SSHV2 Sink for Q3

[amandarae]

Hello,
How big of a heat sink do I need for Q3 in the SSHV2:
H+ in = ~200 Vdc
Regulated DC out (B+)= ~ 150Vdc
Current: 10 mA + 20 mA draw (fspare SSHV2)
Dissipation: 20 mA (150V) = 3W?

Thanks!

Abe

 

[merlin el mago]

As per SSHV2 Guide:

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.

 

[amandarae]

As per SSHV2 Guide:

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.

Thanks for the reply! Yes, I read that from the build guide and have difficulty finding documentation to calculate 1.5C/W size heatsink. What have you use in your build? Can you post a pic? I am thinking of using the chassis as the sink. Thanks!
Abe

 

[merlin el mago]

Mine advice is not use the chassis for HV reg.

Attached pic with the heat sink I use 12cmx10cmx3.8cm

 

[rayma]

Mine advice is not use the chassis for HV reg.

Definitely no.

 

[amandarae]

Thank you guys!
Merlin, that is huge! What is your H+ going into the SSHV? I have about 210V, with B+ at 150V.
I thought the write up says spare I x B+ = Watts. Did I miscalculated it? 20 mA x 150V = 3W?
Abe

 

[amandarae]

Here's what I am planning to use. It's 6 cm. x 5 1/2 cm. x 2 1/4 cm aluminum.

An externally hosted image should be here but it was not working when we last tested it.

 

[rayma]

Are you electrically isolating the device from the heat sink properly?
This is not trivial with a TO-220 package.
http://www.aosmd.com/res/application_notes/package/AN101_TO220_Guidelines.pdf

 

[amandarae]

Yes! Mica spacer, then thermal paste. Verified with ohmmeter!
Abe

 

[merlin el mago]

You have to isolate also the heat shink from the chassis if it's metal.

Abe better ask to Salas help here Simplistic Mosfet HV Shunt Regs

 

[amandarae]

You have to isolate also the heat shink from the chassis if it's metal.

Abe better ask to Salas help here Simplistic Mosfet HV Shunt Regs

Thank you sir!
I wonder, since the MOSFET is already isolated, is isolating the sink from the chassis just in case the MOSFET shorts to the sink?


Abe