Boost / step up converter dc to dc

Thread Starter

Coucou80

Joined Apr 7, 2018
16
Hello,
I have acces to a 170v DC - 2amp power supply (from isolation transformer /w rectifier power supply). If I need to double the voltage from this, what type of consideration I need to take when building my boost converter? Is it first possible to do so with a boost converter ?
 

Papabravo

Joined Feb 24, 2006
16,777
In any power conversion scheme, the primary consideration is: what power output can I achieve. The immutable rule of power conversion is: power out will always be less than power in. Sometimes it will be much less. So for reasons unknown, you want to start with an input power of 340 Watts = 170 Volts x 2 Amperes. Assume for the sake of argument that you can come up with a scheme that is 85% efficient. So 340 Watts x 0.85 = 289 watts. So in a 1:2 boost converter of whatever technology you choose you will have 340 Volts @ 850 mA. Is that acceptable? Would a worse outcome also be acceptable?

If I was doing this it is not the way I would go.
 

Thread Starter

Coucou80

Joined Apr 7, 2018
16
@Papabravo thank you for your quick response.
Yes I could live with something a little less than 1 amp.
I agree I could use a different approach. I thought of using a royer ZVS oscillator or a simple photo flash oscillator, but since I have this bulky isolation transformer, its always impressive to use it :)
 

Papabravo

Joined Feb 24, 2006
16,777
@Papabravo thank you for your quick response.
Yes I could live with something a little less than 1 amp.
I agree I could use a different approach. I thought of using a royer ZVS oscillator or a simple photo flash oscillator, but since I have this bulky isolation transformer, its always impressive to use it :)
Do you have a candidate design in mind?
 

MisterBill2

Joined Jan 23, 2018
9,258
Actually there is indeed a much simpler scheme available, and also it wll cost less and work quite well the very first time. And since you already have the isolation transformer it will not pose a "mains connected" shock hazard.
The circuit is commonly called a voltage doubler, or a full-wave voltage doubler to avoid confusing it with a half-wave voltage doubler. The circuit uses two diodes and two larger filter capacitors. From a nominal 120 volts RMS source, such as your transformer, you can expect to get about 370 volts at no load..
It is exactly like the second circuit in post #5, which appeared while I was writing this post. So you can see how simple the circuit is.
 

Thread Starter

Coucou80

Joined Apr 7, 2018
16
Thanks all for your response
I will have to digest all the above recommendation ... you guys brought a very good point, I never thought that I could acheive the desire effect by just reorganising the caps & diodes arround
 

Papabravo

Joined Feb 24, 2006
16,777
Thanks all for your response
I will have to digest all the above recommendation ... you guys brought a very good point, I never thought that I could acheive the desire effect by just reorganising the caps & diodes arround
When considering this approach, make sure that none of the ratings on the components in the existing supply will be exceeded in the rearranged version.
 

Ian0

Joined Aug 7, 2020
3,221
And watch out for the ripple! It will have four times as much ripple on the output for the same value of smoothing capacitor.
 

Papabravo

Joined Feb 24, 2006
16,777
And watch out for the ripple! It will have four times as much ripple on the output for the same value of smoothing capacitor.
I had a mad friend who observed, once upon a time, that there was something about every system that sucks. He was talking about software and operating systems, but it seems that his observation just might be more universal.
 

MisterBill2

Joined Jan 23, 2018
9,258
In engineering we know that most designs are a compromise. There is a line that goes: Good, Quickly Done, Cheap, Pick two. The voltage doubler does work but there is a bit more ripple to deal with and the regulation is not as good with the same value of components.
 

Papabravo

Joined Feb 24, 2006
16,777
In engineering we know that most designs are a compromise. There is a line that goes: Good, Quickly Done, Cheap, Pick two. The voltage doubler does work but there is a bit more ripple to deal with and the regulation is not as good with the same value of components.
There are designs where that will be a feature rather than a bug.
 
Top