Regulator for fan, relays...
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JojoD818
diyAudio Moderator

Join Date: Mar 2003
Location: searching...
Regulator for fan, relays...

Hi,

I need to derive 12Vdc from my transformer which has a rectified/filtered output of 55V. Will the attached regulator work? It will only be used to power the fan and relays for the protection circuit. Maximum output current must be around 750mA which I think the regulators can easily handle.

JojoD
Attached Images
 fan regulator.jpg (9.4 KB, 386 views)

 25th August 2003, 01:25 PM #2 peranders   Electrons are yellow and more is better! diyAudio Member     Join Date: Apr 2002 Location: Göteborg, Sweden Check the max voltage of the 7824! Some types can take 60 volts other take less.... Use a LM317HV for example. You could also use a series resistor to burn power, together with a 7812. __________________ /Per-Anders (my first name) or P-A as my friends call me Group buy: DCT03 DC trap for big toroidal transformers. Sign up for interest HERE. 65 pcb's in order. 59 paid.
JojoD818
diyAudio Moderator

Join Date: Mar 2003
Location: searching...
Oooopppssss!

Hi,

The 7824 would probably "eject" itself out of the pcb!

Okay here's a new one.

LM317T Input Output Voltage Diff. (Vin-Vout) = 40V

In this case, my LM317 output is 28V which is set by 220Ohms and 4.7K ohms resistors,

then 55V-28V=27V so I'm below the max input for the LM317T which is 40V.

LM7812T Max Input Voltage = 35V;
in this circuit my input to the 7812 is the output of the 317 which is 28V.

Will this work?

JojoD
Attached Images
 fan regulator 2.jpg (13.7 KB, 366 views)

 25th August 2003, 02:36 PM #4 sajti   diyAudio Member   Join Date: Apr 2003 Location: Százhalombatta, Hungary Why not use some cheap darlington, with zener? Use 13V zener, and one darlington power transistor, such as BD651. You don't need two regulators, and the quality of the 12V is no very critical. Sajti
 26th August 2003, 08:47 AM #5 JojoD818   diyAudio Moderator     Join Date: Mar 2003 Location: searching... sajti, I tried your suggestion and it worked. i used a tip29c since it was readily available. However, the transistor was very hot, even with a large heatsink. I was only drawing about 500mA. JojoD
sajti
diyAudio Member

Join Date: Apr 2003
Location: Százhalombatta, Hungary
Quote:
 Originally posted by JojoD818 sajti, I tried your suggestion and it worked. i used a tip29c since it was readily available. However, the transistor was very hot, even with a large heatsink. I was only drawing about 500mA. JojoD
This is OK. If You check the dissipation is: (55V-12V)*0.5A=21.5W But the overall dissipation will be same with the regulators too. You can reduce the dissipation if You put some series resistor before the series-pass transistor. 33-47ohms 15-20W looks OK.
And You can avoid all the regulators with one series resistor:
R=(55V-12V)/0.5A=86ohms. The real value can be 91ohms, with 30W.

Sajti

 26th August 2003, 12:51 PM #7 keyne diyAudio Member     Join Date: Jul 2003 Location: earth jojo, for your circuit with lm317 you need zener diode protection for the lm317 because at switch-on the 40V rating is exceeded until the cap charges up to 15V ! even with resistors you get the same power dissipation, just more in the resistor and less in the device, just to clarify. you can also use more transistors in parallel to ease dissipation requirements per transistor and get improved heat transfer to the heatsink. sajti is right, you don't need regulators for fans and relays. these devices are very tolerant of voltage changes and work perfectly with unregulated voltage. but burning up so much power in a resistor is not very elegant.. better use a second transformer! or a buck converter.. ! regards keyne
 26th August 2003, 01:27 PM #8 sajti   diyAudio Member   Join Date: Apr 2003 Location: Százhalombatta, Hungary There are some 24V, or 48V fans. They are better for this application! Sajti
 26th August 2003, 02:27 PM #9 JojoD818   diyAudio Moderator     Join Date: Mar 2003 Location: searching... Just what I thought... Hi guys! Adding another transformer for this application is exactly what I'm trying to avoid but still considers it if all else fails. As of now, I used two tip29c with a resistor and it seems to be fine. Heatsink is hot but can be touched. Running for 2 hours now with a fan and a couple of relays, drawing around 450mA. Seems ok now. Thanks guys! JojoD
 26th August 2003, 05:40 PM #10 jackinnj   diyAudio Member     Join Date: Apr 2002 Location: Llanddewi Brefi, NJ Maybe this is simpler I don't like this solution of generating heat to move a fan whose purpose is to remove heat -- not particularly a "green" solution. National Semi has an application note on using the LM3524 controller for fan speed http://www.national.com/an/AN/AN-292.pdf with a little creativity you can configure the LM3524 to both act as a buck regulator, or a flyback converter and fan speed controller. Just use an ohmic sensor in the feedback loop. The garden variety LM3524 will take up to 40 Volts so you will need to use a little beefier transistor to stand off the higher voltages.

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