The Isolated Power supply +5 V to +15 V, 500 mA diagram represents a single control block, knowing that all are identical. It is truly classic, and is based on the use of common components. The Isolated Power supply +5 V to +15 V, 500 mA circuit described below is a “modification” that is designed to accommodate all the modules on a single circuit board.
Both terminals J1 and J2 (AC1 and AC1 ‘) is from secondary AC transformer. The AC voltage undergoes a wave rectification through four diodes D1 to D4 connected in a bridge, this voltage then filtered by capacitor C1. Values used in the diagram is 1000UF, may be increased to 2200 uF if the output ripple proved too big for your application. Voltage regulation is entrusted to the LM317 regulator IC, is slightly higher quality than its counterparts 78xx, but especially with the advantage that can be adjusted and able to work well over a wide output range. The capacitor C2 is optional, but it contributes significantly to the reduction of output ripple, therefore it is highly recommended. Two diodes D6 and D7 is also optional and only play a protective role is not always necessary at low currents. he output voltage is determined by the value of two resistors forming a voltage divider between output and ground, and whose midpoint is connected to the pin fitting U1.
Calculation of the output voltage
The DC output voltage is available between J3 and J4, is given by the following formula:
Vs = 1.25 * (1 + (R5 / (R6 + RV1))) – for adjustable voltage
Vs = 1.25 * (1 + (R5 / Rx)) – for fixed voltage
In this second formula, Rx must be replaced by R1, R2, R3 or R4.
For the adjustable version, you can completely customize the values of R6 and RV1 to limit possible variation range. This approach also allows you a more precise adjustment of the output voltage.
Selection of the transformer
The voltage to be issued by each secondary will depend on the voltage you want in the output of the regulator. Note that nothing preventing you from using a transformer with double secondary (two sidefully isolated) to supply simultaneously two control modules. Avoid as much as possible to choose a secondary voltage that is too high compared with the desired output voltage, this to prevent excessive heat dissipation of the regulator. If you want a power supply of +9 V and +15 V for another, use two separate transformers, one with a 9V secondary and the other with a 15V secondary voltage.
This Isolated Power supply circuit is designed to deliver an output voltage adjustable (adjustable by potentiometer) or fixed (determined by the fixed value resistors). You must choose which method you prefer, but should not use both at the same time! The components used for the part are adjustable RV1 and R6, whereas it is the fixed resistors R1 or R2 or R3 or R4 (depending on whether the single jumper will be placed on SW1, SW2, SW3 and SW4). In summary:
– Mode adjustable: cable R6 and RV1, and ignore R1, R2, R3 and R4 and SW1, SW2, SW3, SW4.
– Fixed Mode: cable R1, R2, R3 and R4, SW1, SW2, SW3, SW4, and ignore R6 and RV1.