have a 10V times .15A=1.5Watts loss in heat form inside it, use a small meatal heat sink to defend it from overheating. You will have to consider this loss of course when estimating total power, later if looping is a success, we can discuss how to reduce this loss.
The 7818 regulator IC (any make) can work with a maximum of 35V so your 29V is perfect input voltage for it.
I suggest using still at least a 360 or 420 Ohm loading resistor across your 29V output and then connect the input of the 7818 regulator IC and only then close the loop  i.e. to connect the 7818 output to the input of your circuit, to replace the power supply.  Use a diode 1N4001 or similar in series with the positive output of your power supply voltage to separate  the 7818 output from the power supply voltage. This way the two outputs cannot get connected in parallel, the diode blocks the supply to load the output of the 7818. Hope this all is understandable.

Gyula

[Omnibus]

@DeepCut,

I would also like to know how you achieved this. Obviously it is some part of a research you've discussed elsewhere which I've missed. Could you please elaborate?

[DeepCut]

Gyula, thankyou.

I will grab this one tomorrow :

http://www.datasheetdir.com/TS7818CZ+download

The specs seem appropriate but please correct me if i'm wrong.

I'll set that all up tomorrow and then post results.


Thanks, Gary.