Production of electronic fake, Electronic Load
Keywords: production of electronic fake load
The electronic fake load made in this paper alternatively replaces the conventional load resistor box, slide varistor, etc., in particular, can set a constant current or constant voltage to the field that cannot be solved in the conventional slide varistor. For generators, AC / DC, DC / DC converters, uninterruptible power supplies (UPS), dry batteries, battery, transformers, chargers, etc. are tested. The maximum fake load power is up to 600W, and the fake load resistance can be adjusted at 30mΩ ~ 14.352kΩ.
I. Basic ideas electronic fake load power devices, generally use the farmers and IGBT tubes that are small in the required control. When they choose, there must be more power than full load, avoiding burnout in use; generating electronic false loads A large amount of calories need to be installed, and the thermal resistance between the power devices and the heat sink should be as small as possible, and the heat dissipation fan can be installed if necessary; the power device of the electronic fake load is very susceptible to parasitic self-excitation oscillation, once the oscillation, Not only the working state is completely changed, but also burn the power devices. Therefore, the anti-parasitic self-excitation oscillation is very important, and it is also a determination factor for making the success of electronic fake loads. This production generates a reference voltage to three op amps, through constant voltage, constant current to implement the basic functions of electronic fake loads. The general principle block diagram is shown in Figure 1. Figure 1 block diagram
Second, the principle of circuit principle As shown in FIG. 2, the basic circuit consists of a constant voltage circuit, a constant current circuit, an overcurrent protection circuit, and a driving circuit, from a portion other than the dashed frame 5 and two multimeters. V = 12V input voltage, after the current limit resistor R1 to the triplet adjustable split base source U1 (TL431), the output reference voltage Vr is 2.5 V by the reference terminal R, and the resistor R1 to the adjustment sliding varistor R6, All the way is supplied with a voltage R2 to provide a voltage, and the other path provides a voltage to the U3C. 1. The constant voltage circuit is shown in Figure 2. When the load end input voltage is increased, the U3A is increasing in phase input voltage. When the phase-transigned person voltage is greater than the inverted input voltage (reference voltage), the U3A outputs a high level, and a pressure drop is generated on the field effect tube Q1, Q2, Q3, Q4, so that the drain D and The voltage Vds between the source S is reduced, thereby achieving constant pressure. 2. The constant current circuit is shown in Figure 2. When the load current is increased, the voltage on R19, R22, R25, R28 increases. That is, the sampling voltage on R18, R21, R24, R27 increases, that is, the U3C inverting input voltage increases, when the U3C inverting input voltage is greater than the same phase input voltage, the U3C outputs low, field effect tube The gate G voltage Vg of Q1, Q2, Q3, Q4 is reduced, Q1, Q2, Q3, Q4 internal resistance RDS increased, and the load current decreases, thereby achieving the purpose of constant current. 3. The overcurrent protection circuit is shown in Figure 2. When the load current is increased, the voltage on R19, R22, R25, R28 increases, that is, the sampling voltage on R18, R21, R24, R27 increases, and the U3B inverting input voltage is increased, but the current continues to increase. When the inverting terminal voltage is greater than the reference voltage (insertion voltage in which the phase end input voltage) set is set, the U3B outputs low level, the field effect tubes Q1, Q2, Q3, the gate G voltage Vg of Q4 are reduced, Q1 The internal resistance RDS of Q2, Q3, Q4 increased, and the load current decreases, thereby playing overcurrent protection. 4. The drive circuit is shown in Figure 2. Q1, Q2, Q3, Q4 use high-power field effect tube IRF540 as a power device, but after multiple pipes, due to the corresponding increase of the pole capacitance and distributed capacitance, the high-frequency characteristics of the amplifier become changed, and the amplifier is easily causing the amplifier. Frequency parasics oscillation. To this end, the parallel compartment is generally not more than 4, and the parasitic oscillating resistance is grounded on the base or gate of the gate. R17, R20, R23, R26 are drive resistors, R18, R21, R24, R27 as sampling voltage resistors, R19, R22, R25, R28 as a current limiting resistance. C9 One end of the field effect tube IRF540 drain, and the other end is grounded for preventing shock.
Third, the circuit tests the electronic false load after production, the test circuit wiring diagram is shown in Figure 2. Dotted frame 5 and two multimeter parts. Wanlian Table 1 Test the power output voltage, multimeter 2 Table 2 Table 2 Power output current, two slip resistors are hit by 50%. When the single-knife double-throw switch J1 is hit at 1, the output voltage of the selected power source is maintained at 12.501V, indicating that the electronic fake load has a constant voltage function. When the single-knife double-throw switch J1 is hit at 2, the output current of the selected power source is maintained at 19.993A, indicating that the electronic fake load has a constant current function. The fixed current mode can be used to test the load adjustment rate of the voltage source and the power supply. Changing the extract position of the sliding resistor R6 can change the preset constant voltage current value. The preset current value of overcurrent protection can be changed by sliding resistor R14. In the figure, the dashed frame 5 is the measured power supply (or other power supply can also be used as a measurement power source), and the V∞ is 15V AC voltage. After the bridge rectifier circuits D1, D2, D3, D4 are rectified, DC is obtained by the capacitor filter. The voltage is regulated by the triplet regulator U2 (ML7812), resulting in a stable + 12V DC voltage.
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