This is playing, and seeing what is possible and practical. I bought a couple of blue LED voltmeters today along with a couple of toroids. I'll probably perf board the 555 schematic and see if it works as planned. I have one more major redraw on the 555 first though, I'll add a few more secondaries on the toroid transformer for the meters and see what it would take to make the VM into a reasonably accurate amp meter. Depending on the characteristic of this meter it may not work out.

 

Low parts count, playing with different approaches. In the end it doesn't matter if I use a pot instead of multiple resistors, and if it does I will have learned something.

For example, I may still never build this, but I'm thinking of a new (to me) technique where I use pine board plank for the floor of the unit, metal for the walls (and heatsink support) and a 3D printed plastic panel for the front. A combination of 1930's techniques and uber modern. I have a membership to Dallas Makerspace, might as well use it.

I suspect the panel meters I bought were a waste, they seem to use the power leads as the meter leads too. I'll play with em and verify that.

If you ever go to my albums you will find 100's (thousands?) of schematics, some of them are pretty lame (as in smoke generators). All part of the fun, which is learning new things.

Edit, yeah, the meters were a waste. One of them is bad, so I'll probably get a partial rebate and buy something else.

 

The switcher? Like I said, a commercial unit. They were pretty common around 2 years ago at a steal of a price from many sources. I suspect they will have short lives.

I asked because some fixed switcher can be made adjustable depending on which IC they have used. And also depending on the construction it may also be possible to tweek the current regulator circuit to make your high current adjustable power supply. Of course it may be that you will not be able to adjust the voltage as low as 0.0. But for me that is not something I realy need. But I understand your approach in order to get 0.0 out. In order to do that you have to make the internal reference adjustable. As the output inn that kind of regulator. Can not go below the reference voltage assuming normal operation

<snip>

 

Bill, a thought about your source supply. Many low cost switchers have a minimum load requirement of around 10%. Darn those transformers.

ak

 

Bill, a thought about your source supply. Many low cost switchers have a minimum load requirement of around 10%. Darn those transformers.

ak

There will be some loading just as a matter of course. It remains to be seen how much the 555 circuit will load things down.

There is definitely a try it and see approach to this.

As much for metering as anything I plan on limiting the current to 5A, which gives me an amp (which I do not plan on using) to play with.

When I am done with the individual schematics and preliminary tests I'll draw up a final schematic with all the bells and whistles included.

 

OK, what I am hoping is my final revision of the 555 section.

I'm going to use precision measurements of the wire, by reeling out 12' measured by arm length. The 2:1 will be 6' lengths, and the 2:1.5 will be 9' lengths. Real precision measurements and counts.

I do have some concern about the fact there will be wires going to the two sets of transistors on the voltage regulator and the current regulator, which will be a noise catcher and potential instability for sure. I'll try to keep them as short as possible, and just try it and see. Since both of them are emitter followers a small cap on the base would probably suffice, if needed.

 

Now to wind a transformer and start slinging solder around...

The transformer will be 6' on the primary, 4' on secondaries #1 and #2, and 6' on secondaries #3 and #4. I'll probably use hot glue to attach it to the board.

Bill of Materials
Qty Description
.1 .. U1 LM555
16 . SD1-9, S10-16 1N5817 Schottky Diodes
.1 .. VR1 12V Zener Diode
.1 .. XFMR1
.1 .. R1 4.7Kohm
.6 .. C1, C2, C6, C8, C10, C12 0.1uF
.2 .. C3, C4 10uF
.4 .. C5, C7, C9, C11 100UF

.

 

How is the ratio of transformer of 24V?
If the Vcc of left side is 12V, for a 2:1 ratio then the secondary output should be 6V, is that right?
Or the ratio is 1:2?

 

Yes, but you came in late on this thread.

The 24V is a fixed switching power supply. The 5 V (the 555 will output 10V P-P) will add to the 24V to create 29VDC. For the rational read the first post.

 

Thinking about it, if I do a second design on this section I'll do what AnalogKid suggested in post #8 (schematic displayed in post #11). I have wound the toroid, but due to the thickness of the wire I have dropped the primaries to 4' and the meter windings to 6'.

I'm going to build it and see how it works, I'm kitting parts at this point.

 

OK, almost finished with the 555 prototype, which brings up a project I've had on the back burner for years. That is an Electronic Power Supply Load. I've pulled an old schematic I made and polished it a bit. This is what I came up with:

I've also made a closer to final schematic of the variable power supply. Still have lots of prototyping to do first, but this is what I was thinking of:

Thoughts?

 

Regarding the dummy load, you current sense resistors are in series so they won't give accurate current:voltage sensing.

If you rewired the switch so it only connects ONE current sense resistor in each switch position, the resistors can be 10, 1 and 0.1 ohms exactly, giving correct current:voltage reading.

 

Notice the calibration resistors, labeled test select? With a transistor gain in the neighborhood of 125K very little of the base current is going to be involved, so after calibration it should be good enough.

The thing I'm working on is figuring out how to mount a small heat sink without melting plastic on screw ups.

 

Bill - I'm pretty sure another diode is needed in each charge pump between the catch diode and the output filter cap. For example, another 4148 between CR1 and C9. I've never simulated the circuit without it, but without the extra diode aren't you dividing the pump charge between the two caps in series, lowering the output voltage and increasing ripple?

ak

 

I want less then half the voltage of the 555 power supply. At 1.5KHz the caps should filter well enough. I'm thinking of adding a white or blue LED on the output as a 3.5VDC regulator. I want just enough voltage to get the op amps off the power supply rails. It is why I mentioned some prototyping needs done though.

 

6Vp-p ripple.

ak

 

Instead of a diode to ground just eliminate D1 and add D2, a classic diode rectifier.

Thanks for keeping me honest.

 

Except that the output of a classic diode rectifier always is *less* than the peak value of the input. In this case your input is 12 Vp. Without the catch diode there will be no boost above the 24 V. The output will be the average value of the input, around 6V.

ak

 

Your simulator is missing an important component, even a DVM has 10MΩ resistance. I may need to add something between the +24VDC and Vcc (the LED comes to mind), but there will be a resistance there.

I'm going to move the discussion about the Electronic Load back to Electronic Loads.

 

I'm back on this thread again.

It occurred to me that I could use much smaller heat sinks with a preregulator, a switching version like this...



This is a preliminary drawing, not quite ready for prime time. The idea is to keep the voltage going into the series pass transistors just a couple of volts above what the actual output is, to lower the wattage on the transistors themselves.

Then there is the external voltage source, which I will be testing on a breadboard, to power the op amps.






I'll probably replace CR2 and CR4 with resistors to drop the voltage some. I can always add zeners across the extended outputs to help regulate the voltages.

This is a concept circuit only, the final design will be much different.