A diode can make a good temp sensor, true enough. I use it as a quick and dirty reference. If you need precision use something like a LM317 with out the voltage programing resistors.

I'm in the process of drawing up a protoboard design for the 7555 regulator.

 

Hello,

Did you notice the switching powersupply in the LM317 datasheet?

Bertus

 

I've seen it, trying for my own approach though.

Some of these experiments will wind up in the ebook, maybe.

 

..........................
A 180V P-P square wave at 1A would translate to 24V at 7.5A. A simple circuit such as this should suffice.

..............................

I have my doubts about that circuit. It will have a large DC component in the primary which will tend to saturate the core. The drive should be push-pull to minimize that (tapped primary or bridge driver).
And since the wave is uni-directional for the circuit shown you would only need a single rectifier at the output.

 

Given that you are winding your own transformer, anything that can be done with a single secondary winding and a diode bridge can be done more efficiently with a (different) center-tapped winding an only two diodes. But that works only if the driving impedance of the primary is the same in each electron flow direction; in other words, a half-bridge or full-bridge primary circuit. For a single primary side drive transistor, you are limited to the flyback and forward topologies (without getting into SEPIC, Cuk, resonant, and other more esoteric forms).

ak

 

Well here you guys go.
The full service manuals including schematics and parts lists for both the Lincoln SP-100 Welders (Constant voltage source) that used a simple primary side phase angle based voltage regulation on a iron core 50/60 HZ transformer and the bigger Invertec V300-I (Constant Voltage /Constant Current source) which is a full 300 amp inverter based unit.

 

Just some notes...

As power increases, the core gets bigger and the number of turns gets lesser.
A toroid core acts just like an EI core in its magnetic limits and turns ratios.
The higher the switching frequency, the smaller the inductance required, and the smaller the core.
It's impossible to saturate an air core inductor, but the physical size could become a problem.
You can wind your wire on a long stick and thread the stick through the hole in the toroid.
It is never fun to wind a toroid, but they do have advantages because you will never see grain oriented EI's running at 50KHz.

 

Since this is more of a series of experiments I'm not too worried about finicky details.

A thought about LM393 direct drive did occur. I'll post it when I sketch it up.

 

My latest brain fart...

I may substitute 10Ω for R2. It is to help prevent shoot through.

Edit: A minor redraw

 

393 is open collector. How you gonna pull the gate up with an open collector?
While we're at it...that mosfet is going to play, "source follower" if the output voltage gets anywhere near the supply voltage.

 

one of the latest changes to smps I have found is to ues a double smps. the first takes the rectified line voltage to some other value of dc, and feeds a second which is regulated by feedback from the output. used in some supplies from PULS and others. the first ones I found used a first smps output of around 600 volts, which was sent to 6 sockets you could plug in individual modules to generate what ever your voltage was. around 600 watts altogether. also, I took apart a small wallwart ad found a switcher inside with no voltage feedback at all, 5 volt output (hopefully, it turned out) it actually ran 5.45 volts no load.

 

393 is open collector. How you gonna pull the gate up with an open collector?
While we're at it...that mosfet is going to play, "source follower" if the output voltage gets anywhere near the supply voltage.

Look again, it is a push pull configuration. The open collector on U1b goes to ground, the open collector on U1a drives Q1, which goes to Vcc. You don't have to have a resistor, it is just standard.

The loading for U1a is the Q1 B-E junction.

 

Oops. I thought U1A was an over-voltage gate dump. My bad.
I simply read it badly.

 

This configuration will have applications for other regulators I have made over the years. I feel I have solved a minor technical problem with the LM393 drive.

 

@BillMarsden, you don't by chance have a boost circuit you would share?

Here is one I have been playing with. It's not to big, but maybe fun to build.
The 555 is just an oscillator to generate a triangle wave at around 45Khz.
C2 is a poor mans soft start and holds the FET off until the initial charge of the output cap so the inductor doesn't saturate.
The inductor is a low cost drum rated at about an amp.
Since at low load the switcher runs in discontinuous mode it benefits from the snubber C5, R10 to keep the high frequency noise down.
Q1 provides the feedback to lower the duty cycle when the voltage rises above the set point.
It needs a FET with low gate charge so the 393 can drive it.
I used a pot for U3 because I was playing with various voltages. I settled on 15 volts at 100 to 150 ma, so set it for about 18 to 20 volts with Q1 disconnected and 150 ma. load.
U4 is the output adjustment pot.

Maybe if you talked real nice you could get Bill to build it - I don't have the parts.

 

Thank you ronv

 

My latest brain fart...

Could this use a diode to ground at the point where the source of the MOSFET meets L1 (anode to ground)? It would be a shame to build a switching regulator and waste the energy built up in the inductor.

 

...that mosfet is going to play, "source follower" if the output voltage gets anywhere near the supply voltage.

I think it's ok. I thought something like that at first, until I realized he was using a P-channel MOSFET.

 

The PFET is good, but the source needs to go to Vcc so it can be turned on with a negative on the gate.
Good catch on the diode.

 

I've been putting some thought into power supplies, especially the high current variety. Modern tech has gone over to switchers for the most part. They are small, lightweight, and do the job.

Note: some of the following circuits I'll be discussing only pass muster because they do have a isolation transformer. The voltages and currents are NOT safe, and should be handled by experienced hobbyists.

One of the secrets for switchers is the use of torrid transformers instead of the bulky 50/60Hz units used in many wall warts. The latter are easy to use and pretty safe, but they are big chunks of iron and heavy. Torrid transformers can handle some respectable currents, but not at low frequencies.

So we need a circuit to make a high frequency medium current feed for a torrid. Not too difficult, fully rectified AC with nominal filtering will make 180VDC. Again, if this voltage were to be used directly this thread would be shut down in a heart beat, but the plan is to use it in a sealed circuit.

I am a math brick, to steal a phrase from a friend. I'm debating what the best frequency and windings for a home brewed torrid would be. A 180V P-P square wave at 1A would translate to 24V at 7.5A. A simple circuit such as this should suffice.

Regulation could also be accomplished by simply adding an optocoupler to turn the oscillator on and off with a simple comparator.

Which brings me to regulators, a different subject but related.

My first though probably will not work, though I am tempted to build it and see. This is because of one of the odd problems with MOSFETs, where they require a really substantial drive current to turn them and off quickly. The circuit to turn this on is adequate, but not so for turning it off. 10KΩ will probably not be enough.

To solve this problem I would probably use something like this design.

This is not the first thread I have done on switching power supply regulators, but I have a bit more experience under my belt. Some of this may wind up in the ebook, after experimentation. This is where this project I showed would come in handy.

Project : Electronic Load

Basically I'm putting this thread out for discussion and questions. I'm always willing to learn, though as I get older it does seem harder. I joke with my son, my Alzheimers is firmly under control. For some reason he doesn't find that funny.

Hi there Bill,

I guess i am seeing this thread a little bit late for some reason, but i'd like to add a few notes that might help.

First, if you take apart a modern regulated wall wart you will find a working circuit of the type you are developing. The only difference is that they use a ready made chip that is made for these offline switchers. The chip will have a power transistor built into it already. The transformer may not be a toroid, but it is still the same basic high frequency type, and it's small relative to the power also unlike the 60Hz variety.
So you might get some ideas if you take one apart and look at the circuit and take some waveforms with a scope.
There are also schematics online, and if you cant find one i'll try to dig up a part number that will have a data sheet that will have one.

What i dont like about these chips is that they are limited to whatever the chip can do, so i would like to see a home made version like you are doing too, complete with ideas about winding the toroid and even what kind to use. I would love to build by own from scratch too using more common parts like comparators and MOSFETs or whatever.

What was said about the opto coupler is true, in that they use that to provide the feedback. They use a voltage reference of some kind to compare the output to the reference and provide a signal to the LED inside the opto. I doubt they use the opto in the linear mode but you could check that with a scope.

I happen to have one apart as we speak. It's a low current charger but has the same ol' wall wart circuit inside. If you would like some hi res photos i can take a few and post them so you can look inside.