K04RLM12 Datasheet, PDF (12/23 Pages) Texas Instruments – Operational Amplifier

K04RLM12, LM12CL
SNOSBY8D – MAY 1999 – REVISED APRIL 2013
PARALLEL OPERATION
OBSOLETE
www.ti.com
Output drive beyond the capability of one power amplifier can be provided as shown here. The power op amps
are wired as followers and connected in parallel with the outputs coupled through equalization resistors. A
standard, high-voltage op amp is used to provide voltage gain. Overall feedback compensates for the voltage
dropped across the equalization resistors.
With parallel operation, there may be an increase in unloaded supply current related to the offset voltage across
the equalization resistors. More output buffers, with individual equalization resistors, may be added to meet even
higher drive requirements.
This connection allows increased output capability without requiring a separate control amplifier. The output
buffer, A₂, provides load current through R₅ equal to that supplied by the main amplifier, A₁, through R₄. Again,
more output buffers can be added.
Current sharing among paralleled amplifiers can be affected by gain error as the power-bandwidth limit is
approached. In the first circuit, the operating current increase will depend upon the matching of high-frequency
characteristics. In the second circuit, however, the entire input error of A₂ appears across R₄ and R₅. The supply
current increase can cause power limiting to be activated as the slew limit is approached. This will not damage
the LM12. It can be avoided in both cases by connecting A₁ as an inverting amplifier and restricting bandwidth
with C₁.
SINGLE-SUPPLY OPERATION
Although op amps are usually operated from dual supplies, single-supply operation is practical. This bridge
amplifier supplies bi-directional current drive to a servo motor while operating from a single positive supply. The
output is easily converted to voltage drive by shorting R₆ and connecting R₇ to the output of A₂, rather than A₁.
12
Submit Documentation Feedback
Copyright © 1999–2013, Texas Instruments Incorporated
Product Folder Links: K04RLM12 LM12CL