Sharing of Dual Purpose Variable DC Stabilizer Power Supply Circuit
Dual purpose variable DC regulated power supply is a necessary maintenance instrument for radio enthusiasts. Here is an introduction to an output of ± 1.25V-15V or+1.25V-30V, with an output current of about 1.5-2A. It is easy to make, convenient to use, and easy to use.
The working principle of the circuit is shown in the following figure. The biggest advantage of this circuit is the use of two three terminal adjustable voltage stabilizing blocks LM317 and LM337. During maintenance and use, when the switch K is turned to position "1", the secondary voltage of the power transformer T drops to 17.5V × The AC voltage of 2 is rectified by VD1 ～ VD4 and sent to the input terminals of LM317 and LM337 respectively, and then controlled by the sampling resistors R1 and R2 and the output voltage regulating Potentiometer RPl and RP2, the output terminal can obtain ± 1.25 ～ 15V continuously adjustable voltage. When the selection switch K position is set to "2", the dual output power transformer T group is used as a single group. After rectification and filtering, it is only fed into LM317 to obtain a voltage of+1.25~30V. Single power output, which can be conveniently applied to maintenance circuits that require a single power supply or slightly higher voltage.
R1 and R2 in the circuit are used to provide a load current of no less than 5mA for protection; C5 and C6 are bypass capacitors designed to reduce the ripple voltage at the R1 and R2 ends of the sampling circuit; The design of C7 and C8 is to prevent the occurrence of self excitation phenomenon when the output load is capacitive; VD5 and VD7 prevent the discharge current of c7 and c8 from damaging the three-terminal voltage regulator block when there is a short circuit at the output/input terminals; VD6 and VD8 are designed to prevent the discharge current of C5 and C6 from damaging the three-terminal voltage regulator block when there is a short circuit at the output end.
The pin functions of LM317 and LM337 are shown in Figure 2. All capacitors in this circuit use components with a withstand voltage greater than 50V. The power consumption of two three terminal adjustable voltage stabilizing blocks is about 15W.
Remember to add sufficient heat dissipation fins, and the dotted line at the center of the transformer must be firmly grounded to prevent interference from AC noise.
