Very simple current load in retro style. Semiconductors, resistors and the meter are from the no longer existing state of Czechoslovakia (Czech Republic - Slovakia). It was manufactured by Tesla np (national enterprise).
The voltage BE is obtained from the slider of the potentiometer through the resistor R1, which partially protects the transistor from current overload. The voltage that is divided on the potentiometer is obtained from the voltage drop on CE. This voltage is limited by the zener diode ZD (in this case 5.9V / I didn't have a smaller one /) and resistor R2. Why ZD? It protects the transistor from overvoltage at BE and partially stabilizes the CE current. This means that a change in the voltage of the tested source will more or less (it has certain reserves) not affect the change in the current flowing through the.
I also included a needle measuring device in the circuit, which was originally a 250V DC voltmeter. After removing the primary resistor , I found that it needs 350 µA for full deflection . That's why I connected it with a 0.1 Ω shunt . Now it shows a current of 2500mA at full deflection. Material: KD502 NPN transistor (max. parameters: BE 5V, CE 70V, IC 20A, 150W) ZD 1NZ70 zener diode (Uz 5-6V, Iz 100mA) R1 100Ω / 5W R2 220Ω / 5W Rb 0.1Ω / 5W P1 WXD3590 10 - rotary wire potentiometer 10kΩ.
I'm sorry for my english.
For more information see here: hobbzport electronics
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