Статья Краткое описание

Скачать 0.55 Mb.

Название	Статья Краткое описание
страница	12/12
Тип	Статья

rykovodstvo.ru > Руководство эксплуатация > Статья

1 ... 4 5 6 7 8 9 10 11 12

Аттенюатор для канала X и входного синхросигнала.

http://www.bankreferatov.ru/referats/9CEC7BA5E1EE0E37C32572F100497C80/%D1%8D%D0%BB%D0%B5%D0%BA%D1%82%D1%80%D0%BE-%D0%BB%D1%83%D1%87%D0%B5%D0%B2%D0%BE%D0%B9%20%D0%BE%D1%81%D1%86%D0%B8%D0%BB%D0%BB%D0%BE%D0%B3%D1%80%D0%B0%D1%84.doc.html

Аттенюатор (делитель напряжения) предназначен для регулировки коэффициента отклонения Ха ПО вертикали путем ослабления сигнала

и обеспечивает постоянное значение коэффициента отклонения во всем диапазоне полосы пропускания усилителя ВО, почти неизменное большое входное сопротивление и малую входную емкость при переходе от одного коэффициента деления к другому. Аттенюатор (рис. 9.6) состоит из резисторов сопротивлениями R_l, R₂ и конденсаторов Сl, С2. Коэффициент деления

Кд = Z₂/(Z_I + Z₂) (9.5)

где Z_I=R₁R/(1+j₁C₁); Z₂=R₂R/ (1+j₂C₂) - соответственно полные сопротивления R₁C₁- и R₂C₂цепи. Если в Кд подставить значения Z_l, Z₂ и принять R₁C₁ =R₂C₂, то

Кд = С₁/(С₁ + C₂) = R₂/(R₁ + R₂). (9.6)

Рис. 9.6. Схема делителя напряжения: Uвх.атт Uвых.атт входное и выходное напряжения аттенюатора

Аттенюатор работает как омический в области низких частот в как емкостный в области высоких частот. Теоретически коэффициенты Кд и Ко не зависят от частоты, поэтому аттенюатор называют частотно-компенсированным во всей рабочей полосе частот осциллографа. (Погрешность 'коэффициента деления не' превышает :t 3 %.) Входное сопротивление (за исключением низкоомного входа)

Rвx = R_l + R₂, (9.7)

где R₁>>R₂.

Входная емкость

Свх = C₁ C₂/(C₁ + С₂), (9.8)
где C2>> C1. Процесс определения значения искомого напряжения существенно упрощается, если аттенюатор отградуировать не в значениях коэффициента деления Кд, а в соответствующих значениях коэффициента отклонения Ко:

Кд. . . . .,1/1 1/2 1/5 1/10 1/20 1/50

КО, В/дел. . . . . . . . .. 0,01 0,02 0,05 0,1 0,2 0,5

Кд………………..1/100 1/200 1/500 1/1000 1/2000

КО, В/дел. 1,0 2,0 5,0 10 20

При наличии полевого транзистора типаКП302 с любой буквой можно улучшить характеристики канала вертикального отклонения за счет увеличения его входного сопротивления до 1 МОм на всех поддиапазонах и уменьшения входной емкости до 15—20 пФ.

Принципиальная схема входной части канала вертикального отклонения, собранного на полевом транзисторе, приведена на рис. 46. Нумерация деталей оставлена прежней, а изменены лишь номиналы деталей. Вместо двух ограничивающих кремниевых диодов применен один стабилитрон Д2 типа КС133. Его можно заменить стабилитронами типов КС139, КС147 или КС168 с прямым и обратным сопротивлением не менее 20 МОм при входном сигнале 0,15 В.

h

ttp://www.irls.narod.ru/izm/osc/osc04.htm

https://www.google.ru/url?sa=i&rct=j&q=&esrc=s&source=imgres&cd=&cad=rja&uact=8&ved=0ahUKEwj1o7WA9_jMAhXGPZoKHRPXBKEQjRwIBw&url=http%3A%2F%2Fforum.cxem.net%2Findex.php%3Fapp%3Dcore%26module%3Dattach%26section%3Dattach%26attach_id%3D201175&psig=AFQjCNF8l2dnZ1djEMEsQdr5ohAdKG1lBA&ust=1464391177316579

Аналоговая часть цифрового осциллографа DSOA Mk3

http://forum.ixbt.com/topic.cgi?id=48:841-43

цена сдвоенных токовых операционников оказадась гораздо меньше чем новых full differential усилителей

http://forum.ixbt.com/topic.cgi?id=48:841-47

Вот для обсуждения аналоговый усилитель с полосой 300-350 Мгц (зависит от монтажа и настройки). Достоинства - мегаомный вход, размах до =-1.5В, полный дифференциальный выход с возможностью сдвига опорного напряжения. Т.е можно подключать непосредственно к АЦП с диф входом. Поскольку выход низкоомный, после этого каскада все переключатели делались на КМОП ключах ( аттенюатор 1-2-5,). Коэффициент усиления выбран 1.6, т.к в AD8131 G=2 и истоковый повторитель имеет G~0.8 (зависит от полевика). Потом он корректируеться в делителе 1-2-5. Питание +-5 В. Справляеться двухватный DC-DC преобразователь 5 в+-5.

AD8055/AD8056

Low Cost, 300 MHz Voltage Feedback Amplifiers

FEATURES FUNCTIONAL BLOCK DIAGRAMS

Low Cost Single (AD8055) and Dual (AD8056)

Easy to Use Voltage Feedback Architecture

High Speed

300 MHz, –3 dB Bandwidth (G = +1)

1400 V/_s Slew Rate

20 ns Settling to 0.1%

Low Distortion: –72 dBc @ 10 MHz

Low Noise: 6 nV/√Hz

Low DC Errors: 5 mV Max VOS, 1.2 _A Max IB

Small Packaging

AD8055 Available in SOT-23-5

AD8056 Available in 8-Lead microSOIC

Excellent Video Specifications (RL = 150 _, G = +2)

Gain Flatness 0.1 dB to 40 MHz

0.01% Differential Gain Error

0.02_ Differential Phase Error

Drives Four Video Loads (37.5 _) with 0.02% and

0.1_ Differential Gain and Differential Phase

Low Power, _5 V Supplies

5 mA Typ/Amplifier Power Supply Current

High Output Drive Current: Over 60 mA

The circuit shown in Figure 34 shows how an AD8056 can be

used to make a single-ended to differential converter that offers

some advantages over the architecture mentioned above. Each

op amp is configured for unity gain by the feedback resistors

from the outputs to the inverting inputs. In addition, each output

drives the opposite op amp with a gain of –1 by means of the

crossed resistors. The result of this is that the outputs are complementary

and there is high gain in the overall configuration.

Feedback techniques similar to a conventional op amp are used

to control the gain of the circuit. From the noninverting input

of Amp 1 to the output of Amp 2, is an inverting gain. Between

these points a feedback resistor can be used to close the loop.

As in the case of a conventional op amp inverting gain stage, an

input resistor is added to vary the gain.

The gain of this circuit from the input to Amp 1 output is RF/RI,

while the gain to the output of Amp 2 is –RF/RI. The circuit

thus creates a balanced differential output signal from a singleended

input. The advantage of this circuit is that the gain can be

changed by changing a single resistor and still maintain the

balanced differential outputs.

Горошков. Транзисторный детектор

http://slava37md.narod.ru/6-14.htm

(рис 6.14)

Детектор может работать на частоте свыше 200 кГц. На частоте 500 кГц погрешность передачи амплитуды входного сигнала ещё не превышает 0,5%. Граничная частота такого детектора может в 100 раз превосходить граничную частоту диодного детектора, который на частоте 1 кГц имеет коэффициент передачи К=1, а уже на частоте 5...7 кГц К=0,95.

Bent deflection plates?

http://oscilloclock.com/archives/2008

I discovered quite late in the project that the tube was displaying a square as a trapezoid! Sadly, I didn’t get a photo at the time… but the (exaggerated) drawing at right gives an idea of the shape.

To make matters worse, the beam was well-focused at the top left, but extremely fuzzy at the bottom right corner.

Yes, it’s true that without the CRT shield, stray magnetic fields can cause some interesting effects. But these are usually translational; they move the image, but don’t change its shape or the focussing. What could be going on here?

I tried rotating the entire scope in all axes along the earth’s magnetic field, but as expected, this didn’t affect the shape; only its position on the screen. So perhaps the original transformer had some residual magnetic field that was affecting the beam? I tested this by rotating only the CRT along its z-axis… And found that no, the trapezoid rotated as well!

So the only conclusion is that the tube itself has some internal deflection defect. It’s likely that the plates have been shaken and bent a little, or are even loose. Not surprising as this scope has done a LOT of traveling…!

But All was not lost!

A few well-placed magnets on the neck of the CRT helped correct the shape to some extent. They also improved the focus enough that I could sleep at night!

Magnets needed to correct some trapezoid and astigmatism problems

A portable oscilloscope

http://www.ludens.cl/Electron/scope/scope.html

Технические характеристики не указаны. :-(

The VCR converter: 12V to 120V, 20 Watt

http://www.ludens.cl/Electron/dcdc/dcdc.html

Many modern pieces of home electronics, like video recorders, have switching power supplies that can accept any voltage from about 90 to 250V AC, at frequencies of 45 through at least several hundred Hertz. But it is less known that most of these power supply can perfectly well accept DC voltage too! That DC voltage should be at a level of close to what the AC peak would be, that is, typically this equipment will accept about 110 to 320V DC.

I live in a place where sometimes we get power cuts. It does not happen really often now, but when it happens, I hate having to re-program the memories and timer of my video cassette recorder! It looses memory as soon as the power outage lasts for more than a few seconds. But I have a large storage battery in my radio room, under constant charge, and given the low power consumption of a VCR, I decided to put it on the battery. I looked inside, and tried to inject a backup voltage into the CPU circuitry, but having no schematic diagram I missed the proper spots, and the machine always kept forgetting everything. So I decided to power the entire VCR from the battery, through the AC power input.

The most obvious approach would be to make a DC to AC inverter, having 110 or 220V AC output at 50 or 60 Hz, but this requires a rather large and heavy transformer. So it's better to use a high frequency, at least 25kHz, so a very small and cheap transformer can be used. But sending 25 kHz into a power supply designed for 50 to 60 Hz is no good! The input diodes are not fast enough, and the noise filter at the input would place a heavy reactive load on the inverter! So I decided to rectify the secondary voltage in the converter, and power the VCR with DC.

Here is the schematic. You can get the full resolution version too. The design is a simple saturation-limited push-pull converter. There is no special reason to use PNP transistors; I used them simply because I had a box full of them around. You may well turn over the design to use NPN transistors.

The 2SC945 is a bias switch for startup. When applying 12V power, this transistor applies enough bias to the power transistors to get the oscillation started. Soon later, the 100uF capacitor charges up, the transistor goes off, and the power transistors self-bias into cut-off, such that cross-conduction is eliminated. After removing power, the 6k8 resistor discharges the bias timing capacitor, as otherwise the circuit would be unable to restart!

The secondary rectifiers are ultrafast diodes. These are NOT 1N4007! And the 220nF capacitors for the secondary filter are no typos; the diodes deliver almost pure DC, since the oscillation waveform is square, so only some noise filtering is needed. No electrolytics are necessary here.

Note the filters at both input and output, using ferrite cores. These are necessary to avoid polluting your environment with RF noise! Using these filters, and joining the input and output negative leads, this converter is very quiet and does not cause any problem in my combined HF, VHF and UHF station.

All ferrite cores (for the transformer and for the noise filters) are manufactured by Amidon Associates, and can be ordered directly from them in small quantities. Look for Amidon on the web. The 77-material core used for the transformer is less than ideal. A square-loop ferrite would work more efficiently! This one gets really warm, operating in saturation mode at 25 kHz. But it has worked well enough for two years now. The filter cores, on the other hand, are well chosen, so try to use the exact ones.

For all windings, the schematic states the number of turns. "7t" means 7 turns. As the transformer is quite small for the involved power, use as thick a wire as you can fit, leaving about half of the space for the 2x7 turns primary winding, and the other half for the secondary, while the feedback winding can be made from very thin wire.

The transistors do not need any heat sinks. They are large enough without, and they need to dissipate little heat!