Embodiments of most existing switch-mode DC/DC power converters with analog feedback control take the form as shown in FIG. 1 which depicts an existing DC/DC power converter 10 having dual (two) outputs. In the power converter 10 fluctuating, irregular input voltage feeds 12 the input filter 15 that serves to block switching noise from returning to the input port. With the power switch(es) 20 turned ON/OFF by the controlled switch driver(s) 25, a transformer/inductor device 30 passes the input voltage on the primary side to the secondary in unidirectional pulsating form after processing at respective rectifier blocks 35A, 35B. The output filters 40A, 40B extract the direct-current (DC) component from the respective pulsating source and feeds it to a respective output load 45A, 45B. A fraction of the DC output voltage is taken as a signal 48 that is fedback to an analog error amplifier 50 with a very high gain (amplification). By referencing the feedback 48 to a command reference 55, an error signal, 60, which is an indication of how much the output deviates from the desired target, is generated. The error signal 60, a DC voltage, is compared against a built-in oscillating reference carrier (not shown) embedded in a PWM (Pulse Width Modulator) device 65. The action of comparing the two signals produces a rectangular waveform 75 with variable width that drives the power switch(es) ON/OFF ratio of switch drivers 25 until the output(s) are within an acceptable, specified level.
However, as can be seen in the device 10 of FIG. 1 having two outputs, only a single feedback loop exists to perform the closed-loop regulation. In that case, very often the single loop closing is assigned to the one output load with the heaviest load (current). As a result, the other output is left at the mercy of component tolerance, operating conditions, and is poorly regulated.
Provisions may be made to add a local series regulator 41 to the second output filter 40A, such as shown in the modified switch-mode DC/DC converter device 10′ having two outputs of FIG. 2, which tends to therefore make that output also regulated. This practice however, adds hardware weight, size, and, the most undesirable, higher cost.
FIG. 3 shows a further modified switch-mode DC/DC converter device 10″ having two outputs with alternating, switched feedback. In this design, a fraction of the DC output voltage at the second output filter 40A is taken as an additional signal 49 that is fedback to a second analog error amplifier 51 with a very high gain (amplification). By referencing the further feedback 49 to a further command reference 56, a second error signal, 61, which is an indication of how much the output of the second load deviates from the desired target, is generated. Each error signal 60 and 61, a DC voltage, are switched using Double-Throw, Single Pole (DTSP) switching device 63, for input to the PWM element 65 for comparison against the built-in oscillating reference carrier (not shown) embedded in the PWM device 65. The action of comparing the two signals produces the rectangular waveform 75 with variable width that drives the power switch(es) ON/OFF ratio of switch drivers 25 until both output(s) are within an acceptable, specified level.
This design of FIG. 3 nevertheless will not work since both analog error amplifiers consist of passive resistors (R) and capacitors (C) network. RC networks when switched take time to settle because capacitors tend to retain charge. The settling process in effect introduces transient disturbance and causes output spiking. This is therefore not a solution either.
It would be highly desirable to provide an improved regulated DC/DC switch-mode power supply with multiple outputs.