Charging Circuit: How a Capacitor Gets 330V from 1.5V Battery

[n1caboose]

Hello, would anybody please tell me how a charging circuit works, such as one for a capacitor in a disposable camera...how can the 1.5V battery fully charge a 330V capacitor? I believe transformers are involved to kick up the voltage, but how is DC converted to AC for that? I'd also like to know the components I would need to make my own rugged version of a charger like this...

Thank you!

 

[berkeman]

Hello, would anybody please tell me how a charging circuit works, such as one for a capacitor in a disposable camera...how can the 1.5V battery fully charge a 330V capacitor? I believe transformers are involved to kick up the voltage, but how is DC converted to AC for that? I'd also like to know the components I would need to make my own rugged version of a charger like this...

Thank you!

If you don't know how the circuit works, I'm not sure you should be trying to build one that boosts up to several 100s of volts... What do you intend to do with the circuit?

You can learn more about these kinds of circuits by using the search terms "DC-DC Converter", "Boost Converter" and "Flyback Converter". You can search at wikipedia or National Semiconductor or Maxim Semiconductor, or just with Google.

 

[paulfr]

Hello, would anybody please tell me how a charging circuit works, such as one for a capacitor in a disposable camera...how can the 1.5V battery fully charge a 330V capacitor? I believe transformers are involved to kick up the voltage, but how is DC converted to AC for that? I'd also like to know the components I would need to make my own rugged version of a charger like this...

Thank you!

You are right.
A transformer provides the step up ratio.But transformers only pass AC signals.
So a transisitor driven by an oscillator "chops" the dc to make quasi-square waves
that then are fed into the xformer.

Any flourescent lamp has a ballast that does this because the gas
needs high voltage to arc. Buy one and take it apart and you can see
the components. Cost = $3 - 6 or so.

 

[schip666!]

Any flourescent lamp has a ballast that does this because the gas
needs high voltage to arc. Buy one and take it apart and you can see
the components. Cost = $3 - 6 or so.

Not exactly true according to:
http://en.wikipedia.org/wiki/Fluorescent_lamp

Larger tubes may need a step up, but they don't need "high voltage" -- you may be thinking of "neon" sign tubes. The main task of the ballast is to limit the current, thus the name "ballast".

 

[paulfr]

Not exactly true according to:
http://en.wikipedia.org/wiki/Fluorescent_lamp

Larger tubes may need a step up, but they don't need "high voltage" -- you may be thinking of "neon" sign tubes. The main task of the ballast is to limit the current, thus the name "ballast".

Au contraire ...
High voltage is officially reached at 50 volts.
That my not seem high to many, but the power industry marks it so.
I worked in high energy physics for many years and I know this to be true.
The lamp operating point will more often than not have a drop grater than 50 volts.
How do i know that ? I designed one of the first electronic ballasts at
Westinghouse for an HID lamp back in 1983.

Furthermore, even with a starting gas, the initial strike voltage for a gas tube
will be typically around 1.5 to 2.5 Kilovolts. That is clearly high voltage.

To the OP ... here is a link where you can see a non magnetic electronic ballast
and its components.

http://en.wikipedia.org/wiki/Compact_fluorescent_lamp

Cheers

 

[n1caboose]

If you don't know how the circuit works, I'm not sure you should be trying to build one that boosts up to several 100s of volts... What do you intend to do with the circuit?

I made a coilgun out of a disposable camera circuitboard hooked up to five 330V 80uF caps found in the cameras. It fires a nail at a very low speed (not enough to penetrate a paper towel), but I was not going for anything crazy since this was really the first electrical project I've ever conducted...

I used the same AA battery to charge the capacitor bank and that took a while - I wanted to speed that up or at least be able to demonstrate how it works.

You can learn more about these kinds of circuits by using the search terms "DC-DC Converter", "Boost Converter" and "Flyback Converter". You can search at wikipedia or National Semiconductor or Maxim Semiconductor, or just with Google.

Thank you, these were helpful.

You are right.
A transformer provides the step up ratio.But transformers only pass AC signals.
So a transisitor driven by an oscillator "chops" the dc to make quasi-square waves
that then are fed into the xformer.

Any flourescent lamp has a ballast that does this because the gas
needs high voltage to arc. Buy one and take it apart and you can see
the components. Cost = $3 - 6 or so.

Thanks a lot, I understand how this works now and took apart a lamp I found lying around. Had some extras at home.

I designed one of the first electronic ballasts at
Westinghouse for an HID lamp back in 1983.

And that's pretty damn cool.

 

[schip666!]

Au contraire ...
High voltage is officially reached at 50 volts.
That my not seem high to many, but the power industry marks it so.

...

Furthermore, even with a starting gas, the initial strike voltage for a gas tube
will be typically around 1.5 to 2.5 Kilovolts. That is clearly high voltage.

Ah, OK. I think of "high voltage" as above your typical mains voltage... say 100's, not 50. This is something I've not worked with, how is the strike voltage generated? I thought it was the little starter thingie in your typical home fluorescent bulb, and that the ballast was there simply to add a load for AC current limit. It appears from the wiki page that ballasts for larger tubes can also be step up xfmrs. So what's the actual operating voltage across the range of sizes then?