Path: ...!weretis.net!feeder8.news.weretis.net!eternal-september.org!feeder3.eternal-september.org!news.eternal-september.org!.POSTED!not-for-mail From: Jeroen Belleman Newsgroups: sci.electronics.design Subject: Re: An actual circuit Date: Fri, 24 May 2024 20:33:55 +0200 Organization: A noiseless patient Spider Lines: 191 Message-ID: References: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Injection-Date: Fri, 24 May 2024 20:31:55 +0200 (CEST) Injection-Info: dont-email.me; posting-host="1b8eac65f247adad29bd6423db90fed9"; logging-data="2577132"; mail-complaints-to="abuse@eternal-september.org"; posting-account="U2FsdGVkX1/yQHB8Gs20wp5yhbi4OQt0" User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.13.0 Cancel-Lock: sha1:DMogcAAPovJr0Cy1Up0xQo6iWL8= Content-Language: en-US In-Reply-To: Bytes: 6338 On 5/24/24 17:59, Edward Rawde wrote: > "john larkin" wrote in message > news:bk815jh3skuecf1tap8o41rpgdh5kkq8o5@4ax.com... >> On Thu, 23 May 2024 13:06:46 -0700, john larkin wrote: >> >>> On Thu, 23 May 2024 15:35:00 -0400, "Edward Rawde" >>> wrote: >>> >>>> I was having a conversation with a younger person who seemed to be of the >>>> view that to make an LED flash you would need something to decide when it >>>> should be on or off. So that would be some kind of software or digital >>>> system. > ... >>> >> >> The classic NPN astable circuit can hang up, with both transistors >> saturated. I wonder if he jfet circuit can hang too, with Idss >> grounding both drains and not enough gain to oscillate out of that >> state. >> >> Even when they have a hang state, luck usually kicks them off into >> oscillation. Your source resistors and asymmetric drain resistors >> help it start up. Try making both drain resistors 3.3K. >> >> If you make the source resistors lower, it will hang up. >> > > Yes I noticed both points when I was designing it. > I wanted to have it start up by itself, preferably without a kickstart > capacitor. > So I had a complicated circuit with two more diodes and a transistor in the > hope that I could detect the hang state and force it off balance. > I couldn't get that to work > Then I accidentally made R2 3,3k and R6 3.3k and I didn't see how it could > start so quickly with no other help. > Eventually I noticed 3,3k which maybe LTSpice takes as 3k. > > If R2 and R6 are both 3.3k then LTSpice says it slowly drifts into operation > after 40 seconds. > But why does it go one way and not the other? > Is that an artefact of asymmetry in the simulation? > Or is there some hidden asymmetry in the circuit I'm not seeing when R2 is > 3.3k? Below are a pair of astable circuits. The left one is like yours, with a hangup state. I start it by specifying an initial condition. The right one will start all by itself. Jeroen Belleman ========================================= Version 4 SHEET 1 1192 680 WIRE -80 -96 -272 -96 WIRE 96 -96 -80 -96 WIRE 240 -96 96 -96 WIRE 416 -96 240 -96 WIRE 864 -96 416 -96 WIRE 1088 -96 864 -96 WIRE -80 -64 -80 -96 WIRE 96 -64 96 -96 WIRE 240 -64 240 -96 WIRE 416 -64 416 -96 WIRE 864 -64 864 -96 WIRE 1088 -64 1088 -96 WIRE -272 32 -272 -96 WIRE 96 48 96 16 WIRE 112 48 96 48 WIRE 128 48 112 48 WIRE 240 48 240 16 WIRE 240 48 192 48 WIRE 768 64 704 64 WIRE 864 64 864 16 WIRE 864 64 848 64 WIRE 704 112 704 64 WIRE 944 112 704 112 WIRE 1040 112 1008 112 WIRE 1088 112 1088 16 WIRE 1088 112 1040 112 WIRE -80 128 -80 16 WIRE 128 128 -80 128 WIRE 384 128 192 128 WIRE 416 128 416 16 WIRE 416 128 384 128 WIRE 96 160 96 48 WIRE 416 160 416 128 WIRE 864 160 864 64 WIRE 992 160 864 160 WIRE 864 176 864 160 WIRE 1088 176 1088 112 WIRE -80 240 -80 128 WIRE -32 240 -80 240 WIRE 0 240 -32 240 WIRE 48 240 0 240 WIRE 240 240 240 48 WIRE 320 240 240 240 WIRE 368 240 320 240 WIRE 704 256 704 112 WIRE 752 256 704 256 WIRE 816 256 752 256 WIRE 992 256 992 160 WIRE 1040 256 992 256 WIRE -272 288 -272 112 WIRE 96 288 96 256 WIRE 416 288 416 256 WIRE 864 320 864 272 WIRE 1088 320 1088 272 WIRE 0 336 0 304 WIRE 0 336 -272 336 WIRE 320 336 320 304 WIRE 320 336 0 336 WIRE -272 352 -272 336 WIRE -272 448 -272 432 FLAG 96 288 0 FLAG -272 288 0 FLAG 416 288 0 FLAG -32 240 G1 FLAG 320 240 G2 FLAG 112 48 D1 FLAG 384 128 D2 FLAG -272 448 0 FLAG 1088 320 0 FLAG 864 320 0 FLAG 1040 112 D4 FLAG 752 256 G3 SYMBOL nmos 48 160 R0 SYMATTR InstName M1 SYMATTR Value 2N7002 SYMBOL res 80 -80 R0 SYMATTR InstName R1 SYMATTR Value 1k SYMBOL res -96 -80 R0 SYMATTR InstName R2 SYMATTR Value 100k SYMBOL voltage -272 16 R0 SYMATTR InstName V1 SYMATTR Value 10 SYMBOL nmos 368 160 R0 SYMATTR InstName M2 SYMATTR Value 2N7002 SYMBOL res 400 -80 R0 SYMATTR InstName R3 SYMATTR Value 1k SYMBOL res 224 -80 R0 SYMATTR InstName R4 SYMATTR Value 100k SYMBOL cap 192 112 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C1 SYMATTR Value 100n SYMBOL cap 192 32 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C2 SYMATTR Value 100n SYMBOL voltage -272 336 R0 SYMATTR InstName V2 SYMATTR Value 3 SYMBOL diode 304 240 R0 WINDOW 0 -33 66 Left 2 SYMATTR InstName D2 SYMBOL diode -16 240 R0 WINDOW 0 -40 61 Left 2 SYMATTR InstName D3 SYMBOL nmos 1040 176 R0 SYMATTR InstName M3 SYMATTR Value 2N7002 SYMBOL nmos 816 176 R0 SYMATTR InstName M4 SYMATTR Value 2N7002 SYMBOL res 1072 -80 R0 SYMATTR InstName R5 SYMATTR Value 1k SYMBOL res 848 -80 R0 ========== REMAINDER OF ARTICLE TRUNCATED ==========