control voltage increases

[wei8xlaiyou]

A new tracking SCR DC Power Supply
[Date :2006-12-22] Source: Electronic Engineers of: Sung Ying Liu Huayi [font: medium and small]

1 Introduction
the information age, BP machine has become a popular communication tool. At present, the total BP station transmitting equipment, machines are used imported equipment, the output voltage is 13.8V, current of 15 ~ 20A. SCR power without some imports,new chanel bags, while China's power grid fluctuations, for the design of this low-cost power supply. Feedback to adjust the design in the series based on the type of power supply fitted with SCR phase control device, with the regulator to control the SCR trigger voltage drop across the conduction angle, adjust the tube to maintain constant pressure drop, which design of high power DC power supply tracking. The power supply limits the power regulator to achieve high power.
the power supply mainly by single-phase half-controlled bridge rectifier filter, linear voltage regulators and control aspects of SCR phase composition, and to install the over-current protection, short circuit protection, thermal protection device and display parts. In the 220V ± 15% mains voltage fluctuations, the output voltage 13.8V, output current up to 20A. As a result of SCR phase control technology, can limit the voltage drop across the regulator is about 3V power consumption less than 40W, improved power efficiency.
when the output current exceeds 20A, the current limiting can reduce the output current. If the output short circuit, output short circuit protection thyristor blocking off the signal. Adjust the tube temperature higher than 60 ℃ start fans, when the temperature is below 40 ℃ fan off, the temperature higher than 80 ℃, off SCR. The SCR trigger with integrated power supply, dual operational amplifier and regulator with temperature compensation for the reference, and with a three-terminal regulator as an auxiliary power supply, to achieve a high precision.
2 specific circuit
circuit block diagram shown in Figure 1.
Select the way the circuit
half controlled rectifier bridge, lower the cost. High power or high current power supply, generally use the L-C filter circuit. However, the high current filter reactor bulky, heavy weight, the price is expensive, so the design of the power supply is still using a large capacitor filter. Some still use a linear regulator adjustable voltage regulator series feedback principle to form a closed loop feedback system. Include: the regulator, sampling circuit, voltage reference, error amplifier comparison. As the power supply output current 20A, current large, therefore, reduce the regulator for the power, in parallel form, in the power supply,cellular cellular pocket, adjust the effective two high-power transistors in parallel, so that current flows through each tube is about 10A . Thus,louis vuitton monogram bag, each tube is not greater than the power consumption of 40W, the regulator reduces power consumption. Collector current of transistor 10A or so, so high-power transistor should be used to select β = 40 ~ 50, so that base current should be up to 2 × 0.3A,buy designer coach bags, or 600mA. Integrated operational amplifier is usually only a few dozen mA output current level can not be compared to the output amplifier to drive the regulator directly, so comparing the output of amplifier circuit and adjustment between the base tube, add promotion level, this Department to select a small power transistor, constitute a form of composite pipe. Startup resistor Rc take 2k. Vibration capacitance C obtain 10μF.
in the regulator circuit, the reference is a reference work of the regulator system, the regulator's ultimate effect depends on the reference level. Therefore, the power supply, the choice of properties with temperature compensation of silicon 2CW234 series regulator as a reference source, and select the stable voltage of 6.4V. By the characteristics of a good three-terminal integrated voltage regulator power supply, current limiting resistors precision metal film resistors R (temperature coefficient of about ± 1 × 10-5 / ℃). In order to reduce the noise, the regulator packaged in a small container of oil Sheng, noise performance will be significantly improved.
voltage sample shown in Figure 2. Will adjust the tubes were set - emitter voltage by the resistor divider, and after the partial pressure emitter voltage comparison amplifier through a resistor into the inverting terminal; sampling circuit in the collector voltage of a regulator in series, management decided to adjust the tube by the pressure drop. Select here to 3.3V. Collector voltage regulator and voltage value minus the partial pressure into the amplifier with the phase-side comparison. To ensure the precision of sampling should be made set - completely symmetrical emitter sense resistor, and select the better temperature characteristics, the same type of precision metal film resistors. Comparison of the amplifier and connected by an integrated amplifier and negative feedback.
that R1 = R3, R2 = R4; set point pressure coefficient n = R2 / (R1 + R2); integrated operational amplifier output Uo; amplification coefficient K; adjustment tube collector voltage UC; emitter voltage regulator UE; A point voltage UA; B point voltage UB; are:
pressure drop increases when the regulator, UcE increased, so that Uo increases, the trigger control voltage Ub increases, while the integration is the negative-type flip-flop KJ785: control voltage increases, the conduction angle decreases. Therefore, the trigger pulse after the shift, the rectifier output decreases.
SCR regulator as the work of the first step, the output voltage changes are caused by changes in conduction angle determined. It is in the phase adjustment control section changes in pressure drop to change the SCR conduction angle, thus changing the rectifier filter circuit output voltage, will adjust the pressure drop maintained at about 3V. The power supply, the use of KJ785 phase thyristor trigger circuit. Because as a power supply products, should strive to achieve the same function under the premise, the device performance, the circuit is simple, easy implementation. The trigger circuit can output a 180-degree difference between the two trigger pulses can range from 0 to 180 degree phase shift, can be used to control the single-phase, two-way thyristor and transistor.
KJ785 storage by the synchronous detection circuit, reference power, sawtooth wave forming circuit, phase voltage and the sawtooth comprehensive comparison of logic control circuit and power amplifier components. 9 foot ramp slope determined by the 10-pin external resistor and external capacitor. External capacitor pulse width determined by the feet, do not take the capacitor, the pulse width determined by the internal capacitance of about 30μs.
KJ785 only single power supply, trigger circuit for the negative, that is, phase voltage increases, conduction angle decreases. Synchronization input voltage from 5 feet, can be directly taken from the grid voltage and current limiting resistor to take power step-down voltage × 103Ω, transformer-isolated input can be applied simultaneously. 7,6 pin provides pulse train and pulse control end the blockade.
the pin functions shown in Table 1.
As the power supply is power supply, there is greater heat transformer, rectifier diode, thyristor, integrated voltage regulator and, more importantly, the regulator is a high-power transistors, heat larger. Therefore, the power supply, the use of fan air, choose cheap, good thermal performance component AD590, to adjust the tube installed in the heat sink. When the temperature reaches about 60 ℃ when the cooling fan starts when the temperature dropped to about 40 ℃, turn off the fan. When the temperature is as high as 85 ℃, sent to the SCR trigger circuit block signals off SCR, then turn off the circuit to prevent overheating damage to the regulator.
circuit shown in Figure 3.
AD590's external features: 0 ℃, its current is 273μA; temperature rise per 1 ℃, current increases 1μA; temperature drop per 1 ℃, current decreases 1μA; operating temperature of -50 ℃ ~ +150 ℃; in order to avoid comparator action or malfunction frequently, select hysteresis width of 1V.
take R = 40kΩ; choose an integrated amplifier and power supply from a single +5 V supply, the partial pressure obtained by CW78M15.
when the set temperature of 65 ℃
comparator reference voltage is EmH, are:
;
; EmL = 15V-(273 +40) μF × 40k = 1.48V;
take R = 40kΩ; choose an integrated amplifier and power supply from a single +5 V supply, the partial pressure obtained by CW78M15.
when the set temperature of 65 ℃
comparator reference voltage is EmH, are:
; EmH = 15V-(273 +65) μF × 40k = 2.48V
; EmH = Er × Rf / (Ri + Rf) + UoH × Ri /
; (Ri + **)
; = * Ei (1-a) 5
; = 1.48V
set temperature of 40 ℃, the comparator reference voltage is EmL, there
check: R1 = 2k; Rf = 10k
check:
So: When the temperature is 61 ℃, start the fan; when reduced to 40 ℃, shut down the fan. When adjusting the tube temperature of about 80 ℃, the comparator output zero level, the blockade SCR, and then turn off the circuit.
the power supply, the short-circuit protection function of the output voltage is detected 2s delay after less than 2V and when to determine the short circuit. SCR blocking signals sent off, the shutdown circuit to prevent damage to the device.
limiting the role of protection when the load current exceeds 20A, the reduced transistor base current, the output current decreases.
3 Conclusion
The new tracking
SCR DC power supply, low cost, better performance, higher precision, the launch pad for BP machine to use. Output voltage range up to 12V to 15V, current up to 20A. Part of the power phase control features, which both SCR and the advantages of series feedback regulator to overcome the traditional series feedback to adjust the adjustable power supply too much power tube defects.