This 5k is what I have around as a dummy load at 280V. The actual tube circuit will be true 60mA at 200VDC. It may correspond to a 3-3.5k equivalent load.
The raw numbers I will have to 'burn' away are 80V @60mA should be 4.8W. I am a little confused because of the unusual shunt design where the power dissipation is happening, CCS or the shunt element. I have not measured anything any voltages yet and don't know where the drop is happening. I went with twice as tall heatsink on the DNxxxx CCS and put quite the heatsink on the shunt mosfet. I'll have to read the manual a couple more times to see how SSHV2 is adjusted!
The raw numbers I will have to 'burn' away are 80V @60mA should be 4.8W. I am a little confused because of the unusual shunt design where the power dissipation is happening, CCS or the shunt element. I have not measured anything any voltages yet and don't know where the drop is happening. I went with twice as tall heatsink on the DNxxxx CCS and put quite the heatsink on the shunt mosfet. I'll have to read the manual a couple more times to see how SSHV2 is adjusted!
*Side Sink
Q3 dissipates Watt power of what spare current you allowed times the B+ voltage. Calculate C/W sink
spec for no more than 60C sink temperature in worse ambient conditions. Look for sinking guides on
the web if never done it. 1.5C/W spec sink should cover most applications for SSHV2 range though.
Sinks etc.:
On board 25.4mm pitch sink for Q1. Example Wakefield 647-10ABP
TO-126 mini sinks for Q4,Q5 (not necessary below 300Vout)
Outboard sink for Q3. See the top of page paragraph
Insulation pads and grommets for two TO-220s, thermal grease, 3pcs 5mm pitch Molex connectors.
Q3 dissipates Watt power of what spare current you allowed times the B+ voltage. Calculate C/W sink
spec for no more than 60C sink temperature in worse ambient conditions. Look for sinking guides on
the web if never done it. 1.5C/W spec sink should cover most applications for SSHV2 range though.
Sinks etc.:
On board 25.4mm pitch sink for Q1. Example Wakefield 647-10ABP
TO-126 mini sinks for Q4,Q5 (not necessary below 300Vout)
Outboard sink for Q3. See the top of page paragraph
Insulation pads and grommets for two TO-220s, thermal grease, 3pcs 5mm pitch Molex connectors.
Ok then 200*0.02=4w on Q3
BUT
isn't the ccs block Q1-Q2 also doing the dropping 280-200=80V? Then 80*(0.06+0.02) margin or 8W?
BUT
isn't the ccs block Q1-Q2 also doing the dropping 280-200=80V? Then 80*(0.06+0.02) margin or 8W?
25V is enough, 50V is fine, 80V no reason. Creates extra dissipation. Better burn most of it in an RC raw DC filter cell with a power resistor before entering the SSHV2.
Most dissipation of full CCS mA * Vdrop across the reg is going to be taken by Q1 and its sink. Up to 1.5-2W should be manageable with the specific board level sink.
What is KO?
IRF840PBF I see over 15K pieces stocked in Mouser again
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I am calculating 6.4w for Q1 assuming the full 80V drop. I am using a 65mm tall (2.5in) board heatsink. I think it'll be fine. I have the feeling that once the real load is attached things may settle down a little more. On the CRCRC, I have a 10u-300ohm-47u-300ohm-47u. I am already burning 1.9w per resistor. I want to test it as it is now and see how it goes. I may have to go with a lower voltage transformer later. 230Vac sec maybe a bit too much.
Q1, Q2, Q5 & Q6 gone.
D1, D2 & D3 gone.
R1, R2 & R5 gone.
IRF840PBF not in stock when I started to populate my SSHV2.
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For reactive load you consider CCS load or Hybrid mu-follower, right?
How to fix?
Better to change the SiHP8N50D for IRF840PBF
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Maybe try 4.7R 47uF RC between the SSHV output and the CCS load for some isolation of reactance. And use two wire output mode if with long output wires to avoid potential RF noise pick up.
Hi Salas,
what use scenario would constitute a reactive load that could cause damage to the board?
what use scenario would constitute a reactive load that could cause damage to the board?
These two mosfets look rather poor in the SOA department. They don't even report a DC trace. It's hard to figure out the margin before a blowup could occur but it's not much.
This enhancement has a very respectable SOA by comparison. From good'ol TSMC and available at mouser. Similar Ciss 1300 v 1600, same difference. And plastic case for better mounting w/o mica. I am thinking about switching these out.
TSM60NE145CIT C0G
