interfacing to a 7-segment decoder: http://www.thelearningpit.com/lp/doc/7seg/7seg.html

4511 datasheet: http://www.datasheetcatalog.org/datasheet/philips/HEF4511BN.pdf

This auction is for 5 pieces of 3W White LEDs mounted on stars

Specifications:

Intensity:                129.5~147.7 Lumins
Viewing Angle:         140°
Forward Voltage:      3.2V-3.8V
Forward Current:      700mA @ 25C°
Color Temp:            5500K
ProLight PN:            PM2A-3LWS-SD (BIN: V2)

Features
● High flux per LED
● Very long operating life(up to 100k hours)
● Various colors
● Good color uniformity
● RoHS compliant
● More energy efficient than incandescent and most halogen lamps
● Low Voltage DC operated
● Instant light (less than 100ns)
● No UV
● Superior ESD protection

Payment methods: I’m PayPal Verified

• We will only ship to PayPal’s Confirmed Address.
• Please Checkout & Pay immediately within 5 days, any questions please contact us, Otherwise an non-paying bidder alert may be issued.

Shipping & Handling:

• Your shipping/billing addresses must match!!
• Our company will not be held responsible for lost, damaged, or stolen mail.
• No Local Pick Up.
• Usually, everything is shipped the following day following full payment of item
• Items purchased before 12am Eastern will ship the SAME DAY
• Expect arrival of item within 3-4 days anywhere in the US.
• All items are packaged in rigid bubble mailers.  We take no responsibility for the package once it has left our premises.
• All items are NEW.   We do not accept returns of any kind due to the low value and profit selling on ebay.  The items are guaranteed to work and are NEW.  You understand this risk you are taking by ordering.
• We take no responsibility for usage of the item.  LEDs are sensitive to current/static and need resistors in-line with them to guarantee a long life.  Buyer acknowledges that they know how to wire the LED properly. By placing an order, you acknowledge you have read and agree to these terms.

An LED can be used as a photodiode used for light detection as well as emission.

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

A cathode is an electrode through which electric current flows out of a polarized electrical device. Mnemonic: CCD (Cathode Current Departs).

Cathode polarity is not always negative. Although positively charged cations always move towards the cathode (hence their name) and/or negatively charged anions move away from it, cathode polarity depends on the device type, and can even vary according to the operating mode. In a device which consumes power, the cathode is negative, and in a device which provides power, the cathode is positive:

* In a diode, it is the negative terminal at the pointed end of the arrow symbol, where current flows out of the device. Note: electrode naming for diodes is always based on the direction of the forward current (that of the arrow, in which the current flows “most easily”), even for types such as Zener diodes or solar cells where the current of interest is the reverse current.

1C = 1A * 1s

One coulomb is also the amount of excess charge on the positive side of a capacitance of one farad charged to a potential difference of one volt:

1C = 1F * 1V

MOSFET (Metal Oxide Semiconductor Field Effect Transistor) – A voltage controlled transistor for amplification and switching.

The circuits in the 555 timer video series use an enhancement mode N-channel type power MOSFET, which is controlled by a positive voltage at the gate. Enhancement mode MOSFETS are off when there is no voltage at the gate. The transistor will be either fully on or fully off for most of the time in this application. When it is off, the transistor’s resistance is very high, so only a very small amount of leakage current will pass through it. When it is on, the resistance is very low. Because the MOSFET will be in these two states for the majority of the time, very little power is consumed, so minimal heat in generated. However, if the current required by the load is high enough, then sufficient heat will be generated due to the resistance of the transistor when it is on that heat will become a issue. Heat sinks and multiple MOSFETs connected in parallel can be used to increase power handling.

The diode in the MOSFET portion of the circuit provides a path for the current resulting from the voltage spikes that occur when the power to an inductive load is switched from on to off. A diode used in this capacity is called a flyback or snubber diode. The maximum forward current rating for the diode should be high enough to handle the full current of the load, which it will be momentarily subject to each time the MOSFET shuts of the power to the load. The maximum repetitive reverse voltage for the diode needs to be as high as the voltage across the load. The diode is only needed across the load when that load is inductive like with an electric motor.

Gate resistor – MOSFET gates have capacitance, and require charging which results in a delay between when the voltage is applied and when the transistor is fully on. MOSFETs also have a small amount of inductance which can react with the capacitance as unwanted oscillations. These oscillations can be controlled by way of connecting a resistance to the gate. This lowers the Q and dampens the oscillations. The resistance also increases the amount of time it takes for the capacitance to charge and discharge, so it increases the amount of time it takes for the transistor to turn on and off. Without an appropriate gate resistor, the oscillations can cause the transistor to turn back on when it should be in the off state. The oscillations can also damage the MOSFET.

MOSFET gate ringing reduction with gate resistors – http://hmin.tripod.com/als/ccs/docs/pdf/Fairchild_AB-9.pdf

Forum threads on MOSFET gate charge and resistors:

http://www.edaboard.com/thread29231.html

http://www.edaboard.com/thread165570.html

The MOSFET power output sub-circuit is described in the following link: Power MOSFET Sub-Circuit

Adjustable 555 PWM Schematic