Why it should be a problem? Just to clarify, if the main supply is SMPS, aux supply is also SMPS, if the main supply is a mains transformer, aux supply is a separate (floating) winding in it. Supplies GNDs, of course, should be tied in one and only one point closest to the power input. Original JBC stations is done in this particular manner.
I was think about the scenario when the main supply is toroid transformer while aux supply is SMPS.
What stabilization circuit? D6,R2,D5,Q1 is removed, Q1 collector-emiter bridged, D5 bridged, aux supply connected to C22. That's all. AC rectifier may be designed as a patch board. There will be some drop on Q13 circuit, but it should produce enough voltage for lower mosfets, even 8V resulting gate voltage would be enough.
D12-C13-R10-ZD1-ZD2-Q5-R9-C12-D11 still need to connect with the 48v (or 24v) supply though.
I don't want to be critical, but that sounds a bit strange. Let say we have a modular design that consists of a certain count of modules , if you want to separate them for using the low parameters transistors you should use modular power supply boards also (cheap transistors/low voltage power supply ) In that case You could assemble 2 -3 independent soldering stations from your modules. What about the Trf. - it has to support all needed voltages and enough power to support 4 independent tools? Or I have to collect 4 of them? Isn't that the advantage of Unisolder, on 1 instrument to play many tools and if there is switching board attached to it, to connect them all the same time and use them 1 by 1
You don’t have to hookup 4 power board to the MCU board at the same time. I said UP to 4 independent channels.
I don't want to be critical, but that sounds a bit strange. Let say we have a modular design that consists of a certain count of modules , if you want to separate them for using the low parameters transistors you should use modular power supply boards also (cheap transistors/low voltage power supply ) In that case You could assemble 2 -3 independent soldering stations from your modules. What about the Trf. - it has to support all needed voltages and enough power to support 4 independent tools? Or I have to collect 4 of them? Isn't that the advantage of Unisolder, on 1 instrument to play many tools and if there is switching board attached to it, to connect them all the same time and use them 1 by 1
My thoughts are MCU aka Control board (with low noise Buck converter for powering opamps on the power board) remains the same while you can connect different module power board to MCU board. Like one power board dedicated to T470 and other high power irons while another board is optimized for 12v tools (C210 and C105). Power board has nothing to do with supporting different tools, as I said before MCU board holds all iron profiles needed.
Modular design - good approach, No cables - easy assemble, less noise, place saving, about swapping power boards - big effort ( open the case and so on ). For me, I am impatient even when I need to change the handle! I want just to grab it and to use it
Modular Power boards isn't for hot-swapping in my opinion. It is more about Balance between budget and performance needed. (You don't need big expensive 100v+ low Rdson MOSFETs for 210 and 105 handles) Another aspect of modular design is that iron Configuration and Firmware should be separated so that Iron Profiled can be easily trimmed or added to the station, besides MCU board could support up to 2 or even 4 independent heating channels, but you can just install one heating channel.
admaverick, minkok, it's much easier to just implement auxiliary DC supply, rather than messing with values and dropping 30-odd Volts on Q1. If I was going to redesign the power board to support higher voltage irons, I'd use 12V supply and get rid of Q1 and Q13 circuits all along. It could be a separate 3W AC-DC supply, like IRM-03-12 or separate 9VAC transformer winding with it's own rectifier and filtering. If you have a toroidal transformer, just wind a turn on top and measure the voltage on it, then wind the remaining.
I totally agrees with you afedorov regarding the auxiliary 12v supply. Unfortunately, per Sparkybg's current design, you have to keep the valley fill circuit near Q1 in order to minimize switching noise around zero crossing. I am planning to do a revamp of Unisolder using STM32 instead of PIC32 and will be all modular design (i.e. you can swap in different power board for different applications while keeping the MCU board).
More adequate is the secondary value J-A = 550mW. Iz = 10mA, but it will work also at around 1mA as is a bigger value than 10mA ( if dissipation is less than 550mW) for a short time, depends on the current allowed to pass through it. The resistor we are going to use ( increased 1206 - common one =250mW and powerfull = 500mW) In my mod I use 300mW zener and 250mW 1206 resistors. It is strange to burn sparky's design if you replace to 1206 R2. That was the reason to increase the R2 to 6.2k
So we did more test on Unisolder with different values of R2 and ZD3
Original configuration: R2=4.7k, ZD3 is 1SMB5939CT3G. ZD3 and Q1 fries instantly on startup.
Change ZD3 to 1SMB5934CT3G, R2=4.7k ZD3 and Q1 works totally fine, but MJD122(Q1)runs up to nearly 100 degrees Celsius.
Keep ZD3 as 1SMB5939CT3G, R2=2.35k, voltage between ZD3 keeps increasing from 36v. We turn off the power supply when we see the voltage keeps going up. Final voltage before shutdown is 37.3v.
First Nowhere is mentioned the kind of the zener nor its power dissipation, not even from you, I meant what was your kind of the zener. Second, you complain from immediate burning and that speaks for non-propper zener working point or other board fails. Instead of to show your knowledge it is better to come with a solution, and ... Yes 6.2k resistor with BZX585-B36 with 2mA Iz will work. It will work correctly also with the Mod, I publish for the 48V supply ( recommended value is 16k for the extra R - less heated Q1). Definitely, I don't expect to be burned this time!
I am definitely not trying to show off my knowledge here and excuse me for making you feel that way. As I said before the Zener Diode used in the picture is 1SMB5938BT3G with 3w rated power dispersion and Izk value of 10ma@36v. Maybe for the particular Zener (1SmB59xxBT3G) it needs larger current in order to work properly.
I mean 36V zener. And I mean to increase the value of R2 to 6.2k. In my opinion, it will limit zener current and will supply enough current to the Q1. You will get not burning and less heating Q1. To be sure , give to me the exact part value of ZD3
Zener diode need to work in Reverse Bias Region in order to regulate the voltage properly.
I mean 36V zener. And I mean to increase the value of R2 to 6.2k. In my opinion, it will limit zener current and will supply enough current to the Q1. You will get not burning and less heating Q1. To be sure , give to me the exact part value of ZD3
What I am saying is yes you do need to limit Zener current but Zener diodes need sufficient current to clamp the voltage properly. I think 1SMB5938BT3G is used here and its Izk@36v is 10ma. Here is a detailed explanation of Izk and Izm here: https://sciencing.com/read-zener-diode-ratings-6160739.html
For sure that needs to be done - 100V Transistor is risky to be used on 48V rail powered by Trf. Not only, but R2 value should also be at least 6.2k and over Look for the right R2 value and this time Q1 will be colder
Are you sure about increasing R2? My guts are that 4.7k does not provide sufficient working current for ZD3. I know it sounds counterintuitive but you do want to DECREASE the value of R2 to provide sufficient Izk for ZD3 (plus base current for Q2).
