TheUC3827familyofcontrollerdevicesprovidesanintegratedcontrolsolution forcascadedbuckandpush-pullconverters.These convertersareknown ascurrentfedorvoltagefedpush-pullconvertersandareideallysuitedfor multipleoutputand/orhighvoltageoutputapplications.Inbothcurrentfed andvoltagefedmodes,thepush-pullswitchesaredrivenat50%nominal dutycyclesandatonehalftheswitchingfrequencyofthebuckstage.In thecurrentfedmode,thetwoswitchesaredrivenwithaspecifiedover-lapperiodtopreventringingandvoltagestressonthedevices. Inthevoltage fed mode, the two switches are driven with a specified gap time between the switches to prevent shorting the transformer across the energy storage capacitor and to prohibit excessive currents flowing through the devices.
The converter's output voltage is regulated by pulse width modulation of thebuckswitch.TheUC3827containscompleteprotectionandPWMcontrolfunctionsforthebuckconverter.Easycontrolofthefloatingswitchis accomplished by the floating drive circuitry. The gate drive waveform is level shifted to support an input voltage up to 72 VDC.
The UC3827 can be set up in traditional voltage mode controlusinginputvoltagefeedforwardtechniqueorin currentmodecontrol. Usingcurrentmodecontrolprevents potentialcoresaturationofthepush-pulltransformerdue tomismatchesintimingandincomponenttolerances. Withaveragecurrentmodecontrol,precisecontrolofthe inductor current feeding the push-pull stage is possible withoutthenoisesensitivityassociatedwithpeakcurrent mode control. The UC3827 average current mode loop canalsobeconnectedinparallelwiththevoltageregulation loop to assist only in fault conditions.
Other valuable features of the UC3827 include bidirectional synchronization capability, user programmableoverlaptime(UC3827-1),userprogrammablegap time(UC3827-2),ahighbandwidthdifferentialcurrent sense amplifier, and soft start circuitry.
Feature
- Ideal for Multiple Output and/or High Voltage Output Voltage Converters
- Up to 500 kHz Operation
- High Voltage, High Current Floating Driver for Buck Converter Stage
- UC3827-1 Current Fed Controller has Push-Pull Drivers with Overlapping Conduction Periods
- UC3827-2 Voltage Fed Controller has Push-Pull Drivers with Nonoverlapping Conduction Periods
- Average Current Mode, Peak Current Mode or Voltage Mode with Input Voltage Feedforward Control for Buck Power Stage
- Wide Bandwidth, Low Offset, Differential Current Sense Amplifier
- Precise Short Circuit Current Control
TheUC3827familyofcontrollerdevicesprovidesanintegratedcontrolsolution forcascadedbuckandpush-pullconverters.These convertersareknown ascurrentfedorvoltagefedpush-pullconvertersandareideallysuitedfor multipleoutputand/orhighvoltageoutputapplications.Inbothcurrentfed andvoltagefedmodes,thepush-pullswitchesaredrivenat50%nominal dutycyclesandatonehalftheswitchingfrequencyofthebuckstage.In thecurrentfedmode,thetwoswitchesaredrivenwithaspecifiedover-lapperiodtopreventringingandvoltagestressonthedevices. Inthevoltage fed mode, the two switches are driven with a specified gap time between the switches to prevent shorting the transformer across the energy storage capacitor and to prohibit excessive currents flowing through the devices.
The converter's output voltage is regulated by pulse width modulation of thebuckswitch.TheUC3827containscompleteprotectionandPWMcontrolfunctionsforthebuckconverter.Easycontrolofthefloatingswitchis accomplished by the floating drive circuitry. The gate drive waveform is level shifted to support an input voltage up to 72 VDC.
The UC3827 can be set up in traditional voltage mode controlusinginputvoltagefeedforwardtechniqueorin currentmodecontrol. Usingcurrentmodecontrolprevents potentialcoresaturationofthepush-pulltransformerdue tomismatchesintimingandincomponenttolerances. Withaveragecurrentmodecontrol,precisecontrolofthe inductor current feeding the push-pull stage is possible withoutthenoisesensitivityassociatedwithpeakcurrent mode control. The UC3827 average current mode loop canalsobeconnectedinparallelwiththevoltageregulation loop to assist only in fault conditions.
Other valuable features of the UC3827 include bidirectional synchronization capability, user programmableoverlaptime(UC3827-1),userprogrammablegap time(UC3827-2),ahighbandwidthdifferentialcurrent sense amplifier, and soft start circuitry.
