Simple key voltage regulator, 15-25/5 volts 4 amps. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Surge Protectors
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Electronic devices made on digital microcircuits do not impose too high requirements on the stability and level of ripple of the supply voltage. Therefore, the simplest key voltage stabilizers can be successfully used to power such devices. They have high efficiency, smaller dimensions and weight compared to continuous stabilizers. The correct design of the key stabilizer allows you to avoid the penetration of high-frequency interference into the powered device.
On fig. 5.28 shows a schematic diagram of a simple key stabilizer. With high energy performance, the quality of the output voltage allows you to connect devices made on digital microcircuits of the K130, KPZ, K134, K155, K156, K561, etc. series to the stabilizer.
(click to enlarge)
The printed circuit board of the device is shown in fig. 5.29.
Fig. 5.29
Main technical characteristics:
- input voltage, V.....15...25;
- output voltage, V.....5;
- maximum load current, A ..... 4;
- output voltage ripple at a load current of 4 A in the entire range of the supply voltage, mV, not more than ..... 50;
- Efficiency, %, not worse.....60;
- operating frequency, kHz.....>20.
When a supply voltage is applied to the input of the device, a current appears in the base circuit of the composite transistor VT2, VT3, as a result of which it opens. The circuit R3, C2 provides a pulsed nature of the occurrence of this current, which contributes to the forced opening of the composite transistor. After it is opened, an increasing current begins to flow through the inductor L1, charging the storage capacitors C3, C4.
When the voltage on these capacitors reaches a certain level, transistors VT4 and VT1 open. The last of them, saturating, connects the capacitor C2 charged in the closing polarity to the emitter junction of the transistor VT2. This contributes to the rapid closing of the composite transistor. The current in the inductor L1 cannot be interrupted instantly, therefore, after closing the transistors VT2, VT3, the diode VD1 opens, which closes the current circuit through the inductor L1. In this period of time, the current in the inductor decreases, and from the moment it equals the load current, it begins to decrease and voltage across capacitors C3, C4. At a certain value, transistors VT4 and VT1 close, and VT2 and VT3 open, and the current in the inductor L1 begins to increase again, the diode VD1 closes.
The voltage on the capacitors C3, C4 continues to decrease, and when the current in the inductor L1 becomes equal to the load current, the voltage on the capacitors C3, C4 starts to increase again, and the stabilizer cycle is repeated. Capacitor C5 creates, on the basis of transistor VT4, the necessary phase shift of the feedback signal, which determines the frequency of duty cycles. Filter L2, C6 is used to reduce the output voltage ripple. The power dissipated by the transistor VT3 and the diode VD1 is negligible. This allows you to get a significant load current without the use of heat sinks for powerful elements. However, during long-term operation with a load current of more than 3,5 A, it is necessary to install these elements on heat sinks.
Author: Semyan A.P.
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