Help me to understand how the circiut works - Page 1
Forum section: electronics / beginners

author: hohlov
author_rank: Newbie
timestamp: June 19, 2013, 02:36:09 pm
content: Hello everyone!I'm newbie in electronics and on this forum. And not sure if I ask right things and use right terms.I've decided to make a nixie clock from an old calculator. I got a scheme but can't quite understand how it works. In particular there are two blocks I don't understand at all - with V1 and V15,V16 transistors.I feel that they are some kind of voltage regulators. Could you explain me how do they work?(sorry for my english)Thanks in advance!

author: Caleb_P
author_rank: Newbie
timestamp: June 19, 2013, 08:16:17 pm
content: What an terrible schematic! Things looping over and around things with no regard for ease of reading...Can you upload a better image? Try scanning it in. Its very hard to tell where the nodes are and are not.A trick I do with difficult schematics like this one is to make a copy of it. Then use multiple colored highlighters or felt tipped pins to trace out the nets. This lets you better see where everything is going and what it is doing.

author: c4757p
author_rank: Super Contributor
timestamp: June 19, 2013, 08:22:29 pm
content: I'm usually the first to bitch about poor schematics and I don't think it's that bad. Clearly it is an attempt to fit the circuit onto one page of a certain size, and I don't think I could get it much clearer myself without using more space. It'd be nice if traces were labeled, but labeling traces beyond pin names really didn't catch on until CAD became popular.Sorry, I'll try to be helpful. I'll see if I can figure it out.

author: c4757p
author_rank: Super Contributor
timestamp: June 19, 2013, 08:31:35 pm
content: The one on the right appears to be a constant current circuit, about 10mA out of the collector of the lower transistor. I'll see if I can rearrange it.

author: c4757p
author_rank: Super Contributor
timestamp: June 19, 2013, 08:37:47 pm
content: Here's the one on the right rearranged a bit. It appears to deliver a fairly constant current into the load (R14), buthighlydependent on the transistor's gain. Definitely an odd circuit. My guess is that it didn't need to be very good, and an oompa-loompa to tweak the trimmer was cheaper than a precision circuit.Edit: Sorry, got it wrong. Read further.

author: c4757p
author_rank: Super Contributor
timestamp: June 19, 2013, 08:41:05 pm
content: The one on the left is just a (very) rough voltage regulator - Zener diodes V2 and V3 provide a reference voltage, adjusted by R12, to V1 acting as an emitter follower. Fairly common circuit. (It's meant to sink current, not source). Because of the high impedance into the base, though, it's going to have a fairly high output impedance.

author: c4757p
author_rank: Super Contributor
timestamp: June 19, 2013, 08:52:28 pm
content: Maybe it's a temperature sensor

author: Rufus
author_rank: Super Contributor
timestamp: June 19, 2013, 08:54:02 pm
content: Quote from: hohlov on June 19, 2013, 02:36:09 pmV1 is a regulator (which only sinks current to ground) producing a rail presumably 15v below the 25v rail.The other circuit is a comparator comparing the 10v rail with a proportion of the 25v rail the output switching to 25v while the 10v is low. Maybe it is some kind of safety thing or inhibit during power up/down.Edit: Actually are those supplies 258v and 108v ? Is B volt in Russian

author: c4757p
author_rank: Super Contributor
timestamp: June 19, 2013, 08:55:24 pm
content: Quote from: Rufus on June 19, 2013, 08:54:02 pmI missed that - stupidly assumed the rails would be fixed.

author: c4757p
author_rank: Super Contributor
timestamp: June 19, 2013, 08:58:35 pm
content: Quote from: Rufus on June 19, 2013, 08:54:02 pmThe Cyrillic letter "aw screw it, the forum won't let me use Cyrillic" is indeed equivalent to a V.

author: Rufus
author_rank: Super Contributor
timestamp: June 19, 2013, 09:06:54 pm
content: Quote from: c4757p on June 19, 2013, 08:58:35 pmSo why are the capacitors rated with VI suddenly thought nixies need high voltage, but, looks like we don't have the whole circuit. Probably is 10 and 25v supply for ancient MOS ICs.

author: c4757p
author_rank: Super Contributor
timestamp: June 19, 2013, 09:11:23 pm
content: Quote from: Rufus on June 19, 2013, 09:06:54 pmThey are, aren't they? Plus all the diodes and transistors labeled "V" ("valve"?) Modern Cyrillic doesn't even have a letter that looks like V, so there must be cases where they switched alphabets in the schematic...

author: c4757p
author_rank: Super Contributor
timestamp: June 19, 2013, 09:14:39 pm
content: Quote from: Rufus on June 19, 2013, 09:06:54 pmAh! Got it! Dude, this ain't no Nixie calculator...(I'm just going to use Latin letters here) See the thing labeled "H1", "backwards-N B-21"? (That's actually N1, IV-21). IV-21 is astandard miniature 8-digit VFD. 20V, appears to be driven directly from the main chip. There are no Nixies in this thing.I've got some of these in my drawer - I actually intend to use them in - wait for it... a calculator.

author: codeboy2k
author_rank: Super Contributor
timestamp: June 19, 2013, 09:47:23 pm
content: Quote from: c4757p on June 19, 2013, 09:14:39 pmI see you're wearing your electron superhero decoder ringI want one of those displays, that would be awesome in a battery powered hand-held frequency counter in a small plastic enclosure.

author: c4757p
author_rank: Super Contributor
timestamp: June 19, 2013, 09:52:05 pm
content: Quote from: codeboy2k on June 19, 2013, 09:47:23 pmI've had to type up and "translate" (OK, using Google Translate, but often with alotof intervention...) enough crusty old Russian datasheets to recognize more than a few Russian electronics-related words and symbols. Don't ask me how to pronounce them, though...QuoteFunny, I've got someNixie tubeswaiting for just that purpose...Quote"Soviet" and "power efficient" are mutually exclusive. Don't plan on getting much battery life! They take a good helping of both filament and anode current...

author: hohlov
author_rank: Newbie
timestamp: June 20, 2013, 11:53:18 am
content: Wow guys! I didn't expect such a hot discussion! Thanks for your comments!You are correct it's IV-21 device. It requests 2.4v to a cathode and 27v-50v on anodes and grids.258 and 108 are 25B and 10B ( B is russian character for sound  ) and mean 25v and 10v.It was very strange for me too why capacitors was marked with V.V (or VT) means Vacuum  for transistors on russian circuits.The right one powered an anode of a 'period' segment ( I mean the dot in "12.34"). So when I connect for example 16(that anode) to 15 (grid) pins the second dot is glowing.What is the purpose of this behaviour? Why this period sign is so important to make separate circuit to power it?