Need be controlled reverse-able.
Thanks

 

Tell us what you would consider easy. My crystal ball is in the shop for repair.

 

It can be done with a controller, 555 or micro, that uses a PWM output.
Max.

 

https://www.maximintegrated.com/en/images/appnotes/2031/2031Fig03.gif

https://www.maximintegrated.com/en/images/appnotes/2031/2031Fig01.gif

https://www.amazon.com/Converter-Vo...c+v+converter&qid=1560978716&s=gateway&sr=8-3

 

IMO, if it is to be controlled anyway, why not do it in one step with less complication.?
Max.

 

A 555 PWM circuit as Max suggested, with the duty-cycle limited to no more that 50%.
Connect to a DPDT switch or a MOSFET H-bridge if you want it reversible.

 

You can also pick up a LMD18200 H-bridge cheap on ebay already on a circuit board.
Max.