Low voltage circuit breaker. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Low voltage circuit breaker. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Clocks, timers, relays, load switches

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This device is connected in series with a load powered by a constant voltage of 8 ... 15 V, and interrupts the current through the load.

The load current can be from a few milliamps to several tens of amperes. At the same time, the own current consumption is negligible. The nature of the interruption, that is, the frequency of the interruption, the duty cycle, is regulated over a very wide range with the help of two variable resistors, one of which regulates the time the load is on, and the other the time it is off. The difference can be up to 100 times.

Low voltage circuit breaker

Adjustment is carried out in two ranges, in the first period you can adjust from 10 seconds to 0,1 seconds. In the second, from 0,1 seconds to 0,001 seconds. That is, in frequency terms - 0,1-10 Hz and 10 Hz-1 kHz.

It is desirable that the adjusting variable resistors be of a slot type with a linear dependence of the resistance adjustment (as in audio graphic equalizers). This is more convenient, since the difference in setting the time of the on and off state of the load is visually perceived well, and if it is necessary to adjust the frequency (that is, both parameters at once), the resistor handles can be moved simultaneously.

Thanks to such wide adjustment ranges, the device can be used for a wide variety of applications. For example, for the periodic supply of light signals, it is possible to adjust the duration of the spotlight on and off in a wide range, or to adjust the brightness of the spotlight, the speed of rotation of the electric motor, by adjusting according to the principle of pulse-width modulation.

If necessary, you can add other ranges by switching the capacitors of the multivibrator timing circuit. The schematic diagram of the breaker is shown in the figure. The basis of the circuit is a multivibrator on the logic elements of the K561LA7 microcircuit. The frequency-setting circuit of the multivibrator consists of capacitors C1, C2 and an R-component, consisting of variable resistors R1, R2, a constant resistor R3 and switching diodes VD1 and VD2. Diodes VD1 and VD2 switch resistors R1 and R2 depending on the phase of the generated pulse. Depending on the set resistance of the corresponding resistor, the time of the phase corresponding to this resistor also changes. Resistor R3 limits the minimum value of the time interval and eliminates the overload of the logic element due to the closure of its output and input at the minimum position of the corresponding variable resistor.

The remaining two elements serve as a buffer between the multivibrator and the output stage on VT1. The output is made on a switching field-effect transistor IRFZ30. Its difference is a large current and a very low resistance of a fully open channel. The current can reach. 30 A, while the channel resistance is hundredths of an ohm. As a result, the power dissipated on it, even at a current close to the maximum, is very small. Therefore, a small, one might say, symbolic plate radiator is quite enough.

The breaker has only two outputs - "+" and "-", with which it is connected to the break in the load power supply. In this case, the power to the multivibrator circuit is supplied from the load power source, through the load. During operation, this voltage jumps, since the VT1 key practically closes the power supply circuit of the D1 chip. To prevent sudden power surges of the microcircuit, there is a circuit of a relatively large storage capacitor C3 and a VD3 diode. At intervals when the load is turned off, capacitor C3 is charged through it through the VD3 diode. At times when the load is on, the VD3 diode closes, since its anode is at a negative potential, and the microcircuit is powered by the charge accumulated by the capacitor C3, and the VD3 diode excludes the discharge of this capacitor through the open channel VT1.

The K561LA7 chip can be replaced with K561LE5 or imported analogues CD4001, CD4011 In general, you can use any chip of the K561, CD series, which has at least three inverter logic elements. That is, it is quite possible K561LA9, K561LE6, K561PN2 and others. Include according to the pinout. Extra elements, for example, four elements of the K561LN2 chip, can be connected in parallel to each other (in place of D1.3, D1.4). This is even better as it increases the output power per key.

Diodes 1N4148 can be replaced with KD522, KD521, KD102, KD103.

Capacitor C1 - any type. Capacitor C2 - type K73-17 or similar (non-polar) C3 - analogue of K50-16. Resistors of any type. Variable resistors can also be of any type, but preferably slotted with a linear dependence of the resistance adjustment.

Before starting work, it is advisable to let the capacitor C3 charge by setting the adjusting resistors to the maximum position.

Author: Lyzhin R.

See other articles Section Clocks, timers, relays, load switches.

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