What are CV, CC, and CV+CC which are often mentioned in LED power supply specification?

CV (Constant Voltage):Conventional power supply will provide stable regulated voltage (constant voltage) for load usage. Regardless of AC input variation (90~264VAC) or load variation, output voltage will be regulated to within voltage tolerance specification (single output unit typically 1~2%). For example, LPV-60-48 used in powering LED driver + LED light strip, output voltage will remain constant at 48V (as shown in figure 2a).
CC (Constant Current): Designed to provide stable output current (constant current), output voltage will be determined by LED total Vf. For example, using LED with Vf = 3.5V @ 350mA and with 12pcs connected in series. The total Vf will be 3.5Vx12=42V. With 2 strips connected in parallel, the total If = 350mAx2 = 700mA。 If MW constant current LED power supply LPC-35-700 (Vin = 90~264VAC, Vout = 48V/700mA) is used to drive LED load directly, LED power supply will work in CC mode. Output voltage will drop to 42VDC while output current remains constant at 700mA (as shown in figure 2b).
CV+CC MW constant current LED power supply possesses both “C.V.+ C.C.” characteristics. During startup it will operate in “C.V. mode”, which is suitable for LED driver IC and series resistor applications. Once output current requirement exceeds rated current of the power supply and reaches the constant current region, the unit will remain in the constant current mode which is suitable for direct drive of LEDs. C.V.+ C.C. characteristics can be used in all types of LED setup making system design more flexible.

How ppm is dominant factor in crystals and so as in real life….!

Must Read:

Clock accuracy in ppm

Crystal Clock accuracy is defined in terms of ppm or parts per million and it gives a convenient way of comparing accuracies of different crystal specifications.


  • ppm parts per million.
  • ppb parts per billion.

The following headings give practical calculations showing the typical errors you will encounter when using a clock of a specific type with a specific accuracy.

How good is a 1% accurate clock ?

If you look at a day’s worth of timekeeping then you have 24 x 60 x 60 = 86400 seconds in a day.  So the maximum error after a day has passed is 1% of 86400 = 864 seconds = 14.4 minutes!

Error: 14.4 minutes error per day.

How good is a typical crystal ?

A typical crystal has an error of 100ppm (ish) this translates as 100/1e6 or (1e-4)  So the total error on a day is 86400 x 1e-4= 8.64 seconds per day. In a month you would loose 30×8.64 = 259 seconds or 4.32 minutes per month.

Error: 8.64 seconds per day

How good is a watch crystal ?

A watch crystal has an error of 20ppm (ish), but you have to design the board layout well, this translates as 20/1e6 (2e-5) which  gives an error over a day of 86400 * 2e-5 = 1.73 seconds per day so in a month it looses 30×1.72 = 51 seconds or 1 minute a month (approx).

Error: 1.73 seconds per day.

One of the other factors in a wrist watch is that you wear it on your wrist – and the human body is at a constant temperature.  Crystals have a temperature coefficient graph meaning that another source of error is temperature (This is why you can buy an OCXO or Oven Controlled Crystal Oscillator – that generates heat and keeps a constant temperature).  The watch crystal will be better because you keep it at a constant temperature!

How good is an oven controller crystal oscillator OCXO ?

A typical spec might be ±1 x 10-9 (1ppb) so the error after a day would be 86.4us and after a month 2.6ms (2.6e-3 seconds or 2.6 thousandths of a second!).  They are not quoted in ppm as it becomes inconvenient to write e.g. this OCXO has a ppm value of 0.001 ppm or 1ppb.

Error: 84.6us per day.

Note: there are many types designed for many different applications and
all costing different amounts!

How good is a rubidium oscillator ?

This is also known as an atomic clock.

A rubidium clock has an accuracy of about ±1 x 10-12 so the error after a day would be 86.4ns (84e-9 seconds 84 billionths of a second!) so the error after a month would be 2.6us.  Again using ppm is also inconvenient for writing : 0.000001ppm or 0.001ppb

Error: 86.4ns per day.

Error: 2.6us per month.

How good is a cesium oscillator ?

This is also known as an atomic clock.

Cesium beam atomic clocks are stable to 1 x 10-13 (8.64ns/day 8 billionths of a second!) or 259ns (259e-9 seconds) a month (ppm is 0.0000001ppm ! or 0.0001ppb).

Error: 8.46ns per day.

Error: 0.259us per month.

Note: A Cesium fountain is stable to 1 x 10-15.

Comparison of oscailltor’s accuracy

Type Accuracy (ppm/ppb) Accuracy Aging /
10 Year
Aging / 10 Year
Crystal 10ppm-100ppm 10-5 – 10-4 10-20ppm 10×10-6
TCXO 1ppm 10-6 3ppm 3×10-6
OCXO 5-10Mhz 0.02ppm
2×10-8 ~0.2ppm (200bpp) 0.2×10-6
5×10-7 ~10ppb 1×10-8
Rubidium Atomic 1×10-6ppm (0.001ppb) 10-12 0.005ppm (5ppb) 5×10-9

Some TCL code for looking at ppm

# Calculate the ppm given a nominal frequency and actual frequency.

# ppm? 20e6 19998485 Returns 75.75 ppm

proc ppm? { nomf f } {

return [expr (abs($f-$nomf)/$nomf)*1e6 ]


# given ppm return decimal e.g. ppm 200 is 0.0002

proc ppm { ppmv } { return [expr $ppmv/1e6] }

# given ppm return decimal e.g. ppb 10 is 1e-8

proc ppb { ppbv } { return [expr $ppbv/1e9] }

# ppm range show max and min of freq:nomf and ppm value

proc ppm_r { nomf ppmv } {

puts [expr $nomf+([ppm $ppmv]*$nomf) ]

puts [expr $nomf-([ppm $ppmv]*$nomf) ]


Download TCL from Active state (free) and download tkcon. Double click tkcon to start it and paste the above procedures into tkcon, then use the them by typing in commands at the tkcon command prompt (Turn on calculator mode in preferences):

e.g. ppm? 20e6 19999391

results in 30.450000000000003

i.e. It shows you the ppm value: 30ppm for given nominal frequnecy and actual measured frequency..

What’s All This PPM Stuff?

More times than not when talking to a customer about clock accuracy and I mention a spec in units of parts per million (PPM) the response is, “Huh? What’s PPM?” Fair enough, but first some background:

Behind every great clock there’s a crystal, a piezoelectric device that vibrates at a precise and known frequency. There are other ways to generate frequencies (a resistor and capacitor combination is one of them), but none are more accurate.

Many of our data logger products provide a built-in date and time clock that the instrument uses to time and date stamp recorded data. If you record temperature and humidity, for example, you’ll be able to determine the date and time of occurrence to a precision that is determined by the accuracy of crystal that drives the date-and-time chip that’s embedded in the instrument.

For reasons known only to crystal manufacturers, crystal accuracy is speced in units of PPM. Lower PPM crystals cost more than higher PPM, and manufacturers like us who use crystals in our products make a price/performance judgement call and then simply spec time-and-date clock accuracy at whatever PPM number is associated with the choice. So how do you use PPM to put the figure into the context of your application? I’ll answer that with an example.

The de facto standard in the industry for crystal inaccuracy is 20 PPM, which is always interpreted as a plus or minus number (±20 PPM). In a general sense, for this inaccuracy figure we can state that after 1 million actual  parts, the registered number may be 999,980 to 1,000,020. In the context of a date and time clock, “parts” can be anything that you want it to be: days, hours, minutes, but most likely seconds since it doesn’t make sense to spec inaccuracy over 1 million days (270+ centuries). So, after 11 days, 13 hours, 46 minutes, and 40 seconds (i.e. 1,000,000 seconds) the date-and-time chip driven by the ±20 PPM crystal will register an actual time of this value, ±20 seconds.

You can also express PPM as a percentage: ±20/1,000,000 = ±0.002%. So after 30 days (2,592,000 seconds) we can expect the clock to drift about ±52 seconds; after 60 days about ±104 seconds, and so on.

Science behind Moon’s color and it’s shapes….!

At low height at horizon in the sky moon looks red, because of red color has to reflect (refract) less compare to blue/violet, so due to degradation/deterioration of visible light, moon looks red (initially) then in full sky During the day, the Moon has to compete with sunlight, which is also being scattered by the atmosphere, so it looks white.emsVisible_mainContent_colors-wavelengths


Science behind shapes of Moon….!

Workshop on 1SHEELD….!

With due to maximum respect I would like to inform you that V.T.Patel Department of Electronics and Communication Engineering of Chandubhai S. Patel Institute of Technology, CHARUSAT, Changa is going to organize a workshop on “To make your Smartphone as a configurable ARDUINO shield (1SHEELD)”. During this workshop, students will go through a very attractive and useful feature of ARDUINO and 1SHEELD’s user Interface and standalone application development. By the end of this workshop, candidates would get a hands-on experience of working with Open source ARDUINO Platform and how to access Smartphone’s sensors remotely (using Bluetooth) along with remote programmable user interface for standalone application. Candidates will get a certificate after successful completion of workshop. Details of the workshop are as followed.

Speaker: i). Mr. Rahul Tanna

ii). Mr. Divyesh Patel

Methodology: Lecture/Presentation, Practical sessions

Time frame for workshop: This is a one day workshop, approximately 6 hour workshop.

Audience: B.E. / B. Tech. Students in group of 4(Allowed of all the departments)

Total Strength: Minimum 10 groups

Skill level requirement of participants: Candidates with basic knowledge of C programming.

Resource Persons: Faculties of CSPIT (EC Department)

Infrastructure: Laboratory, PC

Fee Structure (per group): With ARDUINO UNO: 6700

Without ARDUINO UNO: 5700

Preferable Date: 4th week of January, 2015  

Sub: To make your Smartphone as a configurable ARDUINO shield (1SHEELD)

CSPIT is the first institute established in year 2000 at Education Campus – Changa (now CHARUSAT). The institute is religiously managed through a think tank of technocrats, administrators, scientists, engineers, educationalists, businessmen, stakeholders and other well-wishers from all parts of the world. CSPIT offers B. Tech. program in Computer Engineering, Information Technology, Electronics & Communication, Mechanical Engineering, Electrical Engineering and Civil Engineering with total intake of 660 students. This institute also offers a M. Tech. programme in Electronics & Communication, Computer Science & Engineering, Electrical Engineering and Mechanical Engineering with total intake of 90 students. All the programmes at CSPIT are approved by the All India Council for Technical Education (AICTE). All the programmes are accredited by the National Board of Accreditation (Except Civil Engineering).

Objective of workshop:

Main objective of this workshop is to use of very attractive and useful feature of ARDUINO and Smartphone. Smartphone will interface remotely with ARDUINO using 1SHEELD mounted on top, using Bluetooth of Smartphone. At the end of the workshop, one will have Arduino shield that can link with an Android device and provide a multitude of sensors and advanced functions, and can develop application based project with combination of few application.

By count, there are currently 37 different “shields” that the 1Sheeld can emulate. 11 of those are sensor shields –things like: accelerometer, light, gyroscope, pressure. Another 10 are basic I/O operations, such as: buzzer, keyboard, microphone, gamepad, and a variety of buttons. 7 more handle communications and social networking: Twitter, Facebook, phone, email, Skype. Finally, there are 9 special function shields, including: voice recognition, speech synthesis, notifications, camera, LCD and data logger. One has to simply tap them on the app to add that functionality, though some will require additional setup such as authorizing Twitter. So, 1SHEELD is shield which can replace multiple sensors with only one shield, and make application cost effective.

Reply by post below if anyone is interested.