jung schematic


Posted on Feb 4, 2014

The reference chosen is an LM329 sub-surface (or buried) zener (ZD1). Whilst the circuit symbol is that of a zener, it`s actually an active device, which results in much lower dynamic impedance than a normal zener, of around 1ohm. It also has low noise relative to it`s output voltage (6. 95V nom. ), due to the sub-surface zener reference. Other devi


jung schematic
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ces can be used, depending upon desired output voltage / noise performance. This Zener is biased through a resistor (R5). Note though that the bias voltage is from the regulator +ve sense point, or output, which is the quietest +ve rail of the system. Biasing the device in this manner means that the reference is well isolated from the effects of noise at the regulator input, in effect benefiting from a super-reg to itself! The output of the reference is then filtered, via a simple RC network (R7 / C4). The resistor values are chosen so that the error amplifier (IC2 or IC3) inputs see a low, and matched source impedance of 500 Ohms, thereby facilitating optimum DC stability and dynamic performance and minimising EMC susceptibility. C4 is a very high performance, low E. S. R. device in order to maximise the filtering effect from the low impedances used. The low impedances bring benefits in terms of reducing the inherent noise of the resistors (Johnson noise) and reducing the effects of EMC / EMI on the circuit. D3 and D4 provide protection against excess differential mode voltage at the op-amp inputs. They are not strictly necessary for the AD797 op-amp, and can be left out for some very minor performance improvement, since the AD797 incorporates these diodes internally. This not the case for many other op-amps though. The reference voltage at the input of the op-amp is compared to a proportion of the output voltage, via the...




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