Schemes of two-half-period rectifiers on op amps with switching inputs in accordance with the polarity of the enter voltage are given. The switching of inputs is carried out by a management sign taken from the output of the zero-indicator made on the comparator.
Precision two-half-period rectifiers, whose operation relies on switching inputs in accordance with the polarity of the enter voltage, normally include an op amp, the non-inverting enter of which is shunted by a diode, Determine 1, R1 = R2 = 2R3.
Determine 1 Classical scheme of a precision two-half-period rectifier.
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When a constructive half-wave of the enter voltage enters the enter, the diode D1 is locked. The op amp U1 operates within the mode of a non-inverting amplifier with a transmission coefficient equal to R2/R1. The output voltage is the same as the enter voltage: Uout = Uin.
When a destructive half-wave of the corresponding amplitude arrives on the enter of the gadget, the diode D1 opens, the circuit operates within the mode of an inverting amplifier with a transmission coefficient equal to –1, Uout = –Uin.
The drawback of the circuit is clear: with a low enter voltage of destructive polarity as a consequence of the truth that the diode D1 has a noticeable resistance, Uout ≠–Uin. In follow, the amplitude of the enter sign when utilizing the op amp U1 LM324 and the diode D1 1N4148 needs to be within the vary of two.5 V to the provision voltage.
It’s potential to enhance the operation of a precision two-half-period rectifier by utilizing key parts (FET Q1, Determine 2, or analog swap U2, Determine 3), managed by a zero detector on the comparator U1.1.
The sensible scheme of the primary of the units is proven in Determine 2.
Determine 2 A two-half-period rectifier with switching of the enter of an op amp by a FET.
A zero detector of the enter sign is made on the comparator U1.1 of the LM339 chip. From the output of this detector, the management sign is utilized to the gate of the FET Q1 2N3823, which switches the enter of the op amp U2.1 of the LM324 chip.
The amplitude of the enter sign when utilizing an op amp U2.1 LM324 and a FET Q1 2N3823 needs to be within the vary of 0.5 V from the provision voltage.
It’s potential to enhance a two-half-period rectifier by utilizing an analog U3 swap as a switching ingredient equivalent to Determine 3, for instance, CD4066, or a extra fashionable ingredient with much less losses. To cut back the resistance of the general public key, all 4 channels of the CD4066 swap needs to be related in parallel. The swap S1 can change the polarity of the output alerts.
Determine 3 A two-half-period rectifier with switching of the enter of an op amp by an analog swap.
The precision of the two-half-period rectifier in Determine 3 is operable within the enter voltage vary from 20 mV to the provision voltage of the gadget. The utmost frequency of the rectifier is 100 kHz and will depend on the frequency properties of the energetic parts.
Michael A. Shustov is a physician of technical sciences, candidate of chemical sciences and the writer of over 750 printed works within the area of electronics, chemistry, physics, geology, drugs, and historical past.
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