
UC1861-1868
UC2861-2868
UC3861-3868
SLUS289 - OCTOBER 1998
FEATURES
Controls Zero Current Switched (ZCS)
or Zero Voltage Switched (ZVS)
Quasi-Resonant Converters
Zero-Crossing Terminated One-Shot
Timer
Precision 1%, Soft-Started 5V
Reference
Programmable Restart Delay
Following Fault
Voltage-Controlled Oscillator (VCO)
with Programmable Minimum and
Maximum Frequencies from 10kHz to
1MHz
Low Start-Up Current (150
μ
A typical)
Dual 1 Amp Peak FET Drivers
UVLO Option for Off-Line or DC/DC
Applications
DESCRIPTION
The UC1861-1868 family of ICs is optimized for the control of Zero Current
Switched and Zero Voltage Switched quasi-resonant converters. Differ-
ences between members of this device family result from the various com-
binations of UVLO thresholds and output options. Additionally, the
one-shot pulse steering logic is configured to program either on-time for
ZCS systems (UC1865-1868), or off-time for ZVS applications (UC1861-
1864).
The primary control blocks implemented include an error amplifier to com-
pensate the overall system loop and to drive a voltage controlled oscillator
(VCO), featuring programmable minimum and maximum frequencies. Trig-
gered by the VCO, the one-shot generates pulses of a programmed maxi-
mum width, which can be modulated by the Zero Detection comparator.
This circuit facilitates “true” zero current or voltage switching over various
line, load, and temperature changes, and is also able to accommodate the
resonant components' initial tolerances.
Under-Voltage Lockout is incorporated to facilitate safe starts upon
power-up. The supply current during the under-voltage lockout period is
typically less than 150
μ
A, and the outputs are actively forced to the low
state.
(continued)
BLOCK DIAGRAM
Resonant-Mode Power Supply Controllers
UDG-92018
Pin numbers refer to the J and N packages.
application
INFO
available
Device
UVLO
Outputs
“Fixed”
1861
16.5/10.5
Alternating
Off Time
1862
16.5/10.5
Parallel
Off Time
1863
36014
Alternating
Off Time
1864
36014
Parallel
Off Time
1865
16.5/10.5
Alternating
On Time
1866
16.5/10.5
Parallel
On Time
1867
36014
Alternating
On Time
1868
36014
Parallel
On Time