PIC Micro's For Beginners - Voltage
Regulator
Voltage regulators are essential with digital electronics, as most
devices require a very steady and clean 5 volts to operate
correctly. Some devices require 3.3 volts, but the concept is
exactly the same.
The 7805 is a 3 pin package that is easily
designed for regulating any voltage over 6.5 volts down to a
constant and steady 5 volts. The reason why you need 6.5 volts or
more is to accommodate for the internal requirements of the IC
itself.
Now with any voltage above 6.5 volts and up
to 12 volts (it can go higher, but heat becomes an issue). The
reason why heat places a limit on the upper input voltage, is
because
the 7805 package can only dissipate so much power in the form of
heat. Power is calculated by Volts
Dropped * Load Current.
Lets say you were
using a 24 volt dc adaptor into the
7805 regulator to get your 5
volts output, and the total current being used was a steady 100mA
for your target circuit. This would make the voltage regulator drop
19 volts to maintain the 5 volt output, and in return with 100mA
running through it, there would be 19 * 0.100 = 1.9 Watts. This will
be incredibly hot to touch, and a
heat sink would be required.
The 10uF electrolytic
capacitor is required to maintain a steady input voltage to the
regulator, and should be used in all designs. If you are driving
high current loads, then use a bigger capacitor, but in most cases,
10uF will be suffice. Keep in mind that
electrolytic
capacitors are
polarity sensitive,
and the negative lead is marked with a band on the side of the case.
The 0.1uF ceramic disc capacitor is used to
remove transient noises on the output. These are high
frequency noises/spikes created from a
range of sources and anomalies on your target circuit, and although
not required on non timing crucial applications, I still place one
to ensure the accurate timing operation of the PIC. Ceramic disc
capacitors are not
polarity sensitive.
I've talked about the
7805 and it being a 3 pin
package, but I bet your wondering about the
pin-out of the device,
well here it is;
3.3 Volt regulators are very
similar, but the one I use varies slightly in design. Its the
LD1117V33C,
Once connected you will have a steady 3.3 Volts,
see the
datasheet for more information.
Basics
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