First, assess design indicators
1. Enter parameters: Input voltage size, communication or DC, phase, frequency, etc.
• The international voltage level has single phase 120VAC, 220VAC, 230VAC, etc. The internationally used AC voltage range is 85 to 265V. It is generally included in the input voltage rating and its variation range;
• 3KW The following power is used in single-phase input, and the three-phase input is selected or more.
• Industrial electrical frequency is typically 50Hz or 60Hz, aerospace power supply, ship electricity for 400 Hz.
• There is a Power Factor and a Total Harmonics Distortion indicator
2. Output parameters: Output power, output voltage, output current, ripple, regulator (steady stream) accuracy, adjustment rate, dynamic characteristics (stable time: settling time), power supply start time and hold time.
• Output voltage: Rated value + adjustment range. The upper limit of the output voltage should be as close as possible to avoid unnecessary excessive design margins.
• Output current: Rated value + overload multiple. There is also a steady current requirement to designate the adjustment range. Some power is not allowed to be empty, so the lower limit should also be specified.
• Regulative steady current accuracy: influencing factors include input voltage adjustment rate, load adjustment rate, and aggressive deviation. The reference source accuracy, the accuracy of the detection element, and the accuracy of op amps in the control circuit have a great influence on the regulator.
3. Efficiency: The ratio of the rated input voltage and the rated output voltage and the rated output current and the value of the input active power.
loss:
Loss related to switching frequency: switching loss, iron loss of magnetic components, loss of absorption circuits.
Tong-state loss in the circuit: Tong-state loss of switching devices, copper loss of magnetic components, line loss. This part of the loss depends on the current.
Other loss: Control circuitry, the efficiency of the power supply having a higher output voltage higher than the output voltage is lower than the output voltage. The high output voltage of the power efficiency can reach 90% to 95% efficiency. The efficiency of high-power circuits can be higher than the efficiency of small power circuits.
4. Voltage adjustment rate and load adjustment rate
• Voltage (source) adjustment rate: The power supply adjustment is usually caused by the input voltage variation in the rated load condition. As shown in the following formula:
Vo (MAX) -VO (MIN) / VO (NORMAL)
Alternatively, the amount of deviation of its output voltage must be within the lower limit of the upper limit of the output voltage, that is, the upper limit of the upper limit of the output voltage is absolute.
• Load adjustment: The ability of the load adjustment rate is defined as the switching power supply to the output load current change, providing its stable output voltage. Or under the output load current change, its output voltage deviation must not exceed the upper and lower limit absolute values.
Test method: The power supply to be tested is measured after the normal input voltage and load condition, the output voltage value under normal load is measured, and the light load (MIN) is measured, and its output voltage value under load (MAX) load is (respectively. VMAX and VMIN), the load adjustment rate is usually percentage of its output voltage deviation by the load current change under normal fixed input voltage, as shown in the following formula:
V0 (MAX) -V0 (MIN) / V0 (Normal)
5. Dynamic Characteristics: Changes in Output Voltage Time when load mutation
• Switching power supply ensures that its output voltage is stable by the feedback control loop, and actually, the feedback control circuit has a certain bandwidth, thus limiting the reaction of the power supply to the load current change, which may cause unstable, out of control or oscillation of the switching power supply. . In fact, the load current at the time of power supply is also dynamically changed, so dynamic load test is extremely important to the power supply.
• The programmable electronic load can be used to simulate the most harsh load in the actual operation of the power supply, such as the rapid increase in load current, the slope, cycle, etc., if the power supply is in a harsh load, it is still possible to maintain a stable output. The voltage does not generate overshoot or the undershoot situation, otherwise the power output voltage exceeds the load element (such as the TTL circuit therefor, the transient voltage should be between 4.75V to 5.25V, the TTL logic circuit is not caused. The malfunctional action) Work range.
6. Power Start Time (SET-UP TIME) and Hold Time (HOLD-UP TIME)
• Start time: Refers to the time from the input power supply to its output voltage to rise to the voltage regulator range, with a power supply supply of 5V as an example, the start-up time starts from the power supply to the output voltage of 4.75 The time from V.
• Holding time: The power source starts from the cutting input power supply to its output voltage to the outside of the voltage regulator, with a power supply supply of 5V as an example, the holding time is from the shutdown to the output voltage below 4.75V. Time, a general value of 10-20 ms to avoid the effect of load operation due to short-time voltage disruption (half or a grid voltage cycle) due to short-time voltage interrupts (half or a grid voltage cycle).
7. Cross-adjustment rate of multiple output power supplies:
• Multi-output also needs to consider cross regulation.
What is a cross-adjustment rate?
When the output load changes, the change range of the output voltage is output.
Conventional approach to improving cross-adjustment rate: Adjustment
Such as: small power multi-channel output flyback
Input voltage range. ... ... ... ... .90 ~ 264VAC, 120-370VDC
Input Current. ... ... ... ... ... ..2.0A / 115V 1.1A / 230V, input frequency: 47 ~ 63Hz
electric shock. ... ... ... ... ... .. Cold boot current 20A / 115V 40A / 230V
Leakage current. ... ... ... ... ... ... 2mA / 240VAC
Output voltage regulation range. ... ... ... CH1: -5 ~ 10%
Voltage adjustment rate. ... ... ... ... ... CH1: "1%, CH2:" 1%
Hello Elena. ... ... ... ... ... CH1: "3%, CH2 / 3:" 4-8%
Overload protection. ... ... ... ... ... ..105% ~ 150% protection type: current limit, automatic recovery
Overvoltage protection. ... ... ... ... ... ..115-135% CH1 rated output voltage
Temperature Coefficient. ... ... ... ... ... .. ± 0.03% ° C (0 ~ 50 ° C)
Start, rise, hold time. ... .. 800ms, 60ms, 20ms
Seismic. ... ... ... ... ... ... .10 ~ 500Hz, 2G three axis 10min./1 cycle, 1 hour per axis
Pressure resistance. ... ... ... ... ... ... Input - Output: 3kVAC, Enter - Shell: 1.5kVAC,
Output - shell: 0.5kvac 1 minute
Insulation resistance. ... ... ... ... .. Enter - Output, Input - Ground, Output - Land 500VDC / 100M OHMS
Work temperature, humidity. ... ... ... ..- 10 ° C ~ 60 ° C, 20% ~ 90% RH (0-45 ° C / 100%, - 10 ° C / 80%, 60 ° C / 60% load)
Storage temperature, humidity. ... ... ... ..- 20 ° C ~ 85 ° C, 10% ~ 95RH
Dimensions. ... ... ... ... ... ..199 * 99 * 50mm case 916A
weight. ... ... ... ... ... ... ... 0.6kg; 20PCS / 13KG / 1.17CUFT
safety standard. ... ... ... ... ... .. Meet UL1310, TUV EN60950 requirements
EMC / harmonic standard. ... ... ... ... .. meeting EN55022 Class B / A, EN61000-3-2, 3 EN61000-4-2, 3, 4, 5, 6, 8, 11, ENV50204
Second, choose the appropriate main circuit topology (AC-DC)
Basic principle: power level, cost, efficiency, size
• When the power is below 75 watts, the input side harmonic is generally not limited. Therefore, the circuit is simple and cost-effective. Japan is limited to 50W below. The lighting requires higher, 25W.
• Circuit power is in a general power supply of more than 75 watts. The power supply requirements meet harmonics IEC61000-3-2. Generally, there is a power factor correction, therefore most of the two-stage solutions are used.
Boost Pfc Flyback; "100W
Boost Pfc Half Bridge 100W "" 500W
• When bigger power (more than 500 watts), a half bridge or full bridge can be used. If the cost requires strict, select the half-bridge and the power is large. The push-pull circuit is usually used in the case where the power is large and the input voltage is low.
• When the power is less than 20W, due to the loss of the power supply, the positive loss is small (current small), and therefore selects a simple circuit topology. Simplified solution is selected in terms of magnetic components, switches, and drive losses. Such as DCM Flyback.
• When the loss of the power supply is mainly time (high power, or low voltage large current), it is necessary to consider a solution capable of reducing pondens state loss. For example: synchronous rectification, multi-stage conversion, parallel, mixed topology, etc.
Editor: lyn, read full article, original title: power, how to choose the right main circuit topology?
Article Source: [Micro Signal: A1411464185, WeChat public number: strongerhuang] Welcome to add attention! Please indicate the source of the article.
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