Laboratory Power Supplies
DC sources with a flexible output stage
Programmable power supply units with autoranging
Programmable DC power supply units are essential instruments in electronics laboratory, product development, and in particular, on test stands. Test scenarios usually need to be performed under varying operating conditions; DC power supply units must therefore cover a large range of voltage and current to be able to represent all required operating statuses of the device being tested.
Conventional power supplies have rectangular output characteristics, which means that the maximum output voltage and the maximum output current automatically define the maximum output power (Pmax = Imax x Umax). In practice, this means that conventional DC power supply units are defined based on a restricted current/voltage bandwidth. For example, conventional DC power supply units for high output currents are usually only suitable for relatively low currents.
Each test object needs a suitable DC source
For test stations and laboratory equipment, this results in the need for a greater number of suitable DC sources so that the different operating conditions (high current / high voltage / high current + high voltage) can be represented. As an alternative to multiple DC sources, it would be possible to set up a single, large-dimensioned source that covers all necessary ranges of voltage and current. However, this source would then have to be dimensioned for a very high power level, which would be extremely expensive.
Two different 3-kW consumers with different operating voltages need to be tested: 0–30 V / 0–100 A = 3 kW is required for the first test object. The second test object must be tested with a voltage of 0–60 V and a current of 0–50 A. — To perform both test runs with a single, conventional power supply unit, this must have an output of 6 kW, since 60 V and 100 A are the maximum current/voltage values and these must be supplied by the DC power supply unit:
|Test voltage||Test current||Pmax|
|Consumer 1||0….30V||0-100A||3 kW|
|Consumer 2||0….60V||0-50A||3 kW|
|Conventional DC source:||Max. 60 V||Max. 100 A||6 kW|
This means that although each test object has a power demand of just 3 kW, the power supply unit must be (over-)dimensioned with 6 kW. These unfavourable dimensions drive the costs for the power supply unit upwards.
Autoranging saves costs
Power supply units with autoranging capability do not have rectangular output characteristics, but instead have an extended current and voltage range. The bandwidth of the output voltage and the output current at a medium output power enables more flexible use in comparison to conventional devices. Autoranging devices are therefore suitable for many more applications than conventional power supplies. As a result, fewer power supply units are required in order to fulfil the tasks.
Ideal for test benches
The autoranging concept is suitable, for example, for use on consumers such as wafer heating units or low-voltage plasma applications. In these applications, the initial ignition voltage is relatively high with a comparatively low current demand. However, as the process continues, the holding voltage is considerably reduced while the demand for current increases suddenly and dramatically. Devices with flexible output stages are particularly efficient at meeting this requirement. Another example of areas for application is the wide variety of different energy storage devices such as Ultracaps and lead, NiMH or lithium rechargeable battery packs. In the area of photovoltaics, autoranging power supply units are used for testing inverters. This is because the DC source covers the very wide range of currents required to simulate the solar panels.