Development of Hybrid Microcircuit H2705T DC / DC Converter
Abstract: The development process H2705T thick film integrated DC / DC converter, discussed in detail the working principle of the circuit, component selection, the key solution to the problem, and reliability design and so on.
Key words: DC / DC converter; thick film integration; hybrid circuit
Be
1 Introduction
Mixed microcircuit H2705T DC / DC converter is a new integrated component developed for a wireless height table system for a project. The main features of the product are as follows:
1) Adopt advanced thick film mixed integrated circuit process, mature DC / DC DC transform technology and strictly improved production management system to make circuit structure and line design scientific reasonable, stable quality performance;
2) High switching frequency, transformation, rectification, and filter, high efficiency, small ripple interference, multi-channel output, split control, micro power consumption
3) a wide input range (18 ~ 36V), and with undervoltage, overvoltage, overcurrent protection, and dead-time control function;
4) Full metal electromagnetic shield, small volume structure design;
5) Standard all metal modular packaging, easy to install fixation, strong heat dissipation performance, good shielding performance, small noise interference.
2 Circuit principle and main technical indicators
2.1 circuit schematic
The circuit schematic is shown in Figure 1. H2705T, output ± 5V and + 8V, power is 20W. The product is divided into three units, each unit provides all the way, the same components, except that some circuit parameters are different. The following is an example of + 5V unit, and the working principle is explained.
Figure 1 H2705T circuit schematic
This core is a single-ended circuit a pulse width modulator UC1843, maximum operating frequency of 500kHz, frequency stability of 0.2%, the starting voltage is 7.8V, the maximum operating voltage of 30V, over-current, under-voltage protection function and dead time control . UC1843 Each pin function is shown in Table 1.
Table 1 UC1843 pin function
Pin
Symbol
Function
1
VPAM
compensate
2
Vcon
Feedback control
3
Icon
Current limiting detection
4
RC
Oscillation component
5
GND
land
6
OUT
Modulation pulse output
Seduce
VCC
power supply
8
VREF
The pin 7 of the reference voltage integrated block IC103 (UC1843) is the power supply. After powering, Vin charges the capacitor C106 via R114. When the pin 7 voltage reaches the start voltage, the modulator is activated, and the pin 6 outputs the first serial wide pulse, and the V101 gate is actuated, and the transformer T10 is pushed, and the VIN DC voltage shift Two channels of AC pulse voltages. One way is rectified by D103, and power is powered by the foot 7 of the integrated block IC103; the other route is rectified, the D101 continuation, the L101, C101, C102 are filtered, and the power output is achieved.
In the regulator ring, R101 and R102 are quarantined to the output voltage sample; IC 101 is compared to the output sampling, and converts the comparison error voltage into an error current, acting on the internal light emitting diode of the photocoupler IC 102, which is photocoupled, and conversion For the error voltage, the foot 2 passed to IC103 via R104. The internal IC103 outputs a pulse width according to the error voltage, the correction foot 6 outputs the pulse width, and finally realizes the output regulation.
In the protection circuit, the main circuit is currently sampled by R112, and passing the foot 3 of IC 103 through R110, an overcurrent protection function is implemented. R107, R111 provides a foot 3 overcurrent protection reference level; Vin acts on the V1 base in D1, once there is an overvoltage, V1 will turn off the pin 7 voltage of the integrated blocks IC103 ~ 303 (UC1843), stop the full circuit operation To achieve overvoltage protection.
Further, the high and low level of the control terminal (CNT) acts on the base of V1, and implements the external circuit level control function (i.e., the CNT remote control function). When the CNT is at a high or floating, the base of V1 is high, V1 is turned on, and the pin 7 voltage of the integrated blocks Ic103 to 303 (UC1843) is turned on, and the full circuit is stopped. Conversely, when the CNT is at a low or -vin, V1 is not turned on, and the circuit output is normal.
Therefore, the level control function of the CNT is:
- High or floating, no output;
- Low level or pick -VIN, the full circuit is normal output.
2.2 Main technical indicators
The main technical indicators are shown in Table 2.
Table 2 H2705T technical finger standard
Parameter
Minimum
Maximum
condition
The output voltage
VO1 / V
4.8
5.2
IO1 = 3 a
The output voltage
VO2 / V
7.68
8.32
IO2 = 250 mA
The output voltage
VO3 / V
-4.8
-5.2
IO3 = 200 mA
Ripple
VP_P / MV
Be
30
Full load
Voltage adjustment rate
Sv /%
Be
0.3
IO full load, VIN = 18 ~ 36 V
Hello Elena
Si /%
Be
0.4
VIN = 27 V, IO from 0 - full load
efficiency
η /%
80
-
Full load Note: Even if there is another regulation, the temperature of the environment is - 55 ≤ Ta ≤ 85 ° C
Be
3 development process
3.1 circuit parameter selection
The selection of circuit parameters is mainly based on calculation data and experimental data.
Select UC1843 pulse width modulator, mainly on account of the device belonging to the single-ended current type PWM modulator, having a small number of pins, the peripheral circuit is simple, easy installation and commissioning, excellent performance, etc., to meet the specific volume of the hybrid integrated circuit Require.
Start resistance, capacitance value, to consider starting the required energy, time, and input voltage range, ensuring reliable start, and has been obtained by multiple experiments.
Oscillation resistors, capacitors, determine the operating frequency of the entire circuit, belonging to key components. Among them, the capacitor uses a high-precision NPO capacitor with a high stability slurry with a resistance. The minimum resistance is 1kΩ, the maximum capacitance is 0.1μF, and the frequency is f ≈1.8 / rc. In order to reduce the volume, the frequency is as low as 400 kHz. For these factors, the value of the resistance capacitor can be obtained.
Magnetic materials are based on high frequency, efficient, small volume, high-power requirements, and have a certain power margin, and output different cores.
In the regulator loop, the reference voltage of the IC 102 is 2.495V, and the sampling current is obtained according to the experimental data, and the two factors determine the resistance of R101 and R102.
The overcurrent protects the value of the sampling resistance, depending on the design efficiency, the main circuit current is converted by the output power, and the appropriate overflow point is set, and the sample resistance value is calculated. In order to improve efficiency, the value of the resistance can be reduced, and accurate protection is achieved using the overflow preset level (determined by R107, R111).
According to the basis for the transformer turns, the transformation efficiency is the input, the output voltage, and the third is the modulator's safe working pulse width range. The lacquered wire lines are mainly based on flow through power or current, and generally calculate the 2.5A / mm2.
Entering undervoltage protection is determined by the transformer's own turns.
3.2 Full Circuit Plane Thick Filmization and Mixed Integration
Many components of this product, a total of resistor 78, an integrated circuit 9, the transistor 4, the diode 13, capacitor 31, inductors 3, the transformer 3. The product volume 51mm × 51mm × 13 mm. The electrical resistance is connected with the conduction band to be sintered with a planar thick film, and the resistance resistance, accuracy, power, and stability are guaranteed. Integrated circuits, triodes, diodes, and capacitors use small magnetic ring around surface mount metaders, inductance, and transformers.
The application of thick film technology reduces circuit volume, improves the stability of the circuit, enhances reliability.
3.3 Solution of key issues
1) volume, ripple, thermal distribution and reliability
Since the secondary integration is carried out on a standard package substrate, its effective area. 1881.47mm × 47mm, while the entire circuit consists of nearly 140 yuan devices, overall indicators, especially ripple noise and reliability indicators. The planeization of the entire circuit has become a key issue, which has a big difficulty, mainly taken the following measures.
(1) In a planar layout of the process, considering the characteristics of the line, process characteristics, requirements for mass production, and to avoid the conduction band of the secondary media layout; Component also consider the size, layout, calculation precision power resistors, appropriate Develop an area of the resistance tape, minimize the area of the layout area, reasonably distribute the plane and spatial layout of the component, and ultimately utilize each of the area of the substrate, and finally complete the overall layout.
(2) Large, small current ground, to be bracket, concentrate, and the components are derived in order to avoid mutual interference; close to the output terminal sample, ensure the output regulator accuracy and load characteristics.
(3) Try to ensure that high-power fever is closely to the substrate or housing, reasonably distribute the heat source, avoiding the concentration of the heat source, local overheating, leaving a hidden danger.
Due to strict accordance with the above measures, the ripple noise and reliability indicators have reached the requirements.
2) Circuit debugging problem
After the DC / DC circuit production process is completed, some technical indicators of some products do not meet the design requirements, which requires circuit debugging, mainly through the fine-tuning of individual components parameters, correcting product technical parameters, and achieves design requirements. It became a qualified product.
The circuit debugging technology requires high, complex debugging process, and the adjustment of individual indicators often affects other indicators. Therefore, try to do accurate, concise, avoid duplicate operation, resulting in product damage.
In order to reduce and simplify circuit debugging, in the production process, it is necessary to operate according to process, avoiding film formation, welding, and wiring process. And add inspection and test points to eliminate low-level errors. Develop a strict detailed debugging technical rules, for different situations, give debug programs.
4 conclusion
This product uses advanced thick film mixed integrated circuit technology, circuit and structural design scientific and reasonable, and the circuit performance is stable. It is expected to be 105h according to calculation, and is in the domestic advanced level.
The development of the thick film mixed microcircuit power module H2705T has promoted the progress of the thick film mixed integrated circuit technology, broaden the application of thick film mixed integrated circuit technology, which provides a reference for the development of special high-density high-power circuitry. Technology area
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