Switching power supply, 9 volts 3 amps. Scheme, description

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Switching power supply, 9 volts 3 amps. Encyclopedia of radio electronics and electrical engineering

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The converter (Fig. 5.18) is designed to power devices from a 220 V network with a current consumption of up to 3 A at an output voltage of 9,2 V (any typical linear stabilizer circuit can be used to obtain 5 V or 6 V from this voltage). The proposed converter differs from similar ones in simplicity and in the presence of protection of the power supply against overload in the output circuit in the event of a short circuit. The electrical circuit of the device consists of an input filter (elements C1, C2, C3 and T1); start circuits (R2, R3, R4, C4, VT1); oscillator (VT2, VT3, T2, T3, C5 ... C9); low voltage rectifier (VD5, VD6, C10 ... C13).

(click to enlarge)

The converter is assembled according to a common half-bridge circuit. The input filter of the converter provides attenuation of interference, starting from a frequency of 15 kHz, more than 2 times. The trigger circuit uses a transistor VT1 in the reversible breakdown mode, which allows you to generate short pulses that are necessary at the moment the circuit is turned on to start the operation of the key stage VT2, VT3 in the oscillator mode at a frequency of 30 ... 60 kHz, while the operating frequency is in small limits, you can change the capacity of C5. In the event of a short circuit in the secondary winding circuit of the transformer T3, the feedback in the oscillator is broken and the generation fails until the malfunction is eliminated, the efficiency of the converter at a load current of 2 A is 0,74 (at a load current of 4 A it decreases to 0,63).

Resistors of any type can be used in the device, capacitors C1 of type K73-17 for 630 V; C2, C3 type K73-9 or K73-17 for 250 V; C4, C5 type K10-7; C6, C7 type K50-35 for 250 V; C8, C9 type K73-9 for 250 V; C10.C12 type K10-17; C13 type K52-1V for 20 V. Transistor VT1 can be replaced with KT312A, B, C, transistors VT2 and VT3 with KT838A, KT846V. The T1 inductor is wound on two ring cores glued together, size K20x12x6, made of 2000NM grade ferrite. Windings I and II contain 45 turns of PEV-2 wire with a diameter of 0,25 mm.

The T2 transformer is made on two ring cores glued together, size K10x6x2000, made of 60NM ferrite. Winding I contains 15 turns, windings II and III - 0,15 turns of PELSHO-XNUMX wire each (tap in winding II for current feedback from the third turn).

For the manufacture of. T3 used ring core K28x16x9 (2000NM). Winding I is wound with 250 turns of PEV-2-0,25 wire, windings II and III - with 22 turns of PEV-2 wire with a diameter of 0,51 mm. In the manufacture of transformers, before winding the wire, it is necessary to round off the sharp edges of the cores with a needle file and wrap them with varnished cloth. Winding should be carried out turn to turn, followed by insulation of each layer (it is better to use fluoroplastic tape 0,1 mm thick).

The used diodes VD1.VD4 can be replaced by any high-voltage ones, the replacement of diodes VD5 and VD6, except for KD2998V, is not recommended with another type. The greatest heat dissipation in the circuit occurs on the rectifier diodes VD5, VD6, and they must be installed on a radiator.

The remaining parts of the circuit do not need a heat sink. Structurally, all elements of the circuit, except for the switch S1 and diodes VD5, VD6, are placed on a single-sided printed circuit board 140x65 mm in size. The topology of the printed circuit board is shown in fig. 5.19.

Switching power supply, 9 volts 3 amps

Before turning on the converter for the first time, it is necessary to check the phases of the windings in the VT2 and VT3 base circuits for compliance with the circuit. If the converter, when properly installed, does not immediately start working, then it will be necessary to swap the terminals of the winding I of the transformer T2. II and III transformer T3.

Author: Semyan A.P.

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