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ZVC ZEPROM Voltage Converter (continued)
Message #1 Posted by Dan Grelinger on 17 July 2008, 11:43 p.m.

I still have the photos loaded at http://www.flickr.com/photos/dangrelinger/sets/72157604693293476. I have started a parts manifest, and here is what I have so far:

(1) IC1- MC34063 P1 Voltage Booster ($.77 at Digikey)
(3) D1,2,3 - 1N4001 Diode ($.43 at Digikey)
(1) Cout - 470 uF Capacitor ($.33 at Digikey)
(1) Cin - 100 uF Capacitor (need source)
(1) CT - ?? F Capacitor? (very small, less than .1 uF)
(1) C1 - 0.1 uF Capacitor ($.66 at digikey)
(3) R3,4,5 - 1 Ohm Resistors, 1% Tolerance (Need source)
(1) R6 - 150 Ohm Resistor, 1% Tolerance (Need source)
(1) R1 - 2.4 kOhm Resistor, 1% Tolerance (Need source)
(1) R2 - 22 KOhm Resistor, 1% Tolerance (Need Source)
(1) 220 uH Ferrite Core Indcutor ($1.13 at Digikey)
(1) Double Sided PCB
(1) HP-41 Module contacts and housing

Still working on the schematic.

Dan

      
Re: ZVC ZEPROM Voltage Converter (continued)
Message #2 Posted by Richard Ottosen on 18 July 2008, 12:47 a.m.,
in response to message #1 by Dan Grelinger

Quote:
I have started a parts manifest, and here is what I have so far:

(1) IC1- MC34063 P1 Voltage Booster ($.77 at Digikey) (3) D1,2,3 - 1N4001 Diode ($.43 at Digikey)


Since this is a switching power supply, at least one of the diodes has to be fast switching. The diode on pin 1 of the MC34063 must be a 1N5819 or equivalent.

Quote:
(1) Cout - 470 uF Capacitor ($.33 at Digikey)

Since this capacitor is the output filter working at switching frequencies, it has to be good at high frequencies. This means that it should be a ceramic cap (or several in parallel), a tantalum cap or a low ESR aluminum cap.

Quote:
(1) 220 uH Ferrite Core Indcutor ($1.13 at Digikey)

This inductor must have a high saturation current -- maybe as high as 1 to 2 amps -- and a resistance of much less than an ohm. I don't know what coil you chose but for surface mount, I like the Pulse Engineering P0770, P0752 and P0252 series because they are easy to hand solder. Other companies make nearly identical parts.

I hope this helps you in keeping the smoke in the chips. :-)

-- Richard

            
Re: ZVC ZEPROM Voltage Converter (continued)
Message #3 Posted by Dave Shaffer (Arizona) on 18 July 2008, 11:31 a.m.,
in response to message #2 by Richard Ottosen

Quote:
Since this is a switching power supply, at least one of the diodes has to be fast switching.

I'm under the impression that switching power supplies operate at a few kHz to perhaps a few 10s of kHz. I've never seen a diode that won't switch that fast! Similarly, I suspect that any 470uF capacitor would work just fine.

                  
Re: ZVC ZEPROM Voltage Converter (continued)
Message #4 Posted by Richard Ottosen on 18 July 2008, 12:21 p.m.,
in response to message #3 by Dave Shaffer (Arizona)

Quote:
I'm under the impression that switching power supplies operate at a few kHz to perhaps a few 10s of kHz. I've never seen a diode that won't switch that fast! Similarly, I suspect that any 470uF capacitor would work just fine.

You are right about the operating frequency of the MC34063. The specification says it runs at about 33 KHz. This is very slow by today's standards. I commonly use switchers that run at 1 to 2 MHz.

Even 33 KHz is too fast for a 1N4001 type of diode since it is intended for power line frequencies. It's reverse recovery time can be on the order of 10uS -- way too long even at 33 KHz.

You will have to look at the spec's for the capacitor you intend to use to see if its ESR is low enough at 33 KHz. Remember that it has to have an ESR that is low considering the peak currents used to charge it. As an example, if the peak current is 100 mA and the cap has a 1 ohm ESR then the ripple voltage on the cap will be something like 100 mV.

I looked at the Panasonic FC and FK series of caps and they look like they will work since they have an impedance of less than 0.1 ohms at 100 KHz.

Again, I hope this helps.

-- Richard

                        
Re: ZVC ZEPROM Voltage Converter (continued)
Message #5 Posted by Dan Grelinger on 18 July 2008, 1:25 p.m.,
in response to message #4 by Richard Ottosen

Richard, thanks so much for your help!

What I do know is that the original diodes on the board are all 1N4001. The unit I have works well, I've programmed a ZEPROM several times with it, so they appears to work. I'm still working on the schematic, hope to have it posted this weekend.

Thanks!

Dan

                              
Re: ZVC ZEPROM Voltage Converter (continued)
Message #6 Posted by Garth Wilson on 18 July 2008, 1:39 p.m.,
in response to message #5 by Dan Grelinger

Another important issue is the voltage drop across the diode. The 1N5819 diode someone recommended is a Schottky diode which has a much lower forward voltage drop. This is important for the efficiency of the switching regulator. The first time I made a prototype for a switching regulator for one of our products, I didn't have the Schottky diodes here yet, so just to see if I could get it going, I tried a 1N4001. Although the frequency was 175kHz, it did work, but the efficiency was miserable (for both reasons).

Edit: I should add that we use OS-CON capacitors in our switching regulators. OS-CON is a solid dielectric type, made by Sanyo and Panasonic IIRC. The ESR or these capacitors is far lower than even low-ESR aluminum electrolytic capacitors.

For a clean output, the inductance of the circulating-currents portion of the circuit should be minimized. Keep the traces wide, as short as possible, and use a ground plane. It won't be that critical at 33kHz, but hobbyists' tendencies are to make them unsuitable even at this low frequency.

Edited: 18 July 2008, 1:52 p.m.

      
Re: ZVC ZEPROM Voltage Converter (continued)
Message #7 Posted by Diego Diaz on 18 July 2008, 12:50 p.m.,
in response to message #1 by Dan Grelinger

... is CT capacitor (timming cap.) also unkown? can you read any figures on it?

In the pictures I just see the (yellow) top of it but nothing else... apart from that it's connected to pins 2 and 3 of the IC.

According to the datasheet, values between 470pF and 1.5nF are normal for the timming capacitor

Hope you can finally determine the real value for that part and prepare a fully detailed schemtic.

Richard, to the note on the Fast Switching diode, though positively advisable, it's not a *must* as typycal operarting frequency is low, about 33KHz. In fact, the original design does work with three 1N4001. However, it would improve reliability and efficiency.

I've got a question for those with the real stuff in their hands: Can CMT-10 EPROM modules be programmed with ZVC? (I bet there are little chances for this to be true... but... who knows? :-))

Regards to all.

Diego.

PS: Seems that most part of this post was already discussed... (I should have taken my lunch faster... ;-)) Please forgot about the redundant parts.

Edited: 18 July 2008, 12:54 p.m.

            
Re: ZVC ZEPROM Voltage Converter (continued)
Message #8 Posted by Dan Grelinger on 18 July 2008, 1:34 p.m.,
in response to message #7 by Diego Diaz

The spot on the board for the device is labelled "CT", and it looks like a very small ceramic capacitor, but I am not a discrete device expert, so I could be wrong. It does have a small mark on it. '1n0' When I put that into digkey's part search, it came up with several small capacitors, but of different F values, all pretty low, and most in the range that you specified.

According to the ZEPROM manual, there were three programming fixtures available. The ZVC, a ZEPROM Gang Burner that could program up to 8 ZEPROMS simultaneously, and a ZEPROM Programmer from Firmware Corporation, that could program 2 ZEPROMS simultaneously.

                  
Re: ZVC ZEPROM Voltage Converter (continued)
Message #9 Posted by Diego Diaz on 18 July 2008, 2:11 p.m.,
in response to message #8 by Dan Grelinger

Good!

1n0 means simply 1000 picoFarads (or 1.0 nanoFarads)

Only the final schematic draw and PCB layout, and you're almost done.

Good luck!

Diego.

PS. CMT-10 was another EPROM module for the HP-41, manufactured by CMT. (CMT stands for Corvallis Micro Technologies -Corvallis, OR-)

Edited: 19 July 2008, 8:06 p.m.

                        
Re: ZVC ZEPROM Voltage Converter (continued)
Message #10 Posted by Dan Grelinger on 20 July 2008, 12:16 a.m.,
in response to message #9 by Diego Diaz

I was able to remove the bottom module cover from the ZVC, so I got a full shot of the PCB, which I loaded for viewing at http://www.flickr.com/photos/dangrelinger/sets/72157604693293476 .

After several hours of looking at this thing under bright lights and a magnifying glass, I've finally got the schematic done. I took a picture of my schematic and loaded it at the above link as well. The parts list is earlier in this message.

Dan

Edited: 20 July 2008, 12:24 a.m.

                              
Re: ZVC ZEPROM Voltage Converter (continued)
Message #11 Posted by Richard Ottosen on 20 July 2008, 12:38 p.m.,
in response to message #10 by Dan Grelinger

Quote:
After several hours of looking at this thing under bright lights and a magnifying glass, I've finally got the schematic done.

Dan:

I hope your eyes are recovering. :-)

Having done my share of this kind of reverse engineering, I know how tedious and difficult it is. To help me do this, I have a continuity tester that beeps only for low resistance paths in the circuit. Even more important, the tester does not turn on diode junctions so it can not damage any circuitry.

I compared your schematic to the spec. sheet here:

http://www.onsemi.com/pub_link/Collateral/MC34063A-D.PDF

There appear to some errors in your schematic:

First, the junction of S1 and Cin should probably go to pin 6 rather than pin 7 on the chip.

Second, the junction of R2 and D2 should probably connect to the junction of D1 and Cout.

Also, I think that the right side of the inductor should connect to pin 7, not pin 6, of the chip.

-- Richard

                                    
Re: ZVC ZEPROM Voltage Converter (continued)
Message #12 Posted by Dan Grelinger on 20 July 2008, 4:46 p.m.,
in response to message #11 by Richard Ottosen

Quote:
There appear to some errors in your schematic:
No doubt, the traces were hard to follow in a few cases, as they went under a device, and then through the board. I know that it can be more difficult sometimes to proof another's work than to actually create it, so I am indebted to you for your review.
Quote:
First, the junction of S1 and Cin should probably go to pin 6 rather than pin 7 on the chip.
I examined the board closely again, and I think it is correct the way I drew it. I got out my DVM and measured resistances between SI-Cin and pins 6 and 7. The resistance to pin 6 is about 1/3 of an ohm higher than to pin 7, which would make sense, since they are connected by 3 1-ohm resistors in parallel. So, I think the connection is to pin 7, but being only 1/3 of an ohm further to pin 6, there is not much difference in reality.
Quote:
Second, the junction of R2 and D2 should probably connect to the junction of D1 and Cout.
You are right! I missed a trace! I corrected the schematic and loaded it onto my photos page.
Quote:
Also, I think that the right side of the inductor should connect to pin 7, not pin 6, of the chip.
I looked at that one too, but I think I have it correct. I again "ohm'ed" it, and the resistance from L1 to pin 6 was about 1/3 of an ohm less than to pin 7.

Thanks for the help. I would certainly appreciate any further feedback on possible circuit schematic errors.

My next step will be to add further detail to my parts list and post it for review before committing an order. It looks like I still need help finding some 1% tolerance 1 ohm resistors.

Thanks!

Dan

                                          
Re: ZVC ZEPROM Voltage Converter (continued)
Message #13 Posted by Richard Ottosen on 20 July 2008, 8:33 p.m.,
in response to message #12 by Dan Grelinger

Quote:
I examined the board closely again, and I think it is correct the way I drew it. I got out my DVM and measured resistances between SI-Cin and pins 6 and 7. The resistance to pin 6 is about 1/3 of an ohm higher than to pin 7, which would make sense, since they are connected by 3 1-ohm resistors in parallel. So, I think the connection is to pin 7, but being only 1/3 of an ohm further to pin 6, there is not much difference in reality.

Actually, that 1/3 ohm in the wrong place can be significant. The intent of this resistance is to limit current into the coil. As you have it shown, it will not be able to do its job.

Quote:
I again "ohm'ed" it, and the resistance from L1 to pin 6 was about 1/3 of an ohm less than to pin 7.

It is real hard to measure resistances this low. I don't trust such measurements done with a DVM.

I would recommend that you redraw your circuit more like the examples in the data sheet for the MC34063A. It will then be more obvious what I am talking about.

Quote:
It looks like I still need help finding some 1% tolerance 1 ohm resistors.

Dan, are you intending to do this circuit in through hole or surface mount technology?

-- Richard

                                                
Re: ZVC ZEPROM Voltage Converter (continued)
Message #14 Posted by Dan Grelinger on 21 July 2008, 10:54 a.m.,
in response to message #13 by Richard Ottosen

Richard, Thanks again for your help!

I'll look at the MC34063A data sheet (I've been putting this off) and draw the circuit shematic I have, using the examples as a guide. Might take me a little while to get the time to study it.

I wanted to obtain devices for through hole mounting, and try them out in a circuit breadboard first in case I need to change things. When it is working OK (per measurements of voltage), then my plan is to design and construct a double sided circuit board to mount the parts into.

I am also open to a new design, one that uses an as yet undetermined 'new' voltage converter that does not require so many peripheral devices.

Thanks!

Dan

                                                      
Re: ZVC ZEPROM Voltage Converter (continued)
Message #15 Posted by Richard Ottosen on 21 July 2008, 11:57 a.m.,
in response to message #14 by Dan Grelinger

Quote:
I'll look at the MC34063A data sheet (I've been putting this off)

For future reference... The first thing you should have done is to get and study the data sheets for all of the parts used in the circuit you are reverse engineering.

Quote:
I am also open to a new design, one that uses an as yet undetermined 'new' voltage converter that does not require so many peripheral devices.

A "new" switching regulator will, at most, save the three 1-ohm resistors. There are no wasted parts in the present design.

A new design would operate at much higher frequencies so the parts could be a lot smaller. But -- As mentioned by Garth Wilson in a previous post, the PCB layout will be a lot more critical with the newer, higher frequency parts. In addition, the high frequency switchers absolutely require high frequency diodes and caps to operate properly.

Quote:
I wanted to obtain devices for through hole mounting, and try them out in a circuit breadboard first in case I need to change things. When it is working OK (per measurements of voltage), then my plan is to design and construct a double sided circuit board to mount the parts into.

While you may be able to prototype the present design on a solderless breadboard, you definitely can _not_ do a high frequency switcher on a solderless breadboard. Note that the high peak currents in switching regulators also make prototyping tricky. (That pesky 0.33 ohm resistor allows nearly an amp to flow!)

See here for my notes on how to properly use a solderless breadboard:

http://www.rhoent.com/sbbnote1.htm

http://www.rhoent.com/sbbnote2.htm

http://www.rhoent.com/sbbnote3.htm

-- Richard

                                                            
Re: ZVC ZEPROM Voltage Converter (continued)
Message #16 Posted by Dan Grelinger on 22 July 2008, 12:00 a.m.,
in response to message #15 by Richard Ottosen

Well, Richard, would you believe that we both could be right?

After further inspection, I have verified beyond any doubt on my part that I drew the circuit correctly, as it is implemented in the ZVC. I also acknowledge that your suggested 'modification' is truly the way the chip designer indended this up-converter to be used.

A few days ago Christoph Klug sent me an email which included the following information:

"Form former direct contact with Zengrange I get some of their converter boards free because I found out that the original coil have to small dimensions and get overheated when you are burning a complete rom contents by using the ILBURN command (= burning a full 4KByte rom page image from IL-mass storage drive to the Zeprom). Unfortunately later Zengrange stopped any support for Zenroms and up to now I never get any feedback from than."

Bringing these two pieces of information together, it strongly suggests that Zengrange printed the PCB incorrectly, and eventually fixed the resulting problem (knowingly or unknowingly, who knows?) by increasing the current carrying capacity of the coil.

My dilemma now is.... Do I reproduce exactly, that which I know is working (at least for the half dozen times or so that I have used it), or do I correct Zengrange's original error and design my PCB correctly?

Back to the breadboard, I guess I try both.....

Or do I just buy a regulated 12 volt power supply and make a simple board that drops 12 volts on the ZEPROM's battery power input terminal with a flick of a switch. ;-)

Dan

Edited: 22 July 2008, 12:02 a.m.

                                                                  
Re: ZVC ZEPROM Voltage Converter (continued)
Message #17 Posted by Garth Wilson on 22 July 2008, 5:34 a.m.,
in response to message #16 by Dan Grelinger

Quote:
My dilemma now is.... Do I reproduce exactly, that which I know is working (at least for the half dozen times or so that I have used it), or do I correct Zengrange's original error and design my PCB correctly?
I'd say do it the way the IC manufacturer's data sheet says. It sounds like Zengrange made a mistake and had problems.
Quote:
Back to the breadboard, I guess I try both.....
With newcomers to the field of switching regulators, it is difficult to impress them enough with the importance of good layout. Solderless breadboarding, although it may sort of work, will usually yield terrible results even though the circuit is theoretically hooked up correctly, because you have loads of stray inductance from connections being too long, and loads of stray capacitance between rows of connections. Non-solderless breadboarding is usually slightly better, but still problematic.

I had a bit of a head start since I designed and worked with VHF and UHF power amplifiers (up to several hundred watts) at another company before trying my first switching power supply circuits 15 years ago, but it still took a few bad experiences to make certain things sink in. My first board layout with a switching regulator IC and the support parts (inductor, Schottky diode, and capacitors) made electrical noise at frequencies that got into radios in the aircraft at 600 to 800 times the switching frequency, and "subharmonic" (actually not a very appropriate term) noise from pulse-width jitter and even pulse-skipping that got into the audio. Instead of making just a few PC boards to evaluate initially, they made a ton of them in the first run, and when the problem surfaced, decided it was less expensive to do some manual rework on every one of them and get to market more quickly than to just throw them out and wait for new boards to be made with the improved layout. Doing the rework job correctly was not easy.

Your made-for-home-only switching regulator made for digital work will not be as critical in the electrical noise department, but I tell you this to stress the importance of the layout.

Quote:
Or do I just buy a regulated 12 volt power supply and make a simple board that drops 12 volts on the ZEPROM's battery power input terminal with a flick of a switch. ;-)
What might be safer and easier is to use a wall wart power supply with an output a few volts higher and just bring the voltage down with a linear regulator like the LM78xx series or LM317T.
                  
Re: ZVC ZEPROM Voltage Converter (continued)
Message #18 Posted by Matthias Wehrli on 20 July 2008, 4:22 a.m.,
in response to message #8 by Dan Grelinger

For pictures of all three ZEPROM programmers follow to my website:

file://localhost/D:/Homepage/41accessories.html#programmer

Matthias www.hp-collection.org

      
Re: ZVC ZEPROM Voltage Converter (continued)
Message #19 Posted by PeterP on 20 July 2008, 12:19 p.m.,
in response to message #1 by Dan Grelinger

a few more digi-key parts numbers: 1% 150 Ohm resistor

2.4k Ohm Resistor 1%

22k Ohm resistor 1%

100uF Ceramic Capacitor

100uF Tantalum Capacitor

1000pF Ceramic Capacitor

the only one I was not able to fing a potential link on DigiKey for a reasonable minimum amount was the 1Ohm resistor. They only sell it in packages of 2500...

HTH

Cheers

Peter

            
Re: ZVC ZEPROM Voltage Converter (continued)
Message #20 Posted by Allen on 20 July 2008, 3:10 p.m.,
in response to message #19 by PeterP

May also try http://www.findchips.com/.. they have an excellent bot that searches supply houses for parts. Cheers!

            
Re: ZVC ZEPROM Voltage Converter (continued)
Message #21 Posted by Dan Grelinger on 20 July 2008, 4:50 p.m.,
in response to message #19 by PeterP

Peter,

Thanks for your help! With everyone's help, I'm getting close to a good schematic, and a good manifest of part numbers.

Now, if I can just find someone who wants to buy about 2490 1-ohm resistors..... ;-)

      
Re: ZVC ZEPROM Voltage Converter (continued)
Message #22 Posted by Muhammad Ahmad on 26 July 2008, 12:45 p.m.,
in response to message #1 by Dan Grelinger

For the output filter capacitor you may want to look at Sanyo's Organic Electrolytic capacitors. These have very high F per unit volume and very low ESR, which by the way is the ripple generator. They are available in thru hole and SMT. I have used them in switchers with great success!! I am sure Digi-Key carries them.


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