X-Authentication-Warning: delorie.com: mail set sender to geda-user-bounces using -f X-Recipient: geda-user AT delorie DOT com X-Originating-IP: 88.129.21.118 Subject: Re: [geda-user] Variable voltage supply from fixed To: geda-user AT delorie DOT com References: <84c207a9-df84-c244-96ee-b7e05795d491 AT nksb DOT online> From: "Nicklas SB Karlsson (nk AT nksb DOT online) [via geda-user AT delorie DOT com]" Message-ID: <91a547b6-eadd-e1bf-c5fb-f80d95668180@nksb.online> Date: Tue, 15 Dec 2020 06:02:19 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.5.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Content-Language: en-US Reply-To: geda-user AT delorie DOT com Errors-To: nobody AT delorie DOT com X-Mailing-List: geda-user AT delorie DOT com X-Unsubscribes-To: listserv AT delorie DOT com Precedence: bulk Den 2020-12-15 kl. 02:24, skrev gene glick (geneglick AT optonline DOT net) [via geda-user AT delorie DOT com]: > I've done some of all that. For now, I'll assume you want a positive > supply > > TL431 is a personal favorite. It works very well as a shunt regulator > or with a transistor to form a higher current series regulator. Both > good...depends on the application. > > You did not mention noise or temperature. If noise is important to > you, then you'll need to find a regulator that exposes the voltage > reference so you can filter it. Temperature can affect some of these > regulators. I've run the TL431 to 175C (and higher) with no problems. > The band-gap reference is really very stable. Some regulators have > thermal shutdown at 160C. It's used for switched power electronics so noise is not important. > > Zener references are noisy, if that matters for you. If not, zener + > pass transistor is an okay option. I suspect zener's are not thermally > stable at high temperatures. It's good to know about the noise problem even though not important this time, missed that, guess maybe LDO may amplify noise. I found zener diodes are rather good tolerating high temperature but do not remember about accuracy. > > You can always roll your own with an opamp, a pass transistor, and a > reference. That's pretty much what is inside the TL431 anyway. :D > > Also, if you look at the data sheet for any of the 3-pin fixed > regulators - I'm pretty sure they show ways to raise the output with > either some resistors or zener diodes. I haven't tried this, however. Adjustable have but most are fixed LDO and they do not show resistor divider to get variable voltage. It is possible to get variable voltage from the fixed even though datasheet does not show by using resistor network but ground current add a bias and low resistor value add some power loss, zener diode add some accuracy error. TL431 have no loss problem and good enough accuracy with margin so using this with resistor network on fixed LDO would be a good choice. Only thing that worries me is I happen to come close to instability as I read LDOs may have this problem and then produced in larger numbers it will come back bite my ass. > > For low power, it's hard to beat SOT23 TL431 + SOT23 2N2222 + a couple > resistors. Very small, very flexible. Power is lower but space is a little bit limited, plenty of space at other places of the board but not there needed. > > Hope that helps. Yes it does, it' always good to ask people with more experience. Regards Nicklas Karlsson