MiscEl: Leds

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Calculate/analyses component values for different LED bias circuits. The color bar at the top of the form shows the different wavelengths and their color, the marked areas are the typical diode wavelengths.

Supported circuits

R (DC)Only a resistor, used for DC circuits
T (DC)Discrete constant current source, used for DC circuits
IC (DC)IC constant current source, used for DC circuits
R+D (AC)Resistor+Diode, the most simple AC circuits, low efficiency, very high power loss at high voltage
R+C+D (AC)Resistor+Capacitor+Diode, a better AC circuit, can be used over a wide range of voltages
D+C+R (AC)Diode+Capacitor+Resistor, best for low voltages, rectifies the voltage, this eliminates the mains frequence flashing of the LED
DD+CC+R (AC)Dual diode+Dual capactir+Resistor, best for very low voltage, rectifies the voltage with a voltage doubler, this eliminates the mains frequence flashing of the LED
R+Bridge (AC)Resistor+Bridge, double efficiency of a single diode
R+C+Bridge (AC)Resistor+Capacitor+Bridge, the best AC circuit, can be used over a wide range of voltages with high efficiency

Input values

Input voltageAc or DC voltage used to supply the circuit
FreqFrequence of the AC voltage, when field is empty 50Hz is assumed
Led voltage dropVolts accross LED while on, depends on LED type, check datasheet for actual LED, 2 volt can usual be used (for green/red/yellow leds) when the voltage drop over the resistor/capacitor is more than 3 volts
RVoltage drop resistor, for series capacitor solutions this resistor is used to limit the peek current in the LED
CCapacitor, this can be either series or parallel capacitor depending on circuit, be carefull with the voltage rating!
LED currentDesign for specified current, most LEDS can handle 10mA, some LEDS can handle up to 30mA or more
Peek currentWorst case one time peek current (Vpp/R), usual in the range of 0.1 to 1A, a high peek current gives a good efficiency (Because most voltage is dropped accross the capacitor)
LED RonDynamic on resistance of LED*
Diode RonDynamic on resistance of diode*
DropDiode on voltage drop*
Bridge RonDynamic on resistance of bridge*
DropBridge voltage drop*
TransistorOnly visible when circuit T is shown, select transistor used in circuit
ICOnly visible when circuit IC is shown, select IC used in circuit
* These values are used to make simple components models, when drawing the voltage waveforms, and calculate the current/voltage/power of the components.

Output values

ResistorDesigned resistor, remember to check the power rating
Discharge resistorOptional capacitor discharge resistor. This resistor will discharge the capacitor to 50 volts in 1 second. This resistor is not included in the calculations.
CapacitorDesigned capacitor, remember to check the voltage. For mains connected circuits also be sure to use capacitors with the correct safety marking.
Diode/BridgeA standard diode/bridge, check peek current rating and voltage rating
Current (rms)RMS current in component
Current (peak)Peak current in component, component must be able to withstand this current, for a short time, without fusing.
Voltage (rms)RMS voltage over component
Voltage (peak)Peak voltage over component, component must be able to withstand this voltage, for a short time, without damage
Power (rms)Power dissipation in component
Power (peak)Peak power dissipation in component, component must be able to withstand this power, for a short time, without damage
Peek (each cycle)Peek current due to the AC frequence
Peek (one time)Maximum peek current under worst case conditions: Capacitor charged to Vp, circuit switched in while supply is -Vp, giving Vpp accross the resistor
Peek falloffHow fast the one time peek disappears
Power input (rms)Power used from supply
Power LED (rms)Actuel power delivered to the LED
EfficiencyA low number means your have designed a heater

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