Lossless active snubber for half-bridge output rectifiers
First Claim
1. A pulse width modulated direct current--direct current converter circuit, which comprises a bridge-type primary switching circuit having an input for a direct current at a first voltage and having an output supplying a chopped alternating current signal derived from the direct current, a transformer including a primary winding connected to the output of the primary circuit and a center-tapped secondary winding, a half-bridge rectifier including first and second rectifier diodes connected to each of two end terminals of said center-tapped secondary winding, and a snubber circuit connected across said first and second rectifier diodes, said snubber circuit including a first snubber diode connected in a reverse direction to said first rectifier diode, a first snubber capacitor serially connected to said first snubber diode, said first snubber diode and first snubber capacitor being connected across said first rectifier diode, a first controllable switch connected across said first snubber diode, a second snubber diode connected in a reverse direction to said second rectifier diode and a first control signal input connected to said first controllable switch to turn said first controllable switch ON during a maximum magnitude of a first polarity in a pulse of the chopped alternating current signal.
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Accused Products
Abstract
A bridge-type primary switching circuit (12) is represented by a pulsed voltage source (VSW). The primary switched waveform is transformed to secondary circuit (14) using a transformer (T1) with the required turns ratio N and a center-tapped secondary winding (16). Half-bridge rectifier (18) formed by diodes (DR1) and (DR2) rectifies the secondary waveform and feeds the waveform through a low-pass filter (LF) and (CF) to obtain the desired DC output voltage. The snubber circuit (20) is represented by switch-diode-capacitor combinations (SA-DS1-CS1) and (SB-DS2-CS2) across each rectifier (DR1) and (DR2). Capacitances (CS1) and (CS2) are selected large enough such that their voltages remain essentially constant during a switching cycle. The controlled switches (SA) and (SB) are turned ON with a specific delay after the primary voltage reaches a magnitude close to the input voltage in order to allow the rectifier diodes (DR1) and (DR2) to be commutated. It is crucial that the switches (SA) and (SB) be turned OFF before the primary voltage collapses to zero to avoid current spikes through the switches.
50 Citations
18 Claims
- 1. A pulse width modulated direct current--direct current converter circuit, which comprises a bridge-type primary switching circuit having an input for a direct current at a first voltage and having an output supplying a chopped alternating current signal derived from the direct current, a transformer including a primary winding connected to the output of the primary circuit and a center-tapped secondary winding, a half-bridge rectifier including first and second rectifier diodes connected to each of two end terminals of said center-tapped secondary winding, and a snubber circuit connected across said first and second rectifier diodes, said snubber circuit including a first snubber diode connected in a reverse direction to said first rectifier diode, a first snubber capacitor serially connected to said first snubber diode, said first snubber diode and first snubber capacitor being connected across said first rectifier diode, a first controllable switch connected across said first snubber diode, a second snubber diode connected in a reverse direction to said second rectifier diode and a first control signal input connected to said first controllable switch to turn said first controllable switch ON during a maximum magnitude of a first polarity in a pulse of the chopped alternating current signal.
- 10. A pulse width modulated direct current--direct current converter circuit, which comprises a bridge-type primary switching circuit having an input for a direct current at a first voltage and having an output supplying a chopped alternating current signal derived from the direct current, a transformer including a primary winding connected to the output of the primary circuit and a center-tapped secondary winding, a half-bridge rectifier including first and second rectifier diodes connected to each of two end terminals of said center-tapped secondary winding, and a snubber circuit connected across said first and second rectifier diodes, said snubber circuit including a first snubber diode connected in a reverse direction to said first rectifier diode, a first snubber capacitor serially connected to said first snubber diode, said first snubber diode and first snubber capacitor being connected across said first rectifier diode, a first controllable switch connected across said first snubber diode, a second snubber diode connected in a reverse direction to said second rectifier diode, a first control signal input connected to said first controllable switch to turn said first controllable switch ON during a maximum magnitude of a first polarity in a pulse of the chopped alternating current signal and a second controllable switch connected across said second snubber diode and a second control signal input connected to said second controllable switch to turn said second controllable switch ON during a maximum magnitude of a second polarity opposite to the first sign in a pulse of the chopped alternating current signal.
Specification