Useful information about 12 V power supplies
- What is a 12 V/DC fixed voltage plug-in power supply?
- What is an adjustable 12 V power supply unit?
- What is the difference between stabilized and unstabilized 12 V power supplies?
- What is a 12V plug-in switched-mode power supply?
- What is the distinguishing feature of a 12 V travel power supply?
- How can ich find the suitable 12 V power supply?
What is a 12 V/DC fixed voltage plug-in power supply?
Plug-in power supplies are the perfect solution when it comes to the uncomplicated power supply of small devices. 12V plug-in power supplies play a special role in this. At this voltage, a sufficiently high power can be used without the current becoming too high. As a result, the cables do not have to be Dick over-dimensioned.
This is also the reason why in cars, motorcycles and the like the on-board networks are designed for 12 V DC. But even small island solar systems with solar battery and corresponding consumers work preferably with 12 V DC voltage.
A fixed voltage plug-in power supply is designed to generate a direct voltage at the output, e.g. at the height of 12 V/DC. The two letters DC represent Direct Current, was the same as DC. In contrast to the term DC, the abbreviation AC for Alternating Current is often also given for alternating voltage.
What is an adjustable 12 V power supply unit?
An adjustable 12V plug-in power supply offers the option of using other output voltages in addition to the 12 V voltage. This has the great advantage that the power supplies can be used for the most varied consumers.
This is why the manufacturers provide a variety of low-voltage connectors so that the right connection is available for almost every consumer.
These versatile plug-in power supplies are particularly suitable when consumers are only in operation for a limited period of time. However, before using the device, you have to make sure that the correct output voltage and the correct polarity of the connection plug are set.
Otherwise, there is the risk that incorrect settings of the consumers or the power unit will be destroyed.
The output voltage is set at the yellow rotary knob.
What is the difference between stabilized and unstabilized 12 V power supplies?
With a conventional 12V plug-in power supply with transformer, rectifier and electrolytic capacitor for screening, there was an unpleasant side effect: If the power supply was not loaded, the output voltage could already be 16 - 17 V.
The cause of this apparently incorrect behavior was the capacitor (K), which could charge up to the peak value of the half-wave. As soon as the power supply unit was loaded with a suitable consumer, the voltage returned to the normal value of approx. 12 V.
Unstabilized power supply
Consumers with a low power requirement could then be at risk of being supplied with too high a voltage. For this reason, stabilized plug-in power supplies were developed that output a stabilized output voltage. No matter how high the load is on a consumer.
New plug-in power supplies must meet certain minimum efficiency and idle performance requirements due to the Ecodesign "ERP" directive. These limit values are mostly no longer attainable with classical plug-in power supplies, which contain a mains transformer. This is why almost exclusively electronic switched-mode power supplies are now offered. These do not show any significant voltage overvoltages at idle.
What is a 12V plug-in switched-mode power supply?
With a switched-mode power supply, the 230 V mains voltage is rectified with a rectifier (GR) and smoothed with a capacitor (K1). The resulting direct voltage is led via a transformer (TR) to an electronic switch (transistor).
This transistor (T1) opens and closes the circuit several thousand times per second through the primary coil of the transformer. This induces a voltage on the secondary side of the transformer, which is also rectified (D1) and smoothed (K2).
A control stage (RS) ensures that the pulse width modulation (PWM) on the primary side only feeds as much energy as is required on the secondary side.
In order to preserve the galvanic separation of the primary and secondary sides, an optocoupler (OK) is used for the transmission of the control information. Due to the high clock frequency, the transformer and the charging capacitors can be significantly smaller than with a conventional plug-in power supply with transformer.
The switched-mode power supply technology thus provides for a low weight and at the same time for a high efficiency of the power supplies.
What is the distinguishing feature of a 12 V travel power supply?
Due to the corresponding design of the switched-mode power supply technology, travel power supplies work with a very wide input voltage range.
For this reason, it does not matter whether the travel plug-in power supply is operated at 110 V/60 Hz or 230 V/50 Hz. The output voltage will always be the same.
Only the mechanical plug connections have to be adjusted. For this reason, many travel wall plug transformers come with appropriate adapters to operate the mains adapter on all common sockets.
How can ich find the suitable 12 V power supply?
When selecting a suitable 12V power supply unit, there are a few simple questions that lead quickly and safely to the right product:
1. Should it be a 12 V fixed voltage power supply unit?
If only one consumer is to be supplied with 12 V, a fixed-voltage power supply unit is ideal. If the plug-in power supply unit is to be used alternately for several consumers with different operating voltage, plug-in power supplies with adjustable output voltage are suitable.
2. What is the maximum output current?
If the power supply is only intended for one consumer, the max. output current can be aligned with this consumer. If the consumer needs 800 mA, the plug-in power supply must also be able to provide 800 mA in continuous operation. Due to the tolerances of the components or in certain operating situations, a consumer may have a higher current requirement than specified. In this case, it is better if the power supply unit is capable of providing 1000 mA and can thus reliably cover the increased power requirement.
If the power supply unit is intended for several consumers, it must be selected according to the consumer with the highest power requirement.
If only the operating voltage (V) and the power (W) are indicated for the consumer to be supplied, the current can be calculated. If the information is e.g. 12 V and 6 W, a current of 0.5 A or 500 mA can be calculated according to the following formula:
I = P : U (current = power : voltage)
3. What connection do ich need?
With the naked eye, it is often not clear whether a DC hollow plug with 5.5/2.5 mm or 5.0/2.1 mm (outer diameter/inner diameter) is required for the low-voltage connection of the consumer. However, it is not immediately clear which jack plug is required for the jack sockets. Here you have to check the technical documents of the consumer which DC plug is required. Afterwards, check whether the required connection plug is attached to the cable of the plug-in power supply or can be attached.
If the plug-in power supply is intended for a wide range of devices, a model with a variety of connection adapters would be the best choice. Thus, the suitable connection plug is certainly included for each consumer.
4. How must the connection plug be polarized?
Like the DC plug, the polarity of the plug varies from device to device. To get this problem under control, some power supply manufacturers have supplied the different connection plugs individually. The low-voltage connection cable has the necessary socket to which the different plugs can be connected. If the polarity is not correct, you can change the polarity of the low-voltage connector by simply unplugging, turning and reconnecting it.
(This text is machine translated.)