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TLC5924 for channel switching of a tube amp with LDRs

Willem Bleymueller
Prodigy 100 points
Other Parts Discussed in Thread: TLC5924, TPIC6B595

I'd like to implement a channel switching device which uses LDRs and LEDs as it is used in vacuum tube amplifiers where high voltage swingout might occur.

My archetype is a circuit from Mesa Boogie which uses a shift register and diode logic to switch the corresponding LEDs which are needed for a certain audio path when a certain channel of the amp is selected. The circuit can be seen in the attachement

I was wondering whether it would be possible to drive the LEDs directly with a TLC5924 and do the logic in software. 

For a clean signal it would be mandatory that the LED current is constant and not oscillating. Thus I was asking myself whether the signal that the TLC generates to switch the LED on is clean or whether it does some PWM or such tricks.

So does anyone know whether the TLC5924 produces a constant uninterrupted signal?

One could of course use a TPIC6B595 or something but this requires more external circuitry.

A second question is whether it is possible to use the TLC on the same bus as "real" SPI devices as there is no real CHIP SELECT signal.

Any reply would be appreciated,

Thanks, Willem.

  • 0
    Intellectual 670 points
    "A second question is whether it is possible to use the TLC on the same bus as "real" SPI devices as there is no real CHIP SELECT signal."
    you can use a bus-driver with an enable input and use this as Chip Select. otherwise the TLC can interpret data that is not meant for him...

    for the constant on question - i don't know. thats something ti has to answer.. there is no information in the datasheet about that -
    but it is nowhere written that the constant current is done with an linear driver - so it could be a pwm-based switching.

    sunny greetings
    stefan