How Low Can You Go?

[Ron Hubbard]

I need to cram a TL499AC converter circuit into the smallest,
tightest, area possible so I want to use 1/10 watt resistors. Assuming
I get maximum power drain from the circuit that the convertor will
power, possibly as much as 600 ma (or whatever's the maximum the
converter is capable of), wll thesy tiny resistors be okay?

Ron

 

[Winston]

Ron Hubbard wrote:

I need to cram a TL499AC converter circuit into the smallest,
tightest, area possible so I want to use 1/10 watt resistors. Assuming
I get maximum power drain from the circuit that the convertor will
power, possibly as much as 600 ma (or whatever's the maximum the
converter is capable of), wll thesy tiny resistors be okay?

Does your simulation show that the power dissipated by each resistor
will always be significantly less than the maximum permissible,
(after derating to accommodate the highest local
temperature and resistance tolerance extremes), in each
resistor in question?

See the paragraph that starts with "Note that the nominal power
rating .." in: http://en.wikipedia.org/wiki/Resistor

If so, yes. If not, you get to provide a way to cool the assembly
and / or use components capable of dissipating that power safely.

--Winston

 

[Tim Wescott]

On 12/22/2010 01:03 AM, Ron Hubbard wrote:

I need to cram a TL499AC converter circuit into the smallest,
tightest, area possible so I want to use 1/10 watt resistors. Assuming
I get maximum power drain from the circuit that the convertor will
power, possibly as much as 600 ma (or whatever's the maximum the
converter is capable of), wll thesy tiny resistors be okay?

You can do this in five easy steps:

* Figure out the voltage across, or current through, each resistor
* Use that, plus the resistance, to calculate the resistor power
dissipation.
* Derate appropriately, per the resistors that you intend to use
and your local ambient.
* Choose resistors accordingly.
* Enjoy

IIRC, 0603 resistors are generally 1/16th watt, so 1/10th watt resistors
are no big deal these days.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" was written for you.
See details at http://www.wescottdesign.com/actfes/actfes.html