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Offline LED driver at -40degC

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Flyback

Well-Known Member
Hello,
We have an 40W offline LED driver which uses no electrolytic capacitors...only ceramic ones.
Also, it uses only sequence switched linear regulators, -no SMPS.
It is only surface mount components.
Optocouplers, resistors, caps, diodes, FETs, SFH5711 light sensor, MCP9701 temp sensor, MCP6001 opamp, BZX84C-XX zeners.
Do you think we will have problems at -40degC?
The PCB sits on a rubbery thermal pad which is on a heatsink

We are getting it in the oven at -40degc, but wonder if there are any long term effects.
The product is totally enclosed..no vent holes....a rubbery gasket makes the seal between the optic and the heatsink
 

AnalogKid

Well-Known Member
Most Helpful Member
First, do a datasheet audit of every single component (including wire, connectors, and the pc board material) for their low temperature ratings.

Next, run the thermals. If the unit is 90% efficient, that 4.44 watts has to go somewhere. At -40C ambient, what is the case temperature of the hottest component on the board?

ak
 

schmitt trigger

Well-Known Member
As AK points out...do a datasheet survey.
ICs would be the very first ones, followed by capacitors. Some ceramic types perform poorly at low temps.

My feeling is that, once the circuit starts and warms up, you should be fine. But the circuit's start up sequence you really have to validate in a temperature chamber.
And test many samples, don't get complacent if your first sample works.
 

ronsimpson

Well-Known Member
Most Helpful Member
Do you think we will have problems at -40degC?
I did a design for HP years ago. If the specification was; must start and run at -40C, they did not care about the -40 test. The question was; at what temperature will it fail? We pushed all tests to the failure point. "The HP way"
I have lives in places where the highest temperature in a week was -40C.
 

Pommie

Well-Known Member
Most Helpful Member
Interestingly -40 is the only temperature where you don't need to state Centigrade or Fahrenheit .:)

Mike.
 

gophert

Well-Known Member
Most Helpful Member
Interestingly -40 is the only temperature where you don't need to state Centigrade or Fahrenheit .:)

Mike.
Only true if "-40 degrees" is stated in front of an educated audience. Otherwise, they will still ask.
 
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