Hi,

Oh sorry to hear that. Are you in the USA or no?

The first thing that comes to mind since the range of resistance is so large, is to couple an LDR with an LED, making the LED light temperature sensitive with a sensor. You can get a wide variation in resistance with an LDR (Light Dependent Resistor) so the main chore would be to get the LED light output to vary with temperature enough to drive the LDR in the intended fashion. Perhaps using a thermistor or temperature sensor with analog output to drive the LED perhaps with an added op amp.

Did you really mean 1500k Ohms or did you mean 1.5k (1500 Ohms). 1500k Ohms is really the same as 1.5 Megohms which is quite high.

sorry I mean 1.5K ohms. In USA

 

A. Try file: Landscape-lights-3-mod.asc attached here.

B. Also, you can upgrade Library of your LTspice from here:
http://bordodynov.ltwiki.org/

Great thanks. Whats the reason to connect R3 to collector of Q6 and Q7? Why not connect R3 directly to +13V power supply?

 

sorry I mean 1.5K ohms. In USA

Oh ok, just wanted to be sure. That would be a little easier then. Getting to a perfect 0 Ohms would require a little more thought though. Getting to 10 Ohms would be more practical.

 

Oh ok, just wanted to be sure. That would be a little easier then. Getting to a perfect 0 Ohms would require a little more thought though. Getting to 10 Ohms would be more practical.

Close to 0 ohms but 10 ohms is too sensitive.

 

Close to 0 ohms but 10 ohms is too sensitive.

I mean the stretch would be 10 Ohms to 1500 Ohms.
Is 10 Ohms too high for the lower end?

 

Great thanks. Whats the reason to connect R3 to collector of Q6 and Q7? Why not connect R3 directly to +13V power supply?

You are designer of this device. I am helper only.
You can connect R3 to any node of circuit, you want.
For me, it is better to connect R3 to collector of Q6 and Q7,
because overall deviation of LED current in this case is only 2 mA (99.8-97.8).
When R3 is connected to +13 of V1, overall deviation is 4.3 mA (98.1-93.8).

 

You are designer of this device. I am helper only.
You can connect R3 to any node of circuit, you want.
For me, it is better to connect R3 to collector of Q6 and Q7,
because overall deviation of LED current in this case is only 2 mA (99.8-97.8).
When R3 is connected to +13 of V1, overall deviation is 4.3 mA (98.1-93.8).

Where can you purchase for cheap these two parts that you show in your circuit that matches what you model in circuit: Mbrd340t4 and TL431AB?

 

Where can you purchase for cheap these two parts that you show in your circuit that matches what you model in circuit: Mbrd340t4 and TL431AB?

T L431 50 pcs/lot, price $0.99/lot, free shipping.

I do not recommend to fabricate circuit with Schottky diode - that circuit is good for demonstration only.



ADDED:

You mean the real schoktty diodes wont behave like one jn simulation? I was leaning towards schkotty diodes circuit?

Yes, it will not work as in simulation, because it depends on Vbe of Q2, Bf of Q2, Vf of D1.

 

T L431 50 pcs/lot, price $0.99/lot, free shipping.
I do not recommend to fabricate circuit with Schottky diode - that circuit is good for demonstration only.
View attachment 359337

You mean the real schoktty diodes circuit wont behave in real life like one in simulation? I was leaning towards schkotty diodes circuit?

 

Humans do it so:
View attachment 359006

You have TL431AB LTSpice model? I dont have it.

 

You have TL431AB LTSpice model? I dont have it.

Many-many models you need and will need in future,
are in @Bordodynov library: http://bordodynov.ltwiki.org/
Install them to your LTspice.

 

You have TL431AB LTSpice model? I dont have it.

Hi,

There is also a behavioral model that allows you to understand the operation intuitively if you are interested. The operation of this device is very simple. It's basically a low power shunt voltage regulator.

 

I am just curious why wouldn't 100mA flow thru D5, Q5 in this scenario below circuit? Attached is the .asc.

 

Now, you do need a means of programming it, but those can be had for very little, too. I've seen basic ones for under $10.

You don't even need a programmer anymore:

https://www.microchip.com/en-us/development-tool/DM182030

USD$10.

 

I am just curious why wouldn't 100mA flow thru D5, Q5 in this scenario below circuit?

Change value of R3:

 

Change value of R3:

View attachment 359860

It works great for constant dc supply of 12.5vdc. However when I switch from 9V to 4V it gives lower than 100mA???

 

Hello,

With 4 volts supply, the headroom to regulate the current is to small.

Bertus

 

It works great for constant dc supply of 12.5vdc. However when I switch from 9V to 4V it gives lower than 100mA???

Your circuit works exactly as you design it.
If do not like, redesign circuit for your needs.
Or use circuit from post #20.

ADDED:

Ok i was just trying to improvise some things diode can give constant volt as well.
I have no idea how you come up with 27.5k value wither.
Instead of U1 can I get schoktty diode connect it across r8 and change resistance to get 100mA?
Will that work for all the voltages shown in post #20 snapshot?

No. It will not work at all.

Did you already spend $1 for 50 pieces TL431?
Offer ends Dec 4:

 

Your circuit works exactly as you design it.
If do not like, redesign circuit for your needs.
Or use circuit from post #20.

Ok i was just trying to improvise some things diode can give constant volt as well. I have no idea how you come up with 27.5k value wither. Instead of U1 can I get schoktty diode connect it across r8 and change resistance to get 100mA? Will that work for all the voltages shown in post #20 snapshot?

 

I am just curious why wouldn't 100mA flow thru D5, Q5 in this scenario below circuit? Attached is the .asc.

View attachment 359856

You have to show some measurements like what is the collector current for Q4.
If Q4 is turned 'on', it will shunt most of the current from R3 to ground and so Q5 will always be turned 'off'.
You also have to show the power supply source that connects to R3 and D5.

What is that current source B1 doing. It's only function would be to pump current through V2 in that circuit.