LED driver

On Sat, 19 Jul 2014 18:36:15 -0700 (PDT), snipped-for-privacy@yahoo.com wrote:

OK, that's a hazard if, when VK is slamming down, M3 begins to turn off (nfb) before the schmitt snaps. With a lower schmitt threshold of 4 volts, set by the fuzzy gate threshold of M2, that could be worrysome. The fix is to raise the lower schmitt trip point, and maybe use a bipolar for M2, to make it more predictable. A voltage reference somewhere would be nice, if we had any current to run one.

Delays do help keep VK coming down, but I'd better not suggest depending on delays.

This is better, with lower switch threshold about 7 volts.

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 240 32 240 -144 WIRE 576 32 240 32 WIRE 784 32 784 -16 WIRE 880 32 784 32 WIRE 960 32 880 32 WIRE 784 96 784 32 WIRE 240 128 240 32 WIRE 384 176 304 176 WIRE 480 176 480 -16 WIRE 480 176 384 176 WIRE 576 176 576 32 WIRE 656 176 576 176 WIRE 736 176 656 176 WIRE 480 208 480 176 WIRE 240 320 240 224 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 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 1Meg 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 SYMBOL npn 304 128 M0 WINDOW 0 103 33 Left 2 WINDOW 3 97 70 Left 2 SYMATTR InstName Q1 TEXT -208 216 Left 2 !.tran 25 uic TEXT -248 88 Left 2 ;Hybrid HV Blinker TEXT -264 136 Left 2 ;J Larkin July 18, 2014 TEXT 576 -424 Left 2 ;Test Gen

I've only relied on delays to set a lower trip point... once... in that 6nA oscillator I mentioned here before... but it definitely had delay ;-)

...Jim Thompson

It seems it's a cold day in hell, as well as in Sydney; JT admits it's possible JL is right :)

I'm with JL on hazards. One of my favourite quotations is: "One in a million chances have a nasty habit of coming up nine times out of ten".

I can only create that "hazard" by manually setting it. I don't think it can happen in actual practice since all the Vbe's are shunted by resistors. The "4-layer trigger" has the distinct advantage of requiring minimal current until triggered, thus met the original power requirement. ...Jim Thompson

I'll have a several-KV power supply and a roughly 100 KHz, 5 KV pulse generator a few inches away. If there is a time window when glitching the PNPN will make it latch, we'll soon find it.

I can't get it to work in LTSpice. Maybe I did something wrong.

Which circuit doesn't work? What doesn't it do?

On 7/21/2014 9:20 AM, John Larkin wrote:

The one from Jim's Web site. It seems to give a brief pulse once at start-up and then stays latched. I will attach it and, if you are interested, you can tell me if I did something wrong.

Version 4 SHEET 1 1396 776 WIRE -96 -352 -256 -352 WIRE 384 -352 -96 -352 WIRE 624 -352 384 -352 WIRE 960 -352 624 -352 WIRE 1088 -352 1040 -352 WIRE -256 -192 -256 -352 WIRE -96 -80 -96 -352 WIRE -256 -32 -256 -112 WIRE -256 -32 -464 -32 WIRE -160 -32 -256 -32 WIRE 624 48 624 -352 WIRE -464 64 -464 -32 WIRE -256 64 -256 -32 WIRE -96 112 -96 16 WIRE -96 112 -192 112 WIRE -96 176 -96 112 WIRE 1088 208 1088 -352 WIRE 384 272 384 -352 WIRE -256 320 -256 160 WIRE -96 320 -96 256 WIRE -96 320 -256 320 WIRE -48 320 -96 320 WIRE 112 320 32 320 WIRE 320 320 112 320 WIRE 1088 320 1088 288 WIRE 112 336 112 320 WIRE 384 384 384 368 WIRE 384 384 176 384 WIRE -96 416 -96 320 WIRE 384 416 384 384 WIRE 624 496 624 112 WIRE -464 544 -464 128 WIRE -96 544 -96 480 WIRE -96 544 -464 544 WIRE 112 544 112 432 WIRE 112 544 -96 544 WIRE 384 544 384 496 WIRE 384 544 112 544 WIRE 560 544 384 544 WIRE 384 608 384 544 WIRE 624 656 624 592 WIRE 384 736 384 688 FLAG 1088 320 0 FLAG 384 736 0 FLAG 624 656 0 SYMBOL zener -448 128 R180 WINDOW 0 24 64 Left 2 WINDOW 3 24 0 Left 2 SYMATTR InstName D1 SYMATTR Value BZX384B27 SYMATTR Description Diode SYMATTR Type diode SYMBOL pnp -160 16 M180 SYMATTR InstName Q1 SYMATTR Value 2N3906 SYMBOL npn -192 64 M0 SYMATTR InstName Q2 SYMATTR Value 2N3904 SYMBOL npn 176 336 M0 SYMATTR InstName Q3 SYMATTR Value 2N3904 SYMBOL npn 320 272 R0 SYMATTR InstName Q4 SYMATTR Value 2N4124 SYMBOL npn 560 496 R0 SYMATTR InstName Q5 SYMATTR Value 2N3904 SYMBOL res -272 -208 R0 SYMATTR InstName R1 SYMATTR Value 1.5Meg SYMBOL res -64 304 M90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R2 SYMATTR Value 22k SYMBOL res 368 400 R0 SYMATTR InstName R3 SYMATTR Value 330 SYMBOL res 368 592 R0 SYMATTR InstName R4 SYMATTR Value 30k SYMBOL res -112 160 R0 SYMATTR InstName R5 SYMATTR Value 1.5Meg SYMBOL cap -112 416 R0 SYMATTR InstName C1 SYMATTR Value 100n SYMBOL res 1056 -368 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R6 SYMATTR Value 1.5Meg SYMBOL LED 608 48 R0 SYMATTR InstName D2 SYMATTR Value LedWHITE SYMATTR Description Diode SYMATTR Type diode SYMBOL voltage 1088 192 R0 WINDOW 123 0 0 Left 2 WINDOW 39 0 0 Left 2 SYMATTR InstName V1 SYMATTR Value PULSE(0 200 1 .001) TEXT -864 384 Left 2 !.tran 100 uic

It needs the storage cap.

Oops! Yer right. But, that puts a spike of 1.25A through the base of Q1 for about .7us.

BTW, I changed the supply to an arbitrary voltage source with V=30*time and the plot stop time to 100 seconds so as to ramp up the supply voltage.

Makes sense. Q1Q2 is an SCR, discharging C1 into C2.

Well, the only problem with it that I can see is that it does not start flashing until it reaches 70V when using a 22M source resistor.

I take that back. It will latch up if the supply voltage rises slowly enough (like .5V/sec) and there will be 20uA continuously through the LED after the supply gets above about 400V.

Oh.

Hi,

Here is a 600V (max) input LED driver:

cheers, Jamie

The trick is to separate triggering mechanism from holding-current mechanism, as in...

VoltageIndicator_NoHang.pdf

on the S.E.D/Schematics page of my website. ...Jim Thompson

Misnamed. It has an obvious latch state.

Where do you buy those 1Nxxxx diodes?

Prove it.

Magicland >:-} ...Jim Thompson

I'll leave it, as you like to say, as an "exercize for the student."

I was right last time, wasn't I?