DC booster circuit suitable for use with multimeter
The multimeter is an essential tool for electricians and electronic technicians. Its high resistance usually uses a 9V, 15A or 22.5V laminated battery. This kind of battery is not only expensive, but also has a short life, so it is uneconomical to replace it frequently. Here are several small DC booster circuits suitable for multimeters. These circuits have simple structure and few components. After modification, the circuit board can be directly placed in the position of the laminated battery in the multimeter to replace it.
As shown in the figure is a DC booster circuit with an output voltage up to 22.5 V, which can be used to replace the 22.5 V laminated battery.
It is powered by a 1.5V battery in the multimeter, the working current is 25mA, and the output current is about 0.5mA, which is sufficient for the high resistance of the multimeter. In the circuit, VT1 and VT2 form a complementary multivibrator, and its oscillation frequency is about 2kHz. T is a step-up transformer, the primary is the load of the complementary multivibrator, and the secondary is the boost winding, which outputs a higher pulse voltage. The voltage is rectified and filtered by the diode VD1 and the capacitor C2 to become a DC high voltage, and then stabilized by the resistor R3 and the voltage regulator tube VD2 to output a relatively stable high voltage.
The transformer T in the circuit can be a 502-type audio output transformer used in a transistor radio, and the secondary is used as the primary of the step-up transformer. The taps in the middle of the primary are not used, and the taps at both ends are used as the secondary of the step-up transformer. If you can't find a suitable transformer, you can also use the silicon steel sheet of the radio input and output transformer to make your own. The primary uses a high-strength enameled wire with a diameter of 0.25mm to wind 110 turns, and the secondary uses a high-strength enameled wire with a diameter of 0.21mm to wind 520 turns. . A layer of insulating paper should be added between the primary and secondary coils, and attention should be paid to the end with the same name of the primary and secondary coils.
As shown in the figure is a small DC booster with a very simple structure, which can be used to replace the 15V laminated battery. The core component of the circuit, the transformer T, used a dedicated transformer for pocket money detectors. The circuit consumes about 40mA and the output voltage is 15V. If the positive pole of the 15V battery of the multimeter is connected to the negative pole of the 1.5V battery, just adjust the polarity of VD1 (C1, VDZ) in Figure 7-70, so that a -15V voltage will be output.
A voltage-stabilizing direct current boosting circuit. This circuit can boost a 1.5V battery to 9V to replace the 9V laminated battery. The no-load input current of the circuit is lower than 1.2mA, and the conversion efficiency is as high as 60%. The circuit is composed of an oscillating circuit and a voltage stabilizing circuit, in which VT1, VT2, and C2 form an oscillator, the color code inductor L is an energy storage inductor, VD2 is a rectifier diode, C3 is an output filter capacitor, and VT3, VD1, VD3, and R2 are stable Output voltage regulator circuit. The output voltage is approximately equal to the regulated value of VD3.
Using 1.2V, 500mAh nickel-cadmium battery as the inverter power supply circuit, the output DC voltage is 9V, which can be used by digital multimeters. In Figure 7-72, the transformer T is made of a 15mm magnetic ring (the power switch of the digital multimeter is marked in the component parameter diagram.
Self-controlled digital meter inverter power supply circuit. It does not need to separately set up a power switch or modify the switch in the meter. The circuit has the characteristics of low power consumption, stable and reliable, and does not affect the accuracy of the instrument. The transformer T in the circuit is made of E3 type ferrite core, and each corner is folded off and then processed into a square shape, with L2 inside and L1 outside. When the whole inverter works, the working current of the battery is about 70mA.
