# Boost / step up converter dc to dc

#### Coucou80

Joined Apr 7, 2018
59
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
20,590
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.

#### Coucou80

Joined Apr 7, 2018
59
@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
20,590
@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

#### Ian0

Joined Aug 7, 2020
8,938
170v DC - 2amp power supply (from isolation transformer /w rectifier power supply)
Then can't you just rearrange the diodes and capacitors to make 340V?Left circuit is probably what you already have.
Right circuit will give 340V DC.

#### MisterBill2

Joined Jan 23, 2018
16,475
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.

#### Coucou80

Joined Apr 7, 2018
59
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
20,590
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
8,938
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
20,590
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
16,475
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
20,590
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.