---------------------------------------------------------- AeroElectric-List Digest Archive --- Total Messages Posted Fri 01/07/22: 3 ---------------------------------------------------------- Today's Message Index: ---------------------- 1. 12:04 PM - Re: Next Gen 9005 (Eric Page) 2. 03:56 PM - Re: Re: Next Gen 9005 (Robert L. Nuckolls, III) 3. 04:12 PM - Re: Re: Next Gen 9005 (Robert L. Nuckolls, III) ________________________________ Message 1 _____________________________________ Time: 12:04:55 PM PST US Subject: AeroElectric-List: Re: Next Gen 9005 From: "Eric Page" As a non-engineer/hobbyist I enjoy seeing these projects develop, as I always learn something new. With that in mind, I have a couple of questions. I realize the component values aren't established yet, but I'm not familiar with the arrangement of the voltage reference. I presume that it's a TL431 or similar, but I don't fully understand what it's doing in the circuit. Is it there to provide a stable Vdd that's within limits for the op-amp (max 6V for the MCP602, if that's what you're using)? Am I right that R116 (flag note 1) will need to be something like 270 ohms to keep the 431's cathode current within limits? Frankly, the rest of the circuit's operation is a bit of a mystery to me as well, but I'll take one bite at a time! Thanks, Bob. -Eric Read this topic online here: http://forums.matronics.com/viewtopic.php?p=505624#505624 ________________________________ Message 2 _____________________________________ Time: 03:56:06 PM PST US From: "Robert L. Nuckolls, III" Subject: Re: AeroElectric-List: Re: Next Gen 9005 At 02:04 PM 1/7/2022, you wrote: > >As a non-engineer/hobbyist I enjoy seeing these projects develop, as >I always learn something new. With that in mind, I have a couple of questions. > >I realize the component values aren't established yet, but I'm not >familiar with the arrangement of the voltage reference. I presume >that it's a TL431 or similar, but I don't fully understand what it's >doing in the circuit. Is it there to provide a stable Vdd that's >within limits for the op-amp (max 6V for the MCP602, if that's what >you're using)? Am I right that R116 (flag note 1) will need to be >something like 270 ohms to keep the 431's cathode current within limits? > >Frankly, the rest of the circuit's operation is a bit of a mystery >to me as well, but I'll take one bite at a time! > >Thanks, Bob. Yes, it's an LM431, precision adjustable zener. It's Vref is 2.495 Volts. So two equal resistors in the voltage divider will configure a precision 5v zener to establish Vcc for the dual opamp. The tap on the voltage divider also provides the precision reference for the first op amp configured as a comparator with a tad bit of hysteresis. Yeah, we'll pick a current limit resistor which in this case can be pretty big . . . the i.c. Icc is low so the power supply rail doesn't need to be driven so hard. I've been using the LM431 in a lot of designs as Vcc/Vref sources with only 4 components! Bob . . . Un impeachable logic: George Carlin asked, "If black boxes survive crashes, why don't they make the whole airplane out of that stuff?" ________________________________ Message 3 _____________________________________ Time: 04:12:49 PM PST US From: "Robert L. Nuckolls, III" Subject: Re: AeroElectric-List: Re: Next Gen 9005 >Frankly, the rest of the circuit's operation is a bit of a mystery >to me as well, but I'll take one bite at a time! The comparator references at the (-) op amp input and samples bus voltage trough a divider at the (+) input. A resistor from output to (+) sets up hysteresis. For the comparator, hysterisis will be on the order of 500 mV at the bus. Second op amp is an astable multivibrator with timing established by the RC time constant of the network between output and (-) input. The multivibrator hysteresis will be about 1/3 and 2/3 of Vcc. When the comparator sees voltage above setpoint it's output will be HI which is conducted through the diode to (-) of the oscillator causing it's output to be clamped LO and holding the FET in an OFF state. As bus voltage drops below setpoint, the comparator output goes LO and releases its grip on the oscillator which then begins to illuminate the warning light at about 2.5 flashes per second. This design lends itself to a real estate conservation technique I've used for years. The 8-pin DIP opamp has pins long enough to STRADDLE a row of four, 1206 case components underneath. Similarly, four more can be lined up between the rows of pins on the bottom. So within the footprint of the i.c., a total of nine components can be wired up. The FET is a SOT23 device so this board should be quite compact. Bob . . . Un impeachable logic: George Carlin asked, "If black boxes survive crashes, why don't they make the whole airplane out of that stuff?" ------------------------------------------------------------------------------------- Other Matronics Email List Services ------------------------------------------------------------------------------------- Post A New Message aeroelectric-list@matronics.com UN/SUBSCRIBE http://www.matronics.com/subscription List FAQ http://www.matronics.com/FAQ/AeroElectric-List.htm Web Forum Interface To Lists http://forums.matronics.com Matronics List Wiki http://wiki.matronics.com Full Archive Search Engine http://www.matronics.com/search 7-Day List Browse http://www.matronics.com/browse/aeroelectric-list Browse Digests http://www.matronics.com/digest/aeroelectric-list Browse Other Lists http://www.matronics.com/browse Live Online Chat! http://www.matronics.com/chat Archive Downloading http://www.matronics.com/archives Photo Share http://www.matronics.com/photoshare Other Email Lists http://www.matronics.com/emaillists Contributions http://www.matronics.com/contribution ------------------------------------------------------------------------------------- These Email List Services are sponsored solely by Matronics and through the generous Contributions of its members.