Powerful load current interrupter. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Clocks, timers, relays, load switches
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The article describes a device that, when connected in series with a load, provides a periodic interruption of the current through it.
DD1.6 remains low, while the transistor VT1 is closed, and the load is de-energized.
The timing generator circuit consists of elements R3, R4. Sat. With the ratings indicated on the diagram, the frequency of the control pulses is approximately 100 Hz with a duty cycle of about 1 4. By selecting these elements, you can change the generation frequency from 0,005 Hz to tens of kilohertz.
Fig. 1
The switching element - field effect transistor IRFP2907 (VT1) in the TO-247AC package is capable of operating at a drain-source voltage of 75 V and a drain current of up to 209 A. The power dissipated by the case reaches 470 W (with a heat sink, of course). The transistor has an extremely low on-resistance of only 0,0045 ohms, which ensures a low voltage drop across the channel. A heat sink is also required at high switching frequencies (maximum chip temperature - 175 °C).
Fig. 2
The main feature of the interrupter in question is its versatility in terms of supply voltage, which allows it to be used in a variety of designs without any alterations, for example, to control the temperature of the soldering iron by supplying it with a pulsed current (in this case, you can replace the VT1 transistor with a lower current one), to control home-made decorative lighting Christmas trees, car turn signal lights, intermittent DC motor control, etc.
Fig. 3
The device is assembled by wire mounting on a technological board with dimensions of 40x35 mm (Fig. 3). Resistors R1 and R2 - C5-5. The remaining resistors and capacitors are any.
The maximum supply voltage of the interrupter is limited to 75 V - the maximum drain-source voltage of the IRFP2907 transistor. However, during testing, the device successfully operated at voltages up to 100 V. For reliable operation at a supply voltage greater than 75 V, the IRFP2907 transistor can be replaced by IRFP150N. IRFP260N IRFP3710 These are n-channel field-effect transistors in the TO-247 package with a large allowable drain-source voltage, but a lower drain current.
The device uses a voltage converter MAX680 in a DIP8 package, which requires four binding capacitors for operation, but MAX681 can be used in a DIP14 package. which does not need external elements at all. Chips DD1 and DA1 on the board are installed in the panel.
It should be noted that when the supply voltage of the interrupter is more than 50 V, an excessively large power is released on the resistors R1 and R2, and in order to prevent overheating, they should be forcibly cooled by a fan. Zener diode VD1 will have to be installed on the heat sink.
The described current interrupter has been successfully operating for two years when testing electronic components for failure-free operation.
Author: M. Kalintsev
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