Roman Black SMPS for 3.3V output?

[jshroff]

Hi All,

I am looking at adapting the Roman Black SMPS circuit to provide 3.3V for an application in an automotive setting so requirements would be
input voltage from 8V to 24V
Output voltage of 3.3 V

Has anyone got a guide (or can suggest an approach) to how to calculate the values of the components to provide the 3.3V output voltage?

Thanks
Jay

 

[cowboybob]

Hi All,

I am looking at adapting the Roman Black SMPS circuit to provide 3.3V for an application in an automotive setting so requirements would be
input voltage from 8V to 24V
Output voltage of 3.3 V

Has anyone got a guide (or can suggest an approach) to how to calculate the values of the components to provide the 3.3V output voltage?

Thanks
Jay

Welcome, Jay!

Not sure why your automotive voltage would be 24VDC, and if it is, then this circuit design won't help, but...

I have not confirmed this circuit: https://www.romanblack.com/smps/smps.htm

but by selecting the correct value zener, you could get the output you're looking for.

You also did not include your current requirement(s).

 

[ericgibbs]

hi Jay,
As Bob asks, whats the load current.?

This circuit was debugged by ETO members back in Aug 2012, so if you do a Search, you may find the information you are looking for.
I still have all the LTSpice simulations we ran for this circuit, so lets know your requirement and I will rerun the sims.
E.

 

[jshroff]

Hi cowboybob,

Just wanted to allow for some headroom given that the alternator voltages could go as high as 14-16 volts...

Sorry forgot about the current requirements - it would be around 600ma.

Thanks for the suggestion I will try playing with the circuit in LTSpice and see what the zener does

Jay

 

[jshroff]

hi Jay,
As Bob asks, whats the load current.?

This circuit was debugged by ETO members back in Aug 2012, so if you do a Search, you may find the information you are looking for.
I still have all the LTSpice simulations we ran for this circuit, so lets know your requirement and I will rerun the sims.
E.

Hi ericgibbs,

I did run across that thread but could not see the sim results itself - maybe that is because I am using google chrome - will try viewing under IE and see if that helps.

Current requirements are around 600ma...

Thanks
Jay

 

[ericgibbs]

hi jay,
As RB's web page states for higher voltage inputs and higher output currents the circuit requires some additional components and some component changes.
You cannot use it for 24V and 3.3v at 600mA, as its shown on his page.

As I see it some redesign of the original circuit is required as it appears that some of the suggested changes have not been checked out.

E

 

[simonbramble]

The LTC3864 is ideal for the application you are trying to do. It will cope with voltages up to 60V and whatever output current you need. You can open up a circuit in LTspice and be simulating within 5 mins. it was designed for such automotive applications:
https://www.linear.com/product/LTC3864

If you need a tutorial on LTspice or dc/dc converters, see my website

Hope this helps

Simon

 

[jshroff]

Hi Simon,

You are correct this would be an "almost" ideal converter except it seems a bit pricey - I will check with LTC if their volume pricing is more in line to some of TI's converters like the LM3485

Thanks for the lead though it does look promising

Jay

 

[simonbramble]

How many are you looking to purchase? Also with a hysteretic mode converter, the output ripple might be a bit high.

 

[jshroff]

How many are you looking to purchase? Also with a hysteretic mode converter, the output ripple might be a bit high.

I am still in the POC stage but I am optimistic that if things go well with the POC might need 1000+. Yes agreed on the hysteretic mode converter the ripple would be higher but I think I could work around it if needed