Gate Control Luo-resonator

14.15 Gate Control Luo-resonator

S 1 S 3 Luo-resonator is shown in Fig. 14.113. It generates the PWM +V

pulse train to drive the static switch S. Luo-resonator is a high efficiency and simple structure circuit with easily adjusting

frequency f and conduction duty k. It consists of three opera- S 2 S 4 tional amplifiers (OA) named OA1-3 and auxiliary. These three 741-type OA’s are integrated in a chip TL074 (which contains four OA’s). Two potentiometers are applied to adjust the fre-

A bipolar voltage source using single voltage source. quency f and conduction duty k. The voltage waveforms are

FIGURE 14.111

shown in Fig. 14.114.

Type-741 OA can work at the power supply ±3 − ±18 V that are marked V +, G, and V − with |V − | = V +. OA2 in Fig. 14.113 acts as the integration operation, its output V C is

L 1 a triangle waveform with regulated frequency f = 1/T con- trolled by potentiometer R 4 . OA1 acts as a resonant operation,

its output V B is a square-waveform with the frequency f. OA3

acts as a comparator, its output V D is a square-waveform pulse +V 1 train with regulated conduction duty k controlled by R 7 .

V Firstly, assuming the voltage V O B = V + at t = 0 and feeds positively back to OA1 via R 2 . This causes the OA1’s out-

put voltage maintained at V B = V +. In the meantime, V B S 2 inputs to OA2 via R 4 , the output voltage V C of OA2, therefore, L 2 decreases towards V − with the slope 1/R 4 C. Voltage V C feeds negatively back to OA1 via R 3 . Voltage V A at point A changes from (mV +) to 0 in the period of 2mR 4 C. Usually, R 3 is set

FIGURE 14.112

A bipolar current voltage source using single voltage slightly smaller than R 2 , the ratio is defined as m =R 3 /R 2 . source.

Thus, voltage V A intends towards negative. It causes the OA1’s output voltage V B = V − at t = 2mR 4 C and voltage V A jumps to mV −. Vice versa, the voltage V B = V − at t = 2mR 4 C and feeds positively back to OA1 via R 2 . This causes the OA1’s switch is 50%. For safety reason, the particular circuitry output voltage maintained at V B = V −. In the meantime, design has to consider some small gap between the turn- V B inputs to OA2 via R 4 , the output voltage V C of OA2, there- over (commutation) operation to avoid the short-circuit fore, increases towards V + with the slope 1/R 4 C. Voltage V C incidence.

feeds negatively back to OA1 via R 3 . Voltage V A at point A The repeating frequency is theoretically not restricted. For changes from (mV −) to 0 in the period of 2mR 4 C. Thus, industrial applications, the operating frequency is usually voltage V A intends towards positive. It causes the OA1’s out- arranged in the range between 10 kHz and 5 MHz, depending put voltage V B = V + at t = 4mR 4 C and voltage V A jumps on the application conditions.

to mV +.

R 3 V + R 2 V off-set

G FIGURE 14.113 Luo-resonator.

14 DC/DC Conversion Technique and 12 Series Luo-converters 347 V A ,V B

A Luo-resonator was designed as shown V +

A design example:

B in Fig. 14.113 with the component values of R mV

V A R 1 =R 2 =R 5 3 =R 6 4

m = 0.95, frequency f = 10–100 kHz and conduction duty

V − k = 0–1.0.

mV −