# Very high gain transformerless boost converter - is it possible

Started by September 2, 2018
```Is it possible to build a 130-150 Watt, 12V input (for example, car cigarette lighter) to 350V output transformerless boost converter. The efficiency should be at least 85%. Assume a resistor load only.

If it is not possible, Would there be any other possible tranformerless solutions?
```
```Possible, yes.  It's possible to shoot onesself to the planet Mars.  That
doesn't mean it's a good idea, or economically sound. :-)

The best is a tapped inductor, and second best is ordinary flyback (isolated
at the transformer level, but you don't need to isolate it, it can be tied
common ground).

Tim

--
Seven Transistor Labs, LLC
Electrical Engineering Consultation and Design
Website: https://www.seventransistorlabs.com/

"Nomadic Electron" <themerchantbay@gmail.com> wrote in message
> Is it possible to build a 130-150 Watt, 12V input (for example, car
> cigarette lighter) to 350V output transformerless boost converter. The
> efficiency should be at least 85%. Assume a resistor load only.
>
> If it is not possible, Would there be any other possible tranformerless
> solutions?

```
```Nomadic Electron typed
>Is it possible to build a 130-150 Watt, 12V input (for example, car cigarette lighter) to 350V output transformerless boost
>converter. The efficiency should be at least 85%. Assume a resistor load only.
>
>If it is not possible, Would there be any other possible tranformerless solutions?

I would not use the word 'gain' here, you meant efficiency I guess.

It's simple (tm)
350 / 12 = 29.166667
So we need 2 x 29 makes 58  12V batteries, oh why not use 11.1 V lipos
then we need
350 / 11.1  = 31.531532
say 2 x 31 makes 62 3 cell lipos.

Use a bunch of antique relays, and
put half the lipos parallel to your 12V battery, with some charging control in series with each lipo.
The other 31 lipos  switched in series to the 350V output

Once in a while when output lipos go low, switch the first 32 to the output (in series)
and the second 31 to the battery (in parallel) for charging.

Have a small electrolytic >350 V cap on the output to cover the relay switch-over time.
make sure you use break before make relays,

This also should work with capacitors and MOSFET switches in place of LIPOs.
It is a well known method but forgot what it is called, switched capacitor converter perhaps?
In the case of caps and MOSFETS you need to switch a bit more often.

All depends on what you have in the junk box...
Note the isolation requirement for the MOSFET drivers.

;-)

```
```On 02/09/2018 11:53, Nomadic Electron wrote:
> Is it possible to build a 130-150 Watt, 12V input (for example, car cigarette lighter) to 350V output transformerless boost converter. The efficiency should be at least 85%. Assume a resistor load only.
>
> If it is not possible, Would there be any other possible tranformerless solutions?
>
A switched mode boost converter would probably work and doesn't need a
transformer but does need an inductor:

https://en.wikipedia.org/wiki/Boost_converter

Why do you want to avoid transformers?  If you are concerned about the
size and weight, a high frequency flyback regulator would be a good
option.  It does require a transformer but it could be fairly small
compared to the half brick sized things designed to work at 60Hz.

If you want to avoid magnetics altogether then it's going to be more
difficult.  A Cockroft-Walton voltage multiplier may be an option but I
don't know what the efficiently would be:

https://en.wikipedia.org/wiki/Cockcroft%E2%80%93Walton_generator

Obviously you would need to generate an AC voltage to drive it but that
can easily be done.

What are you actually trying to do?
```
```On Sunday, 2 September 2018 11:54:04 UTC+1, Nomadic Electron  wrote:
> Is it possible to build a 130-150 Watt, 12V input (for example, car cigarette lighter) to 350V output transformerless boost converter. The efficiency should be at least 85%. Assume a resistor load only.
>
> If it is not possible, Would there be any other possible tranformerless solutions?

It's possible yes, but the choke would run at a low duty cycle. So to get 85% you'd need a big choke to get low copper loss at short high current spikes.

NT
```
```Nomadic Electron wrote:

> Is it possible to build a 130-150 Watt, 12V input (for example, car cigarette lighter) to 350V output transformerless boost converter. The efficiency should be at least 85%. Assume a resistor load only.

Switched capacitor converters do exist, but probably not at this power
level. There are also some experiments with piezoelectric transformers,
but it's still a niche:

http://www.ti.com/lit/an/slyt125/slyt125.pdf

But what's the reason not to use perhaps the most robust electronic
component in the Universe? Coilophobia?

Best regards, Piotr
```
```On 09/02/2018 07:17 AM, Tim Williams wrote:
> Possible, yes.&#4294967295; It's possible to shoot onesself to the planet Mars.
> That doesn't mean it's a good idea, or economically sound. :-)
>
> The best is a tapped inductor, and second best is ordinary flyback
> (isolated at the transformer level, but you don't need to isolate it, it
> can be tied common ground).
>
> Tim
>

It's also probably possible to parallel up the outputs of some boost
converters you can buy off the shelf, e.g. I have a bunch of these
modules which claim to be capable of 40 watts (not had a chance to test
real-world performance may be fairly close to what is claimed)

<https://www.ebay.com/itm/DC-DC-10-32V-to-45-390V-High-Voltage-Boost-Converter-Step-up-Booster-Module-NiHK/223000589035?hash=item33ebdef2eb:g:rZUAAOSwPWRZXF4g>

Two of them seem to share load OK with no further effort but to get the
output power levels as he wants you'd need like four or five, and my
intuition is they'll wreck each other trying to naively load-share
without some kind of closed-loop to make sure they share the load
current equally.

Which you could probably do with current sensing on the input side to
equalize the power for each, there are a number of schemes online
amount of magnetics much larger and heavier and efficiency will deffo
not be anywhere near 85% so you start to wonder once again what the
point of these "make a tasty sandwich without bread" exercises are.
```
```Nomadic Electron wrote...
>
> Is it possible to build a 130-150 Watt, 12V input (for example,
> car cigarette lighter) to 350V output transformerless boost
> converter. The efficiency should be at least 85%. Assume a
>
> If it is not possible, Would there be any other possible
> tranformerless solutions?

As others have said, the low duty cycle of an inductor-only
boost converter, under 4%, spells big trouble for obtaining
high efficiency.  However, there's an easy trick that can
get around the 28x step-up problem: reducing it to two sets
of sqrt 28 = 6x step-up.  A two-stage boost converter, but
with one controller, driving two MOSFETs, inductors, diodes
and capacitors.  Use separate resistors for each gate.

The first MOSFET & inductor creates an intermeduate voltage.
It runs at higher currents, but at lower voltages.

--
Thanks,
- Win
```
```On 9/2/2018 5:53 AM, Nomadic Electron wrote:
> Is it possible to build a 130-150 Watt, 12V input (for example, car cigarette lighter) to 350V output transformerless boost converter. The efficiency should be at least 85%. Assume a resistor load only.
>
> If it is not possible, Would there be any other possible tranformerless solutions?
>

Get a dynamotor or HV photo flash battery
```
```On 2 Sep 2018 10:14:52 -0700, Winfield Hill <hill@rowland.harvard.edu>
wrote:

>>
>> Is it possible to build a 130-150 Watt, 12V input (for example,
>> car cigarette lighter) to 350V output transformerless boost
>> converter. The efficiency should be at least 85%. Assume a
>>
>> If it is not possible, Would there be any other possible
>> tranformerless solutions?
>
> As others have said, the low duty cycle of an inductor-only
> boost converter, under 4%, spells big trouble for obtaining
> high efficiency.  However, there's an easy trick that can
> get around the 28x step-up problem: reducing it to two sets
> of sqrt 28 = 6x step-up.  A two-stage boost converter, but
> with one controller, driving two MOSFETs, inductors, diodes
> and capacitors.  Use separate resistors for each gate.
>
> The first MOSFET & inductor creates an intermeduate voltage.
> It runs at higher currents, but at lower voltages.

That's cool. Thanks.

Combine that with my center-tapped inductor trick maybe to get another
4x.

--

John Larkin   Highland Technology, Inc   trk

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

```