F capacitor at location labeled C1. This capacitor will be
labeled 334.
3. Using the supplied hardware, install the heat sink on U1. The metal back of U1 goes
against the inside back of the heat sink. Line up the heat sink hole near the middle of
the heat sink with the hole in the tab of U1. The other hole goes towards the pins of
U1. The screw goes though the heat sink then through the tab of U1. Secure with the
lock washer and hex nut.
4. Insert and solder the voltage regulator at location U1. The type of regulator supplied
will depend on the voltage. A 7805 is a 5 volt regulator, a 7812 is a 12 volt regulator,
etc. The flat backside of the U1/heat sink assembly must be away from the capacitors
C1 and C3. The bottom of the heat sink should rest lightly on the circuit board as you
solder the pins.
5. Insert and solder a 100uF capacitor at locations labeled C2 and C4. Be sure to
observe to proper polarity.
6. Examine your soldering to be sure there are no shorts or solder bridges.








Figure 1. VR-XX Schematic


Microsystems
UM
Unified

1
2
3
U1
C1
C2
C3
C4
+ Input Voltage
You will connect your supply voltage at the V IN connections. Be sure to observe proper
polarity. The input voltage must be at least 2 volts higher than the rated output voltage.
If the input voltage falls below this rating the regulator will not be able to do its job.

Note that as the load current increases, the input voltage may drop below the
minimum if it is not well regulated. Inexpensive wall-wart type power supplies often
have poor regulation. Be sure that your voltage source can provide the required
voltage at load.

If your voltage source is a battery or a regulated voltage power supply, you will not need
additional input filtering. If your voltage source is a transformer with a diode rectifier,
you will need an additional capacitor between the output of the rectifier and ground, in
parallel with C4. Typical values will be 220uF to 4500uf, depending on the output
voltage of your transformer, the current drawn by the circuit the regulator is powering,
and the type of rectifier used. Be sure the capacitor voltage rating is high enough and the
capacitor is installed with the proper polarity.

Note that with only a transformer and rectifier, the peak voltage will be more than 1.4
times higher than the RMS voltage. Thus if you have a 12V transformer, the voltage at
the regulator input will be 12 X 1.4 = 16.9V. For this application you would want to use
a 25V capacitor.

Heat Considerations
A linear voltage regulator acts as an automatic variable resistor. At low load currents its
effective resistance will be high. As the load current increases, the effective resistance
will reduce, keeping the load voltage constant. The voltage difference between Vin and
Vout multiplied by the current is the power that the regulator must dissipate as heat.

Example: 12 V input, 5 V output, load current = 200ma (.2A)

Power (watts) = Vdiff * Iload = (12V-5V) * .2 = 1.4 Watts

The temperature of U1 will increase approximately 17° C/watt (30.6° F/watt) in calm air.
It is not recommended to run your regulator at more than 4 watts dissipation.

CAUTION! IC U1 AND THE HEAT SINK CAN GET VERY HOT!

Depending on the difference between input and output voltages, and the load current, it
may be necessary to use a larger heat sink and/or use a fan to blow air across the heat
sink.


Unified Microsystems
PO Box 133
Slinger, WI 53086
www.unifiedmicro.com