DC/DC from 12V to 240V@25mA example

[karsten21]

Dear folks,

For my small tube projects I searched always for a small an simple power supply. Until now I used a special small mains transformer and the great Maida regulator. But often I want to use a switching regulator to use very cheap external "Laptop power supplies".
I found a nice solution on Pete Millietts home page. This was the kick to try to build a switching DC/DC regulator by my own.
I choose the TI LM3478 because TI provide a very nice tool to calculate the parts.
Attached you can find the result of a working development PCB. This schematic will NOT work on a bread-broad. I choose "large" 1206 parts and a layout for which the vias can be done by using a small wire. The solution is working very well with high efficiency for Uout=250V and very small ripple of 1.7mV@23mA.

I hope you will find this useful for your own small tube projects.
Thanks a lot for all your help in the last years!

Best regards
Karsten

 

[petertub]

Very interesting.

Do you plan on selling boards or complete devices ?

 

[karsten21]

Very interesting.

Do you plan on selling boards or complete devices ?

Dear Peter,
In general it´s no problem to produce some PCB as well as collect a set of Parts to provide a DIY-Kit. If there are enought interest I will do this.
In this case we have to enhance the input circuit with suppressor diode, fuse and current compensated EMI coil. I will do this in the next days and give a roughly overview about the costs.
Nevertheless: You should be able to solder SOT9 and 1206 parts...

Thanks for your interest!

Regards
Karsten

 

[petertub]

i'll stay tuned to this channel..

 

[jackinnj]

Good idea to read the late Jim Williams application note on high voltage, low noise switchers: http://cds.linear.com/docs/en/application-note/AN118fb.pdf

 

[jackinnj]

Dear Peter,
In general it´s no problem to produce some PCB as well as collect a set of Parts to provide a DIY-Kit.

TI has an evaluation board available from their store or Digikey. It's $79 at DK and in stock.

Great thing about EVM's is that their engineers have already done the heavy lifting with regard to layout, etc.

 

[karsten21]

Hello Jackinnj,

I read the AN before, verry interisting. But all parts relativly expensive or hard to get. Also most of the solutions provide to less power for me.
My proposal of PCB follows mostly the design from TI. The expensive part is the LM3478 ( ~4,- EUR ) and the capacitors. At least I payed less than 20,-EUR for all parts.
Sorry, heavy on load today. I will come back with BOM list and prices..

Best regards
Karsten

 

[trobbins]

That's a lot of step up from 12V. One very cheap (just a few $) alternative dc/dc that I have used is:
http://dalmura.com.au/projects/75W car inverter.pdf

The 'AC inverter' parts can be removed and almost half that pcb can be cut off to allow fitting in to a small metal utility/eddystone type case with a few valves fitted. The B+ power output would be good for 20-30W if you had the 12V power available, and needed the grunt.

 

[petertub]

The goal ( for me ) is to obtain B+ for preamp type of stuff given only small voltage
AC or DC from wall-wart type of power supply ( or common 12-15V transformers)
Transformers applicable for small tubeamp voltages are more and more exinct, using
DC/DC technology will be a solution.

 

[Wavebourn]

Here is a battery powered guitar amp project

 

[ballpencil]

Hi Wavebourn

Obligatory request: where did you get the module? Looks like an DC-AC inverter as suggested by trobbins. if it's DIY module, can you show schematic?

To all,

What do you think about this link if applied to tube amp:
Uzzors2k Hobby Projects Site

 

[karsten21]

Hello,

Attached a small parts list with suppliere and price ( in Germany / EUR ). You will find similar/same part at your local suppliere like mouser..
PCB costs are 39,- EUR for one pcs ( which makes no sense... )

@petertub
Well, I have some parts at home. To etch an PCB is not a big deal. If I ordering the next time some parts, I´m able to order the missing ones ( MOSFET / LM3478 ) and build a module for you if you are realy interested. After testing I can send it to you via post...
Please let me know.

Best regards
Karsten

 

[ruffrecords]

Transformers applicable for small tubeamp voltages are more and more exinct, using
DC/DC technology will be a solution.

Amp Maker: Guitar amp kits and parts :: Power transformers :: 240V/6.3V toroid power transformer

https://www.don-audio.com/Toroidal-Transformer-Mila-sec-250vct-63vct-48V

Cheers

Ian

 

[Bone]

This item on ebay 150W Inverter DC-AC Battery DC12V To AC 220 200 110V Power Converter Transformer | eBay should do what you want just rectify the required output voltage (high speed diodes eg UF4007) . I doubt you could build one for the cost!.

 

[Wavebourn]

Hi Wavebourn

Obligatory request: where did you get the module? Looks like an DC-AC inverter as suggested by trobbins. if it's DIY module, can you show schematic?

To all,

What do you think about this link if applied to tube amp:
Uzzors2k Hobby Projects Site

I used 12V / 240V inverter that I bought on ePay cheap. I removed chopper transistors that were used to produce 50 Hz output, and took rectified high voltage from it.

However, you can buy some ready to use nowadays:

DC12V 24 to DC 200 450V 70W High Voltage Converter Boost Step Up Power Supply | eBay

 

[Tyimo]

I used 12V / 240V inverter that I bought on ePay cheap. I removed chopper transistors that were used to produce 50 Hz output, and took rectified high voltage from it.

However, you can buy some ready to use nowadays:

DC12V 24 to DC 200 450V 70W High Voltage Converter Boost Step Up Power Supply | eBay

Hi!
How is the sound quality with such a converter? (battery+converter)

Greets:
Tyimo

 

[trobbins]

No mains ripple and no sag, so you would need to reverse engineer that in !

 

[smoking-amp]

Those DC 12/24V to 200/450V boost converters on Ebay are NON isolating.
Beware.

DC12V 24 to DC 200 450V 70W High Voltage Converter Boost Step Up Power Supply | eBay

 

[Shoog]

You still have to generate a very beefy 12V DC supply. Is there not a better alternative which goes from mains to HV DC.

Shoog

 

[Wavebourn]

Hi!
How is the sound quality with such a converter? (battery+converter)

Greets:
Tyimo

No hum, of course.