參數(shù)資料
型號: VT900
廠商: PerkinElmer Inc.
英文描述: Photoconductive Cells and Analog Optoisolators (Vactrols)
中文描述: 光導(dǎo)細胞和模擬光隔離器(Vactrols)
文件頁數(shù): 68/76頁
文件大?。?/td> 1240K
代理商: VT900
63
Application Notes—Analog Optical Isolators
Figure 5. Peak Sensing Compressor with Constant Bandwidth
Variable bandwidth can be avoided if the AOI is used in a voltage
divider circuit at the input of a fixed gain amplifier. For the same range
of input signals, the amplifier gain must be 500 and the voltage divider
must have a range of 1000:1. This configuration is shown in Figure 5.
The AOI has been changed to a lower resistance unit to be able to
work over the wider range. Also, A
1
is now a high input impedance,
non-inverting stage to avoid a high insertion loss. This circuit is useful
when the input voltage is high, which allows the use of a lower gain
amplifier.
Speaker Power Limiting
Speakers that are driven fromhigh power amplifiers must be protected
fromexcess drive. While ordinary programlevels may be well within
the rating of the speaker peaks do occur that can be destructive. The
simplest solution is to use a compressor or limter. Unfortunately, the
maximumpower that may be applied is not constant over the
frequency range. Therefore, the limt must be set to provide protection
at the lowest frequency that is expected.
To understand the requirements for effective speaker protection, a brief
review of speaker power limtations follows. Figure 7 is a typical
maximumsine wave voltage limt for a low frequency speaker
commonly called a “woofer”. Above 200 Hz, the maximumallowed
voltage or power is constant. The operating temperature at which wire
insulation and coil bonding fail establishes this value. Below 200 Hz,
the voltage limt is determned by the allowable diaphragmexcursion.
For constant voltage on the speaker, the displacement doubles when
the frequency is reduced by half. The maximumdisplacement is
determned by the mechanical design of the speaker and exceeding
the limt will produce extreme distortion and may even cause
mechanical damage.
Figure 7. Maximumsine wave Voltage and Power for a Typical Woofer
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