high voltage blinker

Or even reduce to just two fets as in this sketch?

piglet

Constant current from 2KV isn't that bad. But with a couple hundred uA of cc, I don't need a blinker.

If I go with a roughly 2KV supply, and use a mult-chip LED, I won't use a blinker at all. Just a resistor and the LED will work well enough.

(Gotta get some 12 and 24 volt LEDs and see how they look at low currents.)

I must have scribbled about 100 blinker circuits so far, and Spiced a dozen of them. Every one, except the bipolar Schmitt thing, turns out to have a fatal flaw. When that happens, either you are having a bad week, or there's something fundamental going on behind the obvious.

An NE-2 does what I want, but at too high a firing voltage. There's no obvious equivalent to be made from conventional semiconductor parts. That's what's interesting here.

There are LED blinker circuits that use the b-e junction of a transistor as a negative-resistance avalanche device, but I don't know that I'd trust that in production.

That's cute, if it doesn't have any hang states.

There might be one: V+ is enough to turn on Q1, limiting V+, but not enough current in the 470r to turn off Q2 and make it snap. Both fets are on, lots of negative feedback. Impossible to fully analyze without Spice or more coffee.

I've come to assume that 99% of such circuits have some gotcha.

It's fun to play the circuit game, sort of like chess puzzles.

The diacs and sidacs that I've looked at have fairly high firing currents, but might work if all the values were chosen carefully (might work with 3 megs, probably not with 25.) The trick of using a PNPN part or circuit is to come up with one that has a low firing current but won't latch on at any current in the operating range.

That's why this is a cool problem; there's always a gotcha.

You might get somewhere with a PUT relaxation oscillator, with a zener or some such circuit to establish the gate voltage. Yet another path to explore.

Dang, you are right. Cute but flawed.

I actually got fixated on emitter coupled schmitts a few days back so I should have ensured Q2s load resistor is lower than Q1s load resistor for an extra hit of positive feedback even when using Q2 coll to Q1 base positive feedback.

piglet

It looks like bipolars are easier to use here than mosfets.

This is an amazing problem. These circuits steals their own power supply, pitiful enough to begin with, so have overall negative feedback. The trick is to get everything to work from 0 volts up.

A PNPN latch can be hazardous here, too.

I chucked it up into LTSpice and it didn't work. Did you draw it correctly? Also, what is up with the AC source; piece-wise-linear would have been a better choice.

?-)

switches on

volts, has

storage or

needs

hard-discharge a

the sim

LED. So

at

On Thu, 17 Jul 2014 09:29:38 -0700, John Larkin wrote:

Here's a mosfet version. It's pretty impressive, firing at around 12 volts and ending near zero. It's just a blinker, so exact thresholds don't matter much.

There is a small startup hazard, fixed by using a higher-threshold fet for M3. We need M1 to come on before M3 can pull any significant current, avoiding the negative-feedback dilemma. I'd use FDV301s and a 2N7002 and futz the resistor values some.

Version 4 SHEET 1 1520 680 WIRE 336 -576 240 -576 WIRE 480 -576 416 -576 WIRE 480 -512 480 -576 WIRE 480 -384 480 -432 WIRE -288 -304 -352 -304 WIRE -224 -304 -288 -304 WIRE -80 -304 -144 -304 WIRE -32 -304 -80 -304 WIRE 48 -304 -32 -304 WIRE 240 -304 240 -576 WIRE 240 -304 112 -304 WIRE 480 -304 240 -304 WIRE 656 -304 480 -304 WIRE 784 -304 656 -304 WIRE 1008 -304 784 -304 WIRE -352 -240 -352 -304 WIRE -80 -240 -80 -304 WIRE 240 -224 240 -304 WIRE 480 -224 480 -304 WIRE 784 -224 784 -304 WIRE 1008 -224 1008 -304 WIRE -352 -112 -352 -160 WIRE -80 -112 -80 -176 WIRE 1008 -48 1008 -144 WIRE 480 -16 480 -144 WIRE 624 -16 480 -16 WIRE 784 -16 784 -144 WIRE 784 -16 704 -16 WIRE 784 32 784 -16 WIRE 880 32 784 32 WIRE 960 32 880 32 WIRE 240 64 240 -144 WIRE 576 64 240 64 WIRE 240 96 240 64 WIRE 784 96 784 32 WIRE 384 176 288 176 WIRE 480 176 480 -16 WIRE 480 176 384 176 WIRE 576 176 576 64 WIRE 656 176 576 176 WIRE 736 176 656 176 WIRE 480 208 480 176 WIRE 240 320 240 192 WIRE 480 320 480 288 WIRE 784 320 784 192 WIRE 1008 320 1008 48 FLAG -352 -112 0 FLAG 240 320 0 FLAG 784 320 0 FLAG -80 -112 0 FLAG 1008 320 0 FLAG 480 320 0 FLAG 480 -384 0 FLAG -32 -304 VC FLAG -288 -304 HV FLAG 656 -304 VK FLAG 384 176 M2G FLAG 656 176 M1G FLAG 880 32 M3G SYMBOL voltage -352 -256 R0 WINDOW 0 54 152 Left 2 WINDOW 3 -9 203 Left 2 WINDOW 123 0 0 Left 2 WINDOW 39 0 0 Left 2 SYMATTR InstName V1 SYMATTR Value PULSE(0 500 0 10 10 2) SYMBOL res 224 -240 R0 WINDOW 0 -82 49 Left 2 WINDOW 3 -107 86 Left 2 SYMATTR InstName R1 SYMATTR Value 20Meg SYMBOL res 768 -240 R0 WINDOW 0 -75 44 Left 2 WINDOW 3 -90 76 Left 2 SYMATTR InstName R2 SYMATTR Value 4Meg SYMBOL nmos 736 96 R0 WINDOW 0 102 32 Left 2 WINDOW 3 81 70 Left 2 SYMATTR InstName M1 SYMATTR Value BSS123 SYMBOL nmos 288 96 M0 WINDOW 0 123 23 Left 2 WINDOW 3 100 63 Left 2 SYMATTR InstName M2 SYMATTR Value BSS123 SYMBOL res 720 -32 R90 WINDOW 0 -47 58 VBottom 2 WINDOW 3 -39 57 VTop 2 SYMATTR InstName R6 SYMATTR Value 20Meg SYMBOL res -128 -320 R90 WINDOW 0 69 60 VBottom 2 WINDOW 3 75 57 VTop 2 SYMATTR InstName R3 SYMATTR Value 3Meg SYMBOL cap -96 -240 R0 WINDOW 0 66 53 Left 2 WINDOW 3 70 84 Left 2 SYMATTR InstName C4

SYMBOL LED 48 -288 R270 WINDOW 0 72 32 VTop 2 WINDOW 3 0 32 VBottom 2 SYMATTR InstName D4 SYMATTR Value LXHL-BW02 SYMATTR Description Diode SYMATTR Type diode SYMBOL nmos 960 -48 R0 WINDOW 0 107 35 Left 2 WINDOW 3 85 68 Left 2 SYMATTR InstName M3 SYMATTR Value 2N7002 SYMBOL res 992 -240 R0 WINDOW 0 -76 43 Left 2 WINDOW 3 -79 77 Left 2 SYMATTR InstName R4 SYMATTR Value 200 SYMBOL res 496 -128 R180 WINDOW 0 72 62 Left 2 WINDOW 3 51 24 Left 2 SYMATTR InstName R5 SYMATTR Value 20Meg SYMBOL res 496 304 R180 WINDOW 0 -63 76 Left 2 WINDOW 3 -80 38 Left 2 SYMATTR InstName R7 SYMATTR Value 4Meg SYMBOL voltage 480 -528 R0 WINDOW 0 129 16 Left 2 WINDOW 3 49 58 Left 2 WINDOW 123 0 0 Left 2 WINDOW 39 0 0 Left 2 SYMATTR InstName V2 SYMATTR Value PULSE(0 20 0 10 10 2) SYMBOL res 432 -592 R90 WINDOW 0 74 58 VBottom 2 WINDOW 3 81 59 VTop 2 SYMATTR InstName R8 SYMATTR Value 1T TEXT -208 216 Left 2 !.tran 25 uic TEXT -248 88 Left 2 ;Mosfet HV Blinker TEXT -264 136 Left 2 ;J Larkin July 18, 2014 TEXT 576 -424 Left 2 ;Test Gen

The one I posted works for me. The sine wave has a nice low startup slope, but linear ramps do look nicer.

The mosfet one is nicer.

volts and

much.

for M3.

avoiding the

resistor

Hysteria hangs ?>:-}

-- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | San Tan Valley, AZ 85142 Skype: skypeanalog | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at

Sorry, I don't have one. It always works for me. Some Spice global setting maybe?

VC is pretty simple: power supply, resistor, cap. The LED can't hold it down to millivolts. Probe around a little maybe, check voltages and currents. C4 should be charging.

I think someone forget to set the flag to start the power supply at 0, otherwise, it just does DC analysis.

In any case, I was able to use a 555 timer in a very basic hysteresis mode with a t network coming back from the output so I could very the duty cycle, diode included of course. I used a up/down ramp DC volts and there is no latching, since it has comparators and the VCC does not seem to mind being varied. A slow charge to the Vcc and everything else the timer needs from that point.

The only thing I didn't do was come up with a fixed current limit that can handle the 5Kv input, I merely varied the supply from 0 to 10 volts for the test.

I would imagine a LMC555 with its low quiescent current would be more attractive, it seems to have more than enough output current to drive a LED and being CMOS, it most likely would current limit just fine for you.

I also dropped a uPowered comparator on the sheet and was able to get a relaxation oscillator with hysteresis to work just fine, too!. That was doing ~ 200uA from the HV lead. But then again, like I said, I just tested it at 10 volts. I am sure a properly working current limit that handles 5K would be just fine.

The key here is using something with a windowing comparator that tracks along with the LEAD supply. And it's obvious you can do this with a few trannies but I think in this case an IC would be less labor.

Jamie

It's the f'ing code for the capacitor, right click it and make it 1U, then try actually reading the schematic sometime, Joerg.

setting

down to

should

Found it. The value for C4 had gotten mangled. Works fine now.

?-)

You didn't find anything you lousy lying little kraut prick- you were told how to fix it.