This article describes a simple design transformer power supply for the most common travolti music players and recorders Sony, Panasonic, Sharp, Philips and others of His feature - improved reliability in emergency situations: he will save himself and the load from excessive current, with no special node protection.
Readers are probably familiar with this emergency: you decided to listen before going to sleep to your favorite tune, but the tape was neprimetnoy. Include rewind... and fall asleep. Cassette stopped, and the engine continues to operate in severe conditions. Thus wear out rapidly the details of the tape drive mechanism. If the music player powered by a galvanic elements, they will last a maximum of an hour. But if from a power supply unit capable of maintaining constant output voltage regardless from the load current (except in the case of a short circuit in it)? As in practice, this often leads to failure of electronic controller of motor speed that is serious.
The proposed power supply - no the universal. It is intended only for music player or recorder. In emergency situations described in the beginning of the article (inhibited rewind mode), this power supply will drastically reduce the output voltage. This is quite enough to save player in substandard conditions without applying special electronic devices, and hence no additional material costs.
The feature of the unit (see diagram) - the presence of additional winding III of [1] to ensure the base current of the transistor VT1. In practice, basic food chain transistor in the voltage regulator from a separate source has some advantages:
The latter is particularly important for automatically perform security functions.
So, most music players nourish 3 V with a current consumption of 160 35... mA. This current increases to 350 mA when the engine is inhibited.The proposed power supply is the following characteristics:
- voltage - 220 V
- input current - 15 mA
- output voltage - 3.1 In (stable) when the current consumption 130 mA
- the maximum current is not more than 260 mA (when the output voltage up to 1.5 V)
The duration of continuous operation a power supply unit in any mode, including emergency, is not limited. His weight with the power cord of the player does not exceed 150 g dimensions - 65x60x44 mm (excluding serving fork).
Structurally, the main volume is a transformer. To manufacture the latter should be approached with extreme care. The cross-sectional area of the magnetic circuit is not less than 1 cm2 for the W-shaped and about 0.8 cm 2 for the toroid. To increase the area of the core is not advisable for two reasons. First, the "powerful" power pack can burn a load in the accident - this is the main reason. Secondly, the power supply becomes more cumbersome and heavy.
The primary winding has turns 9000 the PEV-2 with a diameter of 0.05 mm., the Winding is carried out in bulk, but with a uniform distribution across the width of the frame. To facilitate this procedure is better to use a simple winding machine with counter turns, but the coil with the wire should be placed at a distance of about one meter from the frame, and here why: in the process of winding will be jerks, kazania turns from the coil, before he hits the frame, and other emergency that threatens the broken wire. To be able to stop the winding process, and the need for such stock length. The loop of the reserve should definitely hold tight, suspending small cargo damper directly on the wire. During normal winding process (without jerks) sinker together with wire goes down and stays there, uravnoveshivanie the tension of the wire.
Tracking a sharp rise of the sinker up, we need to immediately stop winding and eliminate the cause of the excessive tension of wire before the wire will break. If there was a break, not worry, secure the last round of masking tape and solder (or weld on the flame of a match) ends, tentatively biting at least two inches of wire from a fault in both directions (the insulation of the wiring in this place is ruined due to the stretching of copper). It is desirable to withdraw the joint place in the region of the frame, not the coated magnetic circuit so as not to reduce the area of the window winder. To isolate the soldering easiest of the same adhesive tape.
Before winding the secondary winding, it is necessary to carefully isolate the primary winding from the secondary, if the frame they are structurally separated. The main thing here is not to allow the secondary wire winding to fail in the primary area between the insulating layer and the edge of the frame. There are two equally reliable way to avoid this. The first is using special insulating plate, the width of which is greater than the width winding, and its edges are cut in the form of the fringe. When you stack this pads fringe needs to be bent up and safely conceal a dangerous gap. Second the method is even simpler: it is necessary to wind in the gap a bit conventional threads by completing the its a kind of "insulating material".
The secondary winding II is wire sew-2 with a diameter of 0.2 mm and contains 800 turns with a branch of the middle. On top of it without insulating plate 600 turns is wound more winding III wire sew-2 of 0.1 mm diameter. If you decide to do one winding II 400 turns and then put a bridge rectifier, you want caution - the power transformer may not be enough for normal operation the player, as it will increase significantly the losses in the rectifier, which for low-voltage load (5 V and less) are only full-wave.
The capacitors selected reserve the stress of being in the idle state all voltage after rectifier will be increased in 3...4 times. The transistor has KT815 the relatively low saturation voltage (typical - 0.2 V [2]), it is the main criterion when changing to another type.
The block is better to issue in the form of a box with mains plug. The output on the player perform a dual flexible wire handy length (typically 1.3 m).
In the process of testing needed to verify the absence of acoustic noise from plates of the transformer at rated load, overheating of the transistor, which is installed without the heat sink and the heating of the magnetic core is not more than +60°C.
In playback mode without cassette when the maximum volume should not listen to the hum. When rewinding the cassette may receive the background and amplified at broken tape the node (the end of the fast) is a payment for a security function. But with so inconvenience can be tolerated, as this mode the player is the subsidiary.
Literature
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