Cheap 75V buck Ideas

[ali_asadzadeh]

Hi,
I want to design a simple 75V input 5V 500ma output Buck converter, I needs to be super cheap!

Do you have any part or idea in mind? I was considering UC3843 as a flyback, but I wanted to know if we have something even cheaper

[mariush]

Richtek RT6210 ?  https://www.richtek.com/assets/product_file/RT6210/DS6210-00.pdf

2.6$ in 10pcs ... though kinda inefficient, around 70% eff. at 70v in , 5v out...

Seems expensive but keep in mind you don't need transformer with custom windings, additional mosfet, extra parts around it etc...

There's also MAX5033 but its maximum voltage is 76v... you'll definitely have to be careful and ideally drop the voltage by a few volts : https://datasheets.maximintegrated.com/en/ds/MAX5033.pdf
It would probably be expensive if you buy low quantities and... it's Maxim, you may have problems buying them at some points.


If you can get your maximum voltage below 50v, you could use cheaper regulators, like let's say a 1.3$ MCP16331 : http://ww1.microchip.com/downloads/en/DeviceDoc/20005308C.pdf
You could do that with a bunch of diodes in series, or if your input voltage is always within some high range, maybe using a dropper resistor.
1n4149 diodes are cheap, 3-5 cents each if you buy 100, and each drops 1v...

 

[mvs]

I was considering UC3843 as a flyback, but I wanted to know if we have something even cheaper

Cheaper then UC384x? Some chinese flyback controllers with integrated switch can cost less then $0.05/pcs in volume. But you will need flyback transformer in both cases...
https://lcsc.com/product-detail/Others_Shenzhen-Chip-Hope-Micro-Electronics-LP3668B_C360134.html
https://lcsc.com/product-detail/Power-Management-Specialized-PMIC_Shenzhen-Chip-Hope-Micro-Electronics-LP3773A_C125952.html

Some buck converters, like XL7036, can be cheaper in total costs, but are less safe to use and dissipate more power.
http://www.xlsemi.com/datasheet/XL7036%20datasheet-English.pdf
https://lcsc.com/product-detail/DC-DC-Converters_XL7036_C89530.html

[SiliconWizard]

Unless you absolutely need isolation, I wouldn't go for a flyback design. You'll need a handful of components including a transformer that can be costly (unless you're targetting very high quantities), and designing a robust flyback converter is not as easy as it sounds. If this is a learning exercise, then why not, you'll certainly learn a few things, but expect to be burning a few transistors before getting it right. And I'm not talking about EMI...

There are high voltage buck converters, mariush gave you some references, you can also find some from LT/AD (for instance, the LTC3894, but there are a few others in the same ballpark depending on the output current you need).

Just my 2 cents.