Looking for low Vin Boost controler with external switch and variable f

[Amper]

Hi!

Im looking for unusual components and solutions again, maybe someone here has encountered the part i need

What im looking for is a small, low Power and foremost low Vin (<2.7V to 5V) switch mode controller for a very compact high voltage supply.
The supply can essentially be seen as a simple boost converter but i have to run it at comparably low Frequencies around the 50kHz range. The Topology is a small coupled inductor feeding a 10 stage cascade made from 0805 mlcc, the primary voltage goes up to a few 10V (switch voltage). Power is low (a few 10 to 100mW).
Id love a small component like so23-5 or similar but soic8 will be fine too.

I had a look around and found this one
https://www.diodes.com/assets/Datasheets/ZXSC4x0.pdf
but sadly its fixed 200kHz which greatly reduces efficiency of the cascade...

Any suggestions? 

[barshatriplee]

One option you can consider for your requirements is the LTC3536 from Linear Technology (now part of Analog Devices). It is a low-power, synchronous boost converter with an input voltage range of 1.8V to 5.5V and a programmable switching frequency.

Here are the key features of the LTC3536:

Input voltage range: 1.8V to 5.5V
Programmable switching frequency: You can set the switching frequency using an external resistor, allowing you to configure it for your desired frequency in the 50kHz range.
Synchronous rectification: The LTC3536 utilizes synchronous rectification to improve efficiency.
Compact package: It is available in a small 8-pin DFN package, which should meet your compact size requirement.
You can refer to the datasheet for more detailed specifications, application circuits, and layout guidelines:
https://www.analog.com/media/en/technical-documentation/data-sheets/3536fa.pdf

[Amper]

Hi and thanks for the reply, sadly this one has internal switches for 5V output, i wont be able to drive a transformer with it in boost mode up to 50V primary peak voltage
Right now im thinking about doing it with two comparators (one as oscillator, one as schmitt trigger for voltage regulation)  But im not happy with it yet.

[Wolfram]

It could also be an option to use an internal switch controller and cascode a high voltage MOSFET on top of the internal switch. As long as you can find a HV MOSFET with low enough Vgs_th this is a very vaible solution. Sadly, most integrated switch controllers have fixed Fsw, particularly low voltage input ones, so I don't have any part numbers to recommend off hand.

What's your target output voltage and current? A plain boost running from 2.7 V will struggle to reach beyond 50 V due to inductor parasitics, and efficiency will be miserable. If you need more voltage than that I would consider cascaded boost converters, adding a voltage multiplier if you only need very low current, or a flyback which could be done with off-the-shelf magnetics. Even doing a tapped inductor boost using a standard 1:1 coupled inductor will help

[Amper]

Hi!
Have a look at the picture i postet. What i want to do is feeding a cascade from a transformer while using the transformers inductance to raise the voltage in addition to just the 1:13 ratio it brings. The Cascade wil be 1:10 (if seen ideal), the transformer 1:13 and the target Voltage 4kV. Thats roughly 30V on the switching transistor driving the transformer, assuming everything is ideal components. So in reality with stray inductances i will need the stated 50V switch as a minimum. 2.7V to 30V will be the rise in voltage from the current transient at the inductor, the rest of it transformer and cascade.

This section already works, driving the cascade, transformer and logic level fet from a freqency generator i get a good output voltage and current, i just lack the component generating the control signal.

[langwadt]

Hi!
Have a look at the picture i postet. What i want to do is feeding a cascade from a transformer while using the transformers inductance to raise the voltage in addition to just the 1:13 ratio it brings. The Cascade wil be 1:10 (if seen ideal), the transformer 1:13 and the target Voltage 4kV. Thats roughly 30V on the switching transistor driving the transformer, assuming everything is ideal components. So in reality with stray inductances i will need the stated 50V switch as a minimum. 2.7V to 30V will be the rise in voltage from the current transient at the inductor, the rest of it transformer and cascade.

This section already works, driving the cascade, transformer and logic level fet from a freqency generator i get a good output voltage and current, i just lack the component generating the control signal.

something like this, https://eu.mouser.com/datasheet/2/360/S8353_8354_E-1696641.pdf

and this scheme to get the voltage, https://www.edn.com/cascode-mosfet-increases-boost-regulators-input-and-output-voltage-ranges/

[Someone]

Right now im thinking about doing it with two comparators (one as oscillator, one as schmitt trigger for voltage regulation)  But im not happy with it yet.

Two comparators? there's an app chip for that:
https://www.eevblog.com/forum/projects/555-timer-boost-converter-(and-buck-converter)-switching-power-regulator/

[Amper]

Hi and thank you very much for the replies, i like both and will look into it a bit...
I tried the 555 schematic form the challenge, it works well in ltspice but adapting it for very high input impedance  seems a bit difficult and its not stable in all cases. Id like it though because the 555 is not going to be difficult to source like some specialized IC or microcontroller with components shortage.