Power supply option. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Power Supplies
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Absolutely not all power sources can provide good protection for your radio equipment that needs to be powered from low voltage. After all, it can happen that when the output voltage is closed (even for a short enough time), the CE junction of the regulating transistor can “burn out”, it’s good if it “burns out”, i.e. the voltage at the PSU output will disappear, and if the CE transition closes then ... goodbye my KENWOOD, because all the voltage that will be at the input of the stabilizer will be at its output.
I want to offer a relatively simple but fairly reliable power source, which is devoid of all the troubles mentioned above and which can be useful to any radio amateur, motorist, and maybe even someone else. With it, you can power radio stations, high and low frequency power amplifiers, etc.
Key Features:
- output voltage from 1,3 to 37 V;
- maximum load current - 15 A;
- current protection against load over 15 A;
- overvoltage protection when the output voltage rises above 15 V and above 30 V;
- protection response time:
a) current - no more than 15 ms;
b) against overvoltage - no more than 8 ms.
- the amplitude of the output voltage ripple, at a load current of 15 A, does not exceed 0,3 V.
(click to enlarge)Principle of operation
When the push-button switch KN1 is pressed, mains voltage is applied to the transformer T1 and the relays K3 and K1 are turned on, the last of which blocks the contacts KN1.1 with its contacts K1.1 The contacts remain closed until the relay K2 operates or until the output voltage remains within the specified norm. Toggle switch ON 1 just serves to set this rate, i.e. if the contacts of this toggle switch are closed, then the overvoltage protection will work when the output voltage rises above 15 V, but if the contacts are open, then the overvoltage protection will work when the output voltage rises above 30 V. Naturally, you can make these limits different, rather than two (or one) D815E zener diodes to put others i.e. to the desired stabilization voltage. If the current strength at the output of the PSU exceeds the established norm, then the reed switch will work, which will turn on the relay K2, and K2 will open the power supply to K3, K1 will turn off the transformer T1 with its blocking contacts, the LED (red glow) SV1 will light up, which will indicate that the power is off or that the one of the defenses.
The transistors KT630 and KT3102 have overvoltage protection. Transistors VT1-VT3 must be installed on a radiator with a surface area of at least 800-1000 cm2, while it is desirable to ensure good thermal contact between the heatsink and the transistors using a heat-conducting paste. The resistances that are in the circuits of the relay windings (because the resistance of the relay winding is in a wide range (look in any "normal" reference book)) should be selected so that the relay supply current exceeds the minimum current (indicated in any "normal" reference book) of operation in by an average of 50%, otherwise the relays may not work at all. The RES-22 relay has four switching contacts, so it is better to parallelize three (in the primary winding circuit of the transformer).
Adjustment of the stabilizing voltage is carried out by a variable resistance of 6,8K, which is located on the nominally 8 leg of KR142EN12. Any T1 transformer with a power of at least 500 W (I have SHL-630), which can provide 28 V at a load current of 20 A. The winding for powering the protection modules can be wound with a fairly thin wire, as long as it provides (just in case) 0,5 A. On KR142EN12, you need to screw a small radiator with a surface area of at least 10 cm2, because it can overheat from base loads (although they are not great).
Diodes D1-D4 must be installed on radiators with an area of 100 cm2, and even better if you put the finished diode bridge on a direct current of at least 20 A and fix it on a common radiator along with transistors. Coil L1 is wound on a frame with a diameter slightly larger than that of the reed switch and contains 3-5 turns of wire with a diameter of 1,5 mm, then the reed switch is inserted into this coil and fixed. The shunt is a short thick (diameter 1,5-2 mm) piece of wire that limits the current passing through the L1 coil, shortening it or lengthening it and taking it away from the reed switch, you can calibrate the protection trip current. At sufficiently high currents, the coil and shunt can be omitted, but the reed switch should be placed perpendicular to the wire or track. The green LED SV2 indicates the power supply is on, SV3 can be omitted.
At will, anyone can modify the switching circuit of the K1 relay, for example, to switch not only the primary winding, but also the output of an already stabilized voltage (in this case, in case of overvoltage, the load will be instantly disconnected from the power source, since high-capacity electrolytic capacitors may not have time to discharge), it is better to take a more powerful relay.
Finally, I want to draw your attention to the information published in the Radio magazine No. 8, 1993, pp. 41-42, which describes the KR142EN12 chip with its inclusion. I will not say whether it is correct or not, however, in this version, I threw away about a dozen microcircuits referring to their marriage, but the probability that ten out of ten will be defective is very small. Therefore, I included this stabilizer as LM317T. By the way, KR142EN12A can be replaced by its analogue (even by inclusion) LM317T.
High resolution power supply schematic (98 kb)
Author: M. Denisenko (UR5IVS), Donetsk region, Makeevka; Publication: N. Bolshakov, rf.atnn.ru
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