Timeline for How can I use a PNP transistor as a switch in a 555 bistable circuit?
Current License: CC BY-SA 4.0
5 events
| when toggle format | what | by | license | comment | |
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| Apr 16, 2023 at 18:38 | comment | added | Sredni Vashtar | I have seen circuits on YouTube that are certainly not the result of any reasoning. "100W amplifiers" that are just glorified distortion generators, switching circuits whose interferences can be picked up on Mars, transformers with a common terminal between input and output, that in some systems might be the live mains wires... My guess is the 'designer' put the transistor backwards by error, noted the circuit worked as expected and since when hooked up right it was too sensostive, called it a day and copied the new schematic. It's just a guess... :-) | |
| Apr 16, 2023 at 17:05 | comment | added | TimWescott | Well, OK -- but if that's the intent then it should have been done by installing the PNP correctly and increasing R2 until the desired results were achieved. Even when you're designing a circuit to use a transistor in its intended mode you don't count on things like \$\mathrm{H_{FE}}\$ to be constant from part to part. | |
| Apr 16, 2023 at 16:49 | comment | added | Sredni Vashtar | Yes the pnp is upside down, but I wonder if it's done on purpose to reduce the sensitivity of the receiver, so that it will require a long push on the remote to turn the output high. Looks like a "let's see what happens if I mix components in this way" design philosophy. | |
| Apr 15, 2023 at 18:39 | comment | added | RickyBoy | Your description is correct... I would characterise the circut as "limping along" as drawn. I turned the PNP round to what I thought it should be and the response is correct and much more responsive. The transmitter is working no problem (in fact TV remote just as effective transmitter). Judging by answers provided the circuit as published is wrong. Thank you. | |
| Apr 15, 2023 at 15:28 | history | answered | TimWescott | CC BY-SA 4.0 |