Monday, January 19, 2015

Mystery of the Switching Paradigm

I was not able to solve a issue with an Enthusiast who tried building a Power Circuit Design of mine. It was a design that was not complete in documentation. I had just put it online for people to study. Marin built it and went thru a lot of trouble.- This was in 2005-6

Story Starts Here -

I built switching power supply with SG3524 (project del20020) from your site

It is working, but not good :-( Voltage and current regulations are very bad. I connect  stabilized 13V to input, and from another stabilized power supply I connect 12V for SG3524 and LF358. For testing I use mosfet BUZ11, and various ferrite inductors, but results are bad.

On output I cant get more than 6V, and output 470uF elco sounds like "bzzzzzzzzzzzzzzz"   I checked, and rechecked all connections several times, but everything is like on your schematic diagram.   Could you tell me if your schematic diagram has any bug?

Did you built any working switcher with this schematic?   Maybe is problem in inductor. Is it critical? I tryed with few toroid and ETD44 EI core with 4 to 40 turns of wire, with no luck :-( Which corre and numbers of turns do you suggest?

Power Supplies Section

Mail from Ing. Marin Antic

Mystery of the Switching Paradigm


delabs Reply

This i  a 15 year old circuit and working well, there may have documentation errors. i will look at it when i have some time. meanwhile troubleshooting is better.

The circuit itself can have errors, and then while you breadboraded there could be mistakes. the inductor is required for proper working around 50uH you will need a LCR meter or make a test jig.

Where is the bzzzz sound coming from is it a lose core of inductor vibrating. you said voltage is 6V does it give good curent, is load regulation good.   the input power needs to be 3-4 volts more than what you need a t output try 15V and also does input power suppy have good current rating like 5 is the input power supply able to able to drive the load you want. probably the input power supply may be loaded.   see for any heating parts. the problem is in the connections or the feedback path. look around the LM358, you can chat with me online. i will certainly try my best to help you.



I think that your schematic can't work good. Do you have continuous voltage and current regulation from 0-12V and 0-5A on your swicher? I think it is impossible with this schematic...

When I modificate sg3524 output stage to the mosfet, I got full voltage on the output not only half like before. But voltage regulation is not continious. Now I can regulate voltage only 6-12V. 0-6V not working. On 6V is step, and then continious regulation.

 I tryed many modifications on connecting LF358 to the output, an now is working. Not very good, but good :-)   Current control is not working ok. What do you think to move current sensing on positive output, not on negative?

mail from IMA


delabs Reply

Just check these points.

vary inductor air gap, make it also more like 100uH. Keep current limit to minimum and try. Or to locate problem disconnect pins  4-5 and then connect 4-5 to ground. Now current control has been disabled, see if vtg control and load-line regulation ok.   C2 and R10 fix frequency of SMPS 2.2k and 10nF plastic, verify.   Mosfet drive part may have to be modified bit as per circuit attached.   try all in the order show or as your understanding..

(see a application note below, not the circuit being discussed but the chip)

sg3524 smps

Sunday, January 18, 2015

Building a mV Milli-Volt Calibrator Source

Hi, I am trying to build this mV source that you have drawn on your site. It requires a 5vdc power source with a 1k resistor in line with a 10K pot. Your schematic shows also with the pot a 10k resistor and a 100E component which I have no idea what that is.

My question to you is... does the 10K pot include the 10K resistor and the 100E component or are they separate from the pot? If they are separate, what is the 100E component?

Thanks, Ken



Dear Ken

I would like to know the Circuit File you were referring, i have many on my site for instruments.  Let us understand the Theory so you can build your own.

First - You need a Regulated Power Supply for these circuits to be accurate enough. We do not need things like 0.01% for Industrial Electronics or Field Calibration. You can always keep one of these accurate ones in your Lab.

Second - Now to bring down the Voltage of say 5V to mV, we need to Attenuate right. An attenuator contains Two Resistors. The High Value - like 1K is a Fixed MFR 1% Resistor. This faces the 5V and Then comes a Multiturn Pot, preferably Bourns or Spectrol 10 turn, This is 10K. These two form just the One part of the attenuator.

Third - This is a 50 ohm or 100 ohm shunt made of 1/2W MFR 1% or Resistors in parallel to get the value. The reason being that the shunt should not even warm up.  The 1K resistor is to protect the pot when wiper is at the 0 ohms end and the shunt is shorted by some mistake.  If all these can be built in a box with a fixed temperature using an artificial oven. AND.  If you make the Regulated Supply using Opamps and a Precision Reference. You have Laboratory grade Instrument, almost.


Hi Anantha

This is the site location that I am referring to. The 100E is confusing me.

Building a mV Milli-Volt Calibrator Source

Thanks


In this Circuit, The 100 ohms is very important as it acts like a Low Impedance Voltage Source. In Fluke Sources 50 Ohms is standard. The Voltage across this resistor is in millivolts due to the attenuation.

10K/100 ohms  is 10,000 ohms divided by 100 ohms. That gives a Divide by 100

5 Volts divided in 100 parts Gives 50 mV (approx as we have the bourns 10 turn pot before the 10K/100 ohms divider. )

See another design here  Current Source mA for calibration

This is easy to rig millivolt source for field calibration or troubleshooting of 4-20 mA current loops. Here a Darlington pair is used for current amplification which reduces the Ib error as gain is very high.

A rotary switch selects, 4-12-20 mA Preset points. A Bourns multi-turn wirewound Pot can also be used with a digital dial. Enclose in a dust proof handheld box. Read more on process calibration.
Current Source mA for calibration

You can also use one of the Arduino Analog Outputs and Attenuate them after filtering with a cap. This creates a Programmable Millivolt Source.

So, the 100E is just a 100 ohm resistor aside from the 10K pot? What does the "E" stand for?



E means Ohms. Philips used this notation first as the Symbol Ohm was difficult to Print.

100 Ohm Resistor is important, when you connect it to a Device to Calibrate it will not load it. A DMM has a 10 Meg Ohm Measurement Load. The Instrument you calibrate must have around 1 Meg or more. That is why we use FET input Opamps  to measure the mV of Thermocouples.

That is where the millivolt source steps in, it is a Thermocouple Simulator.  Read more here

OMEGA Web Technical Reference

 See the Literature at the bottom  OMEGA Web Download Literature



thank you very much Anantha
Ken

Friday, January 02, 2015

HV and Jacobs Ladder or Climbing Arc

I mess with HV stuff and recently I went to adjust my Jacobs ladder with it still switch on I griped  each leg of the ladder with my hands . I had a zap  5Kv at 100mA up my arms and across my chest   Why it did not Kill me is beyond my understanding as it is 3 times the accepted lethal power I have made several changes to the set up now including a physical barrier to the wire legs to prevent a re-occurrence

I will not let my 4 year old Grand son play with the above wooden toy pole pig and helical Jacobs ladder either - I promise

JAH from USA

James Howells Spark

James Howells Spark


i would be glad if you move away from high-voltage to high-current or online education, your experience may be useful to many.  as far as your survival from the zap, it is the grace of god indeed. do not press your luck too far, even god is very stressed right now.

The zap takes the shortest path, left hand to right leg, right hand to left leg 100mA can be fatal. If you were wet or sweating, then the surface of the body provides a safer path. Use silicone gloves and good shoes.  Only a Knight in Shining Armour is safe, not for his chivalry but for his conductive coating.

delabs

Additional Information about Safety with Electricity

Never use Smartphone or Tablet while charging (Near Sensitive Ear or Face). You may get electric shock or lightning discharge leaks. Use Surge protected Switchboards and Isolation Transformers or CVT. The mild shock due to Y caps of EMI filters is not a danger.  If the mains adapter you buy is low quality or there is a freak breakdown, you had it.

The risk is greater when a high voltage leak happens near the ear or face. and Metal parts of the phone gets close to the ear or neck is unsafe. The head and neck have very low resistance and can be damaged with much less Fatal Current.

Use total plastic exterior phones/tablets, wear shoes and use the speakerphone option when you talk/use while charging.