Voltage Regulator for BVA
I'm using an "ALWSR" low noise voltage regulator to power the 8607 BVA. It is designed by Andrew Weekes and is based on Walt Jung's "Super-regulator". Andrew's web pages about the regulator start here: http://www.andrewweekes.talktalk.net/potentially_positive.htm.
The board has a pre-regulator stage but using this requires significant headroom above the output voltage -- abiout 4 - 4.5 volts. Since the oscillator wants 24 volts and the system is run off of 2 "12V" AGM cells in series connected to a float charger, this doesn't allow for much drop if the power goes off and the batteries start to run down. The main advantage of the pre-regulator is to improve the dynamic stability of the system (ie, reduce the output voltage change when there is a sudden change of input voltage). That's not a major issue for this application since the OCXO will draw nearly constant power once it's warmed up. So, I am bypassing the pre-regulator stage to reduce the headroom requirement.
With a 28.8V input, the output voltage is 24.023+ volts. Reducing the input voltage shows a very pronounced loss of regulation at about 24.5V, with about 0.1V reduction of the output over less than 0.1V change of the input. (The "+" signifies that the sixth digit on the HP 3456A voltmeter is cycling in the range of 3 to 7 after the regulator and power supply had been running for about 30 minutes; the DVM has been running for months, but is also a couple of years out of calibration.)
The circuit uses an LED which glows when the circuit is operating properly. The LED extinguishes at about the same point as regulation is lost, so it's a good reference point -- if the LED is fully lit, there's enough voltage to maintain regulation.
As a last bit of data, at 28.8V input, the regulator draws about 32ma with no load other than the DVM.
jra on 12.28.11 @ 03:03 PM EST [link]