MC34066

The MC34066 can be used for the control of series,parallel or higher order half/full bridge resonant converters.The IC is designed to provide control in discontinuousconduction mode (DCM) or continuous conduction mode(CCM) or a combination of the two. For example, in a parallelresonant converter (PRC) operating in the DCM, the IC is programmed to operate in fixed ontime, variable frequencymode of operation. For a PRC operating in the CCM, the ICcan be programmed to operate in the variable frequencymode with a fixed offtime.

When operating with a wide input voltage range, such as auniversal input power supply, a PRC can operate in the DCMfor high input voltage and in the CCM for low input voltage. Inthis particular case, ontime is programmed corresponding toDCM. The deadtime of the chip is programmed to provide thedesired offtime in the CCM. The frequency range is chosento cover the complete frequency range from the DCM to theCCM. When programmed as such, the controller will operatein the fixed ontime, variable frequency mode at lowfrequencies. At the frequency which causes the Oscillator toretrigger the OneShot, the control law changes to variablefrequency with fixed offtime. At higher frequencies thesupply will operate in the CCM with this control law.

Although the IC is designed and optimized for doubleended pushpull type converters, it can also be used forsingle ended applications, such as forward and flybackresonant converters.

MC34066 feature

 Variable Frequency Oscillator with a Control Range Exceeding 1000:1
 Programmable Oscillator Deadtime Allows Constant OffTime Operation
 Precision Retriggerable OneShot Timer
 Internally Trimmed Bandgap Reference
 5.0 MHz Error Amplifier with Precision Output Clamp
 Dual High Current Totem Pole Outputs
Selectable Undervoltage Lockout Thresholds with Hysteresis
 Enable Input
 Programmable SoftStart Circuitry
 Low Startup Current for OffLine Operation