Re: OCXO Kit - Are These Ideas OTT? #ocxo #mods


geoff M0ORE
 

If you use a LM78L05, it will current limit at about 100mA itself. When the heater has warmed up and the current drops, it will voltage regulate to 5 volts. It must be the "L" version. Another way is to use two LM317's, one to control the voltage to the required amount and another to current limit. I've just made a battery charger to charge at 300mA up to a maximum voltage of 4.2 Volts. Just happen to have a bunch of 317's lying around.

Geoff

On 25/07/2019 10:45, Brian George via Groups.Io wrote:
Just starting to build the OCXO kit for my own homebrew project. There is plenty of room in the project case so I wondering whether to incorporate two possible modifications :

a) use a front panel-mounted control for R21 (temp adjust) with a vernier slow-motion drive. Could this be useful or is the setting of R21 truly "set and forget" regardless of the ambient room temperature?

b) take the heater supply via a separate LM317 (with heat-sink) and use a front panel-mounted potentiometer to vary the regulated output voltage from "low" to +5v. It would probably be necessary to feed the LM317 with around +6v to compensate for the drop-out. This would allow control of the oven start-up current, manually cranking up to the full +5v as the oven approaches a stable operating temperature.

Any thoughts on whether or not all this is completely unnecessary / OTT - particularly from those who have built and used this kit?

Thanks
73

Brian
G3ZOH 

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