LED Driver IC needed for demanding application

treez

Intellectual 970 points

Other Parts Discussed in Thread: TPS61500, TPS54160

I need to deisgn a LED Drive circuit (SMPS) which can drive two different LED luminaires which may be connected to it:-

One luminaire is 6 LEDs in series with 330mA current.

The other luminaire is one LED with 650mA current.

The above 330mA must be dimmable down to 22mA (+/- 20%)

The above 650mA LED must be dimmable down to 65mA (+/- 5%)

My supply rail voltage is 14V (+/- 20%).

(it pulsates at 100Hz due to baing secondary of mains power supply)

The LED luminaires will be attached to the LED driver by three metres of cable, so we must put considerable capacitance across the connection to the cable in the LED Driver…

…….we are also worried about EMI from this cable –specially wondering about how PWM type dimming would affect EMI from this cable.

Initial investigations with buckboosts, show that the LED current tends to oscillation if not addressed, and also that supply ripple rejection requires much work with the control loop.

Do you have LED Driver IC’s for this ?

over 14 years ago

0 Jeff F over 14 years ago

TI__Guru*** 143910 points

To clarify, do you need the same circuit for both applications or can we use the same IC but configured differently for each application?

0 Jeff F over 14 years ago

TI__Guru*** 143910 points

The TPS61500 could be configured as a boost or a SEPIC to provide power to the six series LEDs from 14Vin. A boost configuration will be slightly more efficient. The TPS61500 would need to be configured in a SEPIC configuration to drive the single LED from 14Vin.

0 treez over 14 years ago in reply to Jeff F

Intellectual 970 points

It needs to be the same circuit in both cases.

0 treez over 14 years ago in reply to Jeff F

Intellectual 970 points

Thankyou,

we wish to avoid sepic as it can't be PWM dimmed due to the resonating problem of the series cap with output inductor.

With what you have said, we would rather use a higher rail voltage, and go for a buck solution.

Do you have Buck LED Drivers for bucking down from 26 to 34v to the above led string voltages.

We also need the accuracy of LED current and our micro needs to be able to dim the LEDs.

Micro can PWM dim or make analog voltage by pwm'ing an RC network

0 Matthew Day over 14 years ago in reply to treez

TI__Mastermind 36110 points

I suggest the TPS54160 EVM as a good starting point. http://focus.ti.com/docs/toolsw/folders/print/tps54160evm-535.html

0 Jeff F over 14 years ago in reply to treez

TI__Guru*** 143910 points

The TPS61500 takes a PWM input signal and performs analog dimming by changing the Vref voltage to which the sense resistor voltage is regulated. There is a DC current flowing through the LEDs at all times, no pulse currents or fast transients. Although I have not tried it, I do not think such a dimming method will cause a resonating problem with the series cap and output inductor. I will try it in the lab and let you know, unless you do not want to perform analog dimming.

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LED Driver IC needed for demanding application