2 Stück “HIGH PERFORMANCE CURRENT MODE PWM CONTROLLER”-Bausteine vom Typ UC3842 von renommierten Hersteller “ST-Electronics ”. Die ICs werden in der Schaltnetzteile als Kontroller eingesetzt.
Auszuge aus dem Datenblatt:
FEATURES
■ TRIMMED OSCILLATOR DISCHARGE CURRENT
■ CURRENT MODE OPERATION TO 500kHz AUTOMATIC FEED FORWARD COMPENSATION
■ LATCHING PWM FOR CYCLE-BY-CYCLE CURRENT LIMITING
■ INTERNALLY TRIMMED REFERENCE WITH UNDERVOLTAGE LOCKOUT
■ HIGH CURRENT TOTEM POLE OUTPUT UNDERVOLTAGE LOCKOUT WITH HYSTERESIS
■ LOW START-UP CURRENT (< 0.5mA) DOUBLE PULSE SUPPRESSION
DESCRIPTION
The UC384xA family of control ICs provides the necessary features to implement off-line or DC to DC fixed frequency current mode control schemes with a minimal external parts count. Internally implemented circuits include a trimmed oscillator for precise DUTY CYCLE CONTROL under voltage lockout featuring start-up current less than 0.5mA, a precision reference trimmed for accuracy at the error amp input, logic to insure latched operation, a PWM comparator which also provides current limit control, and a totem pole output stage designed to source or sink high peak current. The output stage, suitable for driving N-Channel MOSFETs, is low in the off-state.
Differences between members of this family are the under-voltage lockout thresholds and maximum duty cycle ranges. The UC3842A and UC3844A have UVLO thresholds of 16V (on) and 10V (off), ideally suited off-line applications. The corresponding thresholds for the UC3843A and UC3845A are 8.5 V and 7.9V. The UC3842A and UC3843A can operate to duty cycles approaching 100%. A range of the zero to < 50 % is obtained by the UC3844A and UC3845A by the addition of an internal toggle flip flop which blanks the output off every other clock cycle.
Absolute Maximum Ratings:
Symbol |
Parameter |
Value |
Unit |
Vi |
Supply Voltage (low impedance source) |
30 |
V |
Vi |
Supply Voltage (Ii < 30mA) |
Self Limiting |
|
IO |
Output Current |
+/-1 |
A |
EO |
Output Energy (capacitive load) |
5 |
µJ |
|
Analog Inputs (pins 2, 3) |
– 0.3 to 5.5 |
V |
|
Error Amplifier Output Sink Current |
10 |
mA |
Ptot |
Power Dissipation at Tamb ≤ 25 °C (DIP-8) |
1.25 |
W |
Tstg |
Storage Temperature Range |
– 65 to 150 |
C |
TJ |
Junction Operating Temperature |
– 40 to 150 |
°C |
* All voltages are with respect to pin 5, all currents are positive into the specified terminal.
N° Pin Function
1 COMP: This pin is the Error Amplifier output and is made available for loop compensation.
2 VFB: This is the inverting input of the Error Amplifier. It is normally connected to the switching power supply output through a resistor divider.
3 ISENSE: A voltage proportional to inductor current is connected to this input. The PWM uses this information to terminate the output switch conduction.
4 RT/CT: The oscillator frequency and maximum Output duty cycle are programmed by connecting resistor RT to Vref and capacitor CT to ground. Operation to 500kHz is possible.
5 GROUND: This pin is the combined control circuitry and power ground.
6 OUTPUT: This output directly drives the gate of a power MOSFET. Peak currents up to 1A are sourced and sunk by this pin.
7 VCC: This pin is the positive supply of the control IC.
8 Vref: This is the reference output. It provides charging current for capacitor CT through resistor RT.
Die ICs sind neu und unbenutzt.
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