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Web Links - John Hansknecht**

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My
Purchase
Requisitions

Other Electronics calculators
### dBm to Watt
Conversion Calculator

dBm = log10 (mW)*10

mW =10^(dBm/10)

Some tunes:

Capacitor Charge (Joules) = 1/2C*V^{2
}

## LM317 Voltage
Regulator Calculator

#### The basic LM317
circuit. See the datasheet for advice

on adding capacitors and other enhancements.

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.)*

### Why is my output
voltage a bit off?

The formula used to calculate the regulated voltage is:

#### V_{out}
= 1.25(1 + R2/R1)

However,

- The Reference Voltage is only
*nominally*
1.25V and for different components it can vary from 1.20–1.30V; so with
a 12V aim, the end result will be 12V ±0.5V.
- The resistors won't be exactly what
they say. The cheaper gold-banded are ±5%, brown-banded metal film not
much more expensive and ±1%.
- There's a small error term Iq * R2 to
add to the result. Iq, the Adjustment pin current, is typically only
50µA (0.00005), so it doesn't usually make much difference compared to
the two factors above; only 5mV if R2=1k.

If you need high accuracy, use an adjustable trimpot for all or part
of R2.

### E24 resistor series

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)