Web Links - John Hansknecht
dBm = log10 (mW)*10
Capacitor Charge (Joules) = 1/2C*V2
Enter the required output voltage and value of the R1 resistor to calculate the R2 resistor. Then use the nearest available value (listed at the bottom of the page) or a smaller resistor and series trim-pot for greater accuracy. Maximum output is 37V.
R1 can be changed but should be kept in the range 100-1000 ohms. The regulator should have a minimum load of 10mA for the worst-case specified accuracy; the 240 ohm resistor commonly used gives a 5mA loading which is usually OK.
The second calculator can be used to see the calculated voltage resulting from your stock value resistors. Resistor values must be entered in ohms, '1k' won't work. Sorry.
(Due to voltage losses in the LM317 regulator chip, the input voltage should be at least 2V more than the required output voltage.)
The formula used to calculate the regulated voltage is:
If you need high accuracy, use an adjustable trimpot for all or part of R2.
The E24 series is widely available and goes up in roughly 10% steps as below:
10 ohms, 11, 12, 13, 15, 16, 18, 20, 22, 24, 27, 30, 33, 36, 39, 43, 47, 51, 56, 62, 68, 75, 82, 91...
and decades of the above, eg 120 ohms, 4,700 ohms (4.7k).
Photos by Bob May. Summer 2005. North Carolina's Outer Banks (Good times)