Troubleshooting Bridge Rectifier in LT Spice Simulation

In summary, the conversation revolves around building a linear power supply in four stages, with the second stage requiring the addition of a bridge rectifier. The goal is to obtain a sine wave with negative values reflected into the positive x-axis. The individual is seeking assistance with entering an expression in the program LTSpice and obtaining incorrect results for a full wave bridge with a capacitive filter. The formula given for calculating the DC voltage is Vdc = 1.41 x Vac, using the rms voltage and accounting for 2 diode drops in the rectifier voltage. The individual is advised to check their circuit to see if the regulator input voltage equals the amplitude of the transformer secondary.
  • #1
lukesowersby
9
0

Homework Statement


I am to build a linear power supply in four stages. However, at stage two, i have to add a bridge rectifier to the ouput of my transformer. My lecturer at university says i should get a graph that is a sine wave, with the negative values reflected into the positive x-axis (Volatage). I was wondering were am i going wrong?


2. The attempt at a solution
http://img399.imageshack.us/img399/1367/ltspice1gm7.jpg


Any help would be greatly appreciated.

Thanks.
 
Last edited by a moderator:
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  • #2
You need to plot the difference between rectifidp and rectifidn. Or, alternatively, plot the voltage across your load resistor, R5.
 
  • #3
Yeah, had a suspicion it might have been that, but it took me a while to work out how to enter an expression. Only started using the program a few days ago, so I'm still getting used to it.

http://img218.imageshack.us/img218/138/ltspice2rc0.jpg

Many thanks for your help.
 
Last edited by a moderator:
  • #4
I've got another problem. For a full wave bridge, with a capacitive filter, we are told the following relationship between Vdc [V(Regout)-V(Rectifidn)] and Vac [V(Secondary)]:

Vdc = 1.41 x Vac

However, I'm obtaining the following results:

http://img386.imageshack.us/img386/5310/lt4vr1.jpg

I'm just wondering if i have the wrong formula, or taking incorrect readings?

Thanks.
 
Last edited by a moderator:
  • #5
lukesowersby said:
Vdc = 1.41 x Vac

A couple of things to keep in mind here:

That formula uses the rms voltage, not the amplitude, for Vac.

Also, it does not account for the 2 diode drops in the rectifier voltage.
 
  • #6
Redbelly98 said:
A couple of things to keep in mind here:

That formula uses the rms voltage, not the amplitude, for Vac.

Also, it does not account for the 2 diode drops in the rectifier voltage.
Ah, forgot about rms. Thanks.

That equation was given a bridge rectifier (4 diodes) with a capacitor and load resistor, but exluding the regulator. So i assume to calculate Vac, if i want Vdc of 5, i simply calculate 5+the voltage acrross the regultor, all divided by 1.41.
 
  • #7
You can check that on your Spice circuit, "transformer1 stage 5".

If you plot

V(rectifidp) - V(rectifidn)​
and
V(secondary)​

you can see if the regulator input voltage equals the amplitude of the transformer secondary.
 
  • #8
Yeah, thanks for your help.
 

Related to Troubleshooting Bridge Rectifier in LT Spice Simulation

1. What is LT Spice and how does it work?

LT Spice is a simulation software used to analyze and design electronic circuits. It uses mathematical models to simulate the behavior of electronic components and can be used to predict circuit performance before physically building it.

2. What is a bridge rectifier and what is its purpose?

A bridge rectifier is an electronic circuit that converts alternating current (AC) to direct current (DC). Its purpose is to convert the AC power supply to DC, which is necessary for most electronic devices to function.

3. How do I simulate a bridge rectifier in LT Spice?

To simulate a bridge rectifier in LT Spice, you will need to use four diodes and a voltage source. Connect the diodes in a diamond shape with the positive terminal of the voltage source connected to the top of the diamond and the negative terminal connected to the bottom. This will create a bridge rectifier circuit that can be simulated in LT Spice.

4. What are the advantages and disadvantages of using LT Spice for simulating a bridge rectifier?

The main advantage of using LT Spice for simulating a bridge rectifier is that it is a free and easily accessible software. It also provides accurate and reliable simulation results. However, one disadvantage is that it may require some technical knowledge to use, especially for more complex circuits.

5. Can LT Spice simulate other types of rectifiers besides bridge rectifiers?

Yes, LT Spice can simulate various types of rectifiers, including half-wave rectifiers, full-wave rectifiers, and center-tapped rectifiers. It can also simulate other types of circuits such as amplifiers, filters, and oscillators.

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