## Using a 12V 2A power supply direct and with 3V voltage divider?

Started by in sci.electronics.basics7 years ago 50 replies

I have forgotten everything I learned in the single electrical science class I took in college 25 years ago. Please forgive my ignorance. I...

I have forgotten everything I learned in the single electrical science class I took in college 25 years ago. Please forgive my ignorance. I have a single 12V 2A power supply. I want to simultaneously power a 20W 12V fan and supply a 3V 2mA current via a voltage divider. The fan would be connected direct to the +/- of the PS while a voltage divider with R1=4500 and R2=1500 would provide the...

Started by in sci.electronics.basics7 years ago 47 replies

Now sure how to describe the problem in few words, sorry. I have two circuit boards (to be designed), A and B. A has the power supply= . A and...

Now sure how to describe the problem in few words, sorry. I have two circuit boards (to be designed), A and B. A has the power supply= . A and B will be connected by a longish, 2 conductor wire. The wire will b= e used to supply 12V+ and ground from A to B. B has no other source of powe= r. B needs to signal A when something happens. For various reasons, I can't replace the wire with a...

## Trying to cheat ohm's law

Started by in sci.electronics.basics7 years ago 15 replies

For a circuit I described here recently, I want to be able to cause a brief, temporary, high current draw on a 12v power supply. I'd like to draw...

For a circuit I described here recently, I want to be able to cause a brief, temporary, high current draw on a 12v power supply. I'd like to draw about 2A for a few ms, and at least 0.5A for perhaps 100ms. I have a resistor + capacitor combination that gives a curve I like. A regulated 12v supply that claims to produce 5A, with a 33000uf cap in series with 3.9 ohm resistor across it

## Power Supply Ripple Measurement

Started by in sci.electronics.basics7 years ago 11 replies

Hi, 1. I am trying to measure the output voltage ripple of a 5 Volt , 1A power supply. The input to the power supply is 120V, 60Hz. Can...

Hi, 1. I am trying to measure the output voltage ripple of a 5 Volt , 1A power supply. The input to the power supply is 120V, 60Hz. Can someone please suggest an appropiate Differential probe to do this measurement? Plus I am expecting the ripple to be 2mV peak to peak. If I do not get 2mV peak to peak then what should I do to reduce it. I can not use Voltage regulator at the output. ...

## The ASOD Absolute Silence Of Death; Dead Mother Board or Something Else

Started by in sci.electronics.basics7 years ago 6 replies

The Dell Studio PC is dead. I tried to turn it on and got _nothing_ except the yellow green LED on the power supply which, from what I...

The Dell Studio PC is dead. I tried to turn it on and got _nothing_ except the yellow green LED on the power supply which, from what I understand, only means it's plugged in. I checked the "on" switch with an ohm meter and it works. (Turning it on with the big toe is not damaging apparently.) I removed the power supply and ran a jumper from pin 3 to pin 4 on the 24 wire connecto

## Power Supply

Started by in sci.electronics.basics7 years ago 1 reply

Hi, I have been assigned to do some "switching power" ESD testing recently. I am a beginner engineer. So, please forgive me and do not be...

Hi, I have been assigned to do some "switching power" ESD testing recently. I am a beginner engineer. So, please forgive me and do not be offended, if I ask dumb beginner's questions. I am using the following setup to test the supplies https://www.google.com/search?q=esd+test+table&rlz=1C1OPRB_enUS590US592&espv=2&biw=1360&bih=639&tbm=isch&imgil=3tz5_C44aehh

## smps with a fixed duty cycle?

Started by in sci.electronics.basics6 years ago 8 replies

The classic linear power supply (transformer, bridge rectifier, cap) relies on AC at a fixed frequency of 60 Hz (50 Hz outside the USA?), so...

The classic linear power supply (transformer, bridge rectifier, cap) relies on AC at a fixed frequency of 60 Hz (50 Hz outside the USA?), so that's basically a 50% duty cycle, right? And if higher frequency means less iron is required for the transformer... Would a simple SMPS, operating at several hundred kHz, with a fixed 50% duty cycle still outperform the linear power supply? Thanks, ...

## Picking an inductor

Started by in sci.electronics.basics6 years ago 2 replies

Hi all, silly question. (And I'll most likely just pick something before I get an answer.) So just a simple LP filter for a power supply...

Hi all, silly question. (And I'll most likely just pick something before I get an answer.) So just a simple LP filter for a power supply rail. (SMPS, at ~100-200 kHz.) manufacturer recommends ~10-47 uH (I picked 22 uH) and 22 uF.) max current is 500 mA.. typical current is ~100 mA. On to digikey. After putting in the inductance, current ratings (saturation) for 500mA to 2 A, and s...

## UPS with 12V output

Started by in sci.electronics.basics6 years ago 8 replies

Hello, I have quite a lot of devices that works at 12 or 5V (router, eth. switch, raspberry, etc.). Everyone has is own AC/DC power...

Hello, I have quite a lot of devices that works at 12 or 5V (router, eth. switch, raspberry, etc.). Everyone has is own AC/DC power supply. I'd like to put all the devices under an UPS, but it seems stupid to do AC-DC-AC-DC. So the question is do you know if a UPS with a regulated 12V output (and AC input) exists? The only things I found are UPS with unregulated 12V output (mean

## Cheap oscilloscope kit

Started by in sci.electronics.basics5 years ago 6 replies

I recently built the JYE Tech DSO-150 Shell oscilloscope kit (#15001K) that I got from Banggood for \$24 plus a power supply. These are...

I recently built the JYE Tech DSO-150 Shell oscilloscope kit (#15001K) that I got from Banggood for \$24 plus a power supply. These are single-channel, low-frequency scopes, but would be useful for things one might do with an Arduino or similar microcontroller, such as stepper motors and servos, plus of course general audio stuff. The bandwidth spec is 200 kHz, but I suspect the display...

## Thermopile power supply in water heater control

Started by in sci.electronics.basics5 years ago 12 replies

I recently bought a gas water heater and made a point of getting one that didn't require external electrical power to operate. To my...

I recently bought a gas water heater and made a point of getting one that didn't require external electrical power to operate. To my astonishment, it nonetheless came with what behaves like a digital controller, complete with a green LED status light that must require close to 3 volts to turn on. The electronics are operated from a standard Honeywell thermopile generator producing 750 ...

## Why are computer power supplies like this?

Started by in sci.electronics.basics5 years ago 12 replies

I noticed this before and again last night. I am changing plugs from a bad supply to a good one. There is a connector with 20 or so wires that...

I noticed this before and again last night. I am changing plugs from a bad supply to a good one. There is a connector with 20 or so wires that plugs into the motherboard. 6 different color wires. But all the wire of a poarticular color go to the same trace on the power supply circuit board. So all the reds to one trace, all the yellows to another trace and so on. So why all the different wire...

## Psu for valves

Started by in sci.electronics.basics4 years ago 20 replies

I wish to experiment with valves (or tubes, if you prefer) and I shall begin by building a power supply. What voltages (at what currents)...

I wish to experiment with valves (or tubes, if you prefer) and I shall begin by building a power supply. What voltages (at what currents) should it supply? Where may I find circuits? Naturally, the devices used should be easily obtainable.

## A balanced 12AX7 based buffer

Started by in sci.electronics.basics4 years ago 10 replies

I'd like to "design" and implement a simple 12AX7-based buffer for musical instrument DI purposes. I'd like the output to be balanced for ... no...

I'd like to "design" and implement a simple 12AX7-based buffer for musical instrument DI purposes. I'd like the output to be balanced for ... no good reason at all beyond having balanced inputs to play with. My questions are: - Do I really need 300V for this? What's the trade here? - Is there a nice single-package, preferably switchmode power supply that does 300V and 12.6V heater, or ...

## mosfet bias question

Started by in sci.electronics.basics4 years ago 3 replies

I plan to use a mosfet in a dawn to dusk switching circuit with a 12V regulated power supply. In the application notes they give the...

I plan to use a mosfet in a dawn to dusk switching circuit with a 12V regulated power supply. In the application notes they give the gate source absolute maximum voltage as +/- 10V Gate to Source. (page 1) On page 6 of the same application note they show a "Gate charge test circuit." with a 12 volt battery between the gate and source with a 50 Kohm variable resistor for the current source ...

## Transformerless power supply

Started by in sci.electronics.basics2 years ago 7 replies

Is it reasonable/possible to build an 8 amp 20 V transformerless power supply from a 120Vac line. I calculate about 180uf plus or minus...

Is it reasonable/possible to build an 8 amp 20 V transformerless power supply from a 120Vac line. I calculate about 180uf plus or minus depending on other components. Maybe 9- 20uf caps in parallel? I'd like to build it into a leaf blower. All plastic, absolutely no metal exposed. I think I've answered my question, I have 12, X rated caps in my junk box, but they are only 1uf....

## Transformerless Power Supply

Started by in sci.electronics.basics4 years ago 10 replies

Is it reasonable/possible to build an 8 amp 20 V transformerless power supply from a 120Vac line. I calculate about 180uf plus or minus...

Is it reasonable/possible to build an 8 amp 20 V transformerless power supply from a 120Vac line. I calculate about 180uf plus or minus depending on other components. Maybe 9- 20uf caps in parallel? I'd like to build it into a leaf blower. All plastic, absolutely no metal exposed. I think I've answered my question, I have 12, X rated caps in my junk box, but they are only...

## DC cable puzzle

Started by in sci.electronics.basics4 years ago 16 replies

Tidying up my shed workshop I got an electric shock from a cable pair that had earlier been disconnected from its 14V DC power supply. So...

Tidying up my shed workshop I got an electric shock from a cable pair that had earlier been disconnected from its 14V DC power supply. So I'd expect it to have virtually zero voltage across it, apart from ac noise. Its destination is a garden lamp relay box about 80 ft away from the supply. For some of that distance it runs close to a mains cable (unloaded at the time). My DMM consistently...

## Old Anelex power supply: AC on the DC

Started by in sci.electronics.basics4 years ago 10 replies

This huge, ancient power supply made by Anelex has been serving from under my shed workshop bench for about 25...

This huge, ancient power supply made by Anelex has been serving from under my shed workshop bench for about 25 years: https://www.dropbox.com/s/g11s67bb5jk7bc8/HD-Power-Supply.jpg?dl=0 It supplies a few projects around the house and garden and I generally just ignore it. But a couple of days ago I found that there is 115V AC between the case (connected to the 230V AC mains input) and all th...

## Purpose of cap on ac line of PC power supply

Started by in sci.electronics.basics3 years ago 5 replies

I am re-purposing a PC power supply and there is a "0.47k" cap across the incoming AC line. What's that for?

I am re-purposing a PC power supply and there is a "0.47k" cap across the incoming AC line. What's that for?