Multimeters and process calibrators can be used with 9V batteries.
Multimeter and process calibrator of these instruments are generally not much current, like the general operating current of the digital multimeter is mostly below 20mA, so it can be used 1.5V dry cell (or 1.2V NiMH batteries) through the boost circuit to replace the 9V stacked battery. The following is a simple and easy to make 1.5V to 9V voltage regulator circuit, which can be used instead of the multimeter 9V stacked battery.
Triode 9013 and 8550 form a complementary self-excited multi-harmonic oscillator, the two tubes work in the switching state. t for the step-up transformer, the primary coil as 8550 transistor collector load, 8550 collector output oscillating signal by the transformer T step-up, the secondary stage of the high-frequency alternating current voltage, the voltage is rectified by the Schottky diode 1N5819, C2 filter and the voltage regulator VD2 regulator. The voltage is rectified by Schottky diode 1N5819, filtered by C2 and regulated by voltage regulator VD2, the output at the Vout terminal is a stable 9V voltage.
The oscillation frequency of this circuit is mainly determined by R2 and C1. Generally, the oscillation frequency can be selected from 5 to 20 KHz, and the output voltage of the boost circuit is determined by the regulated value of the voltage regulator VD2. If you need a stable voltage of 9V, you can choose 1N4739 regulator, the regulator value of 9.1V, the power of 1W. due to the secondary output of the transformer is a high-frequency alternating current voltage, so the VD1 should be selected with high-frequency performance of the switching diode or Schottky diode. Capacitor C2 is best used for high-frequency filtering good tantalum capacitors. the size of R3 depending on the voltage at the ends of C2 and the actual operating current of the multimeter. Here it is assumed that the voltage at both ends of C2 is 15V, the current flowing through VD2 is 10mA, and the maximum operating current of the multimeter is 15mA, then R3 can be taken as a 240Ω resistor.
The circuit of the step-up transformer can choose to use a ferrite ring around the system, the ferrite ring can be removed from some of the scrap electronic ballasts or switching power supplies.
When making it, the β of the two transistors is as large as possible. The power switch S in the circuit can use the power switch of the original multimeter. The circuit can be powered by a 5 dry cell battery or a 1.2V NiMH battery.
