Duration: 2:20

336 views

1

555 is a fine timer chip, especially the CMOS version. It can be used to generate a relatively accurate waveform for a lot of things: Here it's switching a high voltage NPN transistor to boost a lower 5V to up to 100v. The CMOS 555 that I am using, which is a superior one made in Taiwan (Yes, indeed, a lot of 555 had been bought over many years. The number of availability for this chip is enormous and most are very cheap and bad. Some special extreme 555 can be very pricey.) can source 150mA and sink 160mA at 50% duty cycle. That means the actual source and sink capacity for this chip is doubled the measured amount, not particular great, but far far better than something an I/O from a MCU can offer, which is about 40mA max. The 555 can be used to step-up a 5v to 170v relatively easily and efficiently, but not this circuit. This circuit is designed for testing transistor.

The NPN transistor tested here is relatively slow, especially with this simple driver, so it can't handle too fast switching speed. The 555 is outputting a waveform from about 100kHz to 700kHz here with 50% for most of the range, and tested with 10mH-47uH inductor values.

PS. the 555 tested here can output a frequency up to 2MHz. 700kHz is not the maximize frequency.
PPS, the simple driver here is not bad at all, especially with a good CMOS output to start with, but a newer one has been designed, so this is not as good.
PPPS, the 555 timer can drive a mosfet much easier than with a MCU. Much better since 555 can go up to as high as 15 volts.