# Need 3.3V regulator

I have a circuit that inputs 24 volts from two 12 volt sla batteries. It has two analog LM317 regulators.One is configured as 5 volts @ 30 ma load, the other @ 3.3 volts @ 250 ma load. The problem is the 3.3 volt regulator gets really hot! The power dissipated on the LM317 measures a heat loss of 200+ deg F! I thought of using a LDO off the 5 volt regulator, but that would just transfer the heat to that regulator. A switching regulator I think would do the job, but is not going to happen due to cost. Trying to keep the cost around $1. - add comment ## 2 Answers The MC34063 is the classic choice for a switching regulator. Take apart any cell phone car charger, and you're likely to find one of these guys. It's available in single quantities for about 75 cents (plus a bunch of external components, which might double that cost), and in production quantities for 25-35 cents. Here's a really good design calculator: http://dics.voicecontrol.ro/tutorials/mc34063/ At the top of that page is a link to Dave Jones' EEVBlog, in which Dave does a pretty good job of explaining the design considerations of a switching regulator. http://www.eevblog.com/2010/09/10/eevblog-110-lets-design-a-dc-to-dc-switchmode-converter/ - +1 for the calculator – stevenvh Jul 16 '11 at 11:43 add comment In 1$ you can get bigger heatsink.

There are no good ways except getting switching DCDC converter, I believe simplest ones with internal switch should be just a little more than your budget.

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To elaborate, the reason there's no good way around the problem without going to a switching supply is because with any other solution you have to dissipate (24V-3.3V) * 250mA = 5.175W worth of power somehow. –  anthony137 Mar 21 '11 at 19:21