Import the surge current and inhibit the application of the module in AC/DC converter
A power up surge current
At present, in view of the volume, factors such as the cost,etc., most AC/DC converters input and commutate and filter and adopt the inputting filtering way of the electric capacity, circuit theory. Because of voltage in capacitor can’t jumping,at the beginning of power up of the rectifier, Filtering capacitance voltage is zero nearly, the equivalent shorts out in order to commutate the Ausgang. Such as situation that is unfavorable in most ‘ The actual value of voltage at the time of power up is the crest value of the mains voltage) Power up, will produce the input surge current far higher than the running current of the rectifier. It is 470& mu to look on as the Filtering capacitance; F and when the power internal resistance is minor, the first electric current crest value will exceed 100A, it is 10 times of the running current crest value.
The surge current will cause the voltage waveform subside of power, make power supply quality poor, even can influence other with to work and make protective circuit act electrical equipment; Because surge current strike the intersection of input and fuse of rectifier, make it until the intersection of several times and the intersection of power up and surge current of course strike but not over load blowout. In order to prevent this kind of phenomenon from taking place, and have to choose the fuse of the higher rated current, but the fuse can’t fuse in appearing in year, will play a role in protecting rectifier and electricity consumption circuit; It doesn’t cause recoverably damage to rectifier and filter capacitor to pass the surge current of high power up. So, must input the surge current to limit the rectifier with capacitor filtering.
Restriction of 2 power up surge current
The most valid method of surge current of limiting power up is, between rectifier and filter capacitor, or add a negative tempperature coefficient thermistor (NTC) on the input side of the rectifier . Utilize negative tempperature coefficient thermistor have high-ohmic come on, limit the intersection of power up and surge current relatively in normal atmospheric temperature state, because NTC flow excess current generate heat to enable his resistance quantity lower by reducing the loss at NTC behind the power up. Though this kind of method is simple, the existing problem is to restrain the surge current characteristic of power up from being influenced by initial temperature of ambient temperature and NTC, in the great of ambient temperature or on the time interval of power up very in short-term, NTC plays a role in limiting the surge current of power up, so, this kind of restriction power up surge current way is only used in the cheap computer power or other low-cost power. On colour television set and display unit, restrain the surge current of power up from adopting a bunch of a Current Limiting Resistance, circuit. The most common application is the colour television set, the advantage of this method is simple, reliability is high, allow to work within the range of wide ambient temperature, its shortcoming losses on Current Limiting Resistance, have reduced power efficiency. The intersection of rectifier and power up, until steady state work, the intersection of current limiter and function of Current Limiting Resistance this already finish in fact, the ones that only played the consumed power, generated heat were defeated by function, so, in the switching power supply greater in power, adopt behind the power up shorting out the Current Limiting Resistance with one mechanical contact or electronic contact after will certainly delay time ing, . This kind of restriction power up surge current way characteristic is good, but the circuit is complicated, it is relatively large to take up the volume. For enable, employ these kind to inhibit surge current way of power up from, it is as convenient as only a bunch of Current Limiting Resistance, this text introduces the power up surge current of the switching power supply and inhibits the module. [1][2]
Tags: heat sink, The capacitor, The converter, the rectifier, the TV
