Switch Frequency: Understand & Duty in SMPS

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In summary: CBS News correspondent who moderated the first U.S. presidential debate, has a Switching Mode Power Supply (SMPS) which uses 500 kHz. In summary, a SMPS uses a high frequency to improve efficiency and stability. It was invented in the 1960's and is used in modern electronics.
  • #1
rama1001
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It is very basic and makes me angry because i did not understand exactly what does switching frequency means and why is the duty if this in SMPS?
Cany one explaine me clearly?
 
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  • #2
I don't fully understand your question but I will reply. Generally the higher the frequency the physically smaller a transformer can be built. A tranformer operates most efficiently at 50% duty cycle. Of course the SMPS in question may not even use a transformer. Please elaborate.
 
  • #3
Averagesupernova said:
I don't fully understand your question but I will reply. Generally the higher the frequency the physically smaller a transformer can be built. A tranformer operates most efficiently at 50% duty cycle. Of course the SMPS in question may not even use a transformer. Please elaborate.
What does switching frequency means and I saw some products which display in their manual like switching frequency is 500kHZ etc..what exactly it specifies. Please I am new this topics.
 
  • #4
A mains power supply works at 50Hz (or 60Hz). This involves a great big transformer and many sweaty components. ASMPS produces a high frequency and then can use a small transformer (that's the way it is with magnetic components). In addition, a SMPS can give you stabilisation, also without getting hot. The switching frequency is the frequency that the power supply uses to do its 'transforming' (which may not actually involve a transformer at all) - but that's for a future discussion.

If you use 500kHz, you won't have problems like power supply hum!
 
  • #5
Here is a very old unregulated (1960's) dc to dc converter (switching mode power supply) circuit using two 2N3055 transistors to generate about 300 volts from a 6 volt battery. This circuit uses a standard 60-Hz transformer, and the switching frequency (determined by the resistor and transformer inductance) is several hundred Hz.

http://www.wbnoble.com/WN_articles/CD-ignition-SK.pdf

This evolved into the Delta Mark Ten kit about 1968. The Delta kit had a pot core transformer instead of a standard 60-Hz transformer.

http://www.selectric.org/delta/index.html

Bob S
 

1. What is Switch Frequency in SMPS?

Switch Frequency in SMPS (Switched-Mode Power Supply) refers to the rate at which the power switch in the SMPS circuit turns on and off. It is measured in Hertz (Hz) and typically ranges from a few hundred Hz to several hundred kHz.

2. Why is Switch Frequency important in SMPS?

Switch Frequency is important in SMPS because it affects the overall performance and efficiency of the power supply. A higher switch frequency allows for smaller and lighter components, but also increases switching losses and electromagnetic interference (EMI). A lower switch frequency reduces these losses but can result in larger and heavier components.

3. How does Switch Frequency affect the output voltage of an SMPS?

The output voltage of an SMPS is inversely proportional to the switch frequency. This means that as the switch frequency increases, the output voltage decreases. This is because a higher switch frequency results in shorter on and off times for the power switch, reducing the amount of energy transferred to the output.

4. What is Duty Cycle in SMPS?

Duty Cycle in SMPS refers to the ratio of the on time to the total period of the power switch. It is expressed as a percentage and determines the average output voltage of the SMPS. A higher duty cycle results in a higher average output voltage and vice versa.

5. How does Duty Cycle relate to Switch Frequency in SMPS?

Duty Cycle and Switch Frequency are inversely related in SMPS. As the switch frequency increases, the duty cycle decreases, resulting in a lower average output voltage. Similarly, a lower switch frequency results in a higher duty cycle and higher average output voltage.

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