Schema, simple power supply

Main features:


Voltage: 5 V, 6 V, 8 V, 9 V, +12 V or +15 V
Current: 1 A
Regulated: Yes

Presentation

This diet is very simple and suitable for a broad category of fixtures, whether analog or digital. If you are looking a little more power efficient, with better load regulation (less variation in output voltage during large variations in current consumed), or that the output voltage must be able to go lower,

The present embodiment uses a fixed voltage regulator type LM78xx, wide spread. The output voltage is here set at 5 V, but adopting other values ​​of +5 V to +15 V is quite possible, with the changes described in the following lines. The current that can be drawn from this power is directly related to the type of controller used here and is limited to 1 A, provided to add a radiator for cooling. This power should even if you do not need an A; remember (or learn it), the current supplied by a power supply is required by the machine that feeds it. If we connect a device that consumes a current of 100 mA power source capable of providing an A, it will provide only 100 mA.

The diagram

The diagram shows all of the food, and is based on the use of common components but experienced.

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Power:

Before starting the description of this assembly, it is useful to specify two or three things about the power you to take this regulated power supply. The type of controller used in theory can provide a maximum current of 1.5 A. Under such a current, the controller can heat a lot, and get in thermal protection if it gets too hot (he cuts himself to protect himself, and is released when the temperature has returned correctly). The heating of the regulator depends on two factors: the potential difference between its input and output, and the current passing through it (which is what the charge will apply). If the potential difference is important, you can not make out a lot of current to the regulator. At the same time, the controller must have its input a voltage of 3 V above the output voltage (for 5 V regulated output, the input voltage must be at least 8 V). Knowing that the regulator accepts a voltage as high as 37V input, you will find what is reasonable between these two limits, depending on the desired current output. In short, if you want to leave a high current (say, 1 A), you should not apply excessive voltage input (say it will be limited to 10 V. .12 V to 5 V output). To be able to work the regulator in the power range for which it is announced, it is imperative to provide a cooling radiator.

Lowering the voltage

Not rocket science, lowering the voltage 230 V sector is provided by the transformer TR1, the secondary voltage depends on the desired output voltage. See text below the diagram, and consider the remarks of the preceding paragraph. For example, if you want an output voltage of 12 V, a transformer 230 V / 12 V will do. Available voltage after rectification and filtering is indeed in the range of 15.5 V, which is sufficient for the regulator is working properly. Note however that for a maximum output current (1 A), the output ripple will increase a little. If this is inconvenient for your application, which favor a transformer secondary voltage is 15 V.

Recovery

The recovery of the AC voltage delivered by the secondary of the transformer, is provided by the diode bridge formed by four diodes D1 to D4. The diodes used here are type 1N4007, which support a current of 1 A.

Main filter

Chemical capacitor (electrolytic) C1 provides filtering of the rectified voltage to obtain a voltage which is more like that of the continuum of alternative. Its value will depend on the maximum output current you want to obtain the value of 2200 uF specified here will allow you enough for filtering an output current of about 1 A. You can reduce it to 1000 uF if you do not draw more than 500 mA from your diet (or even 470 uF accepting a slightly lower quality output voltage).

Regulation

It is entrusted to a voltage regulator like LM7805 (which can also be found under the names uA7805, MC7505, or just 7805) if you want an output voltage of 5 V. Attention did not use the model 78L05, which is smaller (TO92 housing instead of housing TO220) and agrees to a charge current of 150 mA maximum. Unless of course that this model does not suffice you. The capacitor C2 placed between the regulator output and ground is not mandatory, but it is advisable to avoid any risk of parasitic oscillation of the regulator. This capacitor should be placed as close to the regulator itself. The regulator will depend on the output voltage, see text under the scheme (7805 to 5 V, 7806 V for 6, 12 to 7812 V, etc.).

Control lamp

Control the presence of output voltage is provided by the LED D5 in series with the resistor R1, which limits the current flowing through it. The value of this resistance depends on the output voltage. The majority of conventional LEDs (I exclude the high-brightness LEDs and LED low consumption) need to power up correctly, to be traversed by a current between 10 mA and 20 mA, and have a voltage drop about 1.5 V (red LED) to 3 V (LED yellow or green). The calculation of the value of the resistor R1 is performed using the following formula:
R (in ohms) = U (voltage across R1, V) / I (current through R1 and D1, A).
For example, if we use a red LED with a voltage drop of 2 V at a current of 20 mA and the output voltage is 8 V (using a voltage regulator type 7808), resistance R1 is:
R1 = (8 V - 2 V) / 0.02 = 300 ohms
In practice, you can use a resistance of 300 to 470 ohms without any problems.

Controller Pinout

This embodiment relates to a single positive supply, but be aware that there are also integrated circuit voltage regulator negative, the first two digits are "79" (instead of "78" for positive).

Note in passing that the input pins and mass of a negative regulator of type 79xx are reversed from the positive regulator of type 78xx.

PCB

Here it is. Note that the voltage regulator LM78xx is placed on one side of the circuit board to facilitate its attachment to a radiator. The two points marked AC2 and AC2 'must be connected on the secondary of step-down transformer.

Artwork

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