how does power supply regulate its

Posted on Feb 5, 2014

Most all power supplies regulate either their output voltage or output current at a constant level, depending on the load resistance relative to the power supply`s output voltage and current settings. This can be summarized as follows: To accomplish this most all power supplies have separate voltage and current feedback control loops to limit either the output

how does power supply regulate its
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voltage or current, depending on the load. To illustrate this Figure 1 shows a circuit diagram of a basic 5 volt, 1 amp output series regulated power supply operating in CV mode. The CV and CC control loops/amplifiers each have a reference input value. In this case the reference values are both 1 volt. In order to regulate output voltage the CV error amplifier compares its 1 volt reference against a resistor divider that divides the output voltage down by a factor of 5, limiting the output voltage to 5 volts. Likewise the CC error amplifier compares its 1 volt reference against a 1 ohm current shunt resistor located in the output current path, limiting the output current to 1 amp. For Figure 1 the load resistance is 10 ohms. Because this load resistance is greater than (V out / I out) = 5 ohms, the power supply is operating in CV mode. The CV error amplifier takes control of the series pass transistor by drawing away excess base current from the series pass transistor, though the diode OR  network. The CV amplifier is operating in closed loop, maintaining its error voltage at zero volts. In comparison, because the actual output current is only 0. 5 amps the CC amplifier tries to turn the current on harder but cannot because the CV amplifier has control of the output. The CC amplifier is operating open loop. Its output goes up to its positive limit while it has -0. 5 volts of error voltage. The output I-V diagram for this...

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