To power a digital multimeter from 1 AA battery, instead of a 9 V “crown”, I recently assembled this converter. Although you can power anything from it, not necessarily testers. Unlike specialized ones, there are only a couple of transistors and a coil. Mounting is mounted directly on the battery connector. If something happens, you can easily disconnect and return the “crown”.
The most energy-intensive mode in a multimeter is continuity. If the supply voltage drops significantly when the probes are shorted, then you need to increase the diameter of wire L2 (stopped at 0.3 mm PEV-2). The diameter of the L1 wire is not critical, I used 0.18 mm and only for reasons of “survivability”, since thinner ones can be accidentally torn off. As a result, I assembled this circuit with a ring D=12 d=7 h=5 mm on VT1 2SC3420 - it pumps 100 V without load, it turned out to be the best (R1 = 130 Ohm). Also successfully tested were KT315A (a bit weak, R1 = 1 kOhm), KT863 (pumps well).
Disconnect ZD1, instead of R1 we set a tuning resistance of 4.7 kOhm; as a load - R = 1 kOhm. We achieve maximum voltage at the load by changing resistance R1. Without a load, this circuit easily produces 100 volts or more, so when debugging, set C2 to a voltage of at least 200V and do not forget to discharge it.
Important addition. There is no need to use a ring here! We take a ready-made inductor for 330 mH and higher, wind 20-25 turns of L1 over its winding with any wire, and fix it with heat shrink. AND THAT'S ALL! It pumps even better than the ring.
Tested by me with VT1 2SC3420 and IRL3705 (R1 = 130 Ohm, VD1 - HER108). The field-effect transistor IRL3705 works great, but it needs a supply voltage of at least 1 V and between the gate and ground there is a resistor of several kilo-ohms and a zener diode of 6-10 V. If it does not work, then we swap the ends of one of the windings. During experiments, the converter actually worked starting even from 0.8 V!
At the entrance Pin=Iin*Uin=0.053A*0.763V=0.04043W
At the exit Pout=Uout*Uout/Rout =6.2V*6.2V/980=0.039224W (Watt).
Efficiency= Pout/Pin= 0.969 or 96.9% - an excellent result!
Even if it’s 90%, that’s not weak either. Frankly speaking, this circuit with a ring has been known for a long time, I just added feedback on Uout on a field-effect transistor and figured out how to wind it up and use a ready-made inductor, because it’s inconvenient to wind on rings, and it’s too lazy, even if it’s 20 turns. And the dimensions of the ring are larger. Author of the article - Evgeny:)
Discuss the article VOLTAGE CONVERTER 1.5 - 9 VOLTS
Digital multimeters are very popular among radio amateurs and professionals due to their versatility. To power them, as a rule, a nine-volt Krona battery is used, which has noticeable self-discharge, low capacity and a higher price compared to other elements.
The proposed power supply device for a digital multimeter from one AA element with a voltage of 1.5 volts will avoid these operational drawbacks and simplify the operation of the device.
There are many different circuits offered on the Internet for converting 1.5 to 9 volts. Each has its pros and cons. This device is made on the basis of A. Chaplygin’s circuit, published in the magazine “Radio” (11.2001, p. 42).
The difference between this version of the converter is the location of the battery and voltage converter in the cover of the multimeter case, instead of creating a compact power supply installed instead of the Krona battery. This allows you to replace the AA element at any time, without disassembling the device, and, if necessary, turn off the converter (Jack 3.5 connector) with automatic activation of the Krona backup battery located in its compartment. In addition, when manufacturing a voltage converter, there is no need to miniaturize the product. It’s faster and easier to wind the transformer on a ring with a larger diameter, better heat dissipation, and a freer circuit board. This arrangement of components in the cover of the case does not interfere with working with the multimeter.
This converter can be made in any suitable housing and used in a wide variety of devices that require power from a nine-volt Krona battery. These are multimeters, watches, electronic scales and toys, medical devices.
The order of winding the transformer.
1. First you need to prepare the ferrite ring.
To prevent the wire from cutting through the insulating gasket and damaging its insulation, it is advisable to dull the sharp edges of the ferrite ring with fine-grained sandpaper or a needle file.
Wrap an insulating pad around the ring core to prevent damage to the wire insulation. To insulate the ring, you can use varnished cloth, electrical tape, transformer paper, tracing paper, lavsan or fluoroplastic tape.
2. Winding of transformer windings with a transformation ratio of 1/7: primary winding - 2x4 turns, secondary winding - 2x28 turns of insulated wire PEV -0.25.
Each pair of windings is wound simultaneously into two wires. Fold the wire of the measured length in half and with the folded wire begin to tightly wind the required number of turns onto the ring.
To avoid damage to the wire insulation during operation, if possible, use MGTF wire or other insulated wire with a diameter of 0.2-0.35 mm. This will slightly increase the dimensions of the transformer and will lead to the formation of a second winding layer, but will guarantee uninterrupted operation of the voltage converter.
First, the secondary windings lll and lV (2x28 turns) of the transistor base circuit are wound (see converter diagram).
Then, in the free space of the ring, also in two wires, the primary windings l and ll (2x4 turns) of the transistor collector circuit are wound.
As a result, after cutting the loop of the beginning of the winding, each of the windings will have 4 wires - two on each side of the winding. We take the wire from the end of one half of the winding (l) and the wire from the beginning of the second half of the winding (ll) and connect them together. We proceed similarly with the second winding (lll and lV). It should look something like this: (red terminal is the middle of the lower winding (+), black terminal is the middle of the upper winding (common wire)).
When winding the windings, the turns can be secured with glue “BF”, “88” or colored electrical tape indicating the beginning and end of the winding in different colors, which will later help to correctly assemble the transformer windings.
When winding all coils, you must strictly observe one winding direction, and also mark the beginning and end of the windings. The beginning of each winding is marked on the diagram with a dot at the terminal. If the phasing of the windings is not observed, the generator will not start, since in this case the conditions necessary for generation will be violated. For the same purpose, as an option, it is possible to use two different-colored wires from the network cable.
We check that the converter is assembled correctly, connect the battery and use the device to check the presence and magnitude of voltage at the converter output (+9V).
If generation does not occur and there is no voltage at the output, check that all coils are connected correctly. The dots on the converter diagram mark the beginning of each winding. Try swapping the ends of one of the windings (input or output).
The converter is capable of operating when the input voltage is reduced to 0.8 - 1.0 volts and receives a voltage of 9 volts from one galvanic element with a voltage of 1.5 V.
Prepared by: Smirnov I.K.
Has it often happened to you that when you need something urgently, you never find it? This is what happened to me with a 9 volt battery for my multimeter. And with a discharged battery, he begins to shamelessly falsify the readings. Changing the multimeter to a lithium 18650 battery will help you get rid of this trouble!
To do this, we will need to solder a 3.7 V - 9 V boost converter, and also get a 18650 battery (you can disassemble an unnecessary battery from a laptop or from a Tesla Model S, they have the same ones).
First we need to place all the elements inside the multimeter body. To do this, place the battery in place and saw off all the interfering plastic elements of the case. Don't forget to drill a hole for the battery charging connector.
Now we need to solder a boost converter that will raise the battery voltage from 3.7 to 9 volts. I built it on the MC34063A chip. Here is her datasheet. The values of the elements are not so critical in terms of values since I used a trimming resistor, with which you can accurately set the voltage we need to 9 volts.
Here is the list of components:
Here you need to solder a little.
Solder the center pin of the power connector to the positive terminal of the battery.
Solder the side contact of the power connector to the negative terminal of the battery.
From here we solder the wire to the negative input of the converter.
Solder the positive terminal of the battery to the unused terminal on the multimeter switch.
Solder a wire from the other side of the multimeter switch to the positive input of the converter.
Now solder the wires from the 9 volt power input of the multimeter to the output pins of the converter.
Adjust the converter output voltage to 9 volts using a trim resistor.
Then put the multimeter back together! The transfer of the multimeter to the battery can be considered complete.
Now you never have to buy Krona batteries for your multimeter, you just need to charge its battery.
In contact with
It happens like this: from work in the heat you drop into the post office, pick up a package, come home tired and forget about it for several days... Sometimes you remember - well, what's so special about it - dc-dc converters, like dc-dc converters. Let it sit, then I’ll unpack it. Late last night I finally remembered it and didn’t put it off “for later.” I opened the package and a rather voluminous package, tightly wrapped in bubble wrap, fell out.
there are large photos without spoilers
In a bundle - they are original, 4 pieces.
In general, I initially did not intend to write about them.
But then, looking into the package, I was pleasantly surprised.
It would seem like a small thing, a cheap order, one of the lowest prices for these converters, but no, the seller was not too lazy to include a souvenir gift here.
And with a 99.9% probability I won’t need it anywhere, but all the fuss and worries of a hard day have vanished. Nice. And the next time I go to Ali to look for something, I will be one of the first to look for it from this seller.
And with this post I want, in turn, to say THANK YOU to the seller! For uplifting mood and positive emotions.
Here you go. Emotions have been given free rein, let's move on to boring numbers.
Declared performance characteristics
- Input voltage: 0.9V-5V,
- Maximum efficiency: 96%,
- Output current when powered from one AA element: up to 200mA-300mA,
- ========//========= from two AA elements: 500mA-600mA.
Measurements.
First, let's measure the no-load consumption when powered by 1 AA battery, 2 and 3, as the attentive reader has already guessed, batteries. The batteries are already working, the voltage of each is about 1.25V.
I’ll tell you and show you how to reduce the consumption of the converter itself to 30 μA a little lower.
The consumption of the converter at idle is of course an interesting indicator, but it is much more interesting how it behaves when powering, for example, a USB LED lamp for $0.67, “like Xiaomi”.
Let's get a look.
The lamp, when powered from a full 5-volt source (sorry for the tautology), consumes 200 mA.
Now we turn on the Charger Doctor at the output of the converter, turn on the lamp in the Charger Doctor, and power the structure with a number of AA batteries equal to 0 to 3.
We admire the results.
The test results with the number of batteries equal to 0 were not included in the review for obvious reasons.
First the output voltage:
Now the currents:
The photo session of current measurements was carried out under brighter lighting, so in the photographs it seems that the lamp shines differently, but in fact it is the same.
Summary in table form:
The measurements are certainly not comprehensive, but the trend can be discerned.
It can be seen that with a more or less significant load and low input voltage there will not be 5 volts at the output. However, as well as the declared current. As I see it, the best option for powering this converter is a lithium battery, then you can expect a relatively stable 5V output.
A curious reader may ask a completely logical question: “Well, where else can it be used?
And I was prepared, I have the answer here, in the spoiler -
one of the possible applications.
And this option turned out to be an LED lamp with a motion sensor.
Another picky reader (or maybe it’s the same curious one) may quite reasonably object: “Excuse me, why “collectively farm” this device when the floor of Aliexpress and a small cart of online stores are littered with similar lamps for $4-5$?!” And it will be right
If I just needed to illuminate part of the room in the dark when someone appeared in the sensor’s coverage area, I would certainly buy it there.
But in my case, I really wanted to relieve the itching in my hands, check the concept and feasibility of using such a converter to power an autonomous device that works _without turning off the power_. Appearance, aesthetics, and thoughtful design were not decisive factors in the manufacturing process.
For this purpose, the following came in handy:
- A lithium battery extracted from a laptop battery that has lost all its former agility and turned into a pile of spare parts, 
- LED strip illuminating the matrix of the same unfortunate thing,
- Motion sensor, type HC-SR501,
- Photoresistor GL5528, 
- PBS type connector, from which we carefully separate 3 contacts,
- NPN transistor type BC546,547,847 or similar. I installed 2n3904. 
- Resistor 39 Ohm, 
- A little wires, patience, free time and of course the hero of this review - a dc-dc converter, photos of which were above in the plural and from different angles, so I won’t repeat myself
Before everything works out, let me clarify the nuances of some details.
Motion sensor, type HC-SR501. Triggers when there is movement of a heat-emitting object within its visibility radius. It has two trimming resistors with which you can set the response threshold and the time to keep the output in the on state after the factor that caused the response disappears. The yellow jumper selects one of two operating modes:
1 - The sensor was triggered, the output was activated, the countdown of the time specified by the resistor began, regardless of the presence of heat movement in the sensor’s visibility zone, the timer worked - the output was deactivated. After the blocking time has passed (the sensor does not respond to influences), if there is movement, it is triggered again.
2 - The sensor was triggered, the output was activated, the time countdown started, if there is movement in the sensor’s visibility range, the timer is restarted until the movement disappears, the movement has stopped, the time has expired, the output is turned off.
The position of the jumper shown here in the photo corresponds to the first operating mode, then in the finished device - to the second.
To prevent the sensor from triggering during daylight hours, you need to solder a photoresistor into the place provided for its installation - circled in red.
For the lamp I decided to use 5 LEDs from the matrix backlight strip, connected in parallel. Looking ahead, I will say that in this form their total consumption, limited by a 39 Ohm resistor, is about 48 mA, i.e. less than 10mA per LED. It is clear that it is best to install a current-limiting resistor on each LED, but in this design this is redundant. In addition, the LEDs operate at least 30 percent below their rated load, hardly heat up and are securely held on the housing using double-sided tape.
Now it's time for the converter. As we remember, by itself, when powered by 3 AA (about the same as from 1 not fully charged lithium), it consumes almost 2 mA. I think this is a lot for a device that should be in working order for as long as possible.
You can combat this by removing the LED or its current-limiting resistor.
In this simple way, the consumption of the dc-dc converter decreased to 30 μA.
It's time to put everything together.
Since the signal from the motion sensor controller has a level of 3.3V and is supplied to the output pin of the connector through a 1kOhm resistor, LEDs cannot be connected directly to it. No, of course you can connect them, but they won’t light up. In order for the LEDs to light, it is necessary to ensure that sufficient current flows through them for this process. A transistor key will do this task perfectly.
Schematically it looks like this:
After several strokes of a hacksaw, drill, file, soldering iron and hot-melt gun, the following design was obtained:
The total consumption in standby mode is about 0.4 mA, when activated - 80-82 mA.
What can I say... The device was a success. Hung from the ceiling and has been working for almost a month. It turns on several times during the evening. The voltage on the battery dropped from the original by slightly less than 0.1V. 
The wife drew a picture on the wall
In general, I collected it, hung it up and forgot about it. Only sometimes you remember - well, what's so special about it - dc-dc converters, just like dc-dc converters.
Taking into account the input voltage, I strongly recommend the converters; I strongly recommend the seller :)
I'm planning to buy +45 Add to favorites I liked the review +57 +107Low-power converter for powering a 9-volt load from a 3.7-volt Li-ion battery
Some modern low-power devices consume very little current (several milliamps), but for their power supply they require a very exotic source - a 9 V battery, which also lasts for a maximum of 30...100 hours of operation of the device. This looks especially strange now, when Li-ion batteries from various mobile gadgets are almost cheaper than the batteries themselves. Therefore, it is natural that a real radio amateur will try to adapt batteries to power his device, and will not periodically look for “antique” batteries.
If we consider a regular (and popular) multimeter as a low-power load. M830, powered by a “Corundum” type element, then to create a voltage of 9 V you need at least 2-3 batteries connected in series, which is not suitable for us; they simply will not fit inside the body of the device. Therefore, the only way out is to use one battery and a step-up voltage converter.
Selection of element base
The simplest solution is to use a timer type 555 (or its CMOS version 7555) in a pulse converter (capacitive converters are not suitable; the difference between the input and output voltages is too large). An additional “plus” of this microcircuit is that it has an open-collector output, which is quite high-voltage and can withstand voltages up to +18 V at any operating supply voltage. Thanks to this, you can assemble a converter from literally a dozen cheap and common parts (Fig. 1.6).
Pin 3 of the microcircuit is a normal two-state output, it is used in this circuit to support oscillation. Pin 7 is an open-collector output capable of withstanding increased voltage, so it can be connected directly to the coil, without a transistor follower. The reference voltage input (pin 5) is used to regulate the output voltage.
Operating principle of the device
Immediately after the supply voltage is applied, capacitor C3 is discharged, no current flows through the zener diode VD1, the voltage at the REF input of the microcircuit is equal to 2/3 of the supply voltage, and the duty cycle of the output pulses is 2 (that is, the pulse duration is equal to the pause duration), capacitor C3 is charged at maximum speed . Diode VD2 is needed so that the discharged capacitor C3 does not affect the circuit (does not reduce the voltage at pin 5), resistor R2 “just in case”, for protection.
As this capacitor charges, the zener diode VD1 begins to open slightly, and the voltage at pin 5 of the microcircuit increases. As a result, the pulse duration decreases and the pause duration increases until dynamic equilibrium occurs and the output voltage stabilizes at a certain level. The value of the output voltage depends only on the stabilization voltage of the zener diode VD1 and can be up to 15...18 V; at a higher voltage, the microcircuit may fail.
About details
Coil L1 is wound on a ferrite ring. K7x5x2 (external diameter - 7 mm, internal - 5 mm, thickness - 2 mm), approximately 50...100 turns of wire with a diameter of 0.1 mm. You can take a larger ring, then the number of turns can be reduced, or take an industrial inductor with an inductance of hundreds of microhenries (µH).
The 555 chip can be replaced with a domestic analog K1006VI1 or with a CMOS version 7555 - it has less current consumption (the battery will “last” a little longer) and a wider range of operating voltages, but it has a weaker output (if the multimeter requires more than 10 mA, it may not produce such a current, especially at such a low supply voltage) and it, like all CMOS structures, “does not like” increased voltage at its output.
Device Features
The device starts working immediately after assembly, the whole setup consists of setting the output voltage by selecting a zener diode VD1, while a 3.1 kOhm resistor (load simulator) must be connected to the output in parallel with capacitor C3, but not a multimeter!
It is forbidden to turn on the converter with an unsoldered zener diode, otherwise the output voltage will be unlimited and the circuit may “kill” itself. You can also increase the operating frequency by decreasing the resistance of resistor R1 or capacitor C1 (if it operates at an audio frequency, a high-frequency squeak is heard). When the length of the wires from the battery is less than 10...20 cm, a power filter capacitor is not necessary, or you can place a capacitor with a capacity of 0.1 μF or more between pins 1 and 8 of the microcircuit.
Identified deficiencies
Firstly, the device contains two generators (one master oscillator of the ADC microcircuit - the analog-to-digital converter of the device, the second generator of the converter), operating at the same frequencies, that is, they will influence each other (frequency beats) and the measurement accuracy will seriously deteriorate.
Secondly, the frequency of the converter generator constantly changes depending on the load current and battery voltage (because there is a resistor in the positive feedback circuit, not a current generator), so it becomes impossible to predict and correct its influence. Specifically for a multimeter, the ideal would be one common generator for the ADC and converter with a fixed operating frequency.
Second version of the converter
Rice. 1.7. Converter circuit with fixed operating frequency
A generator is assembled on element DD1.1; it clocks the converter through capacitor C2, and the ADC chip through C5. Most inexpensive multimeters are based on the double integration ADC ICL7106 or its analogues (40 pins, 3.5 digits on the display); to clock this microcircuit, you just need to remove the capacitor between pins 38 and 40 (unsolder its leg from pin 38 and solder it to pin 11 DD1.1). Thanks to feedback through a resistor between pins 39 and 40, the microcircuit can be clocked even by very weak signals with an amplitude of a fraction of a volt, so 3-volt signals from the DD1.1 output are quite enough for its normal operation.
By the way, in this way you can increase the measurement speed by 5...10 times - simply by increasing the clock frequency. The measurement accuracy practically does not suffer from this, deteriorating by a maximum of 3...5 units of the least significant digit. There is no need to stabilize the operating frequency for such an ADC, so a conventional RC generator is quite sufficient for normal measurement accuracy.
A standby multivibrator is assembled on elements DD1.2 and DD1.3, the pulse duration of which can be varied from almost 0 to 50% using transistor VT2. In the initial state, there is a “logical one” (high voltage level) at its output (pin 6), and capacitor C3 is charged through diode VD1. After the triggering negative pulse arrives, the multivibrator “overturns”, a “logical zero” (low voltage level) appears at its output, blocking the multivibrator through pin 2 of DD1.2 and opening transistor VT1 through the inverter on DD1.4. The circuit will remain in this state until , until capacitor C3 is discharged - after which the “zero” at pin 5 of DD1.3 will “overturn” the multivibrator back to the standby state (by this time C2 will have time to charge and pin 1 of DD1.1 will also be “1”), transistor VT1 will close , and coil L1 will discharge to capacitor C4. After the arrival of the next impulse, all of the above processes will repeat again.
Thus, the amount of energy stored in coil L1 depends only on the discharge time of capacitor C3, that is, on how open transistor VT2 is, which helps it discharge. The higher the output voltage, the more the transistor opens; Thus, the output voltage is stabilized at a certain level, depending on the stabilization voltage of the zener diode VD3.
To charge the battery, a simple converter on an adjustable linear stabilizer DA1 is used. You only have to charge the battery, even with frequent use of the multimeter, a couple of times a year, so there is no point in installing a more complex and expensive switching stabilizer here. The stabilizer is configured for an output voltage of 4.4...4.7 V, which is reduced by diode VD5 by 0.5.0.7 V to standard values for a charged lithium-ion battery (3.9...4.1 V). This diode is needed to prevent the battery from being discharged through DA1 in offline mode. To charge the battery, you need to apply a voltage of 6...12 V to the XS1 input and forget about it for 3...10 hours. At a high input voltage (more than 9 V), the DA1 chip gets very hot, so you need to either provide a heat sink or lower the input voltage.
As DA1, you can use 5-volt stabilizers KR142EN5A, EH5V, 7805 - but then, to suppress the “excess” voltage, VD5 must be made up of two diodes connected in series. Transistors in this circuit can be used in almost any n-p-n structure; KT315B are here only because the author has accumulated too many of them.
KT3102, 9014, BC547, BC817, etc. will work normally. KD521 diodes can be replaced with KD522 or 1N4148, VD1 and VD2 should be high-frequency, ideally BAV70 or BAW56. VD5 is any diode (not Schottky) of medium power (KD226, 1N4001). The VD4 diode is optional; it’s just that the author had too low-voltage zener diodes and the output voltage did not reach the minimum 8.5 V, and each additional diode in direct connection adds 0.7 V to the output voltage. The coil is the same as for the previous circuit (100. ..200 µH). The modification diagram for the multimeter switch is shown in Fig. 1.8.
Rice. 1.8. Electrical circuit for refining the multimeter switch
The positive terminal of the battery is connected to the central track-ring of the multimeter, but we connect this ring to the “+” of the battery. The next ring is the second contact of the switch, and it is connected to the elements of the multimeter circuit by 3-4 tracks. These traces on the opposite side of the board need to be broken and connected together, as well as with the +9V output of the converter. We connect the ring to the +3 V power bus of the converter. Thus, the multimeter is connected to the output of the converter, and with the multimeter switch we turn the power of the converter on and off. Such difficulties have to be undertaken due to the fact that the converter consumes some current (3...5 mA) even when the load is turned off, and the battery will be discharged with such current in about a week. Here we turn off the power to the converter itself, and the battery will last for several months.
A device correctly assembled from serviceable parts does not need adjustment; sometimes you only need to adjust the voltage with resistors R7, R8 (charger) and zener diode VD3 (converter).
Rice. 1.9 PCB options
The board has the dimensions of a standard battery and is installed in the appropriate compartment. The battery is placed under the switch, usually there is enough space there; first you need to wrap it with several layers of electrical tape or at least adhesive tape.
To connect the charger connector, you need to drill a hole in the multimeter body. The pin layout of different XS1 connectors sometimes differs, so the board may need to be modified slightly.
To prevent the battery and converter board from “dangling” inside the multimeter, they need to be pressed with something inside the case.
See other articles section.
Some modern low-power devices consume very little current (several milliamps), but for their power supply they require a very exotic source - a 9 V battery, which also lasts for a maximum of 30... 100 hours of operation of the device. This looks especially strange now, when Li-ion batteries from various mobile gadgets are almost cheaper than the batteries themselves. Therefore, it is natural that a real radio amateur will try to adapt batteries to power his device, and will not periodically look for “antique” batteries.
If we consider the usual (and popular) M830 multimeter, powered by a “Corundum” type element, as a low-power load, then to create a voltage of 9 V we need at least 2-3 batteries connected in series, which is not suitable for us - they simply will not fit inside the body of the device. Therefore, the only way out is to use one battery and a step-up voltage converter.
Selection of element base
The simplest solution is to use a 555 type timer (or its CMOS version 7555) in a switching converter (capacitive converters are not suitable - we have too much difference between the input and output voltages). An additional “plus” of this microcircuit is that it has an open-collector output, and a fairly high-voltage one – capable of withstanding voltages up to +18 V at any operating supply voltage. Thanks to this, you can assemble a converter from literally a dozen cheap and common parts (Fig. 1.6).
Rice. 1.6. Simple converter circuit
Pin 3 of the microcircuit is a regular two-state output, it is used in this circuit to support oscillation. Pin 7 is an open collector output that can withstand higher voltages, so it can be connected directly to the coil, without a transistor follower. The reference voltage input (pin 5) is used to regulate the output voltage.
Operating principle of the device
Immediately after the supply voltage is applied, the capacitor SZ is discharged, no current flows through the zener diode VD1, the voltage at the input REF of the microcircuit is equal to 2/3 of the supply voltage, and the duty cycle of the output pulses is 2 (that is, the pulse duration is equal to the duration of the pause), the capacitor SZ is charged at maximum speed . Diode VD2 is needed so that the discharged capacitor SZ does not affect the circuit (does not reduce the voltage at pin 5), resistor R2 is “just in case”, for protection.
As this capacitor charges, the zener diode VD1 begins to open slightly, and the voltage at pin 5 of the microcircuit increases. As a result, the pulse duration decreases and the pause duration increases until dynamic equilibrium occurs and the output voltage stabilizes at a certain level. The value of the output voltage depends only on the stabilization voltage of the zener diode VD1 and can be up to 15...18V - at a higher voltage the microcircuit may fail.
About details
Coil L1 is wound on a ferrite ring K7x5x2 (external diameter - 7 mm, internal - 5 mm, thickness - 2 mm), approximately 50...100 turns with wire with a diameter of 0.1 mm. You can take a larger ring, then the number of turns can be reduced, or take an industrial inductor with an inductance of hundreds of microhenries (µH).
The 555 chip can be replaced with a domestic analog K1006VI1 or with a CMOS version 7555 - it has less current consumption (the battery will “last” a little longer) and a wider range of operating voltages, but it has a weaker output (if the multimeter requires more than 10 mA, it can cannot produce such a current, especially at such a low supply voltage) and it, like all CMOS structures, “does not like” increased voltage at its output.
Device Features
The device starts working immediately after assembly, the whole setup consists of setting the output voltage by selecting a zener diode VD1, while a resistor with a resistance of 3...1 kOhm (load simulator) must be connected to the output parallel to the capacitor SZ, but not a multimeter!
It is forbidden to turn on the converter with an unsoldered zener diode - then the output voltage will be unlimited and the circuit may “kill” itself. You can also increase the operating frequency by decreasing the resistance of resistor R1 or capacitor C1 (if it operates at an audio frequency, a high-frequency squeak is heard). When the length of the wires from the battery is less than 10...20 cm, a power filter capacitor is not necessary, or you can place a capacitor with a capacity of 0.1 μF or more between pins 1 and 8 of the microcircuit.
Identified deficiencies
Firstly, the device contains two generators (one is the master oscillator of the ADC microcircuit - the analog-to-digital converter of the device, the second is the converter generator), operating at the same frequencies, that is, they will influence each other (frequency beat) and accuracy measurements will be seriously degraded.
Secondly, the frequency of the converter generator constantly changes depending on the load current and battery voltage (because there is a resistor in the PIC circuit - positive feedback - and not a current generator), so it becomes impossible to predict and correct its influence. Specifically for a multimeter, the ideal would be one common generator for the ADC and converter with a fixed operating frequency.
Second version of the converter
The circuit of such a converter is a little more complicated and is shown in Fig. 1.7.
A generator is assembled on element DD1.1; it clocks the converter through capacitor C2, and the ADC chip through C5. Most inexpensive multimeters are based on a dual ADC
Rice. 1.7. Converter circuit With fixed operating frequency
integrating the ICL7106 or its analogues (40 pins, 3.5 digits on the display), to clock this microcircuit you just need to remove the capacitor between pins 38 and 40 (unsolder its leg from pin 38 and solder it to pin 11 of the DD1.1). Thanks to feedback through a resistor between pins 39 and 40, the microcircuit can be clocked even by very weak signals with an amplitude of a fraction of a volt, so 3-volt signals from the DD1.1 output are quite enough for its normal operation.
By the way, in this way you can increase the measurement speed by 5... 10 times - simply by increasing the clock frequency. The measurement accuracy practically does not suffer from this - it deteriorates by a maximum of 3...5 units of the least significant digit. There is no need to stabilize the operating frequency for such an ADC, so a conventional RC generator is quite sufficient for normal measurement accuracy.
A standby multivibrator is assembled on elements DDI.2 and DD1.3, the pulse duration of which can be varied from almost 0 to 50% using transistor VT2. In the initial state, its output (pin 6) contains a “logical one” (high
voltage level), and the capacitor SZ is charged through the diode VD1. After the triggering negative pulse arrives, the multivibrator is “overturned”, a “logical zero” (low voltage level) appears at its output, blocking the multivibrator through pin 2 of DDI.2 and opening transistor VT1 through the inverter on DD1.4. The circuit will be in this state until the capacitor S3 is discharged - after which the “zero” at pin 5 of DD1.3 will “throw over” the multivibrator back to the standby state (by this time C2 will have time to charge at pin 1 of DD1.1 as well. will be “1”), transistor VT1 will close, and coil L1 will discharge to capacitor C4. After the arrival of the next impulse, all of the above processes will repeat again.
Thus, the amount of energy stored in coil L1 depends only on the discharge time of the capacitor S3, that is, on how strongly the transistor VT2 is open, which helps it discharge. The higher the output voltage, the more the transistor opens; Thus, the output voltage is stabilized at a certain level, depending on the stabilization voltage of the zener diode VD3.
To charge the battery, a simple converter on an adjustable linear stabilizer DA1 is used. You only have to charge the battery, even with frequent use of the multimeter, a couple of times a year, so there is no point in installing a more complex and expensive switching stabilizer here. The stabilizer is configured for an output voltage of 4.4...4.7 V, which is reduced by the VD5 diode by 0.5...0.7 V - to standard values for a charged lithium-ion battery (3.9...4.1 V). This diode is needed to prevent the battery from being discharged through DA1 in offline mode. To charge the battery, you need to apply a voltage of 6...12V to the XS1 input and forget about it for 3...10 hours. At a high input voltage (more than 9 V), the DA1 chip gets very hot, so you need to either provide a heat sink or lower the input voltage.
As DA1, you can use 5-volt stabilizers KR142EN5A, EH5V, 7805 - but then, to suppress the “excess” voltage, VD5 must be made up of two diodes connected in series. Transistors in this circuit can be used in almost any p-p-p structure; KT315B are here only because the author has accumulated too many of them.
KT3102, 9014, VS547, VS817, etc. will work normally. KD521 diodes can be replaced with KD522 or 1N4148, VD1 and VD2 should be high-frequency - BAV70 or BAW56 are ideal. VD5 – any diode (not Schottky!) of medium power (KD226, 1N4001). The VD4 diode is optional - the author simply had too low-voltage zener diodes and the output voltage did not reach the minimum 8.5 V - and each additional diode in direct connection adds 0.7 V to the output voltage. The coil is the same as for the previous circuit (100...200 µH). The modification diagram for the multimeter switch is shown in Fig. 1.8.
Rice. 1.8. Electrical circuit for refining the multimeter switch
The positive terminal of the battery is connected to the central track-ring of the multimeter, but we connect this ring to the “+” of the battery. The next ring is the second contact of the switch, and it is connected to the elements of the multimeter circuit by 3...4 tracks. These traces on the opposite side of the board need to be broken and connected together, as well as with the +9V output of the converter. We connect the ring to the +3 V power bus of the converter. Thus, the multimeter is connected to the output of the converter, and with the multimeter switch we turn the power of the converter on and off. Such difficulties have to be undertaken due to the fact that the converter consumes some current (3...5 mA) even when the load is turned off, and the battery will be discharged with such current in about a week. Here we turn off the power to the converter itself; the rf battery will last for several months.
A device correctly assembled from serviceable parts does not need adjustment; sometimes you only need to adjust the voltage with resistors R7, R8 (charger) and zener diode VD3 (converter).
Printed circuit board options are shown in Fig. 1.9.
Rice. 1.9. PCB Options
The board has the dimensions of a standard battery and is installed in the appropriate compartment. The battery is placed under the switch - usually there is enough space there; first you need to wrap it with several layers of electrical tape or at least tape. To connect the charger connector, you need to drill a hole in the multimeter body. The pin layout of different XS1 connectors sometimes differs, so the board may need to be modified slightly. To prevent the battery and converter board from “dangling” inside the multimeter, they need to be pressed with something inside the case.
I have long dreamed of making a 1.5 - 9 volt voltage converter “Krona” from an AAA battery for digital multimeters. As a housing for a homemade converter, I decided to take the housing from an old Krona battery.
First, I carefully bent the rolled edge of the back of the battery case. In the corners, I carefully bent the folding using a small screwdriver. Removed battery sections. And then I drilled a hole in the back wall with a diameter of 6 mm and inserted a standard socket for a “3.5mm Jack” to charge an AA battery.
The famous paraphrase of Leonardo da Vinci’s aphorism: “Everything ingenious is simple” is perfect for the prototype of our circuit, which we borrowed from one of the amateur radio magazines:
Our circuit consists of only five radio components, two of them are filter capacitances. Instead of an RF rectifier, base-emitter junctions of the transistors of the generator itself are used. Therefore, the value of the base current is proportional to the value of the load current, which makes the design very energy efficient.
C1, C2 – 22µF; VT1, VT2 – KT209K; B1 – 1… 1.5V
Another interesting feature of the generator design is the interruption of oscillations in the absence of a connected load, which 100% solves the problem of effective power management.
Transformer TV1 is made of a 2000NM ring magnetic core with dimensions K7x4x2, on which windings III and IV are wound, each containing 28 turns of copper wire with a diameter of 0.16 mm, and I, II, 4 turns each - 0.25 mm. ()
First, secondary windings III and IV are wound. They need to be wound simultaneously into two wires. We fix the coils with glue, “BF-2” or “BF-4”. Then, in the same way, the primary windings are wound into two wires.
The circuit is assembled using hinged mounting; transistors, capacitors, and a homemade transformer are interconnected by a mounting thread.
Setting up the scheme. To set a given output voltage level, it may be necessary to select the number of turns so that when the voltage on the AAA battery is 1.0 Volts, the output of the converter is 7 Volts. At this minimum voltage, the low battery indicator in the multimeter begins to blink.
If instead of KT209K transistors of a different type are used, then we adjust the number of turns of the secondary winding of a homemade transformer. This occurs due to different voltage drops at p-n junctions for different types of semiconductors. I assembled this design using KT502 transistors with the “native” transformer parameters. The output voltage dropped by about a volt.
Before the final stage of assembling the structure, I connected all the radio components with a flexible stranded wire and checked the operation of the circuit. To protect against short circuits, the pulse converter on the contact side is insulated with sealant.
Radio constructor No. 024, consists of a printed circuit board with a set of radio components and instructions in the package and is intended for initial mastery of the manufacture of voltage converters.
There are many infrequently used devices in everyday life that are powered by a 9V Krona battery, which is very unreliable and can run out at the most inopportune moment. But there are even more devices powered by 1.5V “finger” elements, for example, remote controls, which almost everyone has. And buying a finger element in stores is more accessible and cheaper than “Krona”.
In this situation, a DC/DC voltage converter device may be useful, i.e. DC/DC converter with different voltage and current. In our case, it will be a boost converter from 1.5 volts to 9 volts. The circuit is based on the operation of a blocking generator, which consists of a transistor VT1 and a pulse transformer Tr1, consisting of three windings. The windings must be wound in accordance with their numbering, stretching the winding of turns across the entire width of the frame, marking the beginnings and ends of the windings, winding them in one direction. On the diagram, the beginnings of the windings are marked with dots. If the circuit is externally assembled correctly, but does not work, the beginning and end of the windings are most likely mixed up (especially important for windings I and II). Our circuit uses a KT315G transistor, although you can use any other with a transmission coefficient of at least 50. When using transistors with opposite conductivity (pnp), it is necessary to change the polarity of the power connection. Let's consider the operation of the circuit: the base of the transistor is connected through feedback winding II to a voltage divider across resistors R1, R2. From these resistors, a bias voltage is applied to the base, as a result of which the n-p-n junction of the transistor turns open when voltage is applied. Once on the diagram
voltage is applied, the transistor opens. The current from the battery from the “plus” of the battery through the primary winding I, collector, n-p-n junction, transistor emitter returns to the “minus” of the power supply. When current flows through winding I, a magnetic field appears in the transformer, which induces current in coupling winding II and is supplied to the base, which leads to a sharp closing of the transistor. The current through winding I stops, and accordingly the current in winding II stops. The transistor opens again and everything repeats with a frequency of about 130 KHz, i.e. 130,000 times per second. The circuit operates as a self-oscillator; the magnetic field in the operating transformer induces current in the secondary winding III. The number of turns in this winding exceeds the number of turns in the primary winding, i.e. the voltage in it increases. The alternating voltage is rectified by the Schottky diode VD1 (the diode operates at high frequencies with low losses), capacitor C1 smoothes and filters the rectified voltage, and the zener diode VD2 prevents voltage surges exceeding 10 volts, preventing failure of devices connected to the circuit. A correctly assembled circuit does not need any settings. Observe the correct connection of the transformer windings, power supply, diode, zener diode, electrolytic capacitor C1, and the “Crown” connector (black - plus).
Level: Beginners
“Krona” 9V from AA 1.5V element (024)
Contents of set 024:
1. Circuit board,
2. Battery AA 1.5V,
3. Container for battery,
4. Crown type connector
5. Transistor KT315G,
6. Resistors R1, R2 - 100 Ohm (2 pcs.),
7. Schottky diode VD1 1N5819,
8. Zener diode VD2 10V,
9. Electrolytic capacitor 10 μF,
10. Pulse transformer,
11. Wire for PEL windings,
12. Installation wire,
13. Scheme and description.
The time for continuous soldering of one point should not exceed three seconds
When assembling the circuit, observe the polarity of connecting the power supply, pointer device,
electrolytic capacitor, rectifier diodes and pinout when installing the microcircuit in the socket!
