Traitement en cours

Veuillez attendre...

Paramétrages

Paramétrages

Aller à Demande

1. WO1985000933 - CONVERTISSEUR CONTINU-CONTINU PROPORTIONNEL AUTO-COMMANDE AVEC PROTECTION CONTRE LES SURINTENSITES DE COURANT

Note: Texte fondé sur des processus automatiques de reconnaissance optique de caractères. Seule la version PDF a une valeur juridique

[ EN ]
WHAT IS CLAIMED IS:
1. In a self-driven proportional drive DC-DC converter having a power transformer and a switching circuit to switch a primary current through a primary winding of said power transformer, said switching circuit causing said primary current to alternate between a first polarity and a second polarity opposite said first polarity, an overcurrent protection circuit for limiting the primary current through said primary winding and said switching circuit comprising: means for sensing a level of said primary current above a preselected level; and means responsive to said sensing means for terminating operation of said switching
• circuit for a preselected time to delay the transition of said primary current from one of said polarities to the other of said polarities.
2. An overcurrent protection circuit as set forth in Claim 1 wherein said sensing means includes: means for developing a first voltage as a function of the level of said primary current; means for developing a second voltage as a function of said first voltage, said second voltage increasing in time with respect to said first voltage; and latch means responsive to said second voltage for latching when a preselected voltage araplitide of said second voltage is reached.
3. An overcurrent protection circuit as set forth in Claim 2 wherein said second, voltage developing means includes a resistor and a capacitor coupled in series with each other, the RC time constant of said resistor and capacitor being selected so that said second voltage obtains a preselected amplitude within one half cycle time of said switching circuit when said primary current is above said preselected level.

4. An overcurrent protection circuit as set forth in Claim 3 wherein said terminating means
includes timing circuit means including a capacitor and a resistor for causing said capacitor to be discharged through said resistor starting at the end of said half cycle, for applying a current for said preselected time to said switching circuit, the operation of said
switching circuit being suspended in response to said current.
5. In a self-driven proportional drive DC-DC converter having a power transformer, a first power
transistor and a second power transistor, means for
alternatingly driving the base of each said power
transistor with a base current proportional to a
primary current through a primary winding of said power transformer, and means for connecting each transistor to said primary winding such that a primary current
having a first polarity is generated in said
transformer when said first power transistor is being
driven and has turned on and a primary current having a second polarity opposite said first polarity is
generated in said transformer when said second power
transistor is being driven, said driving means
including a base drive transformer having a first
winding in series with said primary winding, a second
winding coupled to the base of said first transistor
and a third winding coupled to the base of said second transistor and wherein a reversal of polarity in said
second and third windings causes one of said power
transisters to turn off and the other to turn on, an
overcurrent protection circuit comprising: means for
sensing an absolute value of the level of the primary
current greater than a preselected level; means
responsive to said sensing means for setting a latch;

SUBSTITUTE SHEE OMH means responsive to said latch means for maintaining the voltage at the base of the presently on transistor clamped for a preselected time to prevent each of said second winding and third winding from reversing
polarity and for resetting said latch means at the end of said preselected time, such that the polarity of said second winding and said third winding is enabled to reverse after said preselect time has expired.
6. An overcurrent protection circuit as set forth in Claim 5 wherein said means responsive to said sensing means includes an RC timing circuit including a capacitor which is charged by a voltage from said sensing means, the voltage of said capacitor setting said latch means when it becomes greater than a
preselected voltage during the on state of one of said power transistors.
7. An overcurrent protection circuit as set forth in Claim 5 wherein said maintaining means
includes a second RC timing circuit, including a second capacitor, and a clamp transistor connected across one of said second or third windings, said second capacitor being connected to discharge and couple current the base of said clamp transistor to maintain said clamp transistor conductive for said preselected time.
8. An overcurrent protection circuit as set forth in Claim 7 wherein said clamp transistor goes off and said latch means resets when the voltage across said capacitor falls below a preselected voltage.
9. In a self driven proportional drive DC-DC converter which has a power transformer, a first power transistor and a second power transistor, and means for alternatingly driving the base of each of said power transistor with a base current proportional to a primary current through a primary winding of said primary transformer so that said primary current has a first polarity when said first power transistor is
being driven during a first half cycle of said driving means and a second polarity opposite said first
polarity when said second power transistor is being
driven during a second half cycle of said driving
means, said driving means including a base drive
transformer having a first winding in series with said primary winding, a second winding coupled to the base of said first transistor and a third winding coupled to the base of said second transistor said base drive
transformer saturating to cause each said transistor to change state, an overcurrent protection circuit
comprising: means for sensing an absolute value of the level of the primary current greater than a preselected level; means responsive to said sensing means, the
voltage of said second winding at the base for clamping of said first transistor when the level of said primary current is greater than the preselected level; and
means for maintaining the clamped voltage of said
second winding for a preselected time after said first transistor has turned off whereby suspending the
operation of said driving circuit to prevent said
second transistor from changing state.
10. An overcurrent protection circuit as set forth in Claim 9 wherein said sensing means is
operative to sense a level of said primary current
during each said half cycle.
11. An overcurrent protection circuit as set forth in Claim 10 wherein said sensing means includes a series resistor-capacitor timing circuit and a resistor in series with said primary winding for developing a
first voltage as a function of said primary current,
said first voltage being applied to said timing circuit which develops a second voltage as a function thereof, the level of said second voltage indicating an

*m,, . mm.mm. < OMPI
" overcurrent condition if greater than a preselected level at any time during each half cycle.
12. An overcurrent protection circuit as set forth in Claim 10 wherein said clamping means includes: a first transistor which turns on in response to said second voltage with a first polarity exceeding said preselected level; a second transistor which turns on in response to said second voltage with a second polarity opposite said first polarity exceeding said preselected level, each of said first polaity and said second polarity of said second voltage being
commensurate with said first polarity and said second polarity of said primary current; a third transistor which turns on in response to said first transistor turning on to maintain said first transistor on; a fourth transistor which turns on in response to said second transistor turning on to maintain said second transistor on; means for clamping the voltage of said second winding at the base of said first power
transistor to the voltage of the collector of said third transistor when said second voltage has said first polarity and for clamping the voltage of said second winding at the base of said first power
transistor when said second voltage has said second polarity.
13. A power supply system comprising:
rectifying means for rectifying an AC voltage to develop an unregulated DC voltage; a first DC-DC converter responsive to said unregulated DC voltage for developing a high power level DC output voltge, said first converter including a current transformer having a primary winding and a secondary winding, and a switching circuit for switching a primary current through said primary winding with an alternating first polarity and a second polarity; means responsive to said primary current for detecting a level of said
current above a preselected level to suspend operation of said switching circuit for a preselected time; and a second DC-DC converter responsive to said high power
level DC-DC output for developing a plurality of low
power level DC voltages.

SUBSTITUTE SHEI °MH