| Along with the mobile equipment application’s popularization, increases gradually to the negative polarity voltage source’s demand. Has a negative voltage power source this procedure with a positive voltage input source, the cost both are high, and is quite complex, when specially designs needs the positive voltage and the negative voltage two kind of outputs is so. Figure 1 showed an economical simple solution, it combined a voltage invertor and a doubler an electric charge pump electric circuit. This electric circuit can use 5 ~ 6V the input voltage to produce a -5V constant voltage output voltage and a 10V non-constant voltage output voltage. It besides needs a SOT-23 seal the electric charge pump integrated circuit, only needs 5 very small surface mounting the porcelain capacitor and two diodes.
Figure 1 this electric circuit a constant voltage invertor and a doubler combines in together. This does not bring inductor’s DC/DC invertor, its input voltage is 5V, but output voltage and output current respectively be passes through the constant voltage -5V(±5%) and 100 mA. The doubler may (±7% mobility scale) under output 50 mA electric currents in 10.5V. Invertor’s output voltage adjustment satisfies the following relations: (VIN-5)>(VOUT×ROUT); You may the curve which determine when VIN=5V the ROUT value and the VOUT value according to shown in Figure 2. (VIN is other value ROUT value and the VOUT value may look up from the LTC1983 data sheet. ) if these variables do not meet this inequality condition, then the invertor by the split-ring pattern work, and becomes one kind of output voltage VOUT1= - [VIN-(VOUT×ROUT)] low output impedance invertor. You may doubler’s output voltage definition be VOUT2=2VIN-2VD, in the formula VD are diode’s forward loss of voltage. Figure 3 showed this electric circuit’s efficiency above 81%, most probably was 85%. Figure 4 showed between invertor’s output voltage adjustment and the output current relations. This integrated circuit has the short circuit protection and the overheated protection function.
Figure 2 this curve expressed that shown in Figure 1 between electric circuit’s ROUT and the VOUT relations.
Figure 3 this curve expression efficiency and two output current relations.
Figure 4 this curve expression output voltage setting range and output current relations. |
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