stonehenge regulator

The idea of an SCR is to create really high fault currents, so an appropriate low-value 0805 resistor should blow out. If your input is fused, ideally the resistor would go first. The customer could make a repair, if they were brave enough.

Exactly, my worry is the TVS, with its very high dissipation, could fail. Maybe it would fail shorted, but maybe not. An SCR running at 1V is safer. If you really want to be safe, use the serious fail-safe circuit Paul devised:

--
 Thanks, 
    - Win

Way too complex to protect against a low-probability event.

I was just explaining to the kids that life is risky. It doesn't make sense to add weeks or months of engineering to reduce risk a tiny amount. Done is better than perfect. Done can be sold.

--

John Larkin         Highland Technology, Inc 

lunatic fringe electronics

It was protecting $8k of electronic PCBs. I thought the impact in your case would be pretty dramatic as well. A portion of the circuit might be sufficient.

--
 Thanks, 
    - Win

On Saturday, September 28, 2019 at 1:57:03 PM UTC-4, Winfield Hill wrote:

Here's a much simpler method. Replace the switch with a TL431. Watch the wr ap.

Version 4 SHEET 1 1608 1700 WIRE 624 -208 -80 -208 WIRE 880 -208 624 -208 WIRE 880 -160 880 -208 WIRE 624 -144 624 -208 WIRE 768 -144 720 -144 WIRE 816 -144 768 -144 WIRE 832 -144 816 -144 WIRE 768 -80 768 -144 WIRE -80 -48 -80 -208 WIRE -32 -48 -80 -48 WIRE 112 -48 -32 -48 WIRE 176 -48 112 -48 WIRE 320 -48 256 -48 WIRE 384 -48 320 -48 WIRE 464 -48 384 -48 WIRE 608 -48 544 -48 WIRE 672 -48 672 -80 WIRE 672 -48 608 -48 WIRE -80 -32 -80 -48 WIRE 112 -32 112 -48 WIRE 880 -32 880 -64 WIRE 960 -32 880 -32 WIRE 976 -32 960 -32 WIRE 880 0 880 -32 WIRE 768 16 768 0 WIRE 320 48 320 -48 WIRE -80 64 -80 48 WIRE 112 64 112 48 WIRE 208 64 112 64 WIRE 272 64 208 64 WIRE 112 96 112 64 WIRE 880 96 880 80 WIRE 272 112 256 112 WIRE 256 128 256 112 WIRE 112 192 112 176 WIRE 320 192 320 128 FLAG -80 64 0 FLAG 320 192 0 FLAG -32 -48 Vin FLAG 112 192 0 FLAG 608 -48 Q1B FLAG 768 16 0 FLAG 880 96 0 FLAG 816 -144 M1G FLAG 960 -32 Vout FLAG 256 128 0 FLAG 208 64 R1R3 FLAG 384 -48 R2R4 SYMBOL voltage -80 -48 R0 WINDOW 39 0 0 Left 2 WINDOW 3 -54 150 Left 2 SYMATTR Value PULSE(0 50 0 1m 0 0 1m 1) SYMATTR Value2 AC 1 SYMATTR InstName V1 SYMBOL res 160 -32 R270 WINDOW 0 32 56 VTop 2 WINDOW 3 0 56 VBottom 2 SYMATTR InstName R2 SYMATTR Value 10k SYMBOL res 96 -48 R0 SYMATTR InstName R1 SYMATTR Value 10k SYMBOL res 96 80 R0 SYMATTR InstName R3 SYMATTR Value 549 SYMBOL pnp 720 -80 M270 WINDOW 0 -6 42 VLeft 2 WINDOW 3 89 64 VLeft 2 SYMATTR InstName Q1 SYMATTR Value 2N5401 SYMBOL res 560 -64 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R4 SYMATTR Value 10k SYMBOL pmos 832 -64 M180 SYMATTR InstName M1 SYMATTR Value Si7489DP SYMBOL res 752 -96 R0 SYMATTR InstName R5 SYMATTR Value 10k SYMBOL res 864 -16 R0 SYMATTR InstName R6 SYMATTR Value 48 SYMBOL sw 320 144 M180 WINDOW 0 12 104 Left 2 WINDOW 3 17 11 Left 2 SYMATTR InstName S1 SYMATTR Value TL431 TEXT 128 -288 Left 2 !.tran 0 1m 0 1u TEXT 128 -320 Left 2 ;'Overvoltage Protection TEXT 72 288 Left 2 !.model 2N5401 PNP(Is=21.48f Xti=3 Eg=1.11 Vaf=1

00 Bf=132.1 Ne=1.375 \n+Ise=21.48f Ikf=.1848 Xtb=1.5 Br=3.661 N c=2 Isc=0 Ikr=0 Rc=1.6 Cjc=17.63p \n+Mjc=.5312 Vjc=.75 Fc=. 5 Cje=73.39p Mje=.3777 Vje=.75 Tr=1.476n Tf=641.9p \n+Itf=0 Vtf =0 Xtf=0 Rb=10 Vceo=150 Icrating=600m mfg=Fairchild) TEXT 72 424 Left 2 !.model Si7489DP VDMOS(Rg=3 Rd=31.2m Rs=1m Vto=- 2.4 mtriode=2.2 Kp=35 \n+lambda=0.1 Cgdmax=6n Cgdmin=10p A=1 Cg s=4n cjo=200p M=.3 VJ=.9 Is=3.6p \n+Rb=5.5m mfg=Siliconix ksu bthres=.1 Vds=-100 Ron=34m Qg=106n pchan) TEXT 72 248 Left 2 !.model TL431 SW(Ron=1 Roff=1Meg Vt=2.5 Vh=0)

It gets even more complicated when you have a bipolar supply and the load i s damaged if the supply goes out of balance. Last one I did used the Motoro la MC3423 self- contained overvoltage sense and SCR driver, which is about as complicated as your circuit. IIRC the application literature of the time stressed care must be taken to ensure the duration of the gate drive gets past the I2t threshold of activating the protection device. For the mechani cal stuff like breakers and fuses, you need something like 100x peak overcu rrent or more to get the trip in us-ms time frame, and that can't always ha ppen. If that can't happen, then you need to stretch the t in the I2t via t he gate drive. Looks like it's still available from Rochester.

Dunno if they upgraded to a better IC or someone else came in and stole the ir business.

LOL- localize the flames.... I wonder with your hefty relay drive, how the switcher responds to a sudden discontinuation of current loading. Will the series inductor overvoltage for a while conducting through the TVS? I think so. That would be worth running through a sim.

Done that sim, at least enough to demonstrate that the energy in the inductor could pull the +12 up pretty good. I don't have an LT Spice model for the LM2567, which is why I did the little breadboard.

Yes, one reason to have the TVS is to clamp overshoots in the case of sudden unloading of the 12 volt buss. But in this particular case, a bit of overshoot won't do any harm. The +12 is driving relays and

2nd-level switchers that can stand 32 volts in. So the TVS basically protects against a hard switcher failure.

When we have bipolar supplies, we add a big schottky to ground so a supply can't be pulled through to its opposite polarity, which can cause all sorts of problems.

It looks like this entire system can be all-positive power supplies.

--

John Larkin         Highland Technology, Inc 

lunatic fringe electronics

On Saturday, September 28, 2019 at 4:40:18 PM UTC-4, Steve Wilson wrote:

The previous version allowed the input to exceed the 36V maximum of the TL4

1. Here's the fix. Watch the wrap.

Version 4 SHEET 1 1608 1700 WIRE 144 -208 -80 -208 WIRE 384 -208 144 -208 WIRE 688 -208 384 -208 WIRE 944 -208 688 -208 WIRE 144 -160 144 -208 WIRE 384 -160 384 -208 WIRE 944 -160 944 -208 WIRE 688 -144 688 -208 WIRE 832 -144 784 -144 WIRE 880 -144 832 -144 WIRE 896 -144 880 -144 WIRE 832 -80 832 -144 WIRE -80 -48 -80 -208 WIRE -32 -48 -80 -48 WIRE 16 -48 -32 -48 WIRE 144 -48 144 -80 WIRE 240 -48 144 -48 WIRE 384 -48 384 -80 WIRE 448 -48 384 -48 WIRE 528 -48 448 -48 WIRE 672 -48 608 -48 WIRE 736 -48 736 -80 WIRE 736 -48 672 -48 WIRE -80 -32 -80 -48 WIRE 16 -32 16 -48 WIRE 144 -32 144 -48 WIRE 944 -32 944 -64 WIRE 1024 -32 944 -32 WIRE 1040 -32 1024 -32 WIRE 240 0 240 -48 WIRE 304 0 240 0 WIRE 320 0 304 0 WIRE 944 0 944 -32 WIRE 832 16 832 0 WIRE -80 64 -80 48 WIRE 144 64 144 48 WIRE 384 80 384 48 WIRE 384 96 384 80 WIRE 944 96 944 80 WIRE 16 112 16 48 WIRE 48 112 16 112 WIRE 336 112 48 112 WIRE 16 144 16 112 WIRE 336 160 320 160 WIRE 320 176 320 160 WIRE 384 192 384 176 WIRE 16 240 16 224 FLAG -80 64 0 FLAG 384 192 0 FLAG -32 -48 Vin FLAG 16 240 0 FLAG 672 -48 Q1B FLAG 832 16 0 FLAG 944 96 0 FLAG 880 -144 M1G FLAG 1024 -32 Vout FLAG 320 176 0 FLAG 48 112 R1R3 FLAG 448 -48 R2R4 FLAG 144 64 0 FLAG 304 0 Q2B FLAG 384 80 Q2E SYMBOL voltage -80 -48 R0 WINDOW 39 0 0 Left 2 WINDOW 3 3 -182 Left 2 SYMATTR Value PULSE(0 50 0 1m 0 0 1m 1) SYMATTR Value2 AC 1 SYMATTR InstName V1 SYMBOL res 368 -176 R0 SYMATTR InstName R2 SYMATTR Value 10k SYMBOL res 0 -48 R0 SYMATTR InstName R1 SYMATTR Value 10k SYMBOL res 0 128 R0 SYMATTR InstName R3 SYMATTR Value 549 SYMBOL pnp 784 -80 M270 WINDOW 0 -6 42 VLeft 2 WINDOW 3 89 64 VLeft 2 SYMATTR InstName Q1 SYMATTR Value 2N5401 SYMBOL res 624 -64 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R4 SYMATTR Value 10k SYMBOL pmos 896 -64 M180 SYMATTR InstName M1 SYMATTR Value Si7489DP SYMBOL res 816 -96 R0 SYMATTR InstName R5 SYMATTR Value 10k SYMBOL res 928 -16 R0 SYMATTR InstName R6 SYMATTR Value 48 SYMBOL sw 384 192 M180 WINDOW 0 12 104 Left 2 WINDOW 3 17 11 Left 2 SYMATTR InstName S1 SYMATTR Value TL431 SYMBOL npn 320 -48 R0 SYMATTR InstName Q2 SYMATTR Value 2N3904 SYMBOL res 128 -176 R0 SYMATTR InstName R7 SYMATTR Value 10K SYMBOL res 128 -48 R0 SYMATTR InstName R8 SYMATTR Value 10k TEXT 128 -288 Left 2 !.tran 0 1m 0 1u TEXT 128 -320 Left 2 ;'Overvoltage Protection TEXT 72 368 Left 2 !.model 2N5401 PNP(Is=21.48f Xti=3 Eg=1.11 Vaf=1

00 Bf=132.1 Ne=1.375 \n+Ise=21.48f Ikf=.1848 Xtb=1.5 Br=3.661 N c=2 Isc=0 Ikr=0 Rc=1.6 Cjc=17.63p \n+Mjc=.5312 Vjc=.75 Fc=. 5 Cje=73.39p Mje=.3777 Vje=.75 Tr=1.476n Tf=641.9p \n+Itf=0 Vtf =0 Xtf=0 Rb=10 Vceo=150 Icrating=600m mfg=Fairchild) TEXT 72 504 Left 2 !.model Si7489DP VDMOS(Rg=3 Rd=31.2m Rs=1m Vto=- 2.4 mtriode=2.2 Kp=35 \n+lambda=0.1 Cgdmax=6n Cgdmin=10p A=1 Cg s=4n cjo=200p M=.3 VJ=.9 Is=3.6p \n+Rb=5.5m mfg=Siliconix ksu bthres=.1 Vds=-100 Ron=34m Qg=106n pchan) TEXT 72 328 Left 2 !.model TL431 SW(Ron=1 Roff=1Meg Vt=2.5 Vh=0) TEXT 456 136 Left 2 ;Replace the switch with a TL431

Also eliminates any possibility of avalanche breakdown of the coil driver turning off, although almost any output capacitance should buy enough time to prevent that too. There shouldn't be secondary breakdown for a driver turning on.

So what? Do it without a regulator.

I lie, there's a TL431. So what, it's like a single transistor (making this a "10"-transistor-lab product, alas; if you ignore the complementary follower and feedback, the core circuitry uses a mere seven however).

Hmm, don't know if I have any pictures of a finished converter with this. Have built a few though. Works fine. Sometimes weird modes (subharmonics, poorly optimized compensation?), eh, it's simple.

Nice thing about low gain devices (which I think includes the ancient Simpler Switchers, for better and for worse) is they don't make much for harmonics. I've got one of these on a shortwave radio and another on a Theremin, just CLCLC output filters is fine even for such sensitive purposes.

Tim

--
Seven Transistor Labs, LLC 
Electrical Engineering Consultation and Design 
Website: https://www.seventransistorlabs.com/ 

"John Larkin"  wrote in message  
news:79cqoehqeqmmiqt5ekuck5pe7a8r65anic@4ax.com... 
>I have a 48 volt power supply and I want to drive a lot of relays and 
> uPs and FPGAs and stuff, so I figured I'd knock it down to 12 volts 
> first. 
> 
> We have LM2567HV-ADJ in stock, a 52 KHz Simple Switcher probably 
> designed by druids during the last ice age. Figured I'd breadboard the 
> reg just for fun. A boy gets tired of typing all day. 
> 
> https://www.dropbox.com/sh/ajtqs7c1nswfhey/AABi7r0gchljjrxka4aHZItfa?dl=0 
> 
> 
> Works pretty well, actually. Nothing gets very warm at 1 amp out. 
> 
> Yes, that unshielded drum core will spray field everywhere, but then I 
> am simulating alternators. 
>

Posts using LTspice are hard to see, save file, open, etc.

Some issues with your idea: (1) It's a voltage clamp, which must be fast, but also its control loop must be stable at high currents. (2) The Si7489DP FET's Vgs is limited to 20 volts. (3) If a fault persists for any length of time, the Si7489DP will overheat and fail. So you need to add a crowbar.

Paul's circuit handles these issues, and also times actions carefully to avoid employing the crowbar, if the clamp can handle the problem and save the day. As a bonus, it turns off the source's AC power. It would have been nice to add some performance waveforms to the article.

--
 Thanks, 
    - Win

Maybe an updated version of Paul's circuit would be one tiny uP doing all the thinking.

--

John Larkin         Highland Technology, Inc 

lunatic fringe electronics

Posts showing the ASC file are extremely useful. You seem to have managed.

Unfortunately, it is difficult to include the PLT file to show the wavefor ms. Perhaps the solution is to zip the files and upload them to google drv.

Try a different newsreader. I find XNews to be extremely useful to save any post that contains useful information, such as problems with ICs or other information.

It is not a clamp. There is no control loop. It simply opens the FET when t he input voltage exceeds the limit.

I added a 12V zener from gate to src in later versions. Fixed.

Mosfets are available with milliohms of on resistance. This would take a lo t of current to cause overheating. The problem would shift back to the sour ce supply.

A crowbar could make a bad situation worse. A better solution would be to m easure the current and shut the FET off if it exceeds some limit. This woul d need to store the fault and provide a reset. An additional enhancement wo uld be to check for undervoltage and turn off the FET. These additions woul d require some LEDs to indicate the problem and show the status.

Paul's circuit is way too complex. Crowbars can cause severe damage.

No need to shut off the power. Just shut off the FET.

Run the ASC file and look at whatever waveforms you desire. Thanks for your reply.

Excuse me, you are right. OK, that changes everything.

--
 Thanks, 
    - Win

part....

One of my pet weekend projects is to breadboard the LM2575 (actually, using a PCB) and try about a dozen different values for the coil under various loading. I'd just like to get a good feel for the part, since it is dirt s imple to use and is a low-freq switching design.

Of course, I've had the coils for about a year now, and they are still sitt ing in the DigiKey box.

I also wanted to characterize its EMI profile and see if I could get it to oscillate under some "off-datasheet conditions". :)

In general, I think this "old tech" gets a bad rap sometimes. While better designs exist, the old ones are still pretty good! Although I can't remember the last time I used a 7805. :)