Compact 110Vdc to 24Vdc Converter Design for 60mA Output, Max Size 30x40mm

Dear allWe need to convert 110 Vdc to 24 Vdc with a converter which size should not exceed 30x40mm.Maximum output current is 60 mA and output voltage can differ from 23 to 30 V.
We used to use two 4.7 kΩ (10 W) resistors in parallel and a zenner diode to reduce the voltage. but the resistors overheat and can cause damage to other parts of the circuit.
I am asking you all to help me design a simple circuit ASAP.thanks in advanceMehrabi

There are a number of questions I would have about the circuit that you are using, since I find some of your requirements contradictory- for instance with a current of 60mA and a resistance of 2K3 the volt drop is 138V! But rather than get into the limitations of using a resistor/zener to generate a constant voltage supply, I
would suggest you use a switchmode power supply. You should go to the TI
website and use the Webench Designer tool. When presented with 3
options: Nodule/Integrated/Controller- choose Integrated.  I tried it with 100-120VDC input, 24VDC out in and 0.1A output. It should present
you with a design using the UCC28881 or UCC28880 which they claim would occupy
750sq.mm. Of course you are
going to need to produce a PCB-c'est la vie! On second thoughts, there may be a development board- check the output result when you have completed the data entry.

Good
luck!

I agree with Aubrey in that a switchmode power supply will give the best results.The problem you have is that by dropping that much voltage across resistors, you will be dissipating a lot of power. That voltage drop at 60mA guarantees you at least 5.16W dissipation and likely more. That much power dissipation in the small area you have is asking for trouble unless you have significant vertical space for a heatsink.

Hi Mehrabi-I agree with Aubrey and Elizabeth. A switchmode regulator will be your best solution.  The design process for many of these regulators can get very involved.  Here's a simple one: HV9922 This device is intended to be on offline LED driver, but with a couple of simple tweaks it makes a nice non-isolated supply. Look at this design note: DN-H03Switching regulators don't get any simpler than this!-Rick

Thank you very much   Aubrey Kagan ,  Elizabeth Simon and Rick Curl I really do appreciate your help.I used Webench Designer as  Mr. Kagan said and it gave me a circuit using UCC28880D.I'm from Iran and unfortunately this item is not available here, so I'm going to humbly ask you if you could introduce an alternative to that.Thanks again.Mehrabi