The output I-V diagram for this Constant Current operation is shown in Figure 4.įigure 4: Power Supply I-V Diagram, CC OperationĪs we have seen most all power supplies have separate current and voltage control loops to regulate their outputs in either a Constant Voltage (CV) or in a Constant Current (CC) mode. Its output now goes up to its positive limit while it has -0.4 volts of error voltage. In comparison, because the actual output voltage is now only 3 volts the CV amplifier tries to increase the output voltage but cannot because the CC amplifier has control of the output. The CC amplifier is now operating closed loop, regulating the output current to maintain its input error voltage at zero. The CC error amplifier takes control when the voltage drop on the current shunt resistor increases to match the 1 volt reference value, corresponding to 1 amp output, drawing excess base current from the series pass transistor though the diode “OR” network. Figure 3 shows the circuit diagram of our basic 5 volt, 1 amp output series regulated power supply revised for operating in CC mode with a 3 ohm load resistor.įigure 3: Basic DC Power Supply Circuit, Constant Current (CC) Operationīecause the load resistor is lower than (V out / I out) = 5 ohms, the power supply switches to CC mode. Now say we increase the load by lowering the output load resistance from 10 ohms down to 3 ohms. The output I-V diagram for this Constant Voltage operation is shown in Figure 2.įigure 2: Power Supply I-V Diagram, CV Operation Its output goes up to its positive limit while it has -0.5 volts of error voltage. 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 CV amplifier is operating in closed loop, maintaining its error voltage at zero volts. 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. For Figure 1 the load resistance is 10 ohms.īecause this load resistance is greater than (V out / I out) = 5 ohms, the power supply is operating in CV mode. 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. 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. In this case the reference values are both 1 volt. The CV and CC control loops/amplifiers each have a reference input value. 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.įigure 1: Basic DC Power Supply Circuit, Constant Voltage (CV) Operation To accomplish this most all power supplies have separate voltage and current feedback control loops to limit either the output voltage or current, depending on the load. If R load If R load > (V out / I out) then power supply is in CV mode.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. But what exactly takes place inside the power supply that endows it with the ability to regulate either its output voltage or current, depending on the load? If you ever wondered about this, wonder no longer! Operational "How to" Guides SummaryHow Does a Power Supply regulate It’s Output Voltage and Current? DescriptionĬV and CC are fundamental operating modes of most all power supplies.
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