Warm hints: The word in this article is about 971 and reading time is about 10 minutes. Guidance: In the indicator, the most commonly used integrated circuit model of power PWM control circuit is UC3842 or KA3842. The following is a brief introduction to the judgment method of KA3842.
KA3842 Application Note
The KA3842/3843 sequence are excessive overall performance constantfrequency modern-day mode controllers. They are especially designed for Off-Line and DC-to-DC converter functions supplying the dressmaker a priceniceanswer with minimal external components. These integratedcircuits feature a trimmed oscillator for specificobligation cycle control, a temperature compensated reference, highacquire error amplifier, contemporary sensing comparator, and a excessive present day totem pole output ideally proper for driving a power MOSFET. Also covered are protecting facets consisting of enter and reference underneath voltage lockouts every with hysteresis, cycle-by-cycle current limiting, programmable output useless time, and a latch for single pulse metering. These units are on hand in 8-pin dual-in-line ceramic and plastic packagesas nicely as the 14-pin plastic surface mount (SO-14). The SO-14 bundle has separate energy and ground pins for the totem pole output stage. Difference between contributors of this sequence is the under-voltage lockout thresholds. The KA3842as 33 UVLO thresholds of 16 V (on) and 10 V (off), ideally acceptable for off-line converters. The corresponding thresholds for the KA3843 are 8.5 V and 7.9 V.Next
- Trimmed Oscillator Discharge Current for Precise Duty
- Cycle Control
- Current Mode Operation to 500 kHz
- Automatic Feed Forward Compensation
- Latching PWM for Cycle-By-Cycle Current Limiting
- Internally Trimmed Reference with Under voltage Lockout
- High Current Totem Pole Output
- Under voltage Lockout with Hysteresis
- Low Start-Up and Operating Current
- Direct Interface with Motorola SENSEFET Products
KA3842 ELECTRICAL CHARACTERISTICS
- 1. Maximum Package power dissipation limits must be observed.
- 2. Adjust VCC above the Start-Up threshold before setting to 15 V.
- 3. Low duty cycle pulse techniques are used during test to maintain junction temperature as close to ambient as possible. TLOW = 0°C THIGH = +70°C
- 4. This parameter is measured at the latch trip point with VFB = 0 V.
Check KA3842A Pin Voltage
First, check the external components, remove their faults, replace all the damaged components correctly, and then on-line measurement, according to the pin voltage value in the following pictures, judge whether KA3842A is good or bad.
KA3842 Pin Function Description
|1||Compensation||This pin is the Error Amplifier output and is made available for loop compensation.|
|2||Voltage Feedback||This is the inverting input of the Error Amplifier. It is normally connected to the switching power supply output through a resistor divider.|
|3||Current Sense||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 500 kHz is possible.|
|5||Gnd||This pin is the combined control circuitry and power ground (8-pin package only).|
|6||Output||This output directly drives the gate of a power MOSFET. Peak currents up to 1.0 A 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.|
Testing KA3842 With Electric Vehicle Charger
First, remove the switch of the good charger, then add a socket to 3842, and then install a light-emitting diode on the G and S poles of the switch. Because the six legs of 3842 output AC pulse, the light-emitting diode does not need to distinguish polarity.
When testing, insert the 3842 to be tested into the socket, and then connect the charger to the electricity market. If 3842 is good, then the light-emitting diode fire intermittently emits light, which is a fixed frequency.
Although this can only judge whether the 3842 vibration, but it is enough, because another indicator of 3842 is that 8 feet have 5V output, but no 5V output is rare. The worst is still no output. Through practical observation, the frequency increases obviously when testing 3844, and after cutting off the power supply, the flicker of the light emitting diode is stronger than that of 3842. When testing 3843, the flicker is basically the same as that of 3842.
Note: If the measured 3842 does not oscillate, that is, the light emitting diode does not flicker, the 7 feet of 3842 should be put on the ground, that is, the 7 feet and 5 feet of 3842 socket should be short-circuited, and then the 3842 socket should be inserted. That is because when 3842 does not oscillate, the power supply voltage of the seven legs of 3842 will be very high, and the 100 UF capacitor connected by the seven legs will store electricity. If not discharged, insert 3842. Excessive voltage will break down 3842.
It should be noted that the source pole of the switch tube of the power supply, S pole, is usually connected with a small resistance value and a high power resistance as the overcurrent protection detection resistance. The resistance value of this resistance is generally between 0.2 and 0.6. If it is larger than this value, the phenomenon of no load will occur, that is, the sub-extreme voltage is low.
Because the working voltage and output power of UC3842 and KA3842 are far from those of UC3843 and KA3843, the starting and closing voltage of 3842 and 3843 series are also quite different. The start-up voltage of the former is 16V and the turn-off voltage is 10V; the start-up voltage of the latter is 8.5V and the turn-off voltage is 7.6V. These two series of IC can not be directly replaced.