| 摘要 |
A zero crossing detection circuit produces an output signal which changes state to indicate the occurrence of a positive-going zero crossing of an AC input signal. The circuit includes first and second input terminals (100 and 102), a current sensitive switch (124) such as an opto-isolator, first and second current regulators (110 and 118), and a voltage limiter (116). The first current regulator (110) is connected in series with the current sensitive switch (124), and the voltage limiter (116) is connected in parallel with the first current regulator (110) and the current sensitive switch (124). The second current regulator (118) is connected between the first input terminal (100) and the parallel combination of the voltage limiter (116) and the first current regulator (110) and the current sensitive switch (124). The first current regulator (110) limits current through the current sensitive switch to a first, substantially constant, current limit level, and the second current regulator (118) limits current flowing between the first and second input terminals to a second current limit level which is greater than the first current level. The zero crossing detection circuit offers the ability to sense zero crossings of AC input signals having a wide range of AC voltages. <IMAGE> |
