How to select resistors for power module design?
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How to select resistors for power module design?

Author: Zhongyiguang Guangzhou Technology Ltd release time:2020-06-12 14:13:31CTR:

In the circuit principle, people can often see the resistor components, the key starting voltage, separation, load resistance and other functions. The main parameters of resistors of different types will be different, and the points that must be taken into account when applying different power circuits will also be different. Therefore, how to select and apply resistor is very important to the smooth operation of power supply circuit.

Power supply module

In general, most of the resistors only care about tolerance resistance and tolerance, but in the circuit principle, it is not enough to only care about these two main parameters, but also need to care about the maximum power and tolerance voltage value, these two main parameters also have a great harm to the credibility of the system.

It is assumed that the voltage withstand test values under the condition of faulty selection will cause the resistor to be thermally broken and the circuit principle unsuccessful. Such as AC-DC module power supply in the design of the typing front-end development.

Will usually choose when design scheme and grade 1 or 2 M Ω characteristic impedance of the resistor to carry out the kinetic energy of discharge, and type end is high pressure, high pressure in the low pressure test value resistor type side will be invalid.

The basic principle is that when the current terminal voltage is high and the voltage of the over-voltage varistor is opened, the varistor is broken down by heat and the resistance is reduced to separate the current, so as to avoid the latter stage suffering from excessive instantaneous velocity voltage damage or dry torsion.

But the varistor does not show detailed voltage maintenance, it can bear the kinetic energy or output power is insufficient, can not show the continuation of overvoltage protection.

Power supply module

Thermistors are such temperature-dependent components that are divided into NTC and PTC. NTC is a negative temperature exponential thermistor. The higher the temperature is, the smaller the characteristic impedance is.

PTC is a positive temperature exponential thermistor. The higher the temperature is, the greater the characteristic impedance will be. The sensitivity of characteristic impedance to temperature plays a key role in circuit theory.

In the power supply circuit, the key of NTC is to stop the starting current. Usually, because the system software contains the output power supply circuit, capacitance and inductive load, a very large impact current will appear at the moment of starting.

If the instantaneous speed of components is not taken into account in the whole process of motor selection of power circuit components, then the system software is very easy to cause components to be destroyed by thermal breakdown during several starts.

Adding NTC to the power circuit is equivalent to starting the lifting input impedance at the ketting control circuit to reduce the impact current.

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