SU653607A1 - Overload-protected dc voltage stabilizer - Google Patents

Description

the thyristor is connected to the middle terminal of the additionally introduced variable resistor, which is connected to the outermost terminals between the regulating base and the matching transistor collector, and an additionally inserted capacitor is connected between the outermost terminals of the indicated variable resistor.

The functional diagram of the constant voltage stabilizer is shown in the drawing.

The stabilizer contains a regulating transistor 1, a matching transistor 2, a feedback unit 3, a pulsed trigger unit 4, a protective thyristor 5, a variable resistor 6 and a capacitor 7. As is known, the regulating 1 and matching 2 transistors of such a stabilizer are unlocked by the output voltage connection, therefore, when a supply voltage regulator is applied to the input, the output voltage will be absent until the trigger pulse arrives from the pulsed trigger unit, which is a generator to Short impulses following high duty ratio. The first impulse of block 4, acting on block 3 or on the input of transistor 2, causes unlocking of transistors 1 and 2 and the appearance of output voltage. During normal operation of the stabilizer (no output overload), the output voltage is maintained at a predetermined level by the feedback unit 3, and through transistor 2 and resistor 6 a current flows almost equal to the base current of transistor 1 and is proportional to the load current of the stabilizer (collector current of transistor 1 ). Therefore, the voltage across the resistor 6 (capacitor 7), and hence the control voltage applied to the thyristor 5 control transition, will also be proportional to the load current of the stabilizer. Using a variable resistor 6 at the input of the thyristor 5, a control voltage is established to ensure that the thyristor 5 is turned on at a given overload current. As long as the load current does not exceed the value of this overload current, the voltage is not enough to turn on the thyristor 5, the latter is off and does not affect the operation of the stabilizer. As the load current increases (the collector current of transistor 1) exceeds its maximum operating current, the base current of transistor 1 increases proportionally, the voltage across resistor 6 and the control voltage. When the load current reaches an overload current (overload protection threshold), the thyristor 5 is turned on and the voltage between its anode and cathode (between the emitter of transistor 1 and collector of transistor 2) becomes close to zero.

The thyristor 5 takes on the collector current of the transistor 2 and connects the capacitor 7 to the emitter-base junction of the transistor I in the locking polarity.

At the same time, the transistor 1 is forcibly locked, and the output voltage begins to decrease sharply. The capacitor 7 is discharged through the thyristor 5 - resistor 8 and through the resistor 6, keeping the transistor 1 in the closed state until the output voltage drops to the stabilizer self-protection level. After block 3, transistors 1 and 2 are permanently locked. After reducing the anode current of the thyristor 5 (in

during the discharge of the capacitor 7) below the holding current, the thyristor 5 is also turned off, and the stage of the stabilizer is turned off. The stabilizer remains in the off state until the next trigger pulse arrives from

block 4. At startup, the capacitor 7 closes the pulse of the collector current of transistor 2, thereby preventing the thyristor 5 from turning on falsely with a triggering pulse. If the output still has an overload, equal to or greater than the magnitude of the overload current, then after the stabilizer starts up, the base current of transistor 1 increases in proportion to the overload current and charges the capacitor 7 to a voltage sufficient to turn on the thyristor 5. The latter turns on and starts a new stabilizer shutdown cycle. Therefore, if there is a prolonged overload sufficient to trigger the protection, the stabilizer will be periodically turned on for a very short time of action of the triggering pulses. Since the period of the triggering pulses, during which the stabilizer is turned off, is very small, the average power dissipated in the stabilizer power transistors 1 and 2 will be negligible, which ensures reliable protection of these transistors against overloads.

If the current overload (or other reason causing the output voltage to disappear) disappears or is eliminated, the stabilizer is surely triggered by the very first pulse of block 4.

Thus, the resistor 6 performs the function of an overload current sensor, and the thyristor 5 performs the function of a sensitive and high-speed relay element, causing the stabilizer to turn off when overloaded. The rest of the stabilizer circuit, which has the property of self-defense against large current overloads, makes this process irreversible. In other words, in this device, any, including arbitrarily small, current

overloading leads to self-shutdown of the stabilizer, whereas in known schemes this process takes place only at large (multiple) current overloads.

The capacitance value of the capacitor 7 is determined by the size of the output capacitance of the stabilizer and is proportional to it. The output capacitance is the main cause of the final rate of rise and fall of the output voltage when the stabilizer is started and turned off.

This DC voltage regulator with protection against overloads has one more additional feature - the ability to turn off when the input (supply) voltage drops below the permissible level (the level at which the control transistor is saturated and the stabilizer goes out of the output voltage stabilization mode). Indeed, when the supply voltage reaches the saturation level of the transistor 1, the output voltage starts to decrease, which causes a strong unlocking of the block 3, transistor 2 and a significant increase in its collector current. This, in turn, leads to an increase in the voltage on the capacitor 7 to the thyristor on level 5. The latter turns on and off the stabilizer. The whole process of shutting down the stabilizer in this case is completely identical to the described process of shutting down the stabilizer during an overload.

Thus, in this DC voltage stabilizer, it was possible to significantly increase the reliability of the stabilizer (due to the presence of effective protection against small overloads), reduce the size and weight of the heat sink of the transistors 1 and 2 (and hence the stabilizer as a whole) by reducing the power dissipated by these transistors in case of overloads that are lower than the protection threshold (i.e., overloads at which the protection is not yet triggered), reduce the

Electricity stabilizer at overloads, less current overload, to ensure the shutdown of the stabilizer when the supply voltage drops below the permissible level (for normal operation of the stabilizer) level.

Claims (2)

1. USSR author's certificate number 483661, cl. G 05 F 1/58, 1972. 2. USSR author's certificate number 475609, cl. G 05 F 1/56, 1971. }