Ripple Rejection Ratio

Have you ever wondered what Ripple Rejection Ratio is?
Ripple Rejection Ratio or Power Supply Rejection Ratio (PSRR) is a measure of
how well a circuit, component or Power Supply rejects ripple coming from it's input
at various frequencies and is very critical in
many RF and wireless applications. In the case of an LDO(Low Drop Out Regulator),
it is a measure of the output ripple compared to the input
ripple over a wide frequency range (10 Hz to 10 MHz is
common) and is expressed in decibels (dB).

Read more by checking out this PDF file. Or click on the photo below.

Linear & Switching Voltage Regulator Handbook

Here is a great reference manual for you to print out and add to your collection.

Linear & Switching Voltage Regulator Handbook

Transistors Tutorial

Here is lots of great info on transistors. If you want an in depth look into transitors this tutorial is a must read. Click here to read the entire tutorial.

Transformers

This is an important topic, all good technicians not only need to know what a transformer is and what they look like but also need to understand the theory behind how they work. It is also good to understand the different types of construction and there applications. There is a lot more to transformers than you may realize.



A transformer is a device that transfers electrical energy from one circuit to another through inductively coupled conductors — the transformer's coils. A varying current in the first or primary winding creates a varying magnetic field through the secondary winding. This varying magnetic field induces a varying electromotive force (EMF) or "voltage" in the "secondary" winding. This effect is called mutual induction.
If a load is connected to the secondary, an electric current will flow in the secondary winding and electrical energy will be transferred from the primary circuit through the transformer to the load. In an ideal transformer, the induced voltage in the secondary winding (VS) is in proportion to the primary voltage (VP), and is given by the ratio of the number of turns in the secondary (NS) to the number of turns in the primary (NP). To read more click here and here.

Testing MOSFET(Metal Oxide Semiconductor Field Effect Transistor)

Here is some good info on testing MOSFET transistors, one link uses a DMM and the other link is from my friend Jestine Yong, he shows you how to test a MOSFET using an analogue meter and I must say I really prefer Jestines testing methods. Click here for link 1 and Click here for link 2, also click on the photo below for another great link on testing MOSFETs.

How to test BJT(Bi-polar Junction Transistors)

Recently one of my news letter subscribers wrote me looking for some information on testing BJTs, so I thought this would be a good topic for the Blog. Here are 2 links to some good information on testing a BJT , click here for link 1 and click here for link 2 you can also click on the photo below.

Understanding SMPS (Switch Mode Power Supply)

This is a good reference manual on SMPS that I found online.I love reading every day and find it to be very important for a repair technician to help fully understand all the circuits we work on and improve your trouble shooting skills.When you fully understand how circuits work trouble shooting failures becomes easy.This manual will help you to understand how SMPS works.Please click here or click on the photo below to download and read this reference manual.Have a great day and remember to keep reeding about electronics every day, even if it's reading something you have read before just to keep things fresh in your mind.

Types of inverters for CCFLs

Flat-panel liquid LCDs are the display of choice in a wide range of portable products from notebook
computers, tablet PCs, and PDAs to digital cameras and portable instrumentation. Compact coldcathode
fluorescent lamps (CCFLs) provide the necessary light source in these applications, enabling a
readable display in both dim and bright ambient light.
Inverters that supply the power to turn on (strike) and run CCFLs control one of the major power
drains in any battery-powered device. These are technically challenging circuits. First, inverters must
accept a wide range of dc input voltages, typically from 3 to 14 V, and provide ac outputs of 500 to
800 V to run the lamps. Then, to ignite CCFL lamps, these circuits must provide momentary strike
voltages that typically are twice that of their run voltages. Many applications also require efficient
dimming capabilities to allow lamp output to match ambient light conditions and thus prolong both
lamp and battery life.
Typical of the consumer electronics market, inverters for portable products also face on-going
demands for ever-increasing efficiency to reduce heat and prolong battery life, while simultaneously
meeting size reduction and ever-lower cost models.
For many years, display makers employed a Buck/Royer inverter topology to strike and power CCFLs.
This analog power topology is essentially a combination of a step-down Buck voltage regulator and a
self-resonant Royer oscillator with an integral step-up transformer.To read more, and to learn about other types of inverter circuits besides the "buck royer" click the photo below.

Capacitive Reactance

Capacitive Reactance.Learn how capacitors effect AC circuits. Click the photo or click here.

Reading resistor color codes

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SMPS common failures

Most Common SMPS Problems,The following probably account for 95% or more of the common SMPS ailments:

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Supply dead, fuse blown - shorted switchmode power transistor and other semiconductors, open fusable resistors, other bad parts. Note: actual cause of failure may be power surge/brownout/lightning strikes, random failure, or primary side electrolytic capacitor(s) with greatly reduced capacity or entirely open - test them before powering up the repaired unit.
Supply dead, fuse not blown - bad startup circuit (open startup resistors), open fusable resistors (due to shorted semiconductors), bad controller components.
One or more outputs out of tolerance or with excessive ripple at the line frequency (50/60 Hz) or twice the line frequency (100/120 Hz) - dried up main filter capacitor(s) on rectified AC input.
One or more outputs out of tolerance or with excessive ripple at the switching frequency (10s of kHz typical) - dried up or leaky filter capacitors on affected outputs.
Audible whine with low voltage on one or more outputs - shorted semiconductors, faulty regulator circuitry resulting in overvoltage crowbar kicking in, faulty overvoltage sensing circuit or SCR, faulty controller.
Periodic power cycling, tweet-tweet, flub-flub, blinking power light - shorted semiconductors, faulty over voltage or over current sensing components, bad controller.
In all cases, bad solder connections are a possibility as well since there are usually large components in these supplies and soldering to their pins may not always be perfect. An excessive load can also result in most of these symptoms or may be the original cause of the failure. And don't overlook the trivial: a line voltage select switch in the wrong position or between positions (possibly by accident when moving the supply, particularly with PCs), or damaged.

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