andre tchmil
Well-known member
Is there a way to take 48v dc (for phantom) from a regulated 24 poxer supply ?
schematic maybe ?
schematic maybe ?
how to create 48v for phantom from a 24 V DC supply
- Thread starter andre tchmil
- Start date
Help Support GroupDIY Audio Forum:
> Is there a way to take 48v dc (for phantom) from a regulated 24 power supply?
A way? Yes.
An easy? Maybe not.
Oh, an easy way is to use three 9V batteries or a 24V wall-wart, and stack it up on top of the 24V to get 48V.
Of course if you hunt a little more, you can find surplus 48V wall-warts. (The older H-P DeskJet printers used a 48V power pack that outlives the printers.)
Really the next step is to just get a 48V power transformer, rectify and regulate it.
If you -only- have 24V DC, as in field recording: there are ways to convert anything to anything, but not easy. For example, if you are running on car batteries, get a 12VDC-120VAC inverter, and a 120VAC-48VDC power pack. That will work, but the typical phantom supply is much lower power than most inverters, so it will be very inefficent. That three-9V-battery plan is probably a wiser idea.
For general DC step-up, use a transistor and a choke across your DC supply. Switch the transistor on and off pretty fast (if you leave it on too long, the choke or battery burns up). The choke will kick to a high DC voltage, up to maybe 10 times higher with iron-core chokes. Rectify and filter that, and then feedback the output voltage to the transistor controller to cleverly adjust the on/off times and get the desired output voltage. The formulas are said to be simple, but it isn't my thing.
Since you want just 1:2 step-up, the switched capacitor voltage double comes to mind. Get an audio power amplifier chip. Use feedback to make it self-oscillate. Preferably outside the audio band, but not much higher because audio chips aren't made to do that. You get a 23V peak to peak square wave. Two diodes and two caps can voltage-double that to about 45V at light load. It naturally output just double the supply voltage, minus losses, a few volts for a good speaker-amp chip and Phantom sized loading.
Remember that many many "48V" phantom microphones are perfectly happy with 24V.
A way? Yes.
An easy? Maybe not.
Oh, an easy way is to use three 9V batteries or a 24V wall-wart, and stack it up on top of the 24V to get 48V.
Of course if you hunt a little more, you can find surplus 48V wall-warts. (The older H-P DeskJet printers used a 48V power pack that outlives the printers.)
Really the next step is to just get a 48V power transformer, rectify and regulate it.
If you -only- have 24V DC, as in field recording: there are ways to convert anything to anything, but not easy. For example, if you are running on car batteries, get a 12VDC-120VAC inverter, and a 120VAC-48VDC power pack. That will work, but the typical phantom supply is much lower power than most inverters, so it will be very inefficent. That three-9V-battery plan is probably a wiser idea.
For general DC step-up, use a transistor and a choke across your DC supply. Switch the transistor on and off pretty fast (if you leave it on too long, the choke or battery burns up). The choke will kick to a high DC voltage, up to maybe 10 times higher with iron-core chokes. Rectify and filter that, and then feedback the output voltage to the transistor controller to cleverly adjust the on/off times and get the desired output voltage. The formulas are said to be simple, but it isn't my thing.
Since you want just 1:2 step-up, the switched capacitor voltage double comes to mind. Get an audio power amplifier chip. Use feedback to make it self-oscillate. Preferably outside the audio band, but not much higher because audio chips aren't made to do that. You get a 23V peak to peak square wave. Two diodes and two caps can voltage-double that to about 45V at light load. It naturally output just double the supply voltage, minus losses, a few volts for a good speaker-amp chip and Phantom sized loading.
Remember that many many "48V" phantom microphones are perfectly happy with 24V.
NewYorkDave
Well-known member
To add my own comments to the suggestions above:
It might be feasible to use the aforementioned audio power chip in a wien-bridge configuration, running at a high frequency. Since the output would be a sine, not a square, the risk of "hash coupling" would be reduced. The problem is getting enough current out of it. Instead of looking up the current draw of "typical" mics, my own criterion for a phantom supply is that it should be able to source...
I = 48 / (3400 / number of mics)
...without blowing up.
That 3400 ohms represents the load it would see in a worst-case instance of both mic conductors being shorted to ground, with the typical 6800-ohm feeder resistors. So, the idea is that even if some pinhead shorts all your mic lines to their shields, your supply won't cook.
Also: one crude but effective way to step up DC at low current is to use a small audio transformer with a capacitor across it to resonate the primary at a desired frequency. This serves as the tank circuit in a single-transistor class-C oscillator. The output is a sine wave. The current capability is low, the frequency will shift somewhat with changes in load and the regulation isn't very good, but it does the trick in some cases.
I'm assuming that you'll put your stepped-up DC, however you obtain it, through a proper 48V regulator circuit.
It might be feasible to use the aforementioned audio power chip in a wien-bridge configuration, running at a high frequency. Since the output would be a sine, not a square, the risk of "hash coupling" would be reduced. The problem is getting enough current out of it. Instead of looking up the current draw of "typical" mics, my own criterion for a phantom supply is that it should be able to source...
I = 48 / (3400 / number of mics)
...without blowing up.
That 3400 ohms represents the load it would see in a worst-case instance of both mic conductors being shorted to ground, with the typical 6800-ohm feeder resistors. So, the idea is that even if some pinhead shorts all your mic lines to their shields, your supply won't cook.
Also: one crude but effective way to step up DC at low current is to use a small audio transformer with a capacitor across it to resonate the primary at a desired frequency. This serves as the tank circuit in a single-transistor class-C oscillator. The output is a sine wave. The current capability is low, the frequency will shift somewhat with changes in load and the regulation isn't very good, but it does the trick in some cases.
I'm assuming that you'll put your stepped-up DC, however you obtain it, through a proper 48V regulator circuit.
Someone should contaqct these dc to dc guys and tell them that their just might be a market for a 24 to 48 dc converter. No noise, of course, although you could add additional filtering.
It will just be a matter of time before one comes out, if it isn't out alrerady in some Mouser catalog or sumptin.
And no, you can't hook up a dc to dc backwards, ie. 48 to 24 converter.
The main reason for dc to dc converters is for isolation, secondary is the voltage conversion.
I am wondering if there would be any grounding issues, as the converters usually end up in circuits with seperate ground, as there would not be isolation otherwise.
It will just be a matter of time before one comes out, if it isn't out alrerady in some Mouser catalog or sumptin.
And no, you can't hook up a dc to dc backwards, ie. 48 to 24 converter.
The main reason for dc to dc converters is for isolation, secondary is the voltage conversion.
I am wondering if there would be any grounding issues, as the converters usually end up in circuits with seperate ground, as there would not be isolation otherwise.
There are some DC/DC circuits here: http://members.aol.com/sbench101/#Power
I guess the "12 volt to 250, 300 or 350 volts" circuit could be changed to a 24 to 55V circuit easily. The text describes what to change for 24V operation.
Best regards,
Mikkel C. Simonsen
I guess the "12 volt to 250, 300 or 350 volts" circuit could be changed to a 24 to 55V circuit easily. The text describes what to change for 24V operation.
Best regards,
Mikkel C. Simonsen
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