110V to 24V DC-DC Converter Design?

[emax2]

I need a design to convert 110V DC to 24V DC for output current of 500mA to 1A.
The cost is also a factor to consider and probably need a discrete design to lower BOM cost.

Can anyone suggest a similar and simple design/schematic for this application?

 

[BradtheRad]

This buck converter might be fun to experiment with. It uses ordinary components. However it's untested.



There are control IC's designed to operate a buck converter. These contain safeguards, and they would do the job better than an op amp.
You would need one that can tolerate being exposed to 110 VDC. To handle a 110 VDC supply, my schematic has a PNP driven by an NPN.

The .2 ohm resistor at the supply is unnecessary. It depicts some amount of internal resistance in the supply.

 

[emax2]

Thanks BradtheRad for the design.
There are indeed some control ICs available such as LTC3638...
https://www.linear.com/product/LTC3638
but for those ICs either the max input voltage is less than 75V or the current is less. The application note of LTC3638 has two parallel devices to drive 500mA but the cost is relatively high.
For your design what are the specifications for PNP and NPN devices?

 

[BradtheRad]

The transistors should be rated to withstand twice the power supply voltage (a customary practice).

As for ampere rating, the scope trace shows 1.5 A peak through the PNP. However it can be greater, depending on how you adjust the hysteresis. In particular, a slower frequency will result in pulses of 2 or 3 A or more.