Some applications require the sampling of a set of analog voltages to be maintained, and at least two traditional methods are available to meet this requirement. The most common approach is to cascade a classic analog accumulator with a sample-and-hold amplifier. As shown in Figure 1.
The classic analog accumulator is an op amp plus at least three precision resistors. The values ​​of these resistors should be as low as possible to avoid affecting the bandwidth of the accumulator. But these low value resistors consume power. In addition, the structure of the accumulator and the sample-and-hold amplifier brings another disadvantage, which is manifested when the two input voltages have similar amplitudes and opposite polarities. At this time, even if the input voltage amplitude is high, the sum obtained is low, and if the input voltage amplitudes are equal, the sum is zero. Sampling low voltages usually results in relatively large errors in the output voltage because each amplifier has some dynamic error, such as residual parasitic charge coming into the storage capacitor.
There is also a possible way to use an amplifier per channel to summarize their outputs with a classic analog accumulator. Although this configuration avoids the problem that the input voltage amplitude is similar and the opposite polarity causes high output error, the precision resistor of the accumulator still consumes power.
These problems can be avoided by using the circuit structure of Figure 1, which does not use an external resistor. In steady state, the internal logic signal is active high during the internal tracking period, and the followers consisting of A1, B1 and A2 are enabled. Therefore, the ground referenced capacitor C2 is charged to the VINA voltage. The low side of capacitor C1 on IC2 Pin 2 is temporarily grounded through the output of the A2 follower, and it is connected to the high-end charge of IC1 Pin 9 to the VINB voltage. VINA and VINB are the input voltages for the A and B inputs, respectively.
After a stabilization period, when all internal logic control signals are low and all controlled followers are disabled, the QSB control logic signal is high. Since the follower B3 is enabled, the potential of the low side of C1 is from 0V to VC2(tS) = VINA(tS). VC2(tS) is the voltage value stored in capacitor C2, and then the signal transitions to an inactive low level. The high-end potential of C1 thus rises to VC2(tS) + VC1(tS) = VINA(tS) + VINB(tS), as shown in the lower waveform in Figure 2.
This waveform is the only analog waveform in this figure. The low-to-high effective conversion of the sampling command logic signal QS slightly lags behind the QSB logic signal, suppressing glitches on the output voltage. When QS is high, the sample voltage VINA(tS) + VINB(tS) appearing on IC2 Pin 7 is accessed by enable follower B2 and stored in capacitor C3 until the next sample instruction. Follower A3 acts as an impedance transformer. The dual op amp IC6 acts as a branch delay line that combines with a single NOR gate and a dual AND gate to derive a timing-correct internal logic control signal from a single external logic control signal Q.
Product advantages:
1. Stylish, portable, practical and convenient home charger
2. 6-port USB emergency charger, which can be used safely for tablet computers and can charge 6 devices at the same time
3. Built-in IC chip and fuse, protection: over current, over voltage, short circuit protection
4. The latest release, new design, beautiful appearance, high efficiency and energy saving, the best alternative to the original charger
5. Chargers for MP3, MP4, GPS, PDA, e-books, mobile phones, digital cameras, tablets, etc.
Features
(1) Overcharge protection
(2) Over discharge protection
(3) Short circuit protection
(4) Voltage stabilization protection.
(5) Automatic identification of mobile phone current protection.
1. Connect up to 6 USB devices at a time, and each device will receive a unique and tailor-made charge. The maximum output power of QC3.0 is 18W, which can optimize the charging of all devices.
2.2QC3.0+4 ports total 6 charging ports, which can charge 6 devices with a total power of 84W at the same time
3. With multiple protection safety systems, the product will automatically adjust the charging current according to the needs of the device being charged. Automatically detect and adjust the charging current to charge your device at the fastest speed.
One machine for multiple uses
The USB charger can charge 6 devices at the same time, and the smart recognition technology will detect and provide the best charging level for each of your devices.
The maximum output current of a single USB port is 2.4A. 2QC3.0 has 6 charging ports, which can charge 6 devices at the same time without causing shunting or reducing power. The USB charger can quickly charge your devices. Smartphones and tablets can receive up to 2.4 amps of current, so you can use the device as you like while charging.
Over-current, over-charge, and short-circuit protection will make charging safe, without any risk of overheating or damaging the device. Passed CE/FCC/ROSH/PSE/CCC certification. Through safety certification to ensure safe use.
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