# Suitable switching/buck regulator - Vin = 24V and Vout = 5V and max current = 0.4A

Due to a sudden change in design requirements with regards my circuit supply voltage I'm looking to change my voltage regulation on my circuit from the classic LM7805 linear voltage regulator to a switching/buck regulator.

This is my first time attempting to use switching regulator so apologies if some bits of my post sound trivial. In saying this I've gone through this DC-DC Converter Tutorial by Maxim for the theoretical aspects and understood the basics of how the switching regulator works.

### My circuit

My new supply voltage requirement is +24V from +6V and I need a Vout of 5V to be supplied across the circuit. My max current is 0.4Amps. I can't utilise my LM7805 as the heat dissipation is just too much. See calculations based on the calculations below using help from this Power and Thermal Dissipation Tutorial by SparkFun.

$$Power\,dissipation = V \times I = (24V - 5V) \times 0.4A = 19 \times 0.4 = 7.6W.$$

7.6W is too much heat.

Hence my question: which switching regulator (possibly available in the eagle libraries) would be suitable to take in a Vin of 24V or below and deliver a Vout of 5.0V?

Here's my schematic (developed in Eagle):

EDIT:

I've looked further into the use of the switching regulator specifically the LM2575-N to deal with the heat dissipation problem as outlined in my first post. Please see my proposed approach here (Apologies if bits of the diagram are not that clear. I drew my approach by hand before committing time into finding the components in Cadsoft Eagle and subsequently updating my schematic).

I also took the approach as seen here in order to supply +3.3V to the Zigbee module as seen in my schematic above.

The LM2575 on the LHS is for the stepping down of +24V to 5V and the Vout from this LM2575 is to supply +5V to the second LM2575 for stepping down to +3.3V which is supplied to the zigbee module. The +5V from the first LM2575 is also supplied to the rest of the circuit as seen in the circuit diagram above.

Does anyone foresee any problems with the approach e.g. with the selection of the input capacitor, inductor, output capacitor and catch diode? I came up with the approach by following the design procedure as per pages 12, 13, 14 and 16 of the LM2575 datasheet.

• What do you say about LM2596-5? May 21, 2014 at 16:07
• Check if this helps: electronics.stackexchange.com/questions/91438/… May 21, 2014 at 16:20
• Recommendations for specific products are off-topic for this site. Try using the parametric search tools of your favorite distributor. May 21, 2014 at 16:26
• You can get switchmode regulator modules that are intended to be direct replacements for 78xx 3-terminal regulators. See the answers to the question @Ricardo linked above. May 21, 2014 at 17:26
• There is a tool on the TI website where you plug in Vin, Vout, Iout, etc., and it spits out multiple recommendations of regulators and circuits. In some cases you can buy a demo board. Other vendors sites have similar tools. May 21, 2014 at 18:31