1 minute of power. - Page 1
Forum section: electronics / beginners

author: renzoms
author_rank: Regular Contributor
timestamp: October 20, 2019, 08:55:41 pm
content: So I’ve got an LM3302N (IC COMPARATOR QUAD DIFF 14-DIP), LT1101CN8 (IC VOLTAGE COMPARATOR 5-V 8-DIP), and a TLC373CP (IC DUAL DIFF COMP 8-DIP) and I want to build a circuit inspired of the “1 minute of power” circuit in the Art of Electronics 3rd Ed.I looked at the data sheets and I only understood the maximum voltage and I/O current ratings. I’m at chapter one in AOE. I’ve read about 700 pages textbook, so some of the data sheet, buffers, and comparators were not incomprehensible.I think they would all work as long as I don’t exceed 20mA and LT1101 is confusing me with it’s title “voltage comparator.”Sorry if this was too lengthy for you, I’m just getting into electronics.I appreciate any input about data sheets and these chips, keep in mind I’m working through these textbooks.Thanks members of the EEVblog forum.

author: alsetalokin4017
author_rank: Super Contributor
timestamp: October 21, 2019, 08:25:07 pm
content: Well, I can't find a datasheet for the TLC373CP but the LM3302 looks pretty good to me for this project. You will only be using one of the 4 comparators in the chip but that's OK.So you want to build a circuit that starts with an LED (for example) dark, and when you push a momentary-contact pushbutton the LED (for example) lights up, remains lit at constant power for one minute, then goes dark. And you want to do this with an RC circuit and a comparator. Right?Elementary my dear Watson. How far have you gotten so far? Do you have a breadboard, some kind of power supply, some resistors and capacitors in addition to the LM3302 chip?(I don't actually own a copy of TAOE, I only have access to a text edition without diagrams....)So very briefly the Voltage Comparator works by ... comparing voltages! It compares the voltages detected on the inverting and noninverting inputs and changes output state when the two voltages match. The output state can be either High (near the chip's supply voltage) or Low (near zero or ground voltage) while the voltages on the inputs can be anywhere in that range. So in this case you want to compare a fixed voltage that you set, with a varying voltage on a capacitor in an RC circuit as it charges or discharges, and you want the comparator output to flip state when the two voltages match. And of course you want to calculate the correct values for your fixed voltage and your resistor and capacitor so that you get precisely one minute of power at the comparator output as the cap discharges through the resistor.Right?

author: alsetalokin4017
author_rank: Super Contributor
timestamp: October 21, 2019, 08:51:43 pm
content: So start with a little design.Let's assume you use the LM3302 chip since it is very flexible in terms of supply voltage.Power supply? Assume a 9volt battery for now.Max output of the chip is 20 mA but we can get a LED to shine brightly for much less current than that. So let's figure on sending 5 mA through a green LED when the comparator output is HIGH. Current-limiting resistor needed, what is its value if 9V is supply voltage?What if we use 5 Volts power supply? Or 12 volts? Same idea, but different value resistors needed to achieve 5 mA thru our nice green LED.

author: vk6zgo
author_rank: Super Contributor
timestamp: October 21, 2019, 11:48:45 pm
content: There used to be (maybe still is) a radio/TV religious programme called "Hour of Power".When I read this heading, I thought it must be a version of that for people with short attention spans!