How to Connect a Voltage Regulator in a Circuit

How to Connect a Voltage Regulator in a Circuit

In this article, we will see how to connect a voltage regulator to a circuit to obtain a specific regulated DC output voltage.

Depending on the voltage regulator in use, we can get a regulated positive or negative voltage, at whatever voltage we want. the lm78xx voltage regulators are a popular type for regulating and sourcing 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.

Reading: How to connect a voltage regulator

Before we can wire up the circuit, let’s first go over the pinout of the voltage regulator, which is vital to wire 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 downregulate (be it a transformer, battery, etc.) is fed to this pin. so for example if you have 10 volts coming from a transformer that you want to regulate to 5 volts, the output of the transformer (the 10 volts) is fed to the input of the regulator (pin 1) so that the regulator can regulate it down to its desired voltage (5 volts). The voltage regulator should always be powered with as smooth a DC signal as possible (giving the best regulated output) so you can regulate it to your specified voltage. remember, the input voltage has to be greater than the voltage that the regulator regulates. in this case we are using a lm7805, which outputs 5 volts. for the regulator to output 5 volts, the voltage going into it needs to be at least 2 volts higher, so it needs to be at least 7 volts. 7 volts would work perfect. however, for experimental purposes and to make it easier to get parts, we will use a 9-volt battery as the input voltage.

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pin 2 is connected to ground. connects to ground in our circuit. without ground, the circuit could not be complete because the voltage would have no electrical potential and the circuit would not have a return path. the ground is essential.

pin 3 is the output pin. this is the pin that gives the regulated voltage, which in this case is 5 volts. At the end of this experiment, when our circuit is connected, we’re going to read the voltage with a multimeter and it should read about 5 volts.

OK, now let’s build the circuit.

required components

  • 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, follow the instructions. you can buy them at any time and come back to this page and do the experiment.

Let’s view the complete circuit now and explanations will ensue. LM7805 voltage regulator circuit

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The first capacitor, the 0.33uf ceramic capacitor, is connected 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 supplied with a clean DC signal. we don’t want any ac noise (ripple) to be imposed on the dc line voltage. the capacitor, in essence, acts as a bypass capacitor. it shorts the ac signal from the voltage signal (which is noise in the voltage signal) to ground and only the dc part of the signal goes into the regulator.

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The second capacitor, the 0.1uf ceramic capacitor, is connected after the voltage regulator. this capacitor is there again to filter out any noise or high frequency (ac) signals that might be on the dc line voltage. for a circuit like this, where we’re turning on a led, it’s not exactly crucial to have a pure dc signal, but in other applications, like when generating voltage to power a logic chip, you need a precise voltage fed to give the logic output correct, it is crucial. that’s why it’s a good idea to start wiring a voltage regulator correctly from the beginning.

Okay, let’s recap on the circuit. the circuit starts at the 9 volt battery. this produces a voltage of 9 volts. The first capacitor, the 0.33uf ceramic one, cleans the signal if there is any noise (ac) present on it. cuts this noise to ground and allows the pure dc signal to enter the regulator. the regulator regulates this voltage down to 5 volts. after it leaves the regulator, the other capacitor, the 0.1uf ceramic one, cleans up any high frequency or ac noise that might get out, again to produce a clean dc signal. now this crisp clean dc voltage is ready to power whatever you want, in this case the load is a resistor and a led.

Note 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 data sheet of the voltage regulator in use for a circuit to see how to connect it with the necessary external components. usually the only external components needed are just capacitors, although heat sinks may also need to be added when heat dissipation is required. the datasheet specifies what value of capacitors to use, so it’s a good idea to learn from the people who made the chip. furthermore, the circuit may change depending on its intended use. When the load on a circuit is stable and unvarying, as in the example above, it is generally not necessary to add a large electrolytic capacitor at the output to act as a smoothing capacitor. but if you are going to have a variable load, a potentiometer for example, at the output, it is recommended 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 dips in a circuit. This capacitor charges with voltage when the circuit has excessive current spikes and discharges to supply voltage when the circuit has low current. therefore, it has a smoothing and equalizing effect. essentially, it acts as a load balancer. there will be more on this for more advanced projects, but this page is a good start for those starting to connect voltage regulators for basic circuits.

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