|Re: Anyone build a ZVC (Zeprom Voltage Converter) Continued - 2|
Message #1 Posted by Dan Grelinger on 26 July 2008, 10:15 p.m.
I have continued to flush out the parts manifest, but am not quite done. There are two parts I need help with; one needs a little help with specs, and the other a source (where I can buy less than thousands).
But first, here are the specs I have for the ZVC and ZEPROM. This might be helpful in specing out the coil.
When the ZVC is turned on (generating 12.5V), but the ZEPROM is not programming itself, the measured current from the HP-41 battery supply is 4.9 mA.
When the ZEPROM starts programming itself, the total measured combined current for both ZEPROM and ZVC is 14.6 mA average, 15.1 mA peak. (HP-41 power supply is 6 volts, the ZVC provides a 12.5 volt supply to the ZEPROM for programming)
I think I have a set of good specs for the parts, except for one, the coil. What I know is that it is a 220 uH Ferrite Core Inductor (Thank you, Deigo!) and that I measure a resistance across it of approximately 2.2 Ohms (after subtracting lead and contact resistance). When I searched digikey's vast catalog of ferrite core through-hole inductors, I find several that have this approximate DC resistance, and with what appears to me to be a reasonable peak current specification (160 mA - 230 mA). Unfortunatly, none of them are stocked, and minimum quantities are 500, for a total price of $56.88. What is a minimum max. current spec that I should use? Anything over 100 mA would seem to be reasonable, given the ZVC measured current values.
The 1-ohm, 1% tolerance, 100 ppm/C spec'ed resistors are hard to find in reasonable quantities as well. Digikey has them, but I have to buy 2500 or 5000 minimum quantity. I don't need more than 30 of them.
Update Part Manifest (digikey part numbers):
(1) IC1- MC34063 P1 Voltage Booster (296-17766-5-ND)
(3) D1,2,3 - 1N4001 Diode (1N4001-TPMSCT-ND)
(1) Cout - 470 uF Capacitor (565-1660-ND)
(1) Cin - 100 uF Capacitor (P963-ND)
(1) CT - 1000 pF Capacitor? (BC1072CT-ND)
(1) C1 - 0.1 uF Capacitor (BC1148CT-ND)
(3) R3,4,5 - 1 Ohm Resistors, 1% Tolerance 100 ppm/C (Need source)
(1) R6 - 150 Ohm Resistor, 1% Tolerance (P150CACT-ND)
(1) R1 - 2.4 kOhm Resistor, 1% Tolerance (P2.40KCACT-ND)
(1) R2 - 22 KOhm Resistor, 1% Tolerance (P22.0KCACT-ND)
(1) 220 uH Ferrite Core Indcutor (Need Source)
(1) Double Sided PCB
(1) HP-41 Module contacts and housing (anyone know a source?)
Thanks for any and all help!