# LT spice result analysis, Capacitance Multiplier vs RC filter circuit

• brainbaby
In summary, the CM circuit causes the load current to increase, while the RC filter reduces the ripple.

#### brainbaby

Hi friends,

I have simulated two circuits, one is an RC filter and other is a Capacitance multiplier.
My aim of experiment is to validate a decrease in Iout (load current) of CM circuit as compared to load current in RC filter circuit.

Theoretically,
Iout (CM circuit) < Iout (RC filter)
Vp-p (CM circuit) < Vp-p (RC filter)

My results:
1.RC filter

Vout (dc) = 0.0458716 ( .op 300ms)
Iout (dc) = 0.00458716

Vout (ac) = 43.7 ~ 48 mV (.tran 300ms)
Iout (ac) = 4.80 ~ 4.37 mA

Vp-p (ripple) = 0.00437018 (.meas)

2.CM circuit

Vout (dc) = 0.323751
Iout (dc) = 0.0323751
Vout (ac) = 322 ~ 327 mV
Iout (ac) = 32.65 ~ 32.15 ma

Vp-p (ripple) = 0.00521016 (.meas)

From the above results its quite clear that implementing CM circuit causes Iout to increase which particularly against the aim of the CM circuit. As the CM circuit works by decreasing the load current which according to load POV can be visualised as increase in capacitance.
We can also see the peak to peak ripple voltage in both the circuits, Vp-p for CM circuit should be less than Vp-p ripple of an RC filter, but again the simulations results are quite opposite.

What's wrong here??

#### Attachments

• RC FILTER STANDLONE.ASC.txt
1,014 bytes · Views: 128
• capacitance multiplier.asc.txt
1.8 KB · Views: 126

Why make it so complex ? You have too many places in the circuit to hide difficulties and differences. If the two circuits were merged into one_file.asc, you could compare the results directly.

1. Why specify two voltage sources in series when the DC offset can be specified in one ?

2. What is so special about the detailed 2N4401 model ? Why can you not use a traditional 2N2222 that is included in every version of LTspice ?

3. When 50 Hz is “full wave” rectified, the ripple approximates a saw-tooth with a fundamental frequency of 100 Hz. By specifying a 50 Hz sinewave, you are analysing a frequency component that does not exist, while ignoring every significant harmonic.

Because the CM circuit is buffered with the emitter follower, it has a higher output voltage and therefore a higher output current when operating into the same load resistance. The ripple in the CM circuit is also less because load current is not being drawn from the capacitor.

I have given the input waveform a 100 Hz saw-tooth.
Also, offset the DC of the CM voltage in the plot to get better resolution.

#### Attachments

• merged-10.asc.txt
2 KB · Views: 186
• merged-10.plt.txt
311 bytes · Views: 105
Last edited:

## 1. What is LT spice result analysis?

LT spice result analysis is the process of examining the output data from a simulation in LTspice, a popular electronic circuit simulation software. This analysis allows for a deeper understanding of circuit behavior and performance.

## 2. What is a Capacitance Multiplier circuit?

A Capacitance Multiplier circuit is an electronic circuit that uses capacitors to increase the effective capacitance of a system. This can be useful in situations where a large capacitance is needed but a single capacitor may be too expensive or physically large.

## 3. What is an RC filter circuit?

An RC filter circuit is a type of electronic filter that uses a combination of resistors and capacitors to filter out unwanted frequencies from a circuit. It is commonly used in audio and power supply circuits to remove noise and improve signal quality.

## 4. What are the advantages of using a Capacitance Multiplier over an RC filter circuit?

One advantage of using a Capacitance Multiplier over an RC filter circuit is that it can provide a larger effective capacitance without the need for a physically large or expensive capacitor. Additionally, a Capacitance Multiplier can have lower output impedance compared to an RC filter, resulting in better filtering performance.

## 5. How can I interpret the results of a Capacitance Multiplier vs RC filter circuit simulation in LTspice?

The results of a simulation in LTspice can be interpreted by examining the output waveforms and frequency response plots. The output waveforms will show how the circuit responds to different input signals, while the frequency response plot will show the filter characteristics of the circuit. It is important to compare the results of the Capacitance Multiplier and RC filter circuits to determine which one is better suited for a specific application.

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