Semiconductor voltage limiters. Reference data
Encyclopedia of radio electronics and electrical engineering / Reference materials
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A number of journal publications provided information on the principle of operation and characteristics of semiconductor voltage suppressors for various purposes [1 - 4]. In recent years, the domestic industry has mastered the production of a large group of new voltage limiters.
The range and characteristics of these devices are summarized in Table. 1 and 2, and the housing drawings are shown in fig. 1 - 7.
(click to enlarge)
(click to enlarge)
In In tab. 3 shows the design of instrument cases and their weight. To indicate the polarity of switching on the limiters in the housings KD-34 and KD-71. a white stripe is applied to the case from the side of the positive (cathode) terminal. The symbol of the diode in diode (direct) connection is applied to the body of the remaining devices in the same way as on the cases of zener diodes.
The type name for devices in a miniature case is applied in coded form: on the KD-34 case - in a color code, and KD-71. - in literal. So the limiter KS193A corresponds to a gray strip, KS209A - black, KS209A1 - black and gray, KS209B - two black, KS209B1 - two gray. The letter encoding is presented in Table. 4.
According to the principle of operation, limiters are similar to zener diodes, since the main physical process that characterizes their operation is the threshold appearance of conductivity of the pn junction at a certain reverse voltage ("Zener breakdown"). However, the limiters have a slightly different system of parameters, design and test methods, provide a higher level of permissible current. The limiters are designed to dissipate the energy of powerful single voltage pulses for a limited time.
The industry produces three types of limiters - conventional (or single), symmetrical and low-capacity. The first ones, which make up the largest group, are designed to protect against emergency impulses of DC circuits. To protect AC circuits, either two conventional limiters are included in opposite parallel, or one symmetrical (non-polar), which is a pair of p-n junctions connected in opposite series, as in the case of two-anode zener diodes. It is easy to distinguish a symmetrical limiter from the rest - it does not have a white strip or a diode sign on the case indicating polarity, and the letter C is provided at the end of the name.
All single and symmetrical limiters are summarized in Table. 1, and low-capacity - in table. 2.
Low-capacity limiters are designed to protect high-frequency circuits. The structure of these devices consists of a conventional limiter and a high-voltage diode connected in series with it. When the limiter opens under the action of an emergency pulse, the diode also opens. In the opposite direction, the current structure does not conduct, since the diode is closed. In other words, these limiters are polar ones, which is why they must be included in the protected circuit in pairs in opposite parallel.
The introduction of a series diode makes it possible to greatly reduce the total capacitance of the limiter - up to 90 ... 100 pF. For comparison, we point out that the capacitance of a conventional limiter with an opening voltage of 200 V is approximately 500 pF, while for low-voltage ones it can reach 22000 pF. Low-capacity voltage suppressors (analogues of the foreign LCE6.5A-LCE170A series from General Semiconductor Industries, Inc.) are capable of protecting AC communication lines with a frequency of up to 100 MHz.
The response time of conventional limiters is less than 10-12 s, symmetrical - 10-9 s, and low-capacity - 5∙10-9 s.
Since all the electrical characteristics of the limiters are associated with the application of a reverse voltage to their p-n junction and the flow of a reverse current through the junction, indications of the sign of the parameters and their numerical values are omitted everywhere.
Main electrical characteristics of voltage limiters
- Uopen - voltage of opening (breakdown) of the device at a given test opening current Iopen;
- Iclose - direct current flowing through a closed device (leakage current) at a given voltage Uclose, less than Uopen;
- Uwork - constant operating operating voltage equal to 0,85Uopen and 0,81Uopen for devices with a spread of ± 5% and ± 10% in Uopen, respectively. According to this parameter, the required limiter is selected;
- Ilim.imp.max - the peak value of the current amplitude for a given duration, duty cycle and shape of the pulses, as well as the ambient temperature;
- Ulim.imp.max - the maximum pulse voltage of limitation at the maximum pulse current Ilim.imp.max and given duration, duty cycle and shape of pulses, as well as ambient temperature;
- Rimp.max - the maximum allowable pulse power dissipated by the device for a given duration, duty cycle and shape of pulses, as well as ambient temperature;
- Inp - direct forward current (flowing in the opposite direction to the working one) through a low-capacity limiter at a given forward voltage U.
Limiters are classified by pulse power at given test pulse parameters. In table. 1 and 2 pulse parameters are indicated for an exponential pulse with a duration of 1 ms (often written as 10\1000 μs, where 10 μs is the rise time; 1000 μs is the pulse duration); the form is a decreasing exponent shown in fig. 8.
Foreign devices for protection against excessive voltage pulses, including varistors, are normalized by current pulses with a duration of 1\40 μs, 8\20 μs, 30\60 μs, 10\1000 μs, 1,2\50 ms, depending on the conditions applications. In real operating conditions, depending on the nature of impulse overloads, the impulse parameters can have different values.
The dependences of the pulse power on the duration of the pulses for limiters of various classes are shown in fig. 9.
On fig. 10, as an example, the same dependences are shown for pulses of various shapes.
Foreign voltage suppressors are produced under the trademarks TransZorb, TransiJ, Trisil, Mosopb, Zener Transient Voltage Suppressors, Transient Voltage Suppressors (TVS), etc.
Some voltage suppressors can also be successfully used as zener diodes. So, the KR228A limiter (an analogue of the Motorola 1N5349B device) has additionally normalized "zener diode" parameters - stabilization current, differential resistance, static power.
Literature
- Kadukov A. TVS-diodes - semiconductor devices for limiting dangerous overvoltages in electronic circuits. - Components and technologies, 2001, No. 1, p. 32-36.
- Kolosov V., Muratov A. Protection of electronic equipment against high-voltage impulses in the network. - Radio, 1998, No. 7, p. 52,53.
- Tolkacheva R. Protective microassemblies ZA-0 and ZA-1, Radio, 1999, No. 8, p. 60.
- Kolosov V. "Killers" of electronic equipment - electrical networks. - Live Electronics of Russia, 2000, p. 50-53.
Authors: T.Loseva, V.Minaev, B.Popov, Novosibirsk
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