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Leakage inductance of half-bridge power adapter converter

source:power adapter     Popular:adapter     release time:2021-04-28 09:08:51     Article author:sznbone    

  The half-bridge power adapter converter does not have the troublesome leakage inductance spike problem as in the single-ended forward and push-pull topology, because the transistor Q1Q2 is connected in parallel with the diodes D5 and D6, which clamps the leakage inductance spike voltage of the transistor to Vdc.

Leakage inductance of half-bridge power adapter converter(图1)

  When Q1 is turned on, the load current and excitation current flow through Q1, the leakage inductance of transformer T, the parallel excitation inductance of Np, and the equivalent impedance of the secondary load converted to the primary by the square of the turns ratio, and finally flow through Cb to nodes C1 and C2. , The voltage at the end of the same name of Np is positive.

  When Q1 is turned off, the magnetizing inductance forces the polarity of all windings to reverse. Through the flyback (secondary to primary), the voltage at the same name terminal of Np becomes negative. If this state continues, Q1 will withstand a voltage much greater than Vdc , It may damage it, and it may also cause Q2 to withstand back pressure and be damaged. However, D6 clamps the voltage at the same name terminal of T1 so that the voltage at the same name terminal of T cannot be lower than the negative terminal of the DC input bus.

  In the same way, when Q2 is turned on, the magnetizing inductance stores energy, and the homonymous end of Np is negative voltage relative to the synonymous end (the voltage across the primary winding of T1 is close to Vdc/2); when Q2 is turned off, the magnetizing inductance makes all winding voltage polarities Reverse. The voltage at the Np end with the same name is trying to become positive, but due to the existence of D5, the voltage at the Np end with the same name is clamped to the positive bus voltage. In this way, the leakage inductance stored energy during the on-time will be fed back to the power adapter Vdc via D5 and D6.

  Comparison of half-bridge power adapter converter and double-ended forward power adapter converter

  Since the turn-off voltage of the half-bridge notebook power adapter converter transistor and the turn-off voltage of the double-ended forward power adapter converter (picture) are also V4 (not 2V), the power adapter composed of these two topologies is on the Internet. It has been widely used in European market equipment with a voltage of 220V. It is necessary to compare the two.

  The main difference between the two is that the secondary output of the half-bridge Korean certified power adapter converter is full-wave rectification instead of half-wave rectification from the output of the double-ended forward power adapter converter. Therefore, the square wave frequency of the half-bridge power adapter converter is twice that of the forward power adapter converter, so that the output inductance L and output capacitance C of the half-bridge power adapter converter are much smaller.

  Supplement: The term "frequency" has little meaning when used in dual-ended and single-ended power adapter converters. It is more appropriate to use it to study the repetition rate of the secondary pulse. If the secondary pulse repetition rate (usually twice the switching frequency of the single-ended power adapter converter) is the same, the transferred conversion power is also the same. This is only related to the (frequency-related) power conversion method, and has nothing to do with the difference between the power ratings (double-ended and single-ended power adapter converters). For example, in the case of push-pull, an output pulse is generated for each of the positive and negative half cycles, resulting in two pulses per cycle (the pulse frequency is doubled). So simply make the single-ended topology generate two pulses in the same cycle, and you will get the same output at the output.

  The essential difference between single-ended and double-ended power adapter converters is reflected in the magnetic induction increment. The push-pull power adapter converter changes the magnetic flux from the negative end (third quadrant) of the BH loop curve to the positive end (first quadrant), while the single-ended power adapter converter only changes between zero magnetic flux and positive magnetic flux, that is, the former It is twice the magnetic flux of the latter. However, generally when the switching frequency is above 50kH, the peak-to-peak value of the magnetic core loss limiting the magnetic flux swing must not exceed 200mT. This magnetic flux swing is easily derived from push-pull and single-ended power adapter converters.


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