Mysterious schematic symbol - Page 1
Forum section: electronics / beginners

author: MacIntoshCZ
author_rank: Regular Contributor
timestamp: August 11, 2020, 10:04:17 am
content: Hello,I am wondering whats this symbol really means?Its connected to oscillator and to reference pin in Op amp.BTW why is there current source connected to ground?Its like there is by default 0,12/ 0,7 V or higher due to pin 5 and 4?Thanks

author: Dabbot
author_rank: Regular Contributor
timestamp: August 11, 2020, 10:21:36 am
content: You forgot to link / attach schematic.

author: MacIntoshCZ
author_rank: Regular Contributor
timestamp: August 11, 2020, 10:45:27 am
content: But i can see it. Its from tl494 onsemi datasheethttps://www.electro-tech-online.com/attachments/1597138910974-png.126356/

author: T3sl4co1l
author_rank: Super Contributor
timestamp: August 11, 2020, 10:56:08 am
content: That site doesn't hotlink images.You mean this?https://www.onsemi.com/pub/Collateral/TL494-D.PDFI don't see anything between REF and oscillator.If you mean the battery (cell) symbol, that's shorthand to say there's an offset of this voltage present. The voltage is sensible because, presumably, the comparators have near zero offset voltage by themselves, but we can measure their response (given suitable logic conditions are met) because their inputs connect to pins whose voltages we can set or measure.The 0.7V offset, for example, is likely a Vbe drop from an emitter follower. I'm not sure what the 0.12V would be from; it's a bit high to be an unbalanced diff pair, and far too small to be a Vbe drop.If you're very curious, there's actually an extensive breakdown of the internal circuitry in the appnote:https://www.ti.com/lit/an/slva001e/slva001e.pdf?ts=1597143182100Apparently the 0.12V offset is two balanced Vbe offsets (one emitter follower, one diode-strapped BJT), and some extra resistance which is unbalanced. (Presumably the bias currents are equal, so the Vbe's cancel out.)Tim

author: fourfathom
author_rank: Super Contributor
timestamp: August 11, 2020, 02:40:14 pm
content: The image attachments have been problematic on this forum for a while, sometimes the wrong image or none at all are displayed.But I can see the schematic. Those symbols are voltage offsets (battery symbol). These indicate a subcircuit that provides an offset voltage, details not shown. That current source shows a subcircuit (no details) indicating the current that is drawn from the feedback input pin. All these symbols are there to give you a clue as to how the device operates, not to show the detailed schematic implementation.

author: TimFox
author_rank: Super Contributor
timestamp: August 11, 2020, 03:33:40 pm
content: The standard schematic symbol for a "cell" is two parallel lines, one shorter than the other. A "battery" is a series connection of cells and indicated by a set of parallel lines where alternate lines are longer or shorter. The original drawing convention on cells is that the longer line is the positive terminal, but careful practice is to indicate the + and - signs explicitly. In the case of your drawing, these are not physical cells, but subcircuits (not detailed) that provide offset voltages, as stated by "fourfathom".

author: FriedMule
author_rank: Frequent Contributor
timestamp: August 12, 2020, 10:11:12 pm
content: To be completely specific, does that symbol mean "single element battery" while several of the two line means more than one element battery.

author: fourfathom
author_rank: Super Contributor
timestamp: August 12, 2020, 10:27:16 pm
content: Quote from: FriedMule on August 12, 2020, 10:11:12 pmThe single element is a "cell" (such as a 1.5V carbon-zinc D-Cell), and the multi-element one is a "battery" (such as a 12V lead-acid car battery, consisting of six 2.1V cells).