Regulated power supply for current up to 1 ampere. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Power Supplies
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To power many portable household devices or repair radio equipment, it is convenient to have a stationary universal source of stabilized DC voltage. Usually, for such a source, it is sufficient to adjust the output voltage from 1,5 ... 30 V at a maximum current in the load up to 1 A.
Such a source can easily be made on an integrated circuit from the K142EN12A (B) series, fig. 4.6. Its switching circuit is typical and does not need special explanations.
Rice. 4.6. Electrical diagram of the power supply (click to enlarge)
The chip inside has overcurrent protection and allows you to dissipate power up to 10 watts on the radiator.
In the manufacture of a universal power supply with output voltage regulation over a wide range, in order to provide a lightweight mode for the power transistor, a network transformer with a sectioned secondary winding is often used. In this case, the transformer taps are connected manually using a switch, depending on the level of the output voltage, so that the difference between the input and output is not very large. Instead of a switch, this task may well be performed by an automatic device, highlighted in the figure by a dotted line.
To switch the four taps of the secondary winding of the transformer T1, only two relays with two groups of switching contacts are sufficient.
Relays turn on in a certain sequence. The diagram shows the initial position of contacts K1 and K2 when neither of them is turned on.
The switch has three switching thresholds and the relay operation is controlled as follows:
1) as soon as the output voltage exceeds 7,5 V, relay K1 will turn on;
2) when the level of 15 V is exceeded, relay K2 will operate;
3) when the level of 22,5 V is exceeded, K1 will turn off.
In this case, the voltage taken from the secondary windings of the transformer T1 will increase in steps.
The switching threshold level is determined by the operating voltage of the applied zener diodes (VD4.VD6). In this version of the circuit for KS175A zener diodes, it is 7,5 V. This allows you to change the voltage from 1,5 to 30 V at the output of the power supply with only one regulator (R6).
The circuit eliminates the bounce of the relay contacts during switching and, if the switch is properly installed, it does not need to be configured.
The device used parts: a variable resistor R6 type SPZ-4a, the remaining resistors are MLT or C2-23. Polar capacitor C3 is better to use tantalum, for example, type K52-1B, K53-4A; C1, C2 and C4 can be of any type.
Transistors VT1, VT2 must be with a high gain and can be replaced by KT829 (A.G).
Relays K1, K2 are used for an operating voltage of 24 ... 27 V and must have two groups of switching contacts that allow switching current up to 1 ... 2 A.
For example, these are RPG-8-2602 for 24 V, RES48, RS4.520.203, RES47, RF4.500.407 and some others.
Network transformer T1 can be used from a series of unified. CCI255-220-50, CCI276-220-50, CCI292-220-50. It is also not difficult to make a network transformer based on any transformer iron you have.
Chip DA1 is installed on the radiator. In this case, the radiator should not have electrical contact with the body of the structure, since in DA1 pin 8 is connected to the fastening element of the microcircuit.
Author: Shelestov I.P.
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