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MC34063/33063 LED Driver

Kiran Ramaprasad
Prodigy 50 points
Other Parts Discussed in Thread: MC34063A, TPS54160, TPS54140, TPS62110, TLV431

Hi,

 

I have a requirement for a very low cost (cost-effective) LED Driver for 5V to 35V DC Input.

Current Requirements are 350mA to 700mA

Can i use the MC34063 for this?

Reason:MC34063 offers the lowest cost solution.

I had read an article from TI on using this IC in one of the electronic design websites..not able to trace the link back.  This was on designing hysteritic control LED Driver using 34063

Please advise.

Thanks,

Kiran

  • 0
    TI__Guru*** 140106 points

    Hello Kiran,

    Was this schematic in the article?

    I do not believe this circuit will work well. The current limit of the MC34063A does have a reliable threshold, but the effect on the timing capacitor voltage is not as predictable.  The CT pin can become super charged (much higher voltage) between the time the current limit is reached and the coil current falls below the limit. This makes the off time much longer and proportion to VCC.  Also the driver current on pin 8 will change significantly as VCC goes from 5V to 35V.

    I would normally suggest using a buck converter setup with the LED and current sense resistor as the load and feedback point. However, the voltage loss would be too much for 5V operation.

    Regards,
    Ron M.

  • 0
    TI__Guru*** 142860 points

    Kiran,

    Here is an app note that discusses using the TPS54160 as an LED driver: http://focus.ti.com/lit/an/slva374/slva374.pdf  There is also an EVM available that you can order.  The TPS54160 meets your specs, as does the TPS54140, which would be a little cheaper.

    To reduce the power loss in the sense resistor, you can bias up that voltage with a TLV431, as described in this EVM for the TPS62110: http://focus.ti.com/lit/ug/slvu254/slvu254.pdf

  • 0 in reply to Ron Michallick
    Prodigy 10 points

    hello Ron. this circuit works very well , with minor modifications , just add a simple resistor (100k) at CTpin. For me works for 6 months , and is awesome circuit . Very low count component . carefull at selection of inductor , in rest is very well .Maximum current achieved in safe conditions is 700mA , but is enough for my applications .