10/30/50/100W LED application driver (UC3843A)
The operation of power LEDs calls for constant current source for higher performance. (> = 1A)
As an example, of operating a 30W was shown LED to a modified Step-Up Converter (boost) here.
One is to use 30W power led with the following parameters:
- Power: 30W
- Color temperature: 3000-3500 k
- Operating voltage: 30-38V
- Operating current: 1A
- Light output: 2600-2800 lumens
- Life duration: > 50,000 hours
On the laboratory power supply, the operating current of 1A at approx. 38V adjusts itself.
No constant current source is available, it can be operated LED with under voltage at low light output degradation. This voltage is selected, where the current is 10% less operating current (900mA). It is to make sure that the power, caused by thermal drift, specified does not exceed the operating current of the manufacturer.
Using a Step-Up transformer (boost), this led also to voltage sources can be operated, whose output voltage < = operating voltage is. (E.g. batteries, rechargeable batteries, power supplies)
- Input voltage: 10-32V
- Output voltage: 12-35V
- Input current: 10A (16A Max with extended cooling)
- Output power: 100W (150W Max with extended cooling)
- Efficiency: 94% (input 16V, output 19V 2.5A)
- Ausgangsspannungsripple: 2% max
- Load regulation: -0.5%
- Voltage regulation: -0.5%
- no short circuit and reverse polarity protection
Als Leistungsschalter findet ein STP75NF75 Einsatz (75V 80A NMOS), Leistungsdiode ist STPS2045C (45V 30Arms Schottky). Ohne Austausch des Leistungsschalters und der Diode sind somit Ausgangsspannungen von maximal 45V möglich.
Following figure shows the original circuit:
This has the disadvantage of being unstable in higher load ranges and/or translation ratio. At UIN = 12V4, Uout = 32V and Rload = 15R2 (Iout = 2A, pout = 67W) shows the measurement to the following of the unmodified circuit behavior (Orange = Vout, blue = VInduktor):
For subsequent simulation (original), C1 is replaced with a resistor (100 k). 20V input voltage, 32V output voltage (4A/120W) reveals the instability of the arrangement:
To stabilize are changed in the other R1 and R99 worth (modification 1).
The example simulation to 20V input voltage, output voltage (5A/160W) 32V shows:
For use as a purely limited voltage LED driver the circuit can be modified, as shown below, continue. Be changed to the value R1/R7/R99, the connection of R99 is now on the 9V (7809). Note the minimum input voltage for different outputs.
A modification is necessary for constant current mode as shown in the following figure. R9(R99) is equipped with 9 k 1 / 10 k to be provided. Furthermore a measuring shunt 0.33Ohm (load resistance), a standard diode (1N4148 or similar), as well as a 5kOhm potentiometer (10 speed potentiometer/trimmer preferred) needed. The shunt is inserted "low side" in the output circuit, the potentiometer accordingly connected to the shunt, VfB (Pin2), as well as the Vref (Pin8).
R2/R3 represent the (newly added) potentiometer, Rload the LED in the simulation. The open circuit voltage is adjusted with the already existing potentiometer, this shall be less than the voltage value of the output capacitor. For proper operation, it is essential that the output voltage (or voltage of the LED) at the nominal current is greater than the input voltage of the Step-Up Converter. The test setup is shown below. For higher currents, the value of the shunt is reduced to minimize voltage drop and power dissipation. The structure shown here has with 1A nominal power (LED) an efficiency of ~ 86%.
The circuit tag in the summary:
Because the circuit with R8 (measuring shunt 10 mohm) is a bit on the low end, it is, to replace it with 50mOhm. This results in a higher control loop stability, also the feedback (compensation) to be interpreted high-ohmig. The changes for constant voltage/constant current shown below:
Finally some pictures of the color impression on each fixed white balance (daylight) / Aperture / Shutter speed (separately for both subjects):
For great Step-Up ratios, it has proven to replace the coil against models from Coilcraft. Without further alteration, 33uH work here without any significant heating - even at 12V-> 36V and 150W power consumption.
If voltage ripple is not an issue,
could be used.
If you would like to know more, look in the D amp-Forum over.
LTSpice simulation: Download (zip)