Bridge Rectifier

Background information

Another central circuit can be created by placing two half-bridges in series and connecting both through a bridge branch. In this way, one obtains the full bridge or H-bridge (s. figure 1).

From the H-bridge, many different circuits can be derived. figure 1 left shows the Wheatstone measuring bridge, in which the resistor $R_{\rm L}$ can be determined using a potentiometer $R_{\rm 2}$ and a voltmeter. In the right image, the switching full bridge is shown, which can, for example, drive a motor. The middle image shows the bridge rectifier, which will be described in more detail later.
Always pay attention in full-bridge circuits to where the input and output voltages are located.

Experimental Tasks

In figure 2 the circuit of a bridge rectifier is shown.

1. Enter the current arrows correctly.
2. Draw the connection between the oscilloscope and the circuit in order to measure the output voltage $u_{\rm R}$ at the rectifier.
3. Explain why one cannot measure the secondary voltage of the transformer and the output voltage of the bridge rectifier at the same time.
   
   
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   Fig. 2

   
   
   

4. Build the circuit and connect the oscilloscope.
5. Sketch the voltage curve before and after the bridge rectifier, i.e. the voltages $u_{rm Sec}$ and $u_{\rm R}$. However, note that you connect the ground of the oscilloscope before or after the bridge rectifier for the respective measurement.
6. Give the oscilloscope settings used.
   
   
   Fig. 3 Channel 1: $ \frac{V}{\rm DIV} = $
   
   Channel 2: $ \frac{V}{\rm DIV} = $
   
   Time basis: $ \frac{T}{\rm DIV} = $
   
   

1. Connect a capacitor (electrolytic capacitor) with 100 µF in parallel to the resistor $R_{\rm L}$ and sketch the voltage curve of $u_{rm Sec}$ and $u_{\rm R}$ again in figure 3 with a different color.
   Warning: When using an electrolytic capacitor (Elko) the correct polarity must be observed!
   
2. Measure the following values with the help of the oscilloscope in the circuit and enter the results into table 1 (100 µF):
   

   Tab. 1: Bridge-Rectifier measured values

   
   

3. Consider a measure by which the ripple voltage can be reduced.
4. Draw the circuit with your found solution into figure 4 and measure the voltage curves $u_{rm Sec}$ and $u_{\rm R}$.
5. Enter these into the screen image figure ## with a third color.
   Fig. 4

1. Carry out the corresponding measurements – as above – again on the bridge rectifier. These were the secondary-side voltage of the transformer $û_{\rm Sec}$, the frequency of the secondary transformer voltage $f_{\rm Sec}$, the peak-to-peak value of the ripple voltage $u_{\rm PP-ripple}$, the ripple frequency $f_{\rm Ripple}$, the average value of the rectified voltage $|ū_{\rm R}|$ and the peak value of the rectified voltage $u_{\rm R,~max}$.
2. Enter the results in the second free line of table 1.

Test questions - Bridge Rectifier