Need Feedback on High Voltage DC-DC converter

[bobledoux]

The task: I need to charge up a 22uf capacitor to 100 volts and discharge once a minute for 60 minutes. This cycle repeats weekly. Power source is a standard 9 volt battery.

Goal: Balance long battery life with simple hardware.

Approaches. I’ve looked at boost and flyback DC-DC converters. Figure 3 and figure 16 in this link have appeal:

Flyback Converters for Dummies

I like these because they don’t require a chip with a short market life.

I’ve also been looking at disposable cameras. These typically use a simple transistor oscillator to power a transformer which charges a capacitor for the strobe.

So questions:

What feedback can you provide? Links?

Where do I find off-the-shelf 1:10 ratio transformers for a flyback circuit? I don’t see them in my Mouser catalog? What about winding cores?

Would the camera type circuit be the most efficient? What about a full wave rectifier on output?

Does the camera type circuit work better with a sine versus square wave oscillator?

 

[ronv]

Here's one. The xformer is available from Digikey I think.
https://www.electro-tech-online.com/custompdfs/2011/03/dn303f.pdf

 

[bobledoux]

I see the camera circuits are not linear circuits. The oscillator is not a sine wave but a pulse for a boost/flyback circuit. .

Pre-made transformers for SMPS supplies are expensive. While Coiltronics will provide fee samples, Digi-Key wants about $12 for very small units. They appear not to be stock items.

I have a supply of cameras, but they all use 1.5 volts to generate 330v. I haven't figured whether any of these circuits could be reduced to 100 volts.

 

[moffy]

For your application a flyback makes the most sense.
Transformer: wind your own, its quite simple, the trick is choosing the right core.
Driver: MOSFET say driven by 555 timer, which turns off when the capacitor reaches 100v.
But Ronv's suggestion looks good and simple and complete.

 

[ronv]

I think this page/site may help, but you have a chore to trace it out.
Notes on the Troubleshooting and Repair of Electronic Flash Units and Strobe Lights and Design Guidelines, Useful Circuits, and Schematics

 

[bobledoux]

I have Sam's page.

Here is another good one: Flyback Converters for Dummies

From what I'm reading a boost circuit requires a simple inductor but a switching transistor rated for more than the output voltage and high amperage. These can be expensive and may require high control voltage or current.

The flyback uses a transformer rather than an inductor but the switching transistor can be much lower voltage. The transformers are generally not available through standard supply houses so you make your own or request samples.

I haven't seen much to suggest either the boost or flyback have an efficiency advantage over the other.

 

[Mr RB]

I think a flyback will have a higher energy efficiency at the higher voltages, and has less issues if you are dumping the cap into a short circuit.

 

[bobledoux]

Some sources recommend a flyback over a boost converter if voltage out put is more than six times the input.

Here is a source for E cores for transformers: 'E' Cores for Inductors, Chokes, Power Supplies : CWS ByteMark, largest supplier of toroids, ferrite cores, iron powder cores, MPP cores and RF cores