What component to use for a voltage controlled switch? - Page 1
Forum section: electronics / beginners

author: raff5184
author_rank: Regular Contributor
timestamp: March 22, 2018, 03:59:23 am
content: Hi all, very basic question.In the attached figure what component can I use to realize a voltage controlled switch?Basically I want to connect a capacitor to a source or a load based on the voltage across C. The switch happens at about 5V.It is a DC circuit and I don't need high switching performance, just to switch every few minutesThank you

author: Bassman59
author_rank: Super Contributor
timestamp: March 22, 2018, 04:04:58 am
content: Quote from: raff5184 on March 22, 2018, 03:59:23 amAnalog switches like the DG201 and the venerable 4016 and 4066 have logic-level switch control inputs and can switch voltages up to the level of the analog rails. There are many families, it can be confusing. Tradeoffs include on-resistance of the switch, supply rails, etc.You could also use a small relay.

author: raff5184
author_rank: Regular Contributor
timestamp: March 22, 2018, 04:12:32 am
content: thank you, are there also miniaturized versions of the order of 3-4 mm?Also, are these components passive? I mean I don't want to use extra supply voltage

author: Bassman59
author_rank: Super Contributor
timestamp: March 22, 2018, 04:16:00 am
content: Quote from: raff5184 on March 22, 2018, 04:12:32 amYou'll have to look. Maybe start with the Intersil, Vishay or Analog Devices web site parametric search.QuoteRelays are passive. The analog switch chips I mentioned require at least one rail.

author: David Hess
author_rank: Super Contributor
timestamp: March 22, 2018, 02:38:41 pm
content: What are the current requirements? How much capacitance is involved and what is the load resistance?

author: raff5184
author_rank: Regular Contributor
timestamp: March 22, 2018, 03:27:46 pm
content: For the capacity there are two cases:Case I) Capacitor of C of the order of hundreds of mF, max 1F.Case II) Rechargeable battery of about 200 JR = 1 - 2 kCurrents 5-10 mA

author: raff5184
author_rank: Regular Contributor
timestamp: March 22, 2018, 04:27:09 pm
content: Quote from: Mechatrommer on March 22, 2018, 03:49:25 pm5,5 V

author: sairfan1
author_rank: Frequent Contributor
timestamp: March 22, 2018, 04:32:12 pm
content: Quote@Bassman59 I'm hobbyist and looking for same thing, i want to know what do you mean by rail here. thanks

author: Cerebus
author_rank: Super Contributor
timestamp: March 22, 2018, 04:34:23 pm
content: Forget the mechanics of this solution for a second.What are you trying to achieve with the original outline circuit? What's your actual practical goal? What's the underlying problem you are trying to solve?I ask because I have a suspicion that you're trying to re-invent the wheel, and we may be able to offer you some better solutions for your actual underlying problem.

author: Cerebus
author_rank: Super Contributor
timestamp: March 22, 2018, 04:37:39 pm
content: Quote from: sairfan1 on March 22, 2018, 04:32:12 pm"rail" is being used as shorthand for "power supply rail", the 'rail' part of the terminology coming from the common use in everyday transportation of the thing that something rides/comes in along/is carried upon.

author: Mechatrommer
author_rank: Super Contributor
timestamp: March 22, 2018, 04:52:33 pm
content: its like mr potato solar car problem.. a small footprint can be likeSN74LVC1G3157DBVRbut that alone wont solve your problem, you need another comparator or schmitt trigger to switch it on and off at the correct level, and you'll need to power those... ymmv..

author: raff5184
author_rank: Regular Contributor
timestamp: March 22, 2018, 05:08:05 pm
content: Quote from: Cerebus on March 22, 2018, 04:34:23 pmVery simply I have a capacitor or rechargeable battery. I charge the capacitor with a voltage supply unit. As soon as the capacitor is charged to 5.5 V I want to automatically disconnect the supply and connect the capacitor to my load. But the switch should be passive I don't have extra sources to power the switch

author: Cerebus
author_rank: Super Contributor
timestamp: March 22, 2018, 05:13:19 pm
content: Quote from: raff5184 on March 22, 2018, 05:08:05 pmNo, that's a description ofhowyou are trying to solve your problem. What is your actual problem? What is your load? Why aren't you just connecting the supply to the load?You appear to be trying to re-invent some kind of charge pump. Without knowing why you're doing this it's hard to offer suggestions.

author: raff5184
author_rank: Regular Contributor
timestamp: March 22, 2018, 05:32:48 pm
content: Quote from: Cerebus on March 22, 2018, 04:34:23 pmSo I have a mobile device, and this is why I can't connect the supply to the load. My mobile device has a rechargable energy storage (capacitor or battery).The goal is that oftransferring energy to the rechargeable capacityof my mobile system, store it there, and use it to power a non specified load, say an impedance or a load that uses that energy on and off with a certain duty cycle, or use it when I need to

author: Cerebus
author_rank: Super Contributor
timestamp: March 22, 2018, 05:44:58 pm
content: Quote from: raff5184 on March 22, 2018, 05:32:48 pmAh, ha!There will be a specific IC, or probably lots of them, designed to do just that job and because this is exactly mobile phone territory they will be designed to take up absolutely minimum space. In fact, many of them will be so small that they'll be out of the 'home gamer' league (e.g. whole chip smaller than the tip of your soldering iron).A quick look at Mouser shows 4222 'battery management' ICs. Now you have to narrow that down by battery chemistry, charging power voltage and so on. Take a look here:https://www.mouser.co.uk/Semiconductors/Integrated-Circuits-ICs/Power-Management-ICs/Battery-Management/_/N-6j76v/

author: raff5184
author_rank: Regular Contributor
timestamp: March 22, 2018, 06:38:45 pm
content: do these chips provide automatic switching from the charger to the load once the storage is full? And basically, what happens during the charging? Is the "phone" being powered? Because if so it would take longer to charge it

author: Cerebus
author_rank: Super Contributor
timestamp: March 22, 2018, 07:58:26 pm
content: Quote from: raff5184 on March 22, 2018, 06:38:45 pmAll these are possibilities. There is a *huge* array of parts out there. You'll have to narrow it down to a few that suit your basic parameters (voltage, current etc.) and then read the datasheets for a few parts to figure out their capabilities and how they intersect with your usage.