Q:
How to design a circuit that can strobe HB LEDs at high frequencies (1000Hz to 35kHz). It will be overdriving 2-5 Luxeon III (3A, 3.8V each) or 2-5 Osram dragons (2A, 1.8V each). The input voltage will be 24-32 VDC. Is this possible using the MLX10803?
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A:
Let's take as example the configuration with 3 Dragon LEDs from ) OSRAM.
1. Use Coil_Calc software to set the MLX10803 mode. In this case with a minimum switching frequecy 270KHz at 24V.
2. From OSRAM Dragon spec.(LRW5 for example) page 9 follows that for desirable 2A pulse current the max. duty cycle's 3% ( D= 0,03).
3. The maximum strobe frequency starts as (270 * 0,03) / 3 = 2,7 KHz.
In this calculation it is assumed that the minimum strobe duration is 3 periods of 270KHz.
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Q:
I am using an MLX90805 chip to control an induction fan 220vac .5kw without sucess.I have set up the chip configuration to 3 wire operation - rz 470k rm 10k rt 150e cf 100uf. My pot is giving at 5v swing on the set input so it is ok. I want the fan to change speed in relation to the set voltage so that I can control the induction fan from a d to a from a micro controller. Has anyone got any ideas.
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Q:
The values of the resistors and cap are ok. May be RM should be a higher 15K, 18K. You also can try RT 100 Ohms.
As I understood you cannot control the speed of rotation by the pot. Am I right? What type triac do you use? If all is ok on the TRG output (pin 5) you should observed a firing pulses.
Is it possible for you to provide more information?
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Q:
Thank you for your reply. I have tried everything but still no success. The sample chips that I have do not seem to be programmed. Do you know if the chips are supplied unprogrammed and if so , what do you need to do to program them???
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A:
I suppose that you use 8-pin mlx90805 parts. The settings are kept in ROM. The chip cannot be un programmed nor reprogrammed.
I need more information. If is possible to have a look on the schematic. What type triac do you use?
How many samples have you tested?
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Q:
Problem in making an LED driver for 1Amp LED which will be powered by 5V. Use the circuit schematic as shown on the datasheet of the evaluation board EVB10803. Here you can also find an XLS file to calculate component values. The data to enter:
Supply: 5V
LED threshold: 3,75V
Number of LEDs in channel: 1
Feed back diode threshold: 0,9 V
Rsense: 0,33 Ohm
Vpeak at Rsense: 340 mV
Tmonoflop: 1 uS L (the Coil): uH 47
Values for Rosc is 13K Ohm and RIref is 34K Ohm.
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A:
The minimum value that you can use on the ROSC is 39 kOhm to ground, a value below that gives unpredictable results on the internal oscillator. It will stop most likely. See page 10 in MLX10803 IC specification.
Coil_calc is made little bit more general so it should be possible to use for other and future types of buck regulators also, so it does not warn you for a too high switching frequency (or too low). Please control your result to the min and max value in the MXL10803 and MLX10801 IC-specification.
Here are also some warnings for high switching frequencies even if they seem to be a cheaper solution on paper due to smaller coil:
A general rule for all switch regulators is to avoid high switching frequencies due to efficiency loss and noise problems. To get an efficient regulator you should stay below 150kHz also most coils are designed for that.
The noise is always a direct function of the size of the current you switch and the frequency. The worst source of noise is the fly back diode. In a buck topology current regulator you switch quite high currents, actually the peak current. This peak current is independent on the size of the coil. The noise is in principle a direct function of the frequency! The fly back diode generates exact the same noise at every switching occasion.
MLX10803 does the most to suppress noise by randomizing switching, but still you need to pay attention!
If you still want to use high switching frequency, notice that you lose precision, due to the delay in the comparator on the RSENSE pin. Something that all buck regulators have.
In MLX10803 this is deliberately set to 300nS (200 – 400) and named debunch time in the IC-specification. This debunch time is used to filter away switching noise on this pin. The coil_calc excel sheet handles that and will show you the effect.
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Q:
The R vs. T curve of the NTC is flat in high temperature. What is the problem?
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A:
The choice of NTC resistor is precisely described in chapter 8.4 of EVB10803 Datasheet. This datasheet is available on Melexis' website.
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Q:
How to drive several Power LEDs using the Evaluation Board EVB10803?
How to expand an application to drive 8 or more Power LED's with Forward Voltage 3.4VDC @ 350mA, input voltage of 180 to 265VAC 50/60 Hz?
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A:
1. On the Melexis web-site EVB10803 and EVB10803mini are represented and these evaluation boards are targeted for the automotive applications with 6-32VDC input voltage.
2. The MLX10803 can also be used for HV applications as well.
In order to evaluate the behavior of the MLX10803 in the case described above it is suggested to download the Coil_calc software from the Melexis web-site. Then use the following values:
Supply voltage - 300V
Led threshhold - 3,4V
Number Led - 8
Rsense - 1 Ohm
Vpeak - 510 mV
Tmon - 17 us
L - 1500 uH
Coil_cal will generate the next info:
Rosc = 300 K
Riref = 51 K
You can use these values in the application.
Of course it needs to choose the HV transistor (400V) and flyback diode.
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Q:
Which components to use with the MLX10803 to drive high power LEDs from Luxeon (1 A, 3W or 5W, forward voltage about 3.5 V for the 3W type or 6.5 V for the 5 W) or Ostar Ligthning (1A, forward voltage about 21 V)? The supply voltage for the circuit is 24-28 V. The circuit should also allow dimming the LEDs.
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A:
Use the EVB10803:
3W case :
Rosc = 120K
Riref = 36K
coil is the same : Wurth WE-PD, L type, 100uH
you can use the smaller MOSFET transistor in SOT-23 package as PMV213N.
5W case :
Rosc = 56K
Riref = 36K
coil is the same : Wurth WE-PD, type L, 100uH
you can use the smaller MOSFET transistor in SOT-23 package as PMV213N.
Ostar Lighting case ( 21V, 1A )
Rosc = 39K
Riref = 40K
coil is the same : Wurth WE-PD, type L, 100uH.
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Q:
Which settings to program for the MLX10803 to drive a halogen lamp: 100W bulb (e.g. Osram Halostar 64460 U, 24 V, 100 W, D 12/L 44 mm, GY 6,35) with a rating of 24V.
Analog dimming is required as well. The supply voltage of the Melexis chip can be assumed to be >24V e.g. 26V.
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A:
For this case use the next settings :
Rsense = 0,1 Ohm ( EVB10803 has 0,33Ohm)
Rosc = 100K
Riref = 43K
Coil's the Coilraft ( www.coilcraft.com) PCV-2 type, 180uH, you also have to use more powerful flyback diode.
For analog dimming purposes please adjust the value of Riref from 43K to down.
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Q:
What is differences of MLX10803 and MLX10803A?
On Digikey I found MLX10803KDC and MLX1083KDC-ND. I can not find what these number stand for.
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A:
The MLX10803A is an obsolete revision and is no longer available. It has the same features as MLX10803, but the current from the IREF pins is 20uA instead of 50uA. The reference voltage at the ref pins are 10 times higher in contrast to the specification that says 5 times.
The MLX10803KDC-ND is the same as MLX10803KDC. Digikey adds -ND to the manufacturer's part number.
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Q:
I could not find the datasheet of MLX22322 anywhere. Could you please let me know where I can find it. Thanks.
pls tell me about mlx22322&mlx90711 difference.
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A:
MLX90711 is ASSP that can be customized by selecting set of options. MLX22322 is one such customization (or version).
The options and their values are described in the Datasheet. The available customizations are listed on page 11.
In fact MLX90711 is always produced as customazed version for given customer. If you need version with options different from these listed on p.11 we shall produce a version for you.
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Q:
Can you provide the schematic for the MLX10803 to drive 5 LEDs in series at 700mA with LED Forward drop = 3.5V. Input is 160 to 265V AC
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A:
Melexis has developed applications that will fit this need. Please contact your local sales person for more information.
Other parameter that is important to know is:
Expected power form factor.
We can also support you with solutions that are possible to dim using normal wall (triac) dimmers. (Many LED driver solutions are not even surviving triac dimmers.)
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