so i've had ideas over the years that require linear ramp generators. i've also got a few circuits for a transistor curve tracer dating back to the 1970s, unfortunately, it used UJT's as ramp generators. UJT devices have long been obsolete, i've found a circuit using two bipolars to perform the same function as a PUT (programmable unijunction) (2N6027=$3.00, 1ea 2N2222/2907=$0.50). which while not a perfect replacement for all UJT uses, seems to be perfect for ramp and pulse generator circuits. the circuit of the "device" itself is very similar to the simulation of a SCR with two transistors, with the addition of an internal resistor. it's shown here with a capacitor which is charged by a constant current source. the constant current makes a very linear ramp across the capacitor, and the "put" device discharges the cap when the "anode/gate" junction begins to conduct.
the three transistors on the left are the current source for this ramp generator (i could have used a single PNP at the top, but i was converting this FROM a voltage controlled circuit that used the current mirrror). R1 sets the current output of Q5, which is the charging current for C1. when the "put" conducts and discharges C1, R5 sets the "retrace time" (in case you want to use this as a sweep generator). there are two outputs (out-s) and (out-p) which are sweep (ramp) and pulse.
some finer detail of the ramp and pulse outputs can be seen here;
the width of the pulse is determined by the capacitor, and so at any sweep rate, could be used as a blanking pulse in a raster scan device.
i realize there are any number of ways to make a linear ramp generator, but the UJT generators in many older projects are simple and effective, and adding the modern/fancy solutions are usually overkill, or kluges to some extent. yes this device is a kluge all by itself, but one that could be constructed to fit neatly on a circuit board made originally for a ujt.
i've been finding these solutions for devices that have been long obsolete, and at some time might post a compilation of them with test results on how well they replace the original devices.
the three transistors on the left are the current source for this ramp generator (i could have used a single PNP at the top, but i was converting this FROM a voltage controlled circuit that used the current mirrror). R1 sets the current output of Q5, which is the charging current for C1. when the "put" conducts and discharges C1, R5 sets the "retrace time" (in case you want to use this as a sweep generator). there are two outputs (out-s) and (out-p) which are sweep (ramp) and pulse.
some finer detail of the ramp and pulse outputs can be seen here;
the width of the pulse is determined by the capacitor, and so at any sweep rate, could be used as a blanking pulse in a raster scan device.
i realize there are any number of ways to make a linear ramp generator, but the UJT generators in many older projects are simple and effective, and adding the modern/fancy solutions are usually overkill, or kluges to some extent. yes this device is a kluge all by itself, but one that could be constructed to fit neatly on a circuit board made originally for a ujt.
i've been finding these solutions for devices that have been long obsolete, and at some time might post a compilation of them with test results on how well they replace the original devices.
