Actual protection of electronic circuits. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Actual protection of 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

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Electronic devices based on microprocessors and less integrated microcircuits are sensitive to supply voltage parameters. Since switching power supplies sometimes fail, the problem of preserving (sometimes very expensive) electronic resources (printed circuit boards, microprocessor control devices) is very acute and relevant.

To ensure the safe operation of such devices, voltage stabilizers with protection are used. Protection in switching power supplies comes down to stopping the power supply to the circuit in the event of a short circuit in it or a sharp increase in load current.

The "minus" of such stabilizers is that they are quite inert in the protection mode. The protection operation (power supply interruption) 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, but often do not perceive a smooth one. The inertia of switching on protection in 200 ms can cost the owner very dearly. Protection circuits have been published in the literature that respond to changes in load current faster than 100 ns, this is a very good indicator. However, such circuits contain many elements and are difficult for radio amateurs.

A simple protection circuit that operates when the load current changes is shown in fig. 2.4.

Actual protection of electronic circuits
Rice. 2.4. Electrical diagram of the protection unit

Any radio amateur can repeat it. The node contains only one microassembly KMP201UP1A, does not require configuration and adapts to any power source with a common negative wire.

I recommend embedding a node in every home power source (not just switching) that provides radio engineering experiments, and especially in those voltage sources that power expensive electronic device components.

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, power from the PSU is supplied to the protected electronic circuit.

Principle of operation of the device

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 from pin 6, a voltage of 2 ... 3 V is supplied to the control electrode of the thyristor. The thyristor opens and remains open until the circuit is energized or its anode or cathode circuits are not broken.

The relay is on, therefore, the power supply to the protected circuit is stopped.

A wire resistor is used as resistor R6, which is connected in series with one of the poles in the power supply so that when the current in the load increases, a voltage drop appears on this resistor. This voltage drop is perceived by the protection node.

The sensing node can be used in other cases where an immediate response is required to a few microvolts of voltage across resistor R1. 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 contacts for short circuit. The sensitivity of the input signal is regulated by resistor R1.

Switching power supplies are very sensitive to the output voltage and sometimes the accumulating charge of static electricity in the input circuits of the load device connected to them.

It is not uncommon in repair practice when a pulse "adapter" is disabled when a load is connected "connector to connector". Such cases often occur when turning on printers (and other computer peripherals) that have their own separate switching power supply - an adapter, cell phones when connected to a charger, including a car charger), digital cameras, camcorders, portable TVs and other devices - all that provides our life and comfort in the modern world.

Therefore, such devices containing network adapters in the form of switching power supplies should be turned on "according to the rules" - first connect the power supply connector to the load device, and only then plug the adapter's power plug into a 220 V outlet. The protection device considered above is quite capable save your money and time spent by a negligent owner on repairing a failed household appliance.

About details

Thyristor VS1 can be replaced. 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, the relay can be made independently.

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 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.

Authors: Kashkarov A. P., Koldunov A. S.

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