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+5V from +35V

Hello,

I want to obtain supply logic (+5V) from a main power supply (+24V -

+35V DC). The line is quite dirty because it's used by several stepper motors.

I'm looking for a cheap and very low-count components way to regulate the logic supply (Iout < 50 mA).

I tried with a resistor divider but the power rating needed is very high (> 2W) for the series resistor. A DCDC converter would be nice but they are expensive if no external components are needed, or cheap but they will require several components.

There are a smarter way to do this? Also a filter against spikes will be very appreciated... :)

Thanks in advance! Marco / iw2nzm

Reply to
Marco Trapanese
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7805 TO-220 package with a small heatsink

Marco Trapanese wrote:

Reply to
Jacques

Jacques ha scritto:

Are you sure? If I have 35V on the input and 5V on the output the 7805 will have 30V across both terminals. With an output current of 50 mA it should dissipate 15W. I'm afraid the small heatsink can't help enough...

About the motor spikes? Would you connect directly the regulator to the main power supply?

Thanks Marco / iw2nzm

Reply to
Marco Trapanese

Don't top post. And the 7805 isn't a good choice to hook up to a dirty supply voltage that can run up to 35V and spike quite a lot higher.

The adjustable LM317HV can take a 56V volt differential, as can a number of three-lead 5V linear regulators designed for the automotive market. Dropping 50mA into a 5V rail from a 35V rail implies dissipating 1.5W in the regulator. A 750mW 300R series resistor could halve that, while still leaving 4V of headroom when the supply was down to 24V.

-- Bill Sloman, Nijmegen

Reply to
bill.sloman

Marco Trapanese ha scritto:

Pardon, it's 1.5W indeed.

Marco / iw2nzm

Reply to
Marco Trapanese

On a sunny day (Fri, 09 May 2008 12:07:15 +0200) it happened Marco Trapanese wrote in :

30 x .05 = 1.5 7805 is specified at 35 V in max, for 5 V out. Else add a LM317 as pre-regulator to say 15 V, it will take the spikes.

35 V - LM317 - 15 V - 7805 - 5 V Fewer watts and fewer volts per IC. Or 2 x LM317.

Reply to
Jan Panteltje

"Marco Trapanese"

** Use a damn 16volt, 3W zener to fed the 7805.

Cheaper than chips.....

...... Phil

Reply to
Phil Allison

LM2574HV with a 45-50V TVS on the input. One or two more parts than a linear regulator, BFD.

Best regards, Spehro Pefhany

--
"it\'s the network..."                          "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com
Reply to
Spehro Pefhany

Hi Marco,

ask google about roman black converter. I guess this will meet your needs.

Marte

Reply to
Marte Schwarz

Marte Schwarz ha scritto:

Thanks to you too! Marco / iw2nzm

Reply to
Marco Trapanese

Spehro Pefhany ha scritto:

Thanks! Marco / iw2nzm

Reply to
Marco Trapanese

Use a 10W 270R from the 24-35V to a 1N4733 5V1 1W zener to logic GND and bypass the zener with a 4u7 10WVDC ecap...

Reply to
Fred Bloggs

On May 9, 10:02=EF=BF=BDam, Marco Trapanese wrote= :

Spehro beat me to it. The National part would have been my recommendation as well. You might even get the 2575 for the same price? Little higher current output. I have seen them very competitively priced in the past.

For the TO-220 5-pin package, I've found the Avid 7136 heat sink is a really nice compact fit.

-mpm

Reply to
mpm

mpm ha scritto:

Thanks for the tips! Marco / iw2nzm

Reply to
Marco Trapanese

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