opto triac ?
The fodm 3012 is used to trigger the SSR
Are there alternatives?
Could a 6pin opto triac do the job eg moc3021-m or moc3023-sm do the job
or
could an opto transistor be used? eg TCET 1600, or K817p2 (4pin dip)
Presumably the triac style alternatives must be random, not zero crossing, for near instant triggering?
The fodm 3012 is used to trigger the SSR
Are there alternatives?
Could a 6pin opto triac do the job eg moc3021-m or moc3023-sm do the job
or
could an opto transistor be used? eg TCET 1600, or K817p2 (4pin dip)
Presumably the triac style alternatives must be random, not zero crossing, for near instant triggering?
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You must use a random trigger triac.
A triac is used because once it fires, it latches the SSR OFF. If it did not latch (as would be the case for example if a normal Opto wee used), it would cycle on and off.
I am sure there are alternatives, but the device used should be readily available (RS, mouser, Digi-key and some of the 2nd tier catalog houses.
A triac is used because once it fires, it latches the SSR OFF. If it did not latch (as would be the case for example if a normal Opto wee used), it would cycle on and off.
I am sure there are alternatives, but the device used should be readily available (RS, mouser, Digi-key and some of the 2nd tier catalog houses.
One slight fail in the sx doc. In the BOM it says R9=3.3r , 0.5W..
However the pcb says 3.3r 2W.
Is 0.5W sufficient? (It is part of the output zobel)
However the pcb says 3.3r 2W.
Is 0.5W sufficient? (It is part of the output zobel)
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I found RS as stockist but they sell the fodm in packs of 10.
The moc is sold by Farnell in singles and at half the price. This is the only component I don't have.
I'll download the moc and fodm datasheets and see if they are similar.
I think the 6pins can be manipulated to fit the 4 pads.
Thanks.
Just checked the nx doc also. R9 (same resistor) is also said to be 3.3R, 0.5W type. However in this thread it is stated to be 2W.
It will be i tight fitting 2w resistor on this sx pcb 🙂
And in the BOM for the sx amp. The mouser part for the emitter resistors leads to axial 5w 0,33ohm ohmite resistors, not radial which fits better 🙂 The same that is used for the nx (with 5mm spacing) seems to be the correct one.
I have ordered vom3053t in sop 4pin package from Farnell. These should fit the pads and seem to be similar specification to fodm3012.
fodm3011 is also shown in the pdf.
Just in case I also ordered moc3021 in dip 6pin, in case the sop don't fit. The 6 pin can be made to fit.
Cut off pins3 & 5
Bend pins 1, 2 & 6 under
bend pin4 out to meet the pad/trace where the pin 5 should have connected.
fodm3011 is also shown in the pdf.
Just in case I also ordered moc3021 in dip 6pin, in case the sop don't fit. The 6 pin can be made to fit.
Cut off pins3 & 5
Bend pins 1, 2 & 6 under
bend pin4 out to meet the pad/trace where the pin 5 should have connected.
A couple of minor issues in the sx doc.
It says in the BOM that q3 is a smd transistor bc847T115. (847BOT)
However I cannot find any traces on the pcb for smd transistors. Only Q3 I can find is a bc547c in to92 package. And the manual states earlier that Q3 is bc547.
Also the fuse holder clips in the BOM. 504-htc-201m. I guess this is the htc-210m? And that we need 4 of them for each pcb, not 2 like in the BOM?
It says in the BOM that q3 is a smd transistor bc847T115. (847BOT)
However I cannot find any traces on the pcb for smd transistors. Only Q3 I can find is a bc547c in to92 package. And the manual states earlier that Q3 is bc547.
Also the fuse holder clips in the BOM. 504-htc-201m. I guess this is the htc-210m? And that we need 4 of them for each pcb, not 2 like in the BOM?
Andrew/bambadoo,
Thanks for your inputs. I will correct the doc shortly and add comments about the opto -triac alternatives.
Thanks for your inputs. I will correct the doc shortly and add comments about the opto -triac alternatives.
The bc846 is on the bottom. Near Q2 base and collector pads.
The other pair, under R8 & R11, are for the MLCC 10uF smd caps.
You can't lose the base stoppers, they are huge!
I am finding that radiation from the heatsink does not give good enough control of Bias Voltage.
I am considering using NJL with the integrated diodes for the second channel.
Any thoughts?
I could copy Leach's 4diodes in the upper side of the multiplier, or Roender's 4diodes directly generating Bias Voltage, or some other?
I am considering using NJL with the integrated diodes for the second channel.
Any thoughts?
I could copy Leach's 4diodes in the upper side of the multiplier, or Roender's 4diodes directly generating Bias Voltage, or some other?
Details please - how much variation do you see? How are you measuring the bias?
I measure across the emitter resistors and across the emitter pads
Emitter resistors gives Vre times 2. This rises from cold @ 39mVre to 60mVre when warm, but keeps creeping up very slowly.
Emitter pads gives Bias Voltage, this drops from ~1.290V to 1.240V cold to warm. It needs to go down a bit further to compensate for the Junction temperatures in the output stage.
If I turn the Bias Voltage up to double the current the increase in current is more pronounced. 90mVre cold goes to 150mVre warm.
I have not yet tried to warm the sink with a heater fan to see the effect of a warm summer.
The smd is not getting hot enough and seems to lag the heataink.
I thought about adding an aluminium spacer between the sink and the smd.
Emitter resistors gives Vre times 2. This rises from cold @ 39mVre to 60mVre when warm, but keeps creeping up very slowly.
Emitter pads gives Bias Voltage, this drops from ~1.290V to 1.240V cold to warm. It needs to go down a bit further to compensate for the Junction temperatures in the output stage.
If I turn the Bias Voltage up to double the current the increase in current is more pronounced. 90mVre cold goes to 150mVre warm.
I have not yet tried to warm the sink with a heater fan to see the effect of a warm summer.
The smd is not getting hot enough and seems to lag the heataink.
I thought about adding an aluminium spacer between the sink and the smd.
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The vom3053t in sop 4pin fits the PCB.
The moc3021 (dip6) modified by folding the pins under and shortening them slightly can be made to fit.
But the wider package of the 6pin dip overlaps the adjacent electrolytic.
I presoldered the three pads for pins 1, 2 & 6 and soldered it on to my second PCB. Removed it and fitted the vom3053
There are good discussions in both Self & Cordell about the thermal time constants and thermal 'gain'.
I don't think either has the last word on this important topic.
You need to consider a number of important scenarios ... not just thermal runaway.
Use a small amount of thermal grease to couple the sensor transistor to the output device collector lead.
Make sure you also follow the bias current set up.
Make sure you also follow the bias current set up.
The sensor transistor pads are about 3mm away from the collector pad, c/c distance ~4.5mm.
The sensor transistor sits approximately 1mm below the PCB.
The PCB is spaced by the approximately 5mm thickness of the output devices.
The sensor transistor relies on radiation across the ~4mm gap to try to follow the heatsink temperature.
The sensor transistor should be trying to monitor the Tj of the output devices.
The sensor transistor sits approximately 1mm below the PCB.
The PCB is spaced by the approximately 5mm thickness of the output devices.
The sensor transistor relies on radiation across the ~4mm gap to try to follow the heatsink temperature.
The sensor transistor should be trying to monitor the Tj of the output devices.
I have read both D.Self and R.Cordell and as a result understand the problem of trying to maintain an effective tempco for changes in Tj.
According to the perceived wisdom, slow response to a delta Tj can never be solved. The best we can do is to speed up response as much as we can and hope we can stay somewhere within the good operating window.
Bonzai's recommendation to operate at roughly double the optimal Vre goes some way to avoiding under biasing.