Sawtooth Generation using Monostable Multivibrator:

A modified form of the basic monostable multivibrator is illustrated in Figure where the capacitor C₀ charges linearly through the current source comprising of the transistor R₀ - R_A - R_B combination.

Figure: A Modified Form of Monostable Circuit for Sawtooth Generation

The several waveforms exploring the operation of this circuit are illustrated in Figure

Figure: Various Waveforms for the Monostable Multivibrator

I₀  = IC  ≅ I E (( V _cc - V _e )/ R₀

Neglecting base current, we may write

V _BE      = V₂  -(            R _B /( R_A - R_B ) V _cc

V e  = V _BE + R_B /R_A + R_B) V_cc

Since    I₀   = V cc - V_e /R₀  = 1/R₀  - { V_cc  -{V_BE  + ( R_B/R_A+R_B)V_cc )

I₀  = { (V _cc ( R_A /R_A+R_B  )- V_BE /R₀)]

Since Q = C₀ V_c, we may write

dQ/ dt = C₀  ,    dv/ dt

I₀ / C₀  = dV_c/ dt

If T = time taken by the capacitor to charge to a voltage2/3 V_cc, this is found to be

T =   {(2/3) V_cc  -0}/ dV_c /dt =2V_cc C₀ /3I₀

T =       ((2/3) 2 C₀   R₀ V _cc  )/  { V_cc R_A / (R_A  + R_B )- V _BE