Year1
- 电压：
- 6.3V
- 容量：
- 2.2UF
- 封装尺寸：
- 1.6*0.8
Example of replacing the buck converter with The problem of capacitor heating caused by the output capacitor
and ripple current is a prominent problem in the output capacitor of the power supply circuit.
The picture shows the basic circuit of a small step-down converter that is commonly used in electronic equipment such as converters.
As a solution to the self-heating problem in the converter, saving space and improving reliability, the main object of replacing electrolytic capacitors is the output capacitor.
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Note
The basic circuit of the converter (step-down
converter).
The picture shows the basic circuit of a small step-down converter that is commonly used in electronic equipment such as converters. The main circuit of the converter is optimized, and external capacitors and inductors are connected via a printed wiring board (there are also built-in products). The capacitor in the front stage is called the input capacitor, and the capacitor in the rear stage is called the output capacitor. The output capacitor of the converter smoothes the output voltage by accumulating charges, and also plays the role of releasing the AC ripple component to the ground layer side and removing it.
、Comparison of output capacitor characteristics in buck converters
The output voltage of the output capacitor of the buck converter was compared using the following evaluation board. The capacitors used for comparison are ordinary aluminum electrolytic capacitors, tantalum electrolytic capacitors, functional polymer aluminum electrolytic capacitors and electrostatic capacitance.
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. Since
is lower, the ripple voltage is smaller and the self-heating is less
Based on the aforementioned conditions, the output current and output voltage were compared for ordinary aluminum electrolytic capacitors, tantalum electrolytic capacitors, and functional polymer aluminum electrolytic capacitors with electrostatic capacities of .
And the order of ripple voltage that causes self-heating from large to small is ordinary aluminum electrolytic capacitors>tantalum electrolytic capacitors>functional polymer aluminum electrolytic capacitors>.
Functional polymer aluminum electrolytic capacitors are products that use conductive polymer as the electrolyte to achieve low ripple voltage. Compared with ordinary aluminum electrolytic capacitors, the ripple voltage is significantly smaller, but their shape is larger and the price is higher.
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The impedance frequency characteristics and frequency characteristics of each capacitor are as follows.
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The smaller the capacitor, the smaller the ripple voltage can be suppressed. As shown in the chart below, the characteristic is that it is extremely small, only about a few numbers. Therefore, it will perform extremely well with replacement electrolytic capacitors.
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. Advantages of replacing the electrolytic capacitor in the converter with
Replacing the output capacitor from an electrolytic capacitor to a (multilayer ceramic chip capacitor) not only suppresses ripples, but also brings many advantages to the circuit board, including space saving, longer life, and improved reliability through a compact, low-profile shape. .
) Ripple suppression, high reliability, and long life
Higher electrolytic capacitors will heat themselves due to ripple current, thus shortening their lifespan.
The ratio of electrolytic capacitors is reduced by double digits, achieving long life while improving reliability.
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) Miniaturization
By replacing it with a small low-back shape, the circuit board can save more space.
Question Can the ripple current be suppressed by increasing the capacity of the electrolytic capacitor?
The increase in the electrostatic capacity of electrolytic capacitors can be reduced to a certain extent. However, it is generally difficult to suppress ripples by increasing capacity. This is because as the capacity increases, the time constant also increases accordingly.
The response speed of transition phenomena such as the charge and discharge process of a capacitor is expressed by the time constant index. In a circuit composed of a resistor and a capacitor, the time constant (the unit is ohms [], the unit is electrostatic capacity, the unit is farads []). The smaller the time constant, the shorter the time required to charge and discharge the capacitor, and the larger the time constant, the longer it takes.
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If a large-capacity electrolytic capacitor is used, the time constant will also become extremely large, so the converter will switch on and off repeatedly in a short time. , the discharge cannot be completed within the switching time, so there will be residual charge in the electrolytic capacitor. As a result, the voltage cannot be sufficiently reduced, and the voltage waveform becomes distorted, making the output unstable and ultimately failing to achieve good ripple suppression effects (Figure).
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