Thank you, Salas.
Then, for one of the phonos I'm going to build in order to compare, I'll use 2 SSHV2, one for each channel. In such a case, each channel draws 11 Watt (50mA on 220V).
My previous post WAS a mistake, both channels draw 22 Watt.
Then, for one of the phonos I'm going to build in order to compare, I'll use 2 SSHV2, one for each channel. In such a case, each channel draws 11 Watt (50mA on 220V).
My previous post WAS a mistake, both channels draw 22 Watt.
The 840 is a 1C/W RthJC device, assuming a further 1C/W thermal resistance silpad loss and 30% sink derating, a 1°C/W sink should be good enough for Israel. The shunt device burns the extra current allowed above load consumption, not the total, keep that in mind.
Thanks, Salas.
My previous idea of using 2 x SSHV2 is a no go. The power transformer is already ordered and the max current I can draw from it is about 130mA. When both channels draw 100mA + 25mA for each SSHV2, it cannot be done.
Dropping voltage with 3 more 12H chokes (on top of the existing 2 ones) is going to be too expansive for a mere experiment.
So, is there a MOSFET (or another animal) that can withstand 22 Watt?
If yes, what heatsink would I need?
BTW, in the summer in my living room the ambient temperature is about 25 Celsius (in the evening, when I listen to music, after the air conditioner cooled the whole day).
My previous idea of using 2 x SSHV2 is a no go. The power transformer is already ordered and the max current I can draw from it is about 130mA. When both channels draw 100mA + 25mA for each SSHV2, it cannot be done.
Dropping voltage with 3 more 12H chokes (on top of the existing 2 ones) is going to be too expansive for a mere experiment.
So, is there a MOSFET (or another animal) that can withstand 22 Watt?
If yes, what heatsink would I need?
BTW, in the summer in my living room the ambient temperature is about 25 Celsius (in the evening, when I listen to music, after the air conditioner cooled the whole day).
Thanks, Salas.
Maybe I can manage with 2 x SSHV2.
Assuming 50mA load, how low can I go for CCS? Can I go for 15-20mA?
(Voltage headroom is no problem, I can play with the C preceding the first LC).
Maybe I can manage with 2 x SSHV2.
Assuming 50mA load, how low can I go for CCS? Can I go for 15-20mA?
(Voltage headroom is no problem, I can play with the C preceding the first LC).
The guide is clear. +20mA CCS above load max should deliver the 11mOhm Zo spec. So 70mA CCS setting in your example.
Thank you very much.
I can go with 2 x SSHV2, one per channel.
Actually, being cautious, I rated the HV windings of the power trafo 250mA, even though it's LCLC. So there should be no problem.
Anyhow some extra MOSFETs will be ordered, they may well be needed...
Now I'm waiting the 2 x SSHV2 PCBs and Kits.
I can go with 2 x SSHV2, one per channel.
Actually, being cautious, I rated the HV windings of the power trafo 250mA, even though it's LCLC. So there should be no problem.
Anyhow some extra MOSFETs will be ordered, they may well be needed...
Now I'm waiting the 2 x SSHV2 PCBs and Kits.
Carlp's real world safe troubleshooting example exchanges link added in post #1 here and in post #1 GB thread.
According to both logic and the manual, Q3 (IRF840) dissipates only the spare current (say 25mA) times the B+.
In my case, for one phono stage it's, say, 0.025A x 220V = 5.5W per channel.
For the second phono stage, Valve Itch, it's, say, 0.025A x 300V = 7.5W per channel.
What heatsink will do for 7.5W (In Israel)?
Will 1.3C/W like this one: 557-140AB Wakefield | Mouser do?
Work it out.
1.3C/W with 7.5W+5.5W raises the sink temperature by 13*1.3* de-rating factor ~ 16.9*1.3 ~20Cdegrees.
If ambient around the sink is 30°C then Ts ~50°C
The device Rth c-s will be ~0.5C/W
This predicts the Tc as 0.5*7.5 + 50 = 54°C
Now de-rate the device for a Tc of about 54°C
1.3C/W with 7.5W+5.5W raises the sink temperature by 13*1.3* de-rating factor ~ 16.9*1.3 ~20Cdegrees.
If ambient around the sink is 30°C then Ts ~50°C
The device Rth c-s will be ~0.5C/W
This predicts the Tc as 0.5*7.5 + 50 = 54°C
Now de-rate the device for a Tc of about 54°C
Thanks.
It isn't 7.5W+5.5W, it's either, thus max is 7.5W. Should I use one regulator for both channels, max will be 15W.
I didn't get the rest of the symbols in your calculations. What are the de-rating factor, Ts, Tc and Rth c-s?
Using only one FET @ 7.5W results in a higher de-rating factor, maybe around 1.4 to 1.5 times.
A common heatsink saves money and saves space.
I'd assumed you had adopted a common sink due to these savings, but separate sinks can be used.
BTW,
when the CCS mosFET is running at max dissipation the Shunt mosFET is running at zero dissipation.
When the Shunt mosFET is running at max dissipation (output disconnected) the CCS mosFET is running at nominal dissipation.
There can NEVER be a situation where both mosFETs are at max dissipation.
This allows a significant saving in sink size when using a common sink.
A common heatsink saves money and saves space.
I'd assumed you had adopted a common sink due to these savings, but separate sinks can be used.
BTW,
when the CCS mosFET is running at max dissipation the Shunt mosFET is running at zero dissipation.
When the Shunt mosFET is running at max dissipation (output disconnected) the CCS mosFET is running at nominal dissipation.
There can NEVER be a situation where both mosFETs are at max dissipation.
This allows a significant saving in sink size when using a common sink.
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So how do I calculate the necessary heat sink specs for a given power consumption of the shunt MOSFET?