I did have a schematic tht uses an OPAMP as a comparator to switch Tx transformer to a higher voltage when output rises.
Just dunno where I had it stored.
I believe LM393 comparator is a much simpler approach to sense the output and activate ur transistor switch to switch the second Tx

Try googling over voltage comparator. You will find plenty.

PS. If you plan to switch the Tx make sure the capacity voltage is properly rated and high capacitance to store discharge for a few ms.

I found in my bench drawers the TL072 and planning to use it as voltage comparator...



will do a research for how it could be done.
Any ideas or suggestions are of course welcome since i have never used an opamp as a voltage comparator

 

I found in my bench drawers the TL072 and planning to use it as voltage comparator...
.............................
will do a research for how it could be done.
Any ideas or suggestions are of course welcome since i have never used an opamp as a voltage comparator

You can use an op amp as a comparator by connecting one input to the reference voltage where you want the op amp to change states, and the other input to the varying signal voltage.
You typically want to add a resistor from the output to positive input to add some hysteresis and avoid oscillations at the trip point.
Note that the input voltages must be within the common-mode voltage rating. For the Tl072 that's no closer than 4V of the plus and minus supply rails (for example with +/- 15V rails, the input voltage range is +/- 11V).

What do you want to do with this comparator?

 

I managed to solve the issue of Voltage adjustment by replacing the potentiometer with a
multi turn:


View attachment 74687
Now the voltafe adjustment is Very Very smooth
I like this pot alot...

My 50V/4A liner power supply was using LM723, the power is ok, but I don't like the pot and plan to buy the pot as you, and I didn't to do that, I were used two pots to adjust the voltage, although the voltage resolution doesn't like your power, but there was a good benefit, that is to set one pot to 5V, and another pot to adjust the voltage.

 

Try to find LM393 or even 339.
Will make it a hell lotta easier to make a comparator than an OPAMP

 

Well i picked myself the LM 393 as friend above said and will start the experiments this afternoon

For reference voltage i will use this switching 5V 2A little power supply that will be used also for the usb supply in front panel of the case

 

Time to Google !!

For reference you need a Resistor voltage divider. Much easier u know

 

Sorry i did not find the time to continue the project

I have in mind something like the below circuit.
Have never done this before with lm393.

 

I have been trying to simulate the circuit to LTspice.
The Resistors values are for reference









I don't have any expirience with ltspice and althought i managed to upload LM393 from this link http://www.ti.com/product/lm393 and run the simulator of this circuit i don't know if this is ok

To upload LM393 i did the below from this very helpful post:

http://forum.allaboutcircuits.com/threads/importing-models-into-ltspice.36456/


1. On the link you posted, scroll down to the PSpice model, unzip the folder, and open LM339_5.1 with notepad. Save the file in C:/program files/LTC/LTspiceIV/lib/sub as LM339.sub. Change "save as type" to "All files".

2. If LTspice is already open, close and then reopen it.
3. Open a new schematic window (Leftmost icon on toolbar).
4.Click on the component icon (the AND gate on the toolbar).
5. Double-click on [Opamps].
6. Scroll all the way to the end and select opamp2.
7. Click OK.
8. Left-click to place opamp2 symbol on schematic.
9. Right-click on symbol to open Component Attribute Editor.
10. Left-click on Value.
11. In the edit window that says Value = opamp2, change opamp2 to LM339. In general, the value you enter here must be identical to the subcircuit name in the subcircuit file. In this case, that line reads
.SUBCKT LM339 1 2 3 4 5
12. Left-click on the .op icon (rightmost on the toolbar). This is the spice directive icon .
13. Type .lib LM339.sub in the window. Left-click on OK.
14. Place this spice directive on the schematic by dragging it to where you want to place it, and then left-clicking.
15. You are now ready to place and connect other components before simulating.

Here is my ltspice file for circuit


Can someone more experienced help ?

 

I can see the 0-30V input but I am confused with the 5V reference.
I can simulate but will take some time.
I need the voltage value you desire to switch the relay.(comparator)

 

I can't wait to see this thing done ... Keep up the great work..

 

If R4 is intended to provide hysteresis it needs to go from the output to the non-inverting (+) input. As shown both ends are connected to the plus supply.

 

I can see the 0-30V input but I am confused with the 5V reference.
I can simulate but will take some time.
I need the voltage value you desire to switch the relay.(comparator)

I have one separate 5 Volt switching power supply 2A and planning to use it as reference voltage for LM393

About the voltage value from the 0-30V for the comparator must be at 14,3V
This because i am using a 12V Transformer and with rectifier it reaches about 14.5 V so must go to second Transformer above 14,5V

Thanks alot for your effort.

 

Your circuit was quite strange, did you see two pins of R4?

 

I can't wait to see this thing done ... Keep up the great work..

I wish i had more time for this thing...
Thanks for your kind words

 

If R4 is intended to provide hysteresis it needs to go from the output to the non-inverting (+) input. As shown both ends are connected to the plus supply.

Your circuit was quite strange, did you see two pins of R4?

Is this ok ?

 

Is this ok ?

View attachment 74982

The non-inverting input of op amp already has a voltage from R1,R2 voltage divider, when the input voltage get in, maybe they will have a little conflict.

So I just thought that if you want to using V1 to be the input voltage, maybe you can take R1,R2 away.

 

Have changed the circuit as below.
When i run it and use the red voltmeter to take measurements i only have 1v ?
What have i done wrong? I think it has to do with ltspice config...

 

About the voltage value from the 0-30V for the comparator must be at 14,3V
This because i am using a 12V Transformer and with rectifier it reaches about 14.5 V so must go to second Transformer above 14,5V

I think you want the comparator to look at the output of the supply and switch to the higher voltage transformer when more voltage is ask for.

[/QUOTE]

 

Have changed the circuit as below.
When i run it and use the red voltmeter to take measurements i only have 1v ?
What have i done wrong? I think it has to do with ltspice config...

View attachment 75124

There are still have two problems in the circuit, the one is that the V2 connected to Ground, the GND wire should be remove, and the other one is if the V2 is the input voltage then the Vcc for op amp connected with the input voltage are the same, the output voltage will be affected by the input voltage, unless the input voltage only has a tiny vibration.

 

Play with this one.