Bench Suppy for Young Experimenter

RE: Bench Suppy for Young Experimenter

D_Hersey — Wed, 17 Dec 2014 03:19:09 GMT

This paper indicates that tempco is a fn of current to the degree that all signums can be had this way:

http://documentation.renesas.com/doc/products/diode/rej27g0012_zener.pdf

1.3.2

This could be your load:

http://www.ti.com/lit/ds/symlink/lm134.pdf

RE: Bench Suppy for Young Experimenter

Problemchild — Wed, 17 Dec 2014 00:42:23 GMT

This is a very nice project well executed "old school" PSU project

The idea that you can make these things your self must of impressed your Grandson [View:/resized-image/__size/16x16/__key/commentfiles/f7d226abd59f475c9d224a79e3f0ec07-3bb389fe-a423-4526-9383-3bd2c6b067d3/8765.contentimage_5F00_1.png:16:16]

RE: Bench Suppy for Young Experimenter

clem57 — Tue, 16 Dec 2014 20:16:43 GMT

See John,

Such a simple idea can cascade into such complex topics...[View:/resized-image/__size/16x16/__key/commentfiles/f7d226abd59f475c9d224a79e3f0ec07-3bb389fe-a423-4526-9383-3bd2c6b067d3/contentimage_5F00_3890.png:16:16]

clem

RE: Bench Suppy for Young Experimenter

D_Hersey — Tue, 16 Dec 2014 17:56:21 GMT

When you start out with op-amps, you should also imagine how the circuit would be configured with Norton-amps.

http://www.ti.com/lit/an/snoa653/snoa653.pdf

A fellow designer I knew who had a slight tendency toward pontification, which he had earned the right to, through dint of his evident skills stated: "Build Last! Is there a way we can alter our behavior so as to not need this thing we are proposing? How was this problem solved in the classic era? What are the mechanical solutions? The electro-mechanical ones? What was the approach in the thermionic era? How would we do it in linear? How would we do this in jellybeans? In code for a Von Neumann architecture? For (coarse and fine-grained) parallel architecture? Can magnetics play a role? What are the costs? What are the environmental costs? What is the structure of the end-game? Is there a market? Can we serve this market without impediment? What would the possible forms of Pyrrhic victory appear like?"

I'm sure, if March wasn't speaking decades ago, he would have thrown in, "How would we train a programmable logic to our purpose?"

One of the challenges in design engineering is to learn to vet the alternatives without prejudice.

RE: Bench Suppy for Young Experimenter

D_Hersey — Tue, 16 Dec 2014 17:22:27 GMT

What a nice box!

It is hard to demarcate the boundary to the rococo with these things. I had a philosophy teacher use an ancient Greek term for 'tumor doctor' to call the process by which an artist quits working on a particular work. If I ever find that word again, I will be elated! He held that if you kept improving something ad infinitum you will come to sink the project. That said:

You could put PBs by the meters that would verify that the needles weren't stuck. They would mid-scale the meters when depressed.

You could have an OVP crowbar:

http://www.ti.com/lit/ds/symlink/lm431.pdf

[fig 20.]

For current-sense, we could put a 10 - 25 seimens conductor in the collector leg of our power Q. We would be neglecting our base current contribution, to fix this we could put an NPN in front of the power Q in darlington configuration, or we could change the power Q to a N MOSFET on a generously-scaled heat spreader.

This would generate a (in the case of the ten seimens conductor) 100 mV drop from the top at the ampere of flow at which you want to clip. You need to use a fuse of slightly greater current capacity so it doesn't trip first.

To detect this you would need a RRIO comparator. There could be a switchable reference from the top to set the trip point. Upon the crossing of the comparator's threshold, we trigger a F/F which 1) Floods the inverting terminal of the op-amp with current so as to saturate it and shut down (or by another method) the output stage. 2) Turns on a red light. The other side of the F/F is a PB that won't need much debouncing. You might need to provide some dynamic de-sensing (likely a capacitor) to not be hyper on spikes. Of course, provisioning will have to be made to reset the F/F on power-up.

Use comparators or si-gate CMOS for the F/F and it won't need a local regulator.

RE: Bench Suppy for Young Experimenter

Robert Peter Oakes — Tue, 16 Dec 2014 14:47:43 GMT

I like it, I recognize the basis of the circuit, nice to see you applying what we are learning on our journey together, a nice addition might be a current limit, not sure there the pot would fit though [View:/resized-image/__size/16x16/__key/commentfiles/f7d226abd59f475c9d224a79e3f0ec07-3bb389fe-a423-4526-9383-3bd2c6b067d3/6763.contentimage_5F00_1.png:16:16], this way he can protect his projects when not sure of the current requirements

Well done

Peter

RE: Bench Suppy for Young Experimenter

shabaz — Tue, 16 Dec 2014 12:25:20 GMT

Nice! I bet there are not many lucky 8-year olds with equipment with analog meters : )

RE: Bench Suppy for Young Experimenter

gadget.iom — Tue, 16 Dec 2014 11:04:33 GMT

Somehow I already knew they'd be Analogue Meters [mention:f80b53cee57c44bc9d7c577d07d7c791:e9ed411860ed4f2ba0265705b8793d05] [View:/resized-image/__size/16x16/__key/commentfiles/f7d226abd59f475c9d224a79e3f0ec07-3bb389fe-a423-4526-9383-3bd2c6b067d3/contentimage_5F00_1.png:16:16]

RE: Bench Suppy for Young Experimenter

D_Hersey — Tue, 16 Dec 2014 10:31:14 GMT

Let me continue my Illinois chauvinism by recommending PREM brand transformers for this sort of thing. They make a good-quality transformer, are willing to vend small quantities, have good prices and customer-service.

RE: Bench Suppy for Young Experimenter

D_Hersey — Tue, 16 Dec 2014 10:17:28 GMT

Awww John! I got a coupla grandkids, Pops says they are just a little young yet for this sorta thing, can hardly wait. 'SCRATCH' is a popular thing for kids on the computer these days, I'm told.

Pilot light might be nice. Darn! Its nice already. You should get a copy of the Motorola Zener Diode Manual. It is written more at a practical rather than theoretical level, quite breezy and informative, comprehensive but brief. Now, since my copy is at my other locale we will have to rely on my dimming powers of recall: Clarence Melvin Zener*, a Saluki, discovered two types of Zener, a Zener-Zener and an Avalanche Zener. The charge carrier in the Zener is likely to make it through the device, in reverse breakdown mode, as a soliton. But in the case of the higher-breakdown avalanche zener, the mean free path of the charge carrier is longer than the channel length, so a charge carrier is likely to collide with another, dislodging it from the lattice, on the way. Turns out the significance of this (aside from a discussion of noise) is that the two varieties have opposite signums of their respective tempcos!

What they will show you in the book is that you can stack a 6.2 V Zener with a pair of silicon diodes operating in forward-mode. You would have to make a slight adjustment to your voltage ladder to accommodate the new reference, perhaps. But through the range of Brewers' season to Packer's** season and beyond, your g'kids device would remain stable, indoors or out! This is because the various tempco's would cancel each other out so the reference won't drift. The manual is full of other great tips and data sets that you could use to improve this and your other circuits as well.

==========

*ZENr

**Everyone down here, alas with a lump in their throats, is rooting for the Pack now!

==========

I see the pilot light now. Woke up bleary.

RE: Bench Suppy for Young Experimenter

mcb1 — Tue, 16 Dec 2014 07:56:38 GMT

Nice work ... and REAL meters.

One minor suggestion is an Output switch to instantly kill the volts, and allow setting before applying.

Mark

RE: Bench Suppy for Young Experimenter

clem57 — Tue, 16 Dec 2014 01:24:54 GMT

John,

Nice touch to add the meters! Your grandson should be proud.

Clem

RE: Bench Suppy for Young Experimenter

michaelwylie — Tue, 16 Dec 2014 01:16:02 GMT

Love the Grandpa author on your schematic. Nice build.