# high current input (KA) in my boost converter

#### Momentory

Joined Sep 4, 2022
101
i recently designed a new boost converter 24v to 240v 0.2A
it is working fine on ltspice for the output voltage and current but when testing the input current i found it up to 24Ka!!
it that true?

note : (i will use uc3843 but as its spice model not working with ltspice i used lt1243 they are very similar)

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#### Papabravo

Joined Feb 24, 2006
20,994
That is a substantial startup transient. It may or may not be real. You are still trying for a boost ratio of 10 which as I have explained is not practical. I suggest you consult a textbook on boost converters to understand why this project may be impractical.

#### Momentory

Joined Sep 4, 2022
101
That is a substantial startup transient. It may or may not be real. You are still trying for a boost ratio of 10 which as I have explained is not practical. I suggest you consult a textbook on boost converters to understand why this project may be impractical.
but there are boost converter in the market do so and even more than ratio of 10 like yh11068a input 12-24v to 400v

#### Alec_t

Joined Sep 17, 2013
14,219
24kA is the initial charging current for C1. Is C1 really 25Farads?
25uF gives a peak current of 30A.

#### Momentory

Joined Sep 4, 2022
101
24kA is the initial charging current for C1. Is C1 really 25Farads?
25uF gives a peak current of 30A.
I edited this c to 100uf, now it is about 7A

#### Momentory

Joined Sep 4, 2022
101
The current still high i expected to draw 3 or 4 A
How to reduce the current and save the output with no change

#### schmitt trigger

Joined Jul 12, 2010
843
One thing about properly simulating a circuit is to understand the real world parasitic components which are not explicitly included in the model.
Here, I would add a 0.01 to 0.05 ohm series resistor to the supply voltage. 0.001 ohm may be way too low when you factor wiring and connector resistance.

#### Alec_t

Joined Sep 17, 2013
14,219
C1 would also have parasitic resistance and inductance.

#### Papabravo

Joined Feb 24, 2006
20,994
but there are boost converter in the market do so and even more than ratio of 10 like yh11068a input 12-24v to 400v
And you are 100% certain, after looking at a schematic diagram of that commercial product, that it is a boost converter with a boost ratio in excess of 10. If that is what you think then a credibility check might be in order.

#### MisterBill2

Joined Jan 23, 2018
17,800
Probably a different type of circuit, such as an inverter of some kind, would be much more efficient and also much simpler to optimize.

#### Momentory

Joined Sep 4, 2022
101
And you are 100% certain, after looking at a schematic diagram of that commercial product, that it is a boost converter with a boost ratio in excess of 10. If that is what you think then a credibility check might be in order.
ok, if this ratio is very high for single phase boost converter can two phase boost converter gives this ratio and work probably?

calculationS done based on this PDF
https://digitalcommons.calpoly.edu/cgi/viewcontent.cgi?article=1212&context=theses

Except the output and input capacitors not sure yet but it seems the value here is working!

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#### ronsimpson

Joined Oct 7, 2019
2,893
To help the boost ratio I changed L1 into a transformer. L1, L2 note the inductance and K1 statement.
To help the inrush current I changed V1 to have 100uS of ramp up time. This way C1 & C5 charge up slower.
Changed R1, C4.
Not stable yet but just to show what I would have done.

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#### Bordodynov

Joined May 20, 2015
3,166
Add a "Rser" parameter for inductances and aluminum capacitors. It is easier to do this by selecting them from the LTspice database. Or in any case look in the base what values in this base are similar in value and voltage. For inductance similar in value and required current.

#### MisterBill2

Joined Jan 23, 2018
17,800
Once again I suggest that an inverter configuration would be smaller and more stable and much simpler to design and optimize. There is at least one IC that will provide a regulated higher output with very few added components.

#### Momentory

Joined Sep 4, 2022
101
Once again I suggest that an inverter configuration would be smaller and more stable and much simpler to design and optimize. There is at least one IC that will provide a regulated higher output with very few added components.
sorry i did not catch your point, is not inverter convert between ac to dc and vice-versa, why use it while i want to boost 24vdc to 240vdc?

#### MisterBill2

Joined Jan 23, 2018
17,800
sorry i did not catch your point, is not inverter convert between ac to dc and vice-versa, why use it while i want to boost 24vdc to 240vdc?
Inverters are routinely used to convert DC to DC, But there is a serious difference in efficiency with some designs. BOOST switching converters have an area of greatest efficiency at much lower ratios. Besides that, boost supplies also rapidly switch the DC, but wind up storing much more power in the magnetic field of the inductor. THAT is why an inverter of the switch-mode type, with transformer action instead, can deliver better efficiency, and also be less complex to optimize in operation.
So if you do a comparison of the different arrangements versus efficiency you will find that the boost scheme is not the best choice at high step-up ratios. A switch-mode inverter will perform more efficiently and also be simpler to optimize.

#### Momentory

Joined Sep 4, 2022
101
Inverters are routinely used to convert DC to DC, But there is a serious difference in efficiency with some designs. BOOST switching converters have an area of greatest efficiency at much lower ratios. Besides that, boost supplies also rapidly switch the DC, but wind up storing much more power in the magnetic field of the inductor. THAT is why an inverter of the switch-mode type, with transformer action instead, can deliver better efficiency, and also be less complex to optimize in operation.
So if you do a comparison of the different arrangements versus efficiency you will find that the boost scheme is not the best choice at high step-up ratios. A switch-mode inverter will perform more efficiently and also be simpler to optimize.
Do you have example circuit because all i found is just dc to ac inverters

#### ronsimpson

Joined Oct 7, 2019
2,893
Sometimes these are built like this. Note the red circle where the transformer sets on ground not Vin.

#### MisterBill2

Joined Jan 23, 2018
17,800
OK, RS just posted an example that uses a transformer but puts out DC.Transformer step up ratios are more efficient because they depend on turns ratios rather than more energy being stored in an inductor.

#### ronsimpson

Joined Oct 7, 2019
2,893
From post #12 and #18 the schematic are almost the same thing. Turn ratio is an easy boost!