DC to DC 90 volt power converter

[lomack]

Hi everyone
I have a project that I am working on and I could use some input.I have a zenith transoceanic model G-500 tube radio  i built a battery for it out of 60 1.5v AA cells and 6 1.5 v D-cells this gives me 90v B+ voltage and 9v a+ voltage I think my current draw on the B+ side is 25 or 30 milliamps I was wondering if a dc to dc converter would work i would still use batters  for my input voltage and for my A+ side,
  After i watched Dave's video on DC to DC converters I thought this is what I needed. I searched eBay and found a 95 Volt DC to DC converter,  it has voltage adjustment of 60 to 95 volts DC. I contacted the vender and she said it would not work in my application. Below is the data on the converter,  my question is why won’t it work? I can supply the input voltage needed and the output is within my requirements 90 volt around 30 milliamps max   Am i missing something? If this won’t work then what do you think i need to do, build one or do they make something like this for retail? I have looked and I can’t find any 90Volt DC power supplies. This converter  was all i found that boosted DC to DC at 90 volts. I did find a AC to DC battery eliminators on a old radio museum web site but i would like to run this thing off of batteries. It has a AC to DC built in  power supply, it works great on AC, so i wouldn’t need the battery eliminator. The search title for this thing on eBay is :DC 10-32V 12V to DC 60-95V Boost Step-Up Converter Adjustable Charging Module. [/b][/i]   Any input or advice would be greatly appreciated 

Thank You lomack

Module Properties: non-isolated step-up module (BOOST)
Input voltage: DC 10-32V
Output voltage: DC 60-95V continuously adjustable
Output Current: 2A (MAX)
Input Current: 16A (MAX) (Please enhance heat dissipation over 10A)
Output power: natural cooling 70W (MAX), to enhance heat dissipation 100W (MAX) actual power
Conversion efficiency: 85% typical
Output Ripple: 2% (MAX) 20M Bandwidth
Operating temperature: Industrial grade (-40 ? to +85 ?) (ambient temperature exceeds 40 degrees, lower power use, or to enhance heat dissipation)
Full load temperature rise: 45 ?
No-load current: Typical 35mA
Load regulation: ± 0.5%
Voltage regulation: ± 0.5%
Dynamic response speed: 5% 200uS
Short circuit protection: None (Please enter install fuse or protective circuit)
Dimensions: 65 * 47 * 23.5mm


Applications:
DIY an adjustable output vehicle power supply. Connecting to a 12V power supply, the output voltage is 60-95V continuously adjustable. But please be sure that the output voltage can not be lower than the input voltage
Boost charger
Power for your electronic devices
Solar battery charger for electric vehicles

[madires]

Required power at output: 90V * 0.3A = 27W
Required input power: 27W *(100% / 85%) = 31.76W
Current for a 12V battery: 32W / 12V = 2.7A
That's going to be a SLA (sealed lead acid) or a Li-ion pack.

[NiHaoMike]

NiMH can supply that sort of current. But lithium is the way to go nowadays.

[mariush]

If you can raise your input voltage to about 14-16v or more, you could make your own boost regulator from easily available parts.

For example, get two of these (or something similar) to have about 18-22v at input: http://hobbyking.com/hobbyking/store/__16529__Turnigy_2650mAh_3S_1C_LLF_Tx_Pack_Futaba_JR_.html

Then you could use something cheap and simple like a LM3478 to make the boost converter:

picture of schematic and components list attached.  If you go and use Ti's webbench page (here: http://webench.ti.com/webench5/power/webench5.cgi?lang_chosen=en_US&VinMin=14.0&VinMax=24.0&O1V=90&O1I=0.4&op_TA=30 ) and enter the inputs and outputs you can reproduce this and select alternate parts that you can find (you need to create a free account and login to access schematics and play with the values and parts)

[Richard Head]

lomack

Your best solution here I believe will be a simple isolated flyback converter.
Forget about a boost converter as the duty cycle will be ridiculously high and inappropriate.
Unfortunately your biggest problem is not going to be getting the converter to work but getting the EMI to a level that is acceptable for operation right next to an AM radio. You will have to enclose the PSU in a metal box with input and output filters and feedthrough capacitors on all terminals. If you don't do that you will end up with birdies every 50 or 100khz or whatever your switching frequency is. I would probably use a UC3845 or similar but there are plenty of other chips that'll work.

Dick

[NiHaoMike]

Best topology for this would be a "flyboost". That's a flyback converter where the primary is also the inductor for a boost converter, with the output of the flyback connected in series with the output of the boost converter. Very closely related is the tapped inductor boost, but the flyboost solves the leakage inductance problem while the tapped inductor boost doesn't.