On 1/30/12 12:06 AM, Cobra007 wrote:
I actually start off with a 3.6V 1/2AA battery, the higher the input voltage, the lower the currents will be. This will reduce some of the losses in the 'HV switcher'. I know that most 1/2AA batteries cannot supply the required current, but a few can and it's a good choice as they are smaller than a CR2. Of course that is not the whole story, the circuit itself is quite complex as I couldn't find a single IC that would do the same job.
It is nice to use a battery that can be purchased locally. The CR2 is available worldwide. The 1/2AA is a special item. Customers don't like to have to special-order a battery on short notice.
I don't expect to get 40dB out of the nixie tubes, but I think 20dB can be achieved. This would bring the current down from 200mA in bright daylight to 20mA at night, keeping the display always readable. Even 40mA would be good enough as this will already significantly improve the efficiency of the HV circuit.
One thing about Nixie tubes that you may not be aware of is that they need some time to start firing, because the plasma is triggered by an external source of energy such as a photon from the room lighting or a stray cosmic ray. The less ambient light there is, the more time they need to start. If you reduce the duty cycle in the dark, you may find that the display doesn't start reliably.
This is why some Nixie tubes were made with radioactive krypton in the tube. But not the 5870 series, as they were designed to be used in an office environment.
I would suggest experimenting with this dimming idea before committing to it. You would hate to discover later that your watch display is unreliable.
It may be possible to solve this problem by detecting when the current starts to flow in the tube, and leave the tube powered up until the current starts, then begin the PWM operation.
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