Circuit breaker for electronic circuits. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Circuit breaker for electronic circuits. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Protection of equipment from emergency operation of the network, uninterruptible power supplies

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Electronic devices based on microprocessors and less integrated microcircuits are sensitive to supply voltage parameters. To ensure the safe operation of such devices, voltage stabilizers with protection are used. In many power supplies, it comes down to cutting off power to the circuit in the event of a short circuit in it or a sharp increase in load current. Such, for example, are the popular voltage stabilizers KR142EN5.

The "minus" of such stabilizers is that they are too inert in the protection mode: operation (stopping the power supply to the circuit) occurs after 200 - 500 ms and strongly depends on the nature of the current change in the load - simple stabilizer nodes react to an abrupt increase in current, and smooth is often not perceived. The inertia of switching on protection in 200 ms can cost the owner very dearly. Protective circuits have been published in the literature that respond to changes in load current faster than 100 nanoseconds, this is a very good indicator. However, they contain many elements and are difficult for beginner radio amateurs. The author has developed a simpler protection that operates even with a smooth change in load.

Electronic Circuit Breaker
Schematic diagram of the protection unit

Any radio amateur can repeat the proposed scheme. The node contains only one microassembly KMP201UP1A, does not require configuration and adapts to any power source with a common negative wire. I recommend building a node into every home radio power supply, and especially into those power supplies that power expensive electronic instrument assemblies. The device is powered by a constant stabilized voltage of 4 ... 6 V, in the "normal" standby mode it consumes a current of 0,8 mA from the voltage source. Through the normally closed contacts of relay K1, the voltage from the power supply unit (PSU) is supplied to the protected electronic circuit.

As long as the voltage at the input of the circuit does not exceed the limit set by the divider on the resistor R1, the voltage at pin 6 of the microassembly is close to zero. As soon as the set limit is exceeded, a voltage of 6/1 Un is supplied from pin 2 to the control electrode of the thyristor VS3. The thyristor opens and remains open until the circuit is energized or its anode or cathode circuits are broken. The relay is on, therefore, the power supply to the protected circuit is stopped. This voltage drop is perceived by the protection node. The sensing node can also be used in other cases where an immediate response to a few mV increase in R1 is required. For example, using the node as a control circuit for ULF, we get an amplifier with acoustics, which automatically turns on when a signal appears at the input. For this application, a low power relay should be connected directly between pin 6 of DA1 and ground. To switch the load, use short-circuit contacts (the insert in the diagram is shown by a dotted line). The sensitivity of the input signal is adjusted by R1.

Thyristor VS1 can be replaced by KU101B. Relay K1 is any low-power relay that operates at a voltage of 3 ... 4 V. Reed relays are convenient for this purpose. If this is not available, you can make it yourself. For this, 200 turns of PEL transformer wire with a diameter of 0,1 mm are wound on a low-power reed switch with normally open contacts. This winding serves as a self-made relay coil, and the switching contacts are standard reed switch contacts. Such a relay operates at a low supply voltage of 2...4 V and consumes current up to 50 mA. Therefore, it is designed to operate in a pulsed mode and is quite suitable for replacing K1 in our circuit. Fixed resistors type MLT-0,5. Capacitors C2, C3 type KM or similar. Electrolytic capacitor C1 type K50-6. The chain, shown in the diagram by a dotted line, serves to check the node and force the protection to be turned on.

To disable the protection, it is necessary to briefly break the power circuit of this circuit by pressing the S1 button. Now the device tests the input voltage again and is ready to turn on the protection.

Author: A.Kashkarov

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