EK023 Voltage regulator 78xx/78Lxx
Part.no: 41016709
EK023 is a simple kit with circuit board and capacitors compatible with all voltage regulators in the 78L and 78 series.
The board has space for both the smaller regulator 78Lxx (TO-92) and the larger 78xx (TO-220).
The kit includes the necessary capacitors to keep the regulator stable, as well as a universal circuit board with space for either 1x 78Lxx or 1x 78xx regulator.
The connections for input and output voltage are compatible with most connectors with 2.54mm or 5.08mm pitch, such as pin headers or terminal blocks.
For small loads and small differences between input and output voltage, the regulators can function without a heatsink. For heavier loads and larger voltage differences, a heatsink should be used.
Note that the voltage regulator is sold separately. See the list for all compatible regulators.
- Supply voltage: at least 2V above output voltage
- Max current draw: 100mA (78Lxx) / 1000mA (78xx)
- Dimensions: 12 x 36mm
Component list
| RefDes | Value | Qty. | Part.no. | Marking |
|---|---|---|---|---|
| C1, C3 | Ceramic capacitor 100nF | 2 | 41015538 | 104 |
| C2, C4 | El.lyt capacitor 10uF | 2 | 40520021 | 10uF 50V |
| P1a, P2a | Pin header 2.54mm 2p | 2 | 41001167 | |
| P1b, P2b | Screw terminal 5.08mm 2p | 2 | 40210002 |
Assembly guide
Before starting assembly, check that the circuit board is free from damage and scratches. Verify that you have all the components to be installed.
Mount the capacitors in their respective positions. Pay attention to the orientation of the two electrolytic capacitors, C2 and C4. The long lead should be inserted into the hole marked "+".
Regulator selection
There are many different regulators in the 78xx/78Lxx series (and similar compatible models) from various manufacturers. In addition to output voltage and package type, there are some parameters that are worth knowing when selecting a regulator.
The datasheet for each regulator always specifies a maximum input voltage. This is however an absolute maximum and normally the regulator should not be operated at such a high voltage.
It is important to calculate the power dissipation to prevent the regulator from overheating. If, for example, a 3.3V regulator is driven with 30V, the heat generated in the regulator will be too high and it will not function correctly.
The power loss in the regulator can be calculated using PD=(VIN-VOUT)*IOUT. So with 30V in, 3.3V out and 1A load the loss is: PD=(30-3.3)*1 = 26.7W
It is therefore important to keep the input voltage as close to the output voltage as possible without falling below another parameter, the dropout voltage. The dropout voltage is the difference in voltage that occurs across the regulator and which must be exceeded for it to be able to regulate away ripple and noise.
So, a 3.3V regulator with a 2V dropout voltage is best driven with a voltage of approximately 5.5V. This allows the regulator to filter out any ripple and noise with some headroom, without getting too hot.
In cases where the input voltage is very close to the desired output voltage, for example 6V in and 5V out, a standard regulator will not function optimally as the dropout voltage is too high. In that case, select a regulator with a low dropout voltage, also known as an LDO. These typically have a dropout voltage of below 1V.
The power loss in the regulator is, as suggested by the formula above, also dependent on the current being drawn. With a lower current the regulator will have lower losses and can handle a larger difference between input and output voltage.
Other parameters, such as operating temperature, inherent noise, tolerance, etc. are listed in the respective datasheets. The most important thing to understand however is that all voltage that is regulated away is converted to heat in the regulator.
The larger regulators in TO-220 package have an exposed metal surface with a screw hole where a heatsink can be mounted. For higher current draw and large differences in input/output voltage, extra cooling will be required.
Schematic
Drawing
