What is a lab power supply?
When you want to test an electrical circuit, or components, they often need to be powered by a voltage. For example, you could use a mains adapter, but a lab power supply is more suitable. A lab power supply shows the current and voltage, so you can see what is happening. The current and voltage can also be set. In addition, a lab power supply provides useful connections, so that you can easily connect the circuit or load to it.
Controlling current and voltage
A simple lab power supply has two dials and two displays. One setting wheel sets a voltage limit and the other sets the current limit.
A lab power supply has two modes. The lab power supply always operates in one of the two modes. The first mode is the constant voltage (CV) mode. In this mode, the lab power supply supplies the set voltage. The second mode is the constant current mode, in this mode the power supply supplies the set current.
In which mode the lab power supply operates is determined by the set limits. The lab power supply provides the highest possible voltage until it is within one of the limits. Two examples are given below:
The lab power supply is short-circuited. The lab power supply operates in CC mode and the voltage is as good as 0V.
Nothing is connected to the lab power supply, so no power can flow. The lab power supply operates in CV mode.
Switching or linear
There are roughly two types of lab power supplies. Lab power supplies with a linear output and with a switching output. These are the advantages and disadvantages of both types:
| Linear | Switching |
|---|---|
| High losses and therefore needs cooling. Sometimes with fan | Efficient and therefore requires little cooling. |
| Usually with transformer, resulting in bigger and heavier | Compact and small |
| No high-frequency noise | High-frequency noise is caused by switching |
| Can control inductive loads | Can have trouble with inductive loads |
Especially the last point is important to pay attention when choosing a lab power supply. Switching lab power supplies do not always handle inductive loads such as motors or coils well.
You should also look out for linear lab power supplies with motors. Lab power supplies can supply energy to the load and not the other way around. When an engine is slowed down, it works like a dynamo and generates energy. When the lab power supply is connected to the engine that works as a dynamo, the generated energy will enter the lab power supply. There is a good chance that the lab power supply will not survive this. When a motor has to be slowed down, it is best to use a brake chopper.
Manual functions
Modern lab power supplies come with spacious feature sets. The most commonly used features are set out below.
Reading current setting
This function allows you to read what the set current limit is. The lab power supplies that do not offer this function only show the actual current. On a lab power supply without this function, you can set the current accurately by temporarily shortening the lab power supply and then setting the desired value. On a lab power supply with this function you can directly set the current limit accurately. If you only use the current limit to protect the load, then an accurate setting is not necessary.
Switchable output
When the output of a lab power supply can be switched off, you can set the required voltage limit and current limit to the correct values, without the load already being live. Without this function, the load must be disconnected from the lab power supply to remove the voltage.
Number of channels
Many electrical circuits or systems require several different voltages. A multi-channel lab power supply can offer a different voltage and current on each channel. A 2-channel lab power supply is therefore comparable to two separate 1-channel lab power supplies.
In many lab power supplies with 2 or more channels, the channels can be connected in series or in parallel. For example, two 30V channels can be combined into one 60V channel. Or two 3A channels can be combined into one 6A channel.
Finally
This article sheds light on the important aspects of lab power supplies and makes it easier to choose a lab power supply from our broad . In addition to the lab power supply, it is wise to include some cables and clamps to buy. Lab power supplies are usually equipped with 4 mm banana canisters. All cables with 4 mm banana plugs fit in this socket.
The lab power supply on the photos is the Velleman LABPS3003SM. A simple and inexpensive 30V, 3A lab power supply with clear displays.
