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  1. Cirkit

    Understanding N-Channel MOSFETs

    I'm confused by the VGS(TH) and current rating of N Channel MOSFETs. For instance, the attached datasheet for a Fairchild FQPF20N06L quotes an ID current of 15.7A and a VGS(TH) of between (1.0V to 2.5V). However the graph in Figure 2 of the datasheet seems to indicate that a VGS voltage in...
  2. Cirkit

    Removing components connected to large metal planes

    I am trying to rework some PCBs which have pogo pins that are attached to large metal planes with varying amounts of success. I have a high temperature tip however, when melting the solder while pulling the pins from the other side of the board, some of the pads lift. I have tried using flux...
  3. Cirkit

    Using a MOSFET instead of a BJT

    I am currently redesigning a circuit and standardising on components as much as possible. Part of the circuit is an Op-Amp configuration to generate PWM pulses to drive a motor. I thought that substituting a BJT transistor on the output of an LMC6762 Op-Amp with a PMF370 would be a better...
  4. Cirkit

    Ni-MH charging circuit query

    I am trying to work out how a charging circuit for a Ni-MH battery pack is operating and determine why there are powder deposits on one of the terminals of the cells of the battery pack. I have been told that the unit is new so I'm surprised that one of the cells has powder on the positive...
  5. Cirkit

    Parallel LEDs - resistor needed?

    I'm sure this question or similar has been asked asked before but I just wanted some clarification. If I am connecting 7 LEDs in parallel with a forward voltage of 3.3V each to a supply of 3.6V, is a protection resistor needed? The datasheet mentions a maximum forward current of 25mA per LED...
  6. Cirkit

    CMOS 555 driving BC337 - base resistor

    Hello, I am trying to determine the correct base resistor value to drive a BC337 transistor into saturation. The transistor is connected to the output of a CMOS 555 timer via the resistor. The transistor is driving a 3V solenoid which consumes around 200mA when active. The entire circuit is...
  7. Cirkit

    5V boost converter efficiency?

    I purchased a couple of different 5V boost converter boards from eBay to power a 5V solenoid from 2xAAs. The solenoid normally draws about 120mA from a 5V power supply. If I use either of the boost converter boards powered by 2xAAs, the total current consumption (boost converter board and...
  8. Cirkit

    Hot air rework tool

    I bought a DrillPro hot air gun, but recently it fell apart when changing the nozzles. The internal glass insulator around the heating element broke off together with the outer metal casing which was crimped on at the base. The WEP 8508D was purchased as a replacement but the air compressor...
  9. Cirkit

    Green LED power consumption

    I have replaced a red LED (Vf = 1.9V) in a circuit powered by a 3V battery supply with a green LED (Vf = 3.3V). Both LEDs have a specified If of 20mA. As the batteries are Lithium, the voltage starts off slightly higher at approximately 3.4V when new. The current through the green LED is much...
  10. Cirkit

    Convert PWM output to variable frequency

    I have a circuit which outputs a PWM signal to control a motor's speed in response to an input sensor. The sensor amplifier, feedback circuit and PWM signal are based on a series of Op-Amps. I'd like to convert the PWM signal to a frequency variation to control a stepper motor driver based on...
  11. Cirkit

    SOT-32 package

    Why is the SOT-32 package considered surface mount? It looks more like a through-hole package.
  12. Cirkit

    ISP and JTAG headers

    Hello, I am fairly new to micro-controller programming. I am trying to read the code on a circuit containing an Atmel ATmega328P. Here is a photo of the ISP header on the board: How do I connect an Atmel programmer to the header without permanently soldering to it? Also, how will I know...
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