Application of thermally compensated optocouplers in voltage converters. Part 1. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Application of thermally compensated optocouplers in voltage converters. Part 1. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Surge Protectors

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Each designer has his own approaches, his own tricks, his own glitches and standard building blocks repeating from project to project. For those who have looked at least a few pages on this site, something has already caught their eye. I will try to talk about my favorite bricks (in silicon), in relation to the circuitry of car audio and devices that serve lamp devices (power, automation, protection, etc.).

Optocouplers - do not regret!

First of all, we are talking about optocouplers of the 293 series with bidirectional MIS transistors at the output (depending on the circuit, they can be replaced with unidirectional MIS or conventional bipolar ones). Why do I use optocouplers in situations where it would seem easier to put a hybrid key? By definition, galvanic isolation, the absence of the "Miller" effect of the output on the input, but in addition - food for thought ...

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An optocoupler, like a conventional non-polarized relay, implements a logical AND (in addition to the input current, you need AND power for the output circuit).

One control circuit (say, the collector current of a switching transistor) can control several optocouplers. Moreover, optocouplers can be both closing and opening (that is, saving on logic), and if there is a sufficient ceiling of the collector voltage of the primary circuit, their input diodes are switched on in series - saving on the current consumed (and this already applies to lamp circuits, where volts too much, and a milliamp is too little).

MIS optocouplers are quite slow (on 1 ms, off 0.1 ms), which in automation circuits simplifies the suppression of bounce when turning on / off (both associated with the bounce of an external control signal, and with self-excitation).

With all that said, optocouplers are expensive, and the range of output currents is small (up to 200mA in low-voltage devices of the 293 series).

Example: tube preamp power supply, which uses both closing (normally open) and opening (normally closed) MIS optocouplers. The logic of the circuit is such that when the power is turned on, the left optocoupler according to the circuit should be OPEN, and the right one should be CLOSED. It is acceptable to replace a normally closed MIS optocoupler with an npn optocoupler with an additional inverter in the primary circuit, provided that the inverter is powered BEFORE a significant positive voltage appears at the filter output (C2).

Example: switching an independent 6V battery to create a negative voltage source in a car. When the REMOTE signal is removed, a charger is connected to the battery (slow charging with constant voltage). MIS optocouplers of the 293 series with normally closed actuating transistors are required (direct replacement for a relay with a switching triple of output contacts). Of course, the circuit can also be built on conventional, normally open, bidirectional MOS optocouplers, with external inverters (or even better, a bounce suppression latch), but it’s more beautiful! (full scheme)

Application of thermally compensated optocoupler isolation in voltage converters

Example: a key-stabilizer of lamp incandescence in a car amplifier. The optocoupler lower according to the scheme is, in fact, not needed, the REMOTE signal can be applied to the T2 gate as is. But the top - just in its place! Bipolar optocouplers can also be used in the circuit.

Application of thermally compensated optocoupler isolation in voltage converters

Publication: klausmobile.narod.ru

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