1. How To Test a Voltage Regulator
A voltage regulator is a device that takes in an input voltage and regulates it down to the
voltage that it is rated for.
Being that a voltage regulator passes out a regulated output voltage, the only test we must do
to check a voltage regulator is a voltage test.
We check the voltage input into the voltage regulator and the voltage output from the
regulator.
If we read a higher voltage at the input which we feed into it and read the output voltage
which the regulator is rated for, then we know that the voltage regulator is good. If we don't,
then read the correct voltages, then it may be a defective regulator.
So we'll now go through specificially now how to test a voltage regulator.
Before we get into how to read the voltages with a multimeter, first we'll go over the pinout
of a voltage regulator, so that you'll know which pins to read voltages from.
As an example, we'll use the popular voltage regulator, the LM7805. Below is the pinout of
the LM7805 voltage regulator:
2. The input voltage that needs to be regulated down goes into pin 1 (Input). The ground pin is
pin 2. And the regulated output voltage comes out from pin 3 (Output).
Measuring the Input Voltage
When test the voltage of a voltage regulator, we first check the voltage from the input pin to
ground. This is to make sure that voltage is, in fact, being supplied to the regulator. If the
regulator isn't receiving sufficient voltage, of course it will not be able to output its rated
regulated voltage. This is why we do this test.
To test the voltage going into the voltage regulator, we take a multimeter and place it in the
DC voltage setting. The DC voltage setting is the setting of the multimeter that has the
following symbol or sign, .
We take the probes of the multimeter and place the positive probe (normally the red probe)
on the input pin of the voltage regulator and the negative probe (normally black probe) on the
ground pin. The voltage that we should read should be higher than the voltage the regulator is
rated to output. This is normally 1-2 volts higher.
3. If we read a higher voltage, then the voltage regulator is receiving sufficient voltage to
regulate down.
Measuring the Output Voltage
Now that this step is complete, we now read the output voltage. If the regulator is rated to
output 5 volts, then we should read a voltage very near 5 volts coming out from its output.
The LM7805 is a voltage regulator is rated to output 5 volts, so we should read this output.
To measure the output voltage, we place the same multimeter set in the DC voltage setting
and now place the positive probe of the multimeter on the output pin of the regulator and the
negative probe on the ground pin of the regulator. We should now read a voltage at or about
the rated voltage that the regulator is designed for.
4. If the multimeter does read a voltage near its rated output voltage, the voltage regulator is
functional and is good.
If we do not, then the voltage regulator is defectively, as it does not do the job it was
designed for, which is output a regulated voltage.
An adjustable regulator can be tested in the same way. Unliked fixed voltage regulators,
adjustable regulators can be regulated to output adjustable voltages. All a user must do is
calculate the output that the regulator should output and perform the same test as is shown
above to see whether it is good or defective.
5. How to Connect a Voltage Regulator in a
Circuit
In this article, we go over how to connect a voltage regulator to a circuit to get a specific DC
output regulated voltage.
Depending on the voltage regulator in use, we can get a regulated positive or negative
voltage, at whichever voltage we want. The LM78XX voltage regulators are a popular kind
for regulating and outputting positive voltage, while the LM79XX are a popular series of
regulators for negative voltage. In this article, we use a positive voltage regulator, which
outputs 5V, the LM7805 regulator.
Before we can hook up the circuit, let's first go over the pinout diagram of the voltage
regulator, which is vital for hooking up the circuit.
A voltage regulator is a 3-terminal device.
Pin 1 is the Input Pin. The output voltage of whatever voltage source you want to regulate
down (whether it's a transformer, battery, etc.) is fed into this pin. So for instance, if you have
10 volts coming from a transformer that you want regulated down to 5 volts, the output of the
transformer (the 10 volts) is fed into the regulator input (pin 1) so that the regulator can
regulate it down to your wanted voltage (5 volts). The voltage regulator should always be fed
as smooth of a DC signal as possible (which gives the best regulated output) so it can regulate
it down to its specified voltage. Remember, the input voltage has to be larger than the voltage
that the regulator regulates out. In this case, we are using a LM7805, which outputs 5 volts.
In order for the regulator to output 5 volts, the voltage entering has to be at least 2 volts
higher, so it has to be at least 7 volts. 7 volts would work perfect. However, for experimental
purposes and ease of getting parts, we will use a 9-volt battery as our input voltage.
Pin 2 is Ground. It hooks up to the ground in our circuit. Without ground, the circuit couldn't
be complete because the voltage wouldn't have electric potential and the circuit wouldn't have
a return path. Ground is essential.
6. Pin 3 is the Output Pin. This is the pin that gives out the regulated voltage, which, in this
case, is 5 volts. At the end of this experiment, when our circuit is hooked up, we're going to
read out the voltage with a multimeter and it should give out close to 5 volts.
Okay, now let's build the circuit.
Components Needed
LM7805 Voltage Regulator Chip
9-volt Battery
0.33uF Ceramic Capacitor
0.1uF Ceramic Capacitor
1KΩ Resistor
LED
If you don't have all the parts, just follow along. You can buy them at anytime and come back
to this page and do the experiment.
Let's view the complete circuit now and explanations will ensue.
The first capacitor, the 0.33uF ceramic capacitor, is hooked up after the voltage source, in
this case the 9-volt battery, and before the input of the LM7805 regulator. This capacitor is
there to filter out any noise coming from the voltage source (the battery). The voltage
regulator works best and will be most efficient when a clean DC signal is fed into it. We don't
want any ac noise (ripple) imposed on the DC line voltage. The capacitor, in essence, acts as
a bypass capacitor. It shorts the AC signal of the voltage signal (which is noise on the voltage
signal) to ground and only the DC portion of the signal goes into the regulator.
The second capacitor, the 0.1uF ceramic capacitor, is hooked up after the voltage regulator.
This capacitor is there again to filter out any noise or high-frequency (ac) signals that may be
on the DC voltage line. For a circuit like this, where we're lighting an LED, it isn't exactly
crucial to have a pure DC signal, but in other applications, such as when outputting voltage to
power a logic chip, which needs a precise voltage fed into it in order to give the correct logic
output, it is crucial. That's why it's a good idea to get into hooking up a voltage regulator
properly from the sart.
Okay, so let's recap on the circuit. The circuit begins at the 9-volt battery. This produces a
voltage of 9 volts. The first capacitor, the ceramic 0.33uF, cleans up the signal if any (ac)
noise is present on this. It shorts this noise to ground and allows the pure DC signal into the
7. regulator. The regulator regulates this voltage down to 5 volts. After it comes out of the
regulator, the other capacitor, the 0.1uF ceramic, cleans up any high-frequency or ac noise
that may come out, again to produce a clean DC signal. Now this DC voltage, clean and
crisp, is ready to power whatever you want it to, in this case, the load is a resistor and a LED.
Keep in mind that the design of a voltage regulator depends on the voltage regulator being
used and the intended use of a circuit. Always consult the Manufacturer's Datasheet for the
voltage regulator in use for a circuit to see how to hook it up with the necessary required
external components. Usually the only external components necessary are just capacitors,
though heat sinks may also need to be added when heat dissipation is necessary. The
Datasheet specifies which value of capacitors to use, so it's a good idea to learn from the
people who manufacturered the chip. Also, design changes when dealing with the intended
use of the circuit. When the load of a circuit is stable and unchanging, as in the example
above, it is usually not necessary to add a large electrolytic capacitor on the output to act as a
smoothing capacitor. But if you're going to have a varying load, a potentiometer, for instance,
on the output, it is well advised to add an electrolytic capacitor in parallel to the ceramic
capacitor. This electrolytic capacitor acts as a smoothing capacitor, when load resistance
changes cause abrupt voltage spikes and drops, in a circuit. This capacitor charges up with
voltage when the circuit has excess spikes in current and discharges to supply voltage when
the circuit is low on current. Therefore, it has a smoothing effect and even things out.
Essentially, it acts as a load balancer. More will be on this for more advanced projects, but
this page is a good start for those starting off in connecting voltage regulators for basic
circuits.
