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Long distance cell phone detector – I found these schematics on a circuit diagram website. After building it many times it doesn’t work correctly. The circuit designer claims this circuit can detect cell phone waves from a long distance but when I test it I didn’t saw any detection. Read more
Charging a 50-Farad capacitor with voltage follower – The voltage feeding the follower will be 2.9 V to 3.529 V. The “transistor?” would charge a capacitor.
I envisage a diode between transistor and capacitor for protection.
If so, is there a mathematical way to pre-compensate for the voltage drop across diode? Read more
Voltage-controlled current source circuit needed for high currents – I need to make a voltage-controlled current source for nichrome wire. It seems like I need a circuit which translate 0…5 V range voltage input to a 0…8 A current. I can use a DC power supply which can supply this current. Is there a topology or any suggestion circuit for example composed of an opamp and a power transistor? Or any specific IC would work, as well. Read more
Using N-Channel MOSFET as a switch to drive a resistor load – I m trying to drive a resistor (dummy) load rated 24 V, 0.6 A using an Infineon BSP295 N-MOSFET. A power supply is used to provide power to the circuit. A 3.3 V regulator rated at 0.3A is connected to the switch then to a voltage divider before connecting to the gate. When the switch is closed, a voltage divider gives 3V to the gate. The current drawn at the initial phrase goes up to 0.6A for about 5 secs, before slowly reducing to 10mA, as if the MOSFET is not conducting. This is happening consistently. What is wrong with my controlling of the MOSFET? Read more
Open collector comparator pullup – We are using a TS391ILT open collector comparator. Its Vdd is 14V. Its output has a 33k pullup to 3V3, and the output goes to a microcontroller input. This microcontroller is supplied by the same 3V3 that the output pulls up to. On the noninverting input pin we have an 8V3 reference voltage. On the inverting input pin we have a square wave which has a frequency of 10ms and goes from zero volts to 13V. At the output of the comparator, when the output should be pulled up to 3V3…it is instead pulling up to about 3.9V. Do you think this is due to leakage current from the Vdd pin to the output pin? Why does the datasheet not mention it? How high would you expect this leakage current to go with ambient temperature rise to say 85degC? Read more
Improve PSRR of an LDO – I have an LDO whose datasheet only specified the PSRR up to 1MHz. If I need to improve its PSRR above 10MHz (say, 15MHz), do I increase the output capacitance to achieve this? I am using low ESR ceramic capacitors and can use high capacitance. However, I am not sure if it is always true to increase the output capacitance to improve the PSRR in high frequencies. Read more
Connecting telephone wire to USB and 3.5 mm – I want to connect and route telephone wire either to USB or 3.5mm jack with switching using a microcontroller when the call comes in. How can I do that? Read more
Understanding MOSFET driver circuit – This is the circuit which i used to make for MOSFET driving. It used to work fine.
But I then heard about Miller effect in MOSFETs. And then I heard about the MOSFET driver IC IR2110 which takes care of Miller capacitance. (By providing a negetive current when turning off? I am not clear). I found this circuit for a MOSFET driver in a Totem pole configuration.
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The site says applying 5 V to Vclk will turn on QH Bc817 but I see that emitter is still open. Read more
Voltage gain of audio power amplifier – The voltage gain of LM386 is given as 200 by connecting a capacitor. What is the voltage gain mean here in an audio power amplifier? Read more
Synchronizing two different signals – Is there any way to synchronize two signals with different frequencies? For example, the first rising edge should be at the same time. Read more
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