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It is a simple power supply based on set Jabla J-31 + 2 x KD502.
Elements added to J-31:
- two resistors 0,1ohm, one for a final transistor and capacitor 10000uF 50V
- bridge 40A on a heat sink
- diode indicating the main fuse burnt
- 2 switches from the range 12V/30V 2A/7A (7A in the range 12V – 2 transformer windings connected together)
The construction uses Voltmeter/Ammeter LCD with a backlight. Parameters: 0-50V, 0-15A.
An old computer fan (80mm) controlled from a temperature sensor 49 degrees Celsius cools the heat sink. To ensure better cooling in the idle mode, the fan operates on 5V, after exceeding the temperature of the sensor, it switches to 15V.
Switch 12/30V is controlled by a relay for transformer taps.
Switch 2/7A is controlled from resistors of transistors 2A 0,47ohm 7A 0,1ohm.
Link to original thread (useful attachment) – Zasilacz 0-30 V 0-7 A modyfikacja J-31