I looking into shipping heavier packages internationally. Looks like 8oz and under is the break point for reasonable shipping costs. I think I could package board, JFETs and MOSFETs and stay under this threshold. US shipping would be $5 and international would probably be $20 (same as boards only). If there is any interest.
Just looked at Exicon's purchase options.... Looks like the lateral MOSFETs are only available in quantities of 10+. That does make the kit idea look more viable. Otherwise you need to order 20 devices when you only need 4. At the current prices, it would be £83 for 20 TO-247 and £158 for 20 TO-264 MOSFETs + shipping.
If I am not mistaken, the TO-264 collector is isolated from the case and do not need silicone pads and insulated washers. Also the package is ceramic
Are you referring to the Exicon TO-264 devices? I looked at the datasheet for ECW20N20/ECW20P20 and it states "TO-264 plastic package".
I am assuming the source is exposed on the back of the case like the Exicon TO-247 devices, but I do not have any in front of me to confirm.
I am assuming the source is exposed on the back of the case like the Exicon TO-247 devices, but I do not have any in front of me to confirm.
You're right. I see that now. The way their order page is setup is odd. I don't remember it being that way years ago when I bought my batch.
Silicone pads are required. No insulation washers for tightening screw needed.
The discount is high for moderate quantities though. At quantiles of 30 it's over 35%. That adds up when the parts are £6 to £11 each.
Looking at the site I see the warning that it is only a demo. Has anyone (@lineup) successfully ordered there?
Not free. To be transparent on this, the price I am setting is above my costs. This is to guard against me losing money and hopefully coming out a little ahead. Not trying to make a fortune here, just enough to be in the black and hopefully fund future development of more projects like this.
With bare boards, the upfront costs for me aren't bad. If I offer kits, I need to sell above my costs to offset the large upfront cash outlay and mitigate the risk that some of the parts may sit for awhile before I get reimbursed. With JFET and Lateral MOSFETs I'd need to order enough to provide a reasonable discount for builders. It adds up. If I do this, I may start a shop on Etsy to help them sell (I see a few other forum member sell this way). It would also help with shipping estimates, especially for international buyers.
Ultimately, I enjoy doing this and enabling others to give it a try. I recall when I entered the hobby, documentation (or lack of) and figuring out how to actually purchase parts was one of the most daunting aspects. I think this is something experienced hobbyists take for granted. I remember being drawn to AMBs projects - probably due to the excellent documentation and guidance on securing parts.
Story time... I am a Accountant by trade (CPA). I taught Intro to Accounting several years ago at one of the local community colleges. I distinctly remember a realization early on in my first semester; Some of the very basics concepts that I didn't think much of were actually very hard for someone new to accounting to grasp. I try to remember this when instructing others.
Other take away from this: I'm not formally trained in electronics. Please be gentle with me if I've made any grave mistakes (and help educate me!)
With this project, I'm just trying to do my part to pay it forward for all the help this forum has provided to me.
Draft of the changes. These are described in more detail in Post #96. Need to sleep on it and then give them a final check before sending off for production.
Think of splurging on black PCBs.
Note: You may notice that C11 and C12 dropped from 470uF to 330uF. The value for this position is not critical. I changed these to match the values used in C86 - C89 for the V2 PSU. In the original version the V2 PSU used a pair of 470uF caps. These became four 330uF caps. Using 470uF caps in the RCRC filter would be beyond the capacitive drive capabilities of the DC-DC converters. with 330uF it stays within their 1,000uF limits even with if they are all 20% over-spec.
Think of splurging on black PCBs.
Note: You may notice that C11 and C12 dropped from 470uF to 330uF. The value for this position is not critical. I changed these to match the values used in C86 - C89 for the V2 PSU. In the original version the V2 PSU used a pair of 470uF caps. These became four 330uF caps. Using 470uF caps in the RCRC filter would be beyond the capacitive drive capabilities of the DC-DC converters. with 330uF it stays within their 1,000uF limits even with if they are all 20% over-spec.
Attachments
Your layout skills are very good. The board in my opinion is nicely laid out. Labels are not obscured by components and everything else is in its place - nicely done, Brian.
EDIT: I agree with Vunce. The problem that I see if DC fails on the converter the main amp will swing hard to rail and blow main fuses as well, so F81/F82 really is not a protection. BTW the saying goes, for every fuse there is a transistor protecting it, which would fail before the fuse does
EDIT2: Gate diodes D92/92,94,91 is not necessary, they are built into the mosfet already. It would save a bit of board space.
EDIT3: C13 and C14 is really not necessary, the gate capacitance is already high, I have never had any oscillatory problems with Lat MOSGETS (ever) The gate to drain/source capacitance is already high and these capacitors only slows down the MOSFET more.
EDIT4: R10 and R11, could be 270 and 330 ohms respectively and fixed.
EDIT: I agree with Vunce. The problem that I see if DC fails on the converter the main amp will swing hard to rail and blow main fuses as well, so F81/F82 really is not a protection. BTW the saying goes, for every fuse there is a transistor protecting it, which would fail before the fuse does
EDIT2: Gate diodes D92/92,94,91 is not necessary, they are built into the mosfet already. It would save a bit of board space.
EDIT3: C13 and C14 is really not necessary, the gate capacitance is already high, I have never had any oscillatory problems with Lat MOSGETS (ever) The gate to drain/source capacitance is already high and these capacitors only slows down the MOSFET more.
EDIT4: R10 and R11, could be 270 and 330 ohms respectively and fixed.
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@Vunve, Board dimensions are 55mm x 240mm
Thank you for the kind words Nico. I put a lot of work into boards beyond just the basic layout. Like chassis compatibility, device footprints, and the top and bottom silk screen to aid builders. Nice to see it acknowledged.
Interesting thoughts on F81/F82. I did try to simulate different failure mechanisms, including one of the rails failing or the output being shorted. In those cases, the DC-DC converter current draw increased but did not exceed its limitations. One of the reasons I used the larger SIP8 devices is to allow enough dissipation to survive a fault condition. Perhaps the additional fuses are unnecessary. The board size probably won't change much though. Within the footprint for the fuse blocks F81 & F82 are connectors J81 & J82. These provide a pads for tab quick connects if the builder chooses to use an external V2 PSU. There is also jumpers JP80 & JP81. These allow a builder to omit the V2 PSU and provide power from the main rails. I can reorient these and maybe shave a few mm's off the board size, but not much.
You wrote Gate diodes D92/92,94,91... do you mean diodes D94/95 and Zeners D92/93? These are not included in the Exicon to my knowledge. I thought it was D96/D97 that are redundant for the Exicons. As the datasheets don't seem to explicitly show the diodes, I thought it safer to add them as optional components. In either case, these are not necessary for the amp to function. A builder can choose to omit these. This is discussed in section 5.10 of the guide. Omitting D96/D97 has been brought up before. It wouldn't really affect the layout much, so I opted to leave them in as optional.
C13 and C14 may not be needed. Sims do not indicate they are needed, however many builders on this forum using Exicon laterals have indicated problems with oscillation in practice that don't show up in sims. I thought it safer to add them. When I assessed them in simulations, the impact on THD and slew was very small to non-existent. This is mentioned in the build guide in section 5.2.
R10/11 are recommended at 330R/220R for TO-247 and 220R/150R for TO-264. Similar to what you are recommending.
Thank you for the kind words Nico. I put a lot of work into boards beyond just the basic layout. Like chassis compatibility, device footprints, and the top and bottom silk screen to aid builders. Nice to see it acknowledged.
Interesting thoughts on F81/F82. I did try to simulate different failure mechanisms, including one of the rails failing or the output being shorted. In those cases, the DC-DC converter current draw increased but did not exceed its limitations. One of the reasons I used the larger SIP8 devices is to allow enough dissipation to survive a fault condition. Perhaps the additional fuses are unnecessary. The board size probably won't change much though. Within the footprint for the fuse blocks F81 & F82 are connectors J81 & J82. These provide a pads for tab quick connects if the builder chooses to use an external V2 PSU. There is also jumpers JP80 & JP81. These allow a builder to omit the V2 PSU and provide power from the main rails. I can reorient these and maybe shave a few mm's off the board size, but not much.
You wrote Gate diodes D92/92,94,91... do you mean diodes D94/95 and Zeners D92/93? These are not included in the Exicon to my knowledge. I thought it was D96/D97 that are redundant for the Exicons. As the datasheets don't seem to explicitly show the diodes, I thought it safer to add them as optional components. In either case, these are not necessary for the amp to function. A builder can choose to omit these. This is discussed in section 5.10 of the guide. Omitting D96/D97 has been brought up before. It wouldn't really affect the layout much, so I opted to leave them in as optional.
C13 and C14 may not be needed. Sims do not indicate they are needed, however many builders on this forum using Exicon laterals have indicated problems with oscillation in practice that don't show up in sims. I thought it safer to add them. When I assessed them in simulations, the impact on THD and slew was very small to non-existent. This is mentioned in the build guide in section 5.2.
R10/11 are recommended at 330R/220R for TO-247 and 220R/150R for TO-264. Similar to what you are recommending.
I accept your simulations Brian, I am referring to actual experience with these components, but if you want to be certain then that is of course your design. There can never be too much protection in anything. It is mainly economics of scale. I stand to be corrected but remain, well done, world class layout.
P.S. Have you considered self resetable fuses?
P.S. Have you considered self resetable fuses?