I need to drop about 5 Volt in an elegant manner

rrrremus · 20th January 2012, 06:08 AM

I have a 45Volt DC power supply but i need to drop this to about 40 Volt in order to power a LED driver. The maximum current i assume that will be drawn is somewhere around 100mA. My PCB is 12mm wide and 100mm long. MAximum component hight is 10mm.

sofaspud · 20th January 2012, 06:26 AM

LM317LZ, or a 5 volt 1 watt zener diode

rrrremus · 20th January 2012, 07:52 AM

The series zenner should work fine. Thanks. Somehow it slipped my mind, i was thinking of parallel zenner only.
Does the LM317 work at these voltages ?

Elvee · 20th January 2012, 07:59 AM

Zener or 317 will work safely only if your driver has no input bypass.

astankov · 20th January 2012, 08:07 AM

Here is my suggestion.

Regards!

rrrremus · 20th January 2012, 08:24 AM

The driver is TLE4242. What do you mean by input bypass ?

AndrewT · 20th January 2012, 09:39 AM

I'll give my vote to a Zener.

gmphadte · 10:08 AM

LM317 input to output voltage difference allowed is 35 volts maximum. If there is input bypass, which means if there r any capacitors across the supply of the driver(which is quite possible), they will short the output for a very short time. This condition will drop more than 35 volts across the 317 and will become RIP.

On a second thought, why not use a resistor.

Gajanan Phadte

rrrremus · 20th January 2012, 10:14 AM

Thank you all for your suggestions.
I think i will try astankov's circuit first. Thanks a lot.
As for the input capacitor bypass, it is obvious a small cap is needed.

KatieandDad · 20th January 2012, 11:25 AM

If you haven't got a 5V zener just use 7 diodes in series.

20th January 2012, 06:08 AM	#1
rrrremus diyAudio Member Join Date: Sep 2009 Location: Timisoara	I need to drop about 5 Volt in an elegant manner I have a 45Volt DC power supply but i need to drop this to about 40 Volt in order to power a LED driver. The maximum current i assume that will be drawn is somewhere around 100mA. My PCB is 12mm wide and 100mm long. MAximum component hight is 10mm.

20th January 2012, 06:26 AM	#2
sofaspud diyAudio Member Join Date: Nov 2005 Location: San Antonio TX	LM317LZ, or a 5 volt 1 watt zener diode __________________ It is error only, and not truth, that shrinks from enquiry. - Thomas Paine

20th January 2012, 07:59 AM	#4
Elvee diyAudio Member Join Date: Sep 2006	Zener or 317 will work safely only if your driver has no input bypass. __________________ . .Circlophone your life !!!! . . ♫♪ My little cheap Circlophone© ♫♪

20th January 2012, 09:39 AM	#7
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	I'll give my vote to a Zener. __________________ regards Andrew T.

20th January 2012, 10:04 AM	#8
gmphadte diyAudio Member Join Date: Jul 2003 Location: Dona paula, Goa	LM317 input to output voltage difference allowed is 35 volts maximum. If there is input bypass, which means if there r any capacitors across the supply of the driver(which is quite possible), they will short the output for a very short time. This condition will drop more than 35 volts across the 317 and will become RIP. On a second thought, why not use a resistor. Gajanan Phadte Last edited by gmphadte; 20th January 2012 at 10:08 AM. Reason: added content


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20th January 2012, 07:52 AM	#3
rrrremus diyAudio Member Join Date: Sep 2009 Location: Timisoara	The series zenner should work fine. Thanks. Somehow it slipped my mind, i was thinking of parallel zenner only. Does the LM317 work at these voltages ?

20th January 2012, 08:24 AM	#6
rrrremus diyAudio Member Join Date: Sep 2009 Location: Timisoara	The driver is TLE4242. What do you mean by input bypass ?

20th January 2012, 10:14 AM	#9
rrrremus diyAudio Member Join Date: Sep 2009 Location: Timisoara	Thank you all for your suggestions. I think i will try astankov's circuit first. Thanks a lot. As for the input capacitor bypass, it is obvious a small cap is needed.

20th January 2012, 11:25 AM	#10
KatieandDad diyAudio Member Join Date: Nov 2011 Location: UK	If you haven't got a 5V zener just use 7 diodes in series.

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