Control for a series resonant power converter

A control circuit for use in a series resonant power supply of the type which supplies regulated power to an output circuit from an unregulated input voltage, said power supply including a series resonant circuit having first and second switching means, each of said switching means actuable on and off, only one of said switching means being on at any one time, said series resonant circuit producing a resonant current when said switching means are alternately actuated on and off, said circuit comprising:

• (a) driver means for generating signals for actuating said switching means on and off;
• (b) means connected to said driver means for causing said driver means to actuate off that one of said switching means which is then on only when said resonant current amplitude becomes essentially zero;
• (c) means responsive to said unregulated input voltage for determining when any one of a predetermined number of undesirable conditions occurs in said voltage, said means generating a signal indicative thereof;
• and
• (d) means connected to said driver means for causing said driver means to actuate on one of said switching means depending on loading conditions at said output circuit, said on actuating means including means responsive to said indicative signal for inhibiting said on actuating means from causing said driver means to actuate on one of said switching means.

A control circuit for use in a series resonant power supply of the type which supplies regulated power to an output circuit from an unregulated input voltage, said power supply including a series resonant circuit having first and second switching means, each of said switching means actuable on and off, only one of said switching means being on at any one time, said series resonant circuit producing a resonant current when said switching means are alternately actuated on and off, said supply also including means for generating a signal representative of loading conditions at said output circuit, said circuit comprising:

• (a) driver means for generating signals for actuating said switching means on and off;
• (b) means connected to said driver means for generating an actuating signal for causing said driver means to actuate on one of said switching means, said on actuating means having an input;
• (c) low power control means having an input and an output, said output connected to said on actuating means input;
• and
• (d) circuit means for connecting said loading conditions representative signal to said on actuating means input and said low power control means input, said circuit means disconnecting said representative signal from said on actuating means input when said loading conditions are at or below a predetermined level, said on actuating means responsive to said representative signal for generating said actuating signal at a frequency dependent on said loading conditions, said low power means responsive to said representative signal for generating a signal having an essentially constant predetermined amplitude when said loading conditions are above said predetermined level and pulses of a predetermined width and amplitude when said loading conditions representative signal falls below said predetermined level, said on actuating means responsive to said pulses for generating said actuating signal with a fixed time duration.