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Power supply circuit design brief
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About 1 circuit Power supply schematic diagram shown in Figure 1. Among them, the core component is the LM338, it is a high-current adjustable voltage regulator IC, pin arrangement shown in Figure. The integrated circuit in connection with the general, the output voltage range is 1.2 ~ 37V. In order to further broaden its range of output voltage, the circuit is a circuit of its traditional use some improvements. Is briefly as follows: LM338 requires input and output voltage difference can not exceed the maximum 40V, which limits its maximum output voltage. When the power supply output voltage is low, the current is large, all power consumed in the LM338, causing severe fever integrated circuits. To solve this problem, the design of the power supply, input voltage to the LM338 adjustable segments. Controlled by the switch K1-2 JI ~ J9 these nine relay will switch to a different AC voltage input bridge rectifier, the rectified by high and low DC voltage input to the LM338, so to reduce the input of the regulator block voltage and the switch K1-1 synchronous switching LM338 adjust the partial pressure of end resistance to adjust the reference voltage changing the output voltage of 5V to the laws of each file change. As a LM338 input and output voltage difference is limited to a smaller range. In this case, this method not only reduces the loss of voltage regulator ICs, but also increase the maximum output voltage. LM338 has a 1.2V internal reference voltage, and output voltage adjust pin voltage is higher than that, so that the LM338's output voltage to the minimum can only be 1.2V. To make the output voltage to zero, the power supply design with the R10, DW2 and other components of the composition-1.2V reference voltage, the LM338 voltage adjustment down to-1.2V, so not only ensures the output side than the adjusted high demand, but also enable the output voltage from zero volts start. If the access regulator ICs with higher input voltage, the output happens to be empty, then boot, LM338 is easy to over-voltage while the damage in an instant. To solve this problem, adding the input of the LM338 VT1 formed by the input voltage limit circuit, in fact, an emitter follower, with the LM338 circuit to ensure that the input and output voltage difference of up to 5V, so as to avoid over-voltage due to damage to the integrated circuit. Select 2 components In Figure 1, DW1 is mainly used to protect the LM338 is not the breakdown, the election 27V, 1W of the regulator can, DW2 voltage is 1.2V, the choice 2CW100 or 2CW50, can also be used in series two 2CK2 it replaced, but to pay attention to the polarity of access (just the opposite in Figure 1). D1 ~ D4 using the parameter is greater than 6A 100V voltage rectifier diode or full bridge. The power supply transformer is greater than T 300V. Regulator IC model LM338K, take gold seal. J1 ~ J9 small selection of quality 6V relay, contact current is greater than 5A. Trimmer potentiometer output voltage selection WXD3-13 W precision multi-turn wirewound potentiometers. Voltage selector switch K1 selection 2X9 stall a small band switch. R * for the current meter sampling resistor, according to the selected sensitivity of the different headers, the interception of a certain length of wire around the system, if shown to improve the accuracy of the output voltage can be replaced with commercially available products voltmeter V digital DC voltage meter, and the remaining ELEMENT label shown in Figure 1. VT1, IC1 plus one 6cmX8cmX3cm the radiator. 3 Technical Data The power of the technical parameters: DC output range DC 0 ~ 45V: Maximum output current 5A; Voltage regulation rate ≤ 0.001% / V; Ripple ≤ 0.002%: Equivalent internal resistance ≤ 0.15Ω; Voltage coefficient of ≤ 0.005%.