Stabilized power supply 5/9 volt 0,5 amp with relay protection. Scheme, description

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Stabilized power supply 5/9 volt 0,5 amp with relay protection

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Encyclopedia of radio electronics and electrical engineering / Power Supplies

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Many radio amateurs manufacture power supplies (PSUs) with an electronic overload and short circuit protection system. These schemes are a bit complicated and do not always work stably. In my opinion, the power supply system based on electromagnetic relays is much simpler and better. Below is a description of a PSU with such a protection system. The power supply unit has an indication of power on and overload on the LEDs.

This PSU can be used to power any radio devices with a supply voltage of 4,5-6 V, 9 V and a current consumption of up to 500 mA. It is very convenient to use it for tuning work, as it contains an overload and short circuit protection system, which guarantees the safety of work.

Stabilized power supply 5/9 volt 0,5 amp with relay protection

Circuit operation. When you turn on the PSU (see figure) to the network and switch the SA1 toggle switch to the "On" position, the VD1 (green) "On" and VD3 (red) "Overload" LEDs light up. This indicates that the PSU is ready for work. Next, press the button SB1 "Work". Relay K1 is activated, LED VD3 goes out. The BP is ready to go. The voltage selected using the SA2 toggle switch appears on the output terminals. When the device connected to the power supply output is operating, all the current consumed flows through the resistor R * (wire), creating a certain voltage on it, which is applied to the VT1 power supply junction through the VD6 direct junction. The voltage drop across the resistor R*U = IR, i.e. it depends on the passing current at a constant resistance of the resistor R*. Thus, by selecting the resistance of the resistor R *, we find the protection current, since the breakdown voltage of the zener diode is constant.

The voltage regulator circuit has no features. This is a standard compensation type voltage regulator circuit. Transistor VT3 is placed on a radiator with an area of 25-30 cm2. Thus, when the current consumed by the load exceeds the protection trip current, the voltage drop across R * exceeds the breakdown voltage of the direct transition VD6 (0,2-0,6 V), and it is applied to the B-E transition VT1. Transistor VT1 closes like an avalanche, relay K1 de-energizes and disconnects the primary winding T1 from the network, the voltage at the PSU output disappears. The VD3 LED (red) "Overload" lights up. PSU after elimination of overload or short circuit in the load must be put into operation by pressing the button SB1 "Work".

Details. T1 - any transformer with a power of 15 W with an output voltage of 12 V, providing a load current of 500 mA.

VD1 - AL307V.G; VD2 and VD4 - D219A; VD3 - AL307A, B; VD6 - D809; VD5 - KTs402A (KTs405A); VD7 - D809; VD8 -2 x D219A; VD9 - KS156A (168A); VT1 - MP25; VT2 - P309; VT3 -KT802A; K1 - relay RES-9 passport 200.

Author: O.G.Rashitov, Kyiv

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