What's the cheapest way to drop 48v to power the fan (at the very least). At the moment in using 2 power supply's. 1 for driver, and 1 for the fan, to stop the noise getting into the power supply.

Id like to eliminate at least 1 power supply and run it all off the 48v supply.

NO BUCK CONVERTERS. They cost just as much as power supply's.

This image, taken from ebay. Whats this chip?

its a 7812 and above is a stepdown regulator
how i know... i made it some time ago

Why not use 240v fans? Pre-power supply

Hello XXL

You can also use the LM317HV which is a floating regulator and good up to 60v

You will need to get rid of a great deal of heat to power anything substantial!

You might as well buy another 12V supply, the small Meanwell one is only £6. By the time you’ve fiddled with a circuit trying to drop 48V you’d probably have spent more than a small power supply would cost you.

Bton-FM wrote: ↑Sat Jan 30, 2021 12:33 am You might as well buy another 12V supply, the small Meanwell one is only £6. By the time you’ve fiddled with a circuit trying to drop 48V you’d probably have spent more than a small power supply would cost you.

The other advantage of this approach is that you'll keep the noise from the fan off the rig supply rails.

The little 12V Meanwell supplies are actually very useful for other bits and pieces in the rig - some rigs we did recently had two of the 12V jobs - one for the two fans, and the other for a link receiver, audio detector circuit and MP3 / OGG player for loss of link. The PA was run from a 30V supply (a pair of MRF317s (the client has several boxes of them)) and the rigs did 220 Watts every time. We used the Motorola M9583 as the driver. The PAs were reasonably broadband (about 10MHz wide) - they could be built for low, mid or the high end of the band by changing the capacitors in the matching networks and in the filters.

The exciters were also run off the 30V supply, into a 15V regulator, and were similar to the RDVV 6 Watt board in topology, but used Atmel "Tiny" logic and the National LMX2306 for the PLL. The rigs went into 3U 19" cases for rack installation.

There must be a way to cheat and run the fan from the same power supply as the exciter without getting fan noise on it. Like running it through some step down voltage regulators with smoothing caps after or something.

XXL wrote: ↑Sat Jan 30, 2021 9:41 am There must be a way to cheat and run the fan from the same power supply as the exciter without getting fan noise on it. Like running it through some step down voltage regulators with smoothing caps after or something.

I've used those cheap 99p eBay adjustable regulators without any problems but by using two of them. (one for the fans and the other for the PLL).

....With the PLL connected to the same one as the fans there was loud fan noise but when connected to the other seperate one I found there was no noise on the carrier.

Thanks teckniqs, thats exactly what im looking for. Ill give that a try.

Hi step down is best way.. but you can use resistor with TVS diode 15V in parallel with fans... example 36R for 1A 12V https://www.aliexpress.com/item/4000801474938.html

on A bench

This did the job for me - running a Raspberry Pi from 30V, with the Pi being used as a "link receiver" and doing a bit of other houskeeping:
https://www.ebay.co.uk/itm/2PCS-DC-24V- ... 2749.l2649

The price has gone up a bit on Ebay - I bought a few for £1.10 each from DX.com

It has a USB power output and screw terminals too. It runs completely cold powering a R Pi3 with a soundcard, and has very low output ripple.

Why be so difficult?

Marcel wrote: ↑Sat Feb 06, 2021 9:48 am Why be so difficult?

You can't put 50v into a 7824.

https://www.google.com/search?client=fi ... ut+voltage

Take a good look at why the 7824 is isolated.

Hi Marcel

Congratulations for your cheap, simple and innovative "Step-down 48 to 15V linear voltage regulator circuit". I have 2 questions:
- Do you need big heatsinks for regulator ICs?
- Is this type of circuit suitable for 48/12V?

- Do you need big heatsinks for regulator ICs?: No
- Is this type of circuit suitable for 48/12V?: Yes

Thank you Marcel.
I will give it a try to feed a 12V/0.5 circuit.

Both Teckniqs and Marcel are correct!

It all depends on the regulators reference to ground!

When a regulator is connected direct to ground? You will be limited to the maximum input voltage of the device (37v ish)

However a regulator can also 'Float' above ground potential which allows higher voltages to be used!

Isolation is critical for chassis mount in this configuration and will require insulating washers and pads to mount the device!

With regards to device dissipation? Remains as a constant and heat due to losses are un-avoidable.

Cheers for clearing that up Sinus, I didn't know you could do that.

....But I still think that it's not the cheapest way to do it and looks like it will cost more to build than buying one of those ready made 99p eBay jobs (they work fine!).