Hint.  The ratio of successive terms is
$$\frac{(n+1)!x^{n+1}}{1.3.5\cdots(2n-1)(2n+1)}\bigg/
  \frac{n!x^n}{1.3.5\cdots(2n-1)}
  =\frac{n+1}{2n+1}x\ .$$

Find the ratio and interval of convergence for $\sum_{n=1}^{\infty} \frac{n!x^n}{1\cdot 3\cdot 5\cdots (2n-1)}$
Is there any way to get 75 V 1 A output from 78 V input?

I found the TL783 high voltage adjustable regulator. But this can supply only 700mA output current.

I had forgot to tell the details.

Main purpose of this power supply is high precision sensor circuit.

Previously, when required 5V : Step down to 8v with a switching regulator first, then step down to 5v with linear regulator.
It is for the sake of stability of the power supply voltage.

When required 12V : Step down to 15V with a switching regulator first, then step down to 12V with linear regulator.

When required 24V : Step down to 27V with a switching regulator first, then step down to 24V with linear regulator.

This time required 75V and step down to 78v with a switching regulator first, then step down to 75V. I've tried...

This way I have wrong?
