Buck regulator as DC transformer

Yes, the buck converter is a DC to DC converter. Buck is stepping down type. 
Transfer function VOUT = D * VIN where D is duty cycle.

Thanks

-Arief

Hi Arief. Thanks for response. Maybe I didn't configure my question right. I wonder is it possible to arrange buck converter to have fixed step-down ratio (for example 6:1) and to skip regulated output but to make it follow voltage changes at input to output. For example if Vin is 36 Vout 6, then when Vin goes to 24v Vout goes to 4, and so on. 

I think you can possibly do this by running it open loop since the output is not regulated.

So you inject a fixed duty cycle to the gate driver ICs. So lets say you want 6:1 ratio, then you need to create a PWM with duty cycle of 1/6. 
You'll have to use a gate driver ICs to drive the MOSFET. Maybe something like this one
http://www.ti.com/lit/ds/symlink/lm27222.pdf

Thanks

-Arief

Thanks Arief. I will try to configure it to my needs, but problem I see for a start is that gate drivers require separate Vcc and I have available only Vin voltage with limited current capability. 

Hi,

Yes if you use LM27222 the VCC has to be between the 4V and 6.85V. Therefore you need to use an voltage regulator if VIN is higher that these value. As for the current, i believe the IC will some mA ( I would say less than 10mA) of current when it is switching to drive a MOSFET.

Thanks

-Arief

Thanks. I recalculate my application several times and besides my Vin goes up to 40V i have no spare current to power  the chip... My current limit is 40ma in front of  switcher and if the effiecency is approx 70% i will "burn" around 35ma on load. So unfortunatelly this doesnt works for me. 

Thanks Alan. Circuit looks simple and very useful.  As I can see, the buck chip can be any of  adjustable available. Right?

Srdjan

Hi Srdjan,

It can be but the importance of the buck selected is two-fold.

a) Very low quiescent current, this ensures your buck doesn't load up the input.

b) Very high efficiency, it uses a synchronous design hence peak efficiencies of 95% can be obtained further improving the resilience of your circuit.

Thanks,

Anston

Hello Srdjan,

It's been more than a year since you asked this question. But we were curious to know what your application was that required a fixed ratio output to input. Were you successful in completing that design?

Kindly reply.

Regards,

Akshay