Universal power device
A so-called all - current device is an electrical device that can be operated with both direct voltage and alternating voltage . The name is not very specific and in the past was used almost exclusively for radio devices ( all-current receivers ), such as the VE301GW and VE301dynGW people's receivers . For typical electrical heating devices with resistance heating and for incandescent lamps, the type of current was not relevant. B. unregulated irons, soldering irons or heating devices.
In the 1920s, radios were mostly operated from accumulators ( potash collectors , lead accumulators for tube heating, so-called anode batteries ) for the anode voltage, despite the existing power supply in the house (formerly known as the lighting network ) . The desire for easier handling led over time to receivers that could cover their supply with the power grid .
However, until the end of the post-war period around 1950 there was no regionally uniform network voltage and network type (direct or alternating voltage) in Germany, in some cases it was even different within a city. In addition, there were the requirements that resulted from the export of the devices abroad. The all-current devices were developed out of this situation and for reasons of cost. They did not have a power transformer because DC voltage cannot be transformed. The half-wave rectification most often used required a certain polarity of the plug on the DC voltage network.
In all all-current radios (and also in the first tube-equipped TV sets, see below), the metal chassis was connected to the mains phase with the corresponding plug polarity. Touching a metal part posed a lethal risk. The devices each contained a capacitor to separate the ground and antenna connections from the mains voltage. Historical all-current devices only meet the applicable safety requirements when using an isolating transformer .
Another special feature was the heating of the electron tubes , the filaments of which were connected in series in all-current devices. For this purpose, they were designed for a uniform heating current, different heating power requirements were taken into account by differently large voltage drops. The usual rated currents were 50, 100 or 300 mA (TV sets) heating current, depending on the number of tubes. The “rest” of the mains voltage had to be “burned” in an open wire resistor. For current stabilization was an iron-hydrogen resistor and a soft start Urdox interposed resistor.
With a few exceptions, the first CRT televisions were also designed with similar technology. The main reason was to save a network transformer.
Most modern switched-mode power supplies can also work with DC voltage. Some devices are also specified for operation on DC voltage. As they work with a high-frequency intermediate circuit, they have a large input voltage range from 90 V to 264 V. Switching power supplies have protective-insulated transformers and do not cause any dangerous voltage at the output.
The DC voltage intermediate circuit in many switched-mode power supplies is designed for the peak value of the mains voltage. In the case of a sinusoidal voltage curve, this is times the rms value. In a switched-mode power supply operated with 230 volts, the intermediate circuit voltage is approximately 325 volts, for example. If this switched-mode power supply is operated with a DC voltage of the same effective value, the primary current consumption of the switched-mode power supply would increase by the factor with the same secondary load . This could overload the power semiconductors of the switched-mode power supply and thus destroy the switched-mode power supply.
Web links
Individual evidence
- ↑ Definition of all-current device . wissen.de . Retrieved February 16, 2015.
- ↑ http://docs-europe.electrocomponents.com/webdocs/0cdb/0900766b80cdbb06.pdf page 3