Power supply control device

Encyclopedia of radio electronics and electrical engineering / Power Supplies

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When experimenting with complex, in particular microprocessor-based devices, multichannel, galvanically uncoupled power supplies are often required. The proposed article describes a control device for a three-channel power supply with galvanically uncoupled and arbitrarily (polarity) connected sources. It also has the functions of overload protection and an electronic switch. All sources are switched off when one of them is overloaded. The device is galvanically connected only to the +5 V voltage source, which is part of the power supply unit, from the rectifier of which it is powered.

The schematic diagram of the PSU control device is shown in fig. 1. It consists of three RS-flip-flops assembled on the elements DD2.1 and DD2 2, DD2.3 and DD2.4, DD1.3 and DD1.4 with LED indicators HL1. HL2. HL3, respectively, the match node on the element DD3.3. start-stop device, made on the elements DD3.1, DD1.1, DD3.2, DD1.2. and a parametric voltage regulator on a transistor VT3 and a zener diode VD4.

All trigger cells work in the same way, so let's consider the work of one of them. for example, assembled on the elements DD2.1 and DD2.2. When the PSU is turned on with a mains switch, a constant voltage from the output of the rectifier of the +5 V power supply (PS1. Not shown in the diagram) through the buffer diode VD5 is supplied to the voltage regulator of the control device. A stabilized voltage of +5 V through the resistor R3 is supplied to the inputs (pins 4. 5) of the DD3.2 element and the capacitor C2 of the start-stop device. As a result, a voltage pulse with a logic level of 3.2 is formed at the output of DD1, and with a logic level of 1.2 at the output of DD0. The latter, through the decoupling diode VD1, enters the input (pin 6) of the DD2.2 element and sets the trigger DD2.1DD2.2. 1 to the zero state (at pin 1 - low level), which leads to the ignition of the HLXNUMX LED.

Logic level 0 from the output of DD2.1 is fed to pin 13 of the matching element DD3.3. The logic 1 signal that arises at its output opens transistors VT1 and VT2. and LEDs of optocouplers U3, U4 light up. As a result, composite phototransistors open, which prevent the corresponding channels (IP2, IPZ) of the PSU from turning on. Collector current VT2 turns off IP1 (+5 V). Transient processes in the control device proceed faster than in the PSU as a whole, therefore, voltage surges at the outputs of the MT1 - MT are not observed.

To turn on the PSU, press the SB1 ("Start") button. A single vibrator is assembled on the elements DD3.1 and DD1.1. generating an impulse to start the PSU. approximately equal in duration to the half-cycle of the network. This is necessary to limit the short circuit or overload current through the PSU power elements during the triggering pulse when trying to turn on the PSU with an overloaded output. A negative pulse from the output of DD1.1 is fed to pin 2 of the element DD2.1 and sets the trigger to a single state. In this case, the HL1 LED goes out, the logical 1 signal is fed to pin 13 of the match element DD3.3. and since the voltages at the remaining inputs (pins 1 and 2) have the same level, a logic 0 signal appears at its output. As a result, the transistors VT1 and VT2 close, the LEDs of the optocouplers U3 and U4 go out and the closed phototransistors turn on the power supply.

When an overload occurs in IP2, optocoupler U1 is turned on. its phototransistor shunts the input (pin 6) of the DD2.2 element and the trigger, of which it is included, is set to zero. In this case, the HL1 LED lights up. a logical 3.3 signal appears at the output of DD1 and, as a result, the power supply sources are turned off. Indicators HL2 and HL3 remain off, as the rest of the flip-flops continue to be in a single state. Thus, the indication of the BP channel is carried out. in which the overload occurred. After it is eliminated, the unit is turned on by pressing the SB1 button.

Turn off the PSU by pressing the SB2 ("Stop") button. The logical 0 signal that occurs at the output (pin 13) of the DD1.2 element sets all device triggers to the zero state, and the HL1 - HL3 LEDs light up, signaling the PSU is turned off. The HL4 LED indicates that the device is powered.

Optocoupler transistors U3. U4 is connected to the IP2 shutdown circuits. IPZ. optocoupler LEDs U1. U2 - with their current sensors, and pin 12 of element DD2.4 - with current sensor IP1 (+5 V).

It is easy to see that the described device can be easily increased to the required number of control channels by introducing new triggers and replacing DD3.3 with an element with a large number of inputs. It also becomes possible to control the operation of the PSU using other devices with TTL output levels. To do this, it is enough to disconnect one of the inputs (pins 10. 11) of the DD3.1 element from the resistor R1, and one of the inputs (pins 4. 5) DD3.2 - from the resistor R3 and capacitor C2 and connect them to the circuits of devices that generate signals logical 0, respectively, to start and turn off the PSU. The possibility of manual control will remain.

If there is no need to control from external devices. the device can be simplified by excluding the elements DD3.1, DD3.2. DD1.1. DD1.2 and resistor R4. The start-stop unit in this case is assembled according to the schemes shown in Fig. 2, and the free terminals of the inputs of these elements are connected to the positive power wire through a resistor R20 with a resistance of 1 kOhm (the numbering of new resistors continues that started in Fig. 1).

With serviceable parts, the device starts working immediately and does not require adjustment. The author has been using it for a long time as part of a three-channel laboratory PSU. +5 V voltage source which is similar to that described in [1], and the other two are the same and made according to the modified circuit published in [2]. I would like to express my gratitude to the author of [2] for a really successful PSU circuitry.

Literature

1. Mansurov M. Laboratory power supply with trigger protection. - Radio. 1990. No. 4. p. 66 - 70.
2. Mush V. Powerful highly stable power supply. - Radio. 1978. No. 7, p. 56 - 58.

Author: A. Muravtsov, Norilsk

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