Power adapter with timer, 220/9 volts 250 milliamps. Scheme, description

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Power adapter with timer, 220/9 volts 250 milliamps. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Power Supplies

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Most mains power supplies (adapters) for powering portable equipment at home are simple circuits consisting of a compact power transformer, a rectifier bridge, and a 1000 microfarad capacitor.

More complex ones contain adjustable voltage stabilizers. But there are practically no adapters with built-in timers, and this would be very convenient, because often the adapters are constantly connected to the network, regardless of whether the load is working or not, and you can forget to turn off the load itself, for example, a radio receiver. Here it’s not even a matter of excessive power consumption (the adapter consumes little), but of a fire hazard, especially relevant in a hot pet, when all the equipment literally melts. Plus, the ability to use the power supply as a timer.

The figure shows a diagram of supplementing a conventional power supply with a timer, with which you can smoothly (with a variable resistor) set the time in the range from 10 minutes to 2 hours, after which the adapter will turn off completely, with disconnection from the mains.

Power adapter with timer, 220/9 volts 250 milliamps

There are parts not marked on the diagram, these are parts of the network adapter, their little power transformer, rectifier bridge and electrolytic capacitor, adapter, Chinese, made in the form of a large plug, produces a constant voltage of 9 V at a current of up to 350 mA (according to the inscription on it) in the gap of one of the conductors of the primary winding of the transformer, the starting switch S1 and the contacts of the relay K1 are connected. If you are not going to use the timer - turn on the S1 and use the adapter as usual, the timer circuit will not have any effect on it.

To use the timer, you need to plug the adapter into the network as usual, then turn the S1 on and off. After that, the countdown will begin, and then the adapter will turn off completely. Accordingly, the load is turned off.

The timer circuit is based on the CD4060B chip.

At the moment the power is turned on, using the C1-R7 circuit, the counter of the IC D1 is forced to reset. The zero of its most significant digit enters the base of the transistor VT1 and opens it. Turnip K1 is turned on in the collector circuit of the transistor, it closes the contacts. Now, if S1 is turned off, the voltage to the primary winding of the transformer will be supplied through the relay contacts.

From the moment of switching on, the countdown of the time set by the variable resistor R5 begins. Resistor R5 regulates the frequency of pulses generated by the built-in RC multivibrator of the CD4060 chip. Through the internal circuits of the microcircuit, the pulses are fed to a binary 14-bit counter. After some time, which depends on the frequency of the pulses (having counted 8192 pulses), a logical unit appears at the senior output of the counter (pin 3). Transistor VT1 will close and relay K1 will turn off its contacts. The circuit will be completely disconnected from the network

LED HL1 - to indicate the on state. It blinks, and the longer the set time delay, the slower it blinks.

Electromagnetic relay type TRG5-9-VDC-FA-CL in a miniature package measuring only 12x8x10 mm (such relays are used in some computer modems). The contacts are rated for current up to 0,25 A at a voltage of 230 V. You can use another miniature relay with parameters no worse than those indicated.

There is no domestic alternative to the CD4060B chip. However, it is possible to assemble a timer circuit on the K176IE12, K176IE5 or KR512PS10 ICs, but of course, the circuit will be significantly different, since these microcircuits are not direct analogues of the CD4060B.

The figure shows a circuit for remaking a simple 9-volt adapter without adjusting the output voltage. In practice, universal adapters are more common, in which taps are made from the secondary winding of the transformer, switched by a switch. In this case, the circuit must be supplemented with another bridge rectifier, which is connected to the tap, when connected to which the output of the additional rectifier bridge will have a voltage of 8 ... 10 V. Also, an additional blocking capacitor of 470 ... 1000 will be needed. uF to be connected at the output of the additional rectifier bridge.

Author: Tarasenko V.I.

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