Simplify Power Supply Decisions via Free Mobile App

It seems endemic that the final specifications for a power supply to run most new product designs tend to be firmed-up near the final stages of product development. Too often, this occurs when schedules have already slipped. As a result, there tends to be little time allocated to this important task. This happens so frequently that in the trade it has nicknamed ‘the tailpipe syndrome.’

Now, a fast and easy method for the selection of a power supply for your latest new product is as close as your smartphone. TDK-Lambda’s new mobile app works with Android and iPhones to greatly simplify this process. Say ‘goodbye’ to turning catalog pages or running tedious internet searches. The app has been shown to quickly guide the user to a power supply that meets their exact needs. To access this app, go to wbxapp.com/tdk-lambda. After the app loads, just press the AC power plug symbol. This app makes the selection process as easy as 1-2-3:

Step 1. Select Your Application:
LEDs, Medical, General Industrial, Comms, Test & Measure, or Military/COTS

Step 2. Select Your Power Range:
1-25W, 26-50W, 51-150W, 151-600W, or 600W & Higher

Step 3. Select from Available Products:
A number of power supply series that meet your Application and Power Range will be offered. Just click on any of these to view the specs and even detailed datasheets.

Quick Results:
In this example, we needed a Medical power supply with three (3) outputs and a total output power of 600-watts. The NV Series meets these requirements.

More Features:
This unique app includes quick links to YouTube (for power supply demo videos) and to Twitter (for new product info).

Additional information about this handy mobile app and other AC-DC power supplies, power racks, customized solutions, and DC-DC converters, is available at http://www.us.tdk-lambda.com/lp/

What is a Power Supply’s IP Rating?

The popularity of outdoor electronics has brought the subject of a power supply’s IP rating from almost obscurity to an everyday question.  I frequently get asked about it by our sales people now, so I thought it would be nice subject to cover in our blog. In researching this blog article I even discovered something new myself.

IP is the acronym for Ingress Protection and for power supplies the IP Rating Code consists of the letters “IP” and two numbers as defined below.

The first number indicates the power supply’s protection level against the ingress of solid objects or dust.

First Number for Solids or Dust

Level	Size of Object	Type of Object
X	Test not made	Test not made
0	N/A	No protection
1	50mm or larger	Large body surfaces*
2	12.5mm or larger	Fingers
3	2.5mm or larger	Small tools
4	1mm or larger	Screws
5	Dust protected	-
6	Dust tight	-

* Does not include deliberate body part contact

The second number indicates the power supply’s protection against the ingress of water or other liquids.

Second Number for Liquids

Level	Protected against
X	Test not made
0	No protection
1	Water dripping vertically
2	Water dripping at an angle
3	Spray water up to 60° from vertical
4	Splashing water from any angle
5	Low pressure water jets
6	Strong spray jets, heavy seas (ship decks)
7	Temporary immersion (up to 1m)
8	Permanent immersion (deeper than 1m)

Most recently LED power supplies, or drivers as they are often referred to, have ratings of IP66 or higher.  Referring to the charts above, an IP66 rating means the unit has ingress protection from Dust and Strong Jet Sprays of Water.

These IP ratings also apply to the end system of course, and many of our customers utilize a NEMA enclosure to make their products meet a higher rating.

TDK-Lambda's IP66 rated LED Driver (ALC/ALV series)

Mounting Precautions for Power Supplies

Before mounting your power supply, be sure to read its installation manual if you intend to mount it in an orientation other than along the horizontal plane (Fig. A). Many power supplies have restrictions regarding mounting. For example, since heat rises, if you mount some power supplies on a vertical plane (Fig. B, C, & D), the heat from the lower section of the power supply will rise and further heat the upper part of the supply, which may cause over heating problems. Likewise, with some power supplies you are not allowed to mount them upside down (Fig. E) because this traps the heat and restricts the normal convection air cooling around the power supply.

In some cases, vertical mounting of power supplies is permitted as long as you reduce the amount of power that will be drawn from the supply. This is referred to as “Derating” the power supply. Below are the derating curves for the TDK-Lambda’s model LS150-12, a convection cooled 150-Watt, 12V output, AC-DC power supply.

This graph shows the percentage of rated output power on the vertical axis and the operating ambient temperatures on the horizontal axis. Notice when mounting this power supply on the horizontal plane (Fig. A), the power supply is rated at 100% output power from -25°C up to +50°C. However, if you mount this supply on a vertical plane (Fig. B, C, & D), the maximum ambient temperature is reduced to +40°C before the power must be derated.

It is worth mentioning that many low cost competitors do not mention the preferred mounting orientation, and some do not even have an installation manual on their website!

An incorrectly mounted power supply will get too hot resulting in premature electrolytic capacitor degradation, catastrophic semiconductor failure or even a fire due to transformers overheating.

Other general power supply mounting considerations include the following:

• Make sure there is adequate space around the power supply to allow air to circulate.
• Do not block off vent holes on convection cooled supplies or restrict air inlet or outlet ports on fan cooled supplies.
• In the event fans are employed within power supply, a system, or an enclosure make sure the airflow direction for all fans are the same

How to safely power LEDs

For well over 25 years, LEDs (Light Emitting Diodes) have been used in TV remote controls.  These specific LEDs emit invisible light pulses in the infrared (IR) light spectrum.  Because the LED can be turned on and off very rapidly, it easily transmits pulses of binary-coded messages to the receiver built into the TV.  

In addition, early applications of LEDs included red-segment clocks, calculators and even digital watches that have now been replaced by more modern display technologies, such as LCDs (Liquid Crystal Displays).

       

Today, white or multi-colored LEDs are rapidly being employed in modern home/street lighting, signage, traffic signals, large screen displays and backlit LCD monitors, etc.  In these applications, multiple LEDs are placed in either clusters or connected as strings to provide the required light intensity or light distribution. 

LEDs are similar to conventional diodes in that they are designed to conduct current in one direction and when doing so, in most cases, they emit visible light.  A basic LED circuit consists of a voltage source, a current limiting resistor and the LED as shown below.

The current limiting resistor (R) is required to maintain the current flowing through the LED at a safe operating level.  When conducting current LEDs have an inherent “voltage drop” that can vary from 1.2V to 4.0V, depending upon the model.  Referring the circuit diagram, if the LED has a voltage drop of say 2V (Vd) with a safe operating current of 20mA (I), and the voltage source (Vs) is 5VDC, the value of the current limiting resistor can be calculated as follows:

R = (Vs –Vd) ÷ I, therefore, R = (5V – 2V) ÷ 0.02A = 150 ohms

The voltage drop across an LED and its light output will vary with the current flowing through it.  Below are curves that show the forward voltage drop (Vd) versus the current (I) flowing through two sample LEDs.

 

In viewing the white curve above, it’s important to notice that the forward voltage drop across the LED between 3.2V and 3.6V (a 0.4V change), results in a current increase of over five times (from 10mA to 60mA).  In this example, if the maximum allowable LED current is 40mA and if 60mA or more current is allowed to flow through it, the LED could be destroyed or its operational life substantially reduced. 

As current flows through an LED its forward voltage drop times the current results in wasted power (e.g., 3.3V x 40mA = 132mW).  This wasted power, in the form of heat, becomes a real problem when high brightness LEDs is employed in lighting applications.  The internal LED heat must be dissipated by either its design, the substrate it’s mounted on, or via added heat sinks.  As the internal junction of an LED gets warmer, the current through it at a given voltage increases.  If not controlled, this can result in thermal runaway, where the LED self-destructs.

The main point here is that LEDs are “current driven” devices and that this current must be carefully controlled.  In the circuit above, the resistor is used to control the current though the LED.  However, the resistor also causes a voltage drop which contributes further to wasted power.  As a result “constant-current” LED drivers have been developed that maintain the current flowing through the LED (or strings/clusters of multiple LEDs) at a safe level with improved efficiency.

For more information about selecting power supplies and drivers for LEDs, see the article at this web link:  http://power-topics.blogspot.com/search/label/LED%20lights

References:

http://en.wikipedia.org/wiki/LED_circuit

http://led.linear1.org/why-do-i-need-a-resistor-with-an-led/

http://us.tdk-lambda.com/lp/products/ledsigns.htm

Using Power Supplies with DC Motors

There is often confusion regarding the use of external diodes when power supplies are used to power DC motors.  Most people know that a diode has to be used, but are unsure where to place them or what their purpose is.  

From a power supply concern there are two types of DC motors; a brushed DC motor and a brushless DC motor.

Brushed DC motors

With this type of motor, the magnets are stationary and the coil spins.  Electricity is transferred to the spinning coil by the use of “brushes”.

The advantages of this type of motor are low initial cost and easy speed control.

When the power is interrupted, the motor coil will act like an inductor and will try to continue to produce current, effectively becoming an inverted voltage source.  This will apply a reverse polarity to the power supply and can cause damage.  (Back EMF – Electro-Magnetic Flux)

By using a diode, as shown below, the diode provides a current path for the reverse motor current and will clamp the reverse voltage to a level no greater than the forward voltage drop of the diode.  This protects the power supply’s output capacitors and other components from being stressed by the reverse voltage.

Brushless DC motors

Brushless DC motors, often referred to as BDCMs or BLDC motors, have permanent magnets that rotate and the armature is fixed.

Although more expensive, they are more reliable in the long term as there is no brush or commutator wear and position control is more accurate.

When the motor is turned off or reversed, it will act as a generator and produce a high voltage spike.  This spike can cause the power supply’s overvoltage protection to trip, shutting down the unit.

By using a diode in series with the output, as shown below, the spike will be blocked from interfering with the power supply.

In both cases a general purpose diode can be used, providing that the voltage and current ratings for the diode are correctly calculated.