|
A full wave rectifier with a single phase AC source and DC output voltage smoothing, such as for a power supply.
Fed by the 120V 60Hz (standard residential outlet) voltage supply on the left, the transformer steps the voltage down by a factor of ten. The output voltage of the transformer is plotted by the red line. This directly feeds the green and red LEDs to demonstrate the AC nature of the voltage at this point in the circuit.
The rectifier itself is constructed by the four diodes connected in a bridge (not obvious on this diagram, but a simple Google search of a full wave rectifier will show it clearly). The transformer output is connected to two nodes of the bridge, and the DC (-) and (+) nodes connect to the smoothing capacitor.
The smoothing capacitor does what it's name implies; it smooths the DC output voltage from the diode bridge by supplying stored charge as voltage when the AC supply reaches a maximum or minimum (the current reverses direction, leaving the diode bridge momentarily at 0V DC output). The current through the capacitor (the orange line) demonstrates this, as the capacitor will supply its stored charge at this point (try removing the capacitor and see what happens).
Connected in parallel with the smoothing capacitor is the DC load of the circuit; the blue LED. Notice that while it is constantly supplied with DC voltage, this voltage varies slightly (the ripple voltage caused by the rectifier)(the green line). This variation will be at twice the frequency of the AC voltage supply due to the rectifier halving the period of the input signal. The current through the blue LED thus has a ripple as well (the blue line).
The one value in this circuit that is interesting to play with is the value of the capacitor. Very large capacitances (above ~100mF) effectively block any DC current past the capacitor because it cannot charge the capacitor quickly enough to supply voltage during current reversals. The capacitor will very slowly charge in these scenarios, resulting in a significant delay in the circuit supplying the blue LED with current. A value of about 10mF will demonstrate this slow rise in voltage effectively.
Values decreasing from the 1mF originally set will begin to degrade the smoothing ability of the capacitor - as it no longer carries enough charge to supply voltage during current reversals, the ripple effect becomes more accentuated in the DC voltage. Setting the value to ~10uF will demonstrate this.
|
